Release 2 (9.2)
Part Number A96587-01
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| Oracle9i Application Developer's Guide - Advanced Queuing Release 2 (9.2) Part Number A96587-01 |
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In Chapter 1, "Introduction to Oracle Advanced Queuing" a messaging system for a hypothetical company, BooksOnLine, was described. In this chapter the features of AQ in the BooksOnLine sample application are discussed under the following headings:
The operations of a large bookseller, BooksOnLine, are based on an online book ordering system that automates activities across the various departments involved in the sale. The front end of the system is an order entry application used to enter new orders. Incoming orders are processed by an order processing application that validates and records the order. Shipping departments located at regional warehouses are responsible for ensuring that orders are shipped on time. There are three regional warehouses: one serving the East Region, one serving the West Region, and a third warehouse for shipping international orders. After an order is shipped, the order information is routed to a central billing department that handles payment processing.The customer service department, located at a separate site, is responsible for maintaining order status and handling inquiries.
The features of AQ are exemplified within the BooksOnLine scenario to demonstrate the possibilities of AQ technology. A script for the sample code is provided in Appendix C, "Scripts for Implementing BooksOnLine").
In this section, the following topics are discussed:
Oracle supports system-level access control for all queuing operations, allowing an application designer or DBA to designate users as queue administrators. A queue administrator can invoke AQ administrative and operational interfaces on any queue in the database. This simplifies the administrative work because all administrative scripts for the queues in a database can be managed under one schema. For more information, see "Oracle Enterprise Manager Support".
In the BooksOnLine application, the DBA creates BOLADM, the BooksOnLine Administrator account, as the queue administrator of the database. This allows BOLADM to create, drop, manage, and monitor queues in the database. If PL/SQL packages are needed in the BOLADM schema for applications to enqueue and dequeue, the DBA should grant ENQUEUE_ANY and DEQUEUE_ANY system privileges to BOLADM:
CREATE USER BOLADM IDENTIFIED BY BOLADM; GRANT CONNECT, RESOURCE, aq_administrator_role TO BOLADM; GRANT EXECUTE ON dbms_aq TO BOLADM; GRANT EXECUTE ON dbms_aqadm TO BOLADM; EXECUTE dbms_aqadm.grant_system_privilege('ENQUEUE_ANY','BOLADM',FALSE); EXECUTE dbms_aqadm.grant_system_privilege('DEQUEUE_ANY','BOLADM',FALSE);
If using the Java AQ API, BOLADM must be granted execute privileges on the DBMS_AQIN package:
GRANT EXECUTE ON DBMS_AQIN to BOLADM;
In the application, AQ propagators populate messages from the Order Entry(OE) schema to the Western Sales (WS), Eastern Sales (ES) and Worldwide Sales (OS) schemas. The WS, ES and OS schemas in turn populate messages to the Customer Billing (CB) and Customer Service (CS) schemas. Hence the OE, WS, ES and OS schemas all host queues that serve as the source queues for the propagators.
When messages arrive at the destination queues, sessions based on the source queue schema name are used for enqueuing the newly arrived messages into the destination queues. This means that you need to grant schemas of the source queues enqueue privileges to the destination queues.
To simplify administration, all schemas that host a source queue in the BoooksOnLine application are granted the ENQUEUE_ANY system privilege:
EXECUTE dbms_aqadm.grant_system_privilege('ENQUEUE_ANY','OE',FALSE); EXECUTE dbms_aqadm.grant_system_privilege('ENQUEUE_ANY','WS',FALSE); EXECUTE dbms_aqadm.grant_system_privilege('ENQUEUE_ANY','ES',FALSE); EXECUTE dbms_aqadm.grant_system_privilege('ENQUEUE_ANY','OS',FALSE);
To propagate to a remote destination queue, the login user specified in the database link in the address field of the agent structure should either be granted the ENQUEUE ANY QUEUE privilege, or be granted the rights to enqueue to the destination queue. If the login user in the database link also owns the queue tables at the destination, no explicit privilege grant is needed.
Use the dbexecutesql interface from the database for this functionality.
No example is provided with this release.
Oracle supports queue-level access control for enqueue and dequeue operations. This feature allows the application designer to protect queues created in one schema from applications running in other schemas. The application designer needs to grant only minimal access privileges to the applications that run outside the queue schema. The supported access privileges on a queue are ENQUEUE, DEQUEUE and ALL. For more information, see "Oracle Enterprise Manager Support".
The BooksOnLine application processes customer billings in its CB and CBADM schemas. CB (Customer Billing) schema hosts the customer billing application, and the CBADM schema hosts all related billing data stored as queue tables.
To protect the billing data, the billing application and the billing data reside in different schemas. The billing application is allowed only to dequeue messages from CBADM_shippedorders_que, the shipped order queue. It processes the messages, and then enqueues new messages into CBADM_billedorders_que, the billed order queue.
To protect the queues from other illegal operations from the application, the following two grant calls are needed:
/* Grant dequeue privilege on the shopped orders queue to the Customer Billing application. The CB application retrieves orders that are shipped but not billed from the shipped orders queue. */ EXECUTE dbms_aqadm.grant_queue_privilege( 'DEQUEUE','CBADM_shippedorders_que', 'CB', FALSE); /* Grant enqueue privilege on the billed orders queue to Customer Billing application. The CB application is allowed to put billed orders into this queue after processing the orders. */ EXECUTE dbms_aqadm.grant_queue_privilege( 'ENQUEUE', 'CBADM_billedorders_que', 'CB', FALSE);
Use the dbexecutesql interface from the database for this functionality.
public static void grantQueuePrivileges(Connection db_conn) { AQSession aq_sess; AQQueue sh_queue; AQQueue bi_queue; try { /* Create an AQ Session: */ aq_sess = AQDriverManager.createAQSession(db_conn); /* Grant dequeue privilege on the shipped orders queue to the Customer Billing application. The CB application retrieves orders that are shipped but not billed from the shipped orders queue. */ sh_queue = aq_sess.getQueue("CBADM", "CBADM_shippedorders_que"); sh_queue.grantQueuePrivilege("DEQUEUE", "CB", false); /* Grant enqueue privilege on the billed orders queue to Customer Billing application.The CB application is allowed to put billed orders into this queue after processing the orders. */ bi_queue = aq_sess.getQueue("CBADM", "CBADM_billedorders_que"); bi_queue.grantQueuePrivilege("ENQUEUE", "CB", false); } catch (AQException ex) { System.out.println("AQ Exception: " + ex); }
}
You can define transformation mappings between different message payload types. Transformation mappings are defined as SQL expressions that can include PL/SQL functions (including callouts) and Java stored procedures. Only one-to-one message transformations are supported. The transformation engine is tightly integrated with Advanced Queuing to facilitate transformation of messages as they move through the database messaging system. Figure 8-1 shows how transformations are integrated with Advanced Queuing.
Transformation mappings can be used during enqueue, dequeue, and propagation operations. To use a transformation at enqueue, the mapping is specified in the enqueue options. To use a transformation at dequeue, the mapping is specified either in the dequeue options or when you add a subscriber. A mapping specified in the dequeue options overrides a mapping specified with ADD_SUBSCRIBER. To use a transformation at propagation, the mapping is specified when you add a subscriber.
In the BooksOnLine application, assume that the order type is represented differently in the order entry and the shipping applications.
The order type of the Order Entry application (in schema OE) is as follows:
create or replace type order_typ as object ( orderno number, status varchar2(30), ordertype varchar2(30), orderregion varchar2(30), custno number, paymentmethod varchar2(30), items orderitemlist_vartyp, ccnumber varchar2(20), order_date date); create or replace type customer_typ as object ( custno number, custid varchar2(20), name varchar2(100), street varchar2(100), city varchar2(30), state varchar2(2), zip number, country varchar2(100)); create or replace type book_typ as object ( title varchar2(100), authors varchar2(100), ISBN varchar2(20), price number); create or replace type orderitem_typ as object ( quantity number, item book_typ, subtotal number); create or replace type orderitemlist_vartyp as varray (20) of orderitem_typ;
The order item of the shipping application is defined as follows
create or replace type order_typ_sh as object ( orderno number, status varchar2(30), ordertype varchar2(30), orderregion varchar2(30), customer customer_typ_sh, paymentmethod varchar2(30), items orderitemlist_vartyp, ccnumber varchar2(20), order_date date); create or replace type customer_typ_sh as object ( custno number, name varchar2(100), street varchar2(100), city varchar2(30), state varchar2(2), zip number); create or replace type book_typ_sh as object ( title varchar2(100), authors varchar2(100), ISBN varchar2(20), price number); create or replace type orderitem_typ_sh as object ( quantity number, item book_typ, subtotal number); create or replace type orderitemlist_vartyp_sh as varray (20) of orderitem_typ_sh;
The Overseas Shipping application uses a sys.XMLType attribute.
You can create transformations in the following ways:
This representation is preferable for simple transformations or transformations that are not easily broken down into independent transformations for each attribute.
execute dbms_transform.create_transformation( schema => 'OE', name => 'OE2WS', from_schema => 'OE', from_type => 'order_typ', to_schema => 'WS', to_type => 'order_typ_sh', transformation( 'WS.order_typ_sh(source.user_data.orderno, source.user_data.status, source.user_data.ordertype, source.user_data.orderregion, WS.get_customer_info(source.user_data.custno), source.user_data.paymentmethod, source.user_data.items, source.user_data.ccnumber, source.user_data.order_date)');
In the BooksOnline application, assume that the Overseas Shipping site represents the order as an XMLType payload. The Order Entry site represents the order as an Oracle object, ORDER_TYP. Since the Overseas Shipping site subscribes to messages in the OE_BOOKEDORDERS_QUE queue, a transformation is applied before messages are propagated from the Order Entry site to the Overseas Shipping site.
The transformation is defined as follows:
CREATE OR REPLACE FUNCTION CONVERT_TO_ORDER_XML(input_order TYPE OE.ORDER_ TYP) RETURN SYS.XMLType AS new_order SYS.XMLType; BEGIN select SYS_XMLGEN(input_order) into new_order from dual; RETURN new_order; END CONVERT_TO_ORDER_XML; execute dbms_transform.create_transformation( schema => 'OS', name => 'OE2XML', from_schema => 'OE', from_type => 'ORDER_TYP', to_schema => 'SYS', to_type => 'XMLTYPE', transformation => 'CONVERT_TO_ORDER_XML(source.user_data)'); /* Add a rule-based subscriber for Overseas Shipping to the Booked orders queues with Transformation. Overseas Shipping handles all non-US orders: */ DECLARE subscriber aq$_agent; BEGIN subscriber := aq$_agent('Overseas_Shipping','OS.OS_bookedorders_que',null); dbms_aqadm.add_subscriber( queue_name => 'OE.OE_bookedorders_que', subscriber => subscriber, rule => 'tab.user_data.orderregion = ''INTERNATIONAL''' transformation => 'OS.OE2XML'); END;
/* first create the transformation without any transformation expression*/ execute dbms_transform.create_transformation( schema => 'OE', name => 'OE2WS', from_schema => 'OE', from_type => 'order_typ', to_schema => 'WS', to_type => 'order_typ_sh'); /* specify each attribute of the target type as a function of the source type*/ execute dbms_transform.modify_transformation( schema => 'OE', name => 'OE2WS', attribute_number => 1, transformation => 'source.user_data.orderno'); execute dbms_transform.modify_transformation( schema => 'OE', name => 'OE2WS', attribute_number => 1, transformation => 'source.user_data.status'); execute dbms_transform.modify_transformation( schema => 'OE', name => 'OE2WS', attribute_number => 1, transformation => 'source.user_data.ordertype'); execute dbms_transform.modify_transformation( schema => 'OE', name => 'OE2WS', attribute_number => 1, transformation => 'source.user_data.orderregion'); execute dbms_transform.modify_transformation( schema => 'OE', name => 'OE2WS', attribute_number => 1, transformation => 'WS.get_customer_info(source.user_data.custno)'); execute dbms_transform.modify_transformation( schema => 'OE', name => 'OE2WS', attribute_number => 1, transformation => 'source.user_data.payment_method'); execute dbms_transform.modify_transformation( schema => 'OE', name => 'OE2WS', attribute_number => 1, transformation => 'source.user_data.orderitemlist_vartyp'); execute dbms_transform.modify_transformation( schema => 'OE', name => 'OE2WS', attribute_number => 1, transformation => 'source.user_data.ccnumber'); execute dbms_transform.modify_transformation( schema => 'OE', name => 'OE2WS', attribute_number => 1, transformation => 'source.user_data.order_date');
No example is provided with this release.
No example is provided with this release.
With Oracle AQ, you can use object types to structure and manage the payload of messages. The object-relational capabilities of Oracle provide a rich set of data types that range from traditional relational data types to user-defined types.
Using strongly typed content, that is, content whose format is defined by an Oracle object type system, makes the following features available:
You can also create payloads that contain Oracle objects with XMLType attributes. These can be used for transmitting and storing messages that contain XML documents. By defining Oracle objects with XMLType attributes, you can do the following:
XMLType.existsNode(), XMLType.extract(), and so on.The BooksOnLine application uses a rich set of data types to model book orders as message content.
customer_typ.
CREATE OR REPLACE TYPE customer_typ AS OBJECT ( custno NUMBER, name VARCHAR2(100), street VARCHAR2(100), city VARCHAR2(30), state VARCHAR2(2), zip NUMBER, country VARCHAR2(100));
book_typ.
CREATE OR REPLACE TYPE book_typ AS OBJECT ( title VARCHAR2(100), authors VARCHAR2(100), ISBN NUMBER, price NUMBER);
orderitem_typ. An order item is a nested type that includes the book type.
CREATE OR REPLACE TYPE orderitem_typ AS OBJECT ( quantity NUMBER, item BOOK_TYP, subtotal NUMBER);
varray of order items;
CREATE OR REPLACE TYPE orderitemlist_vartyp AS VARRAY (20) OF orderitem_typ;
order_typ. The order type is a composite type that includes nested object types defined earlier. The order type captures details of the order, the customer information, and the item list.
CREATE OR REPLACE TYPE order_typ as object ( orderno NUMBER, status VARCHAR2(30), ordertype VARCHAR2(30), orderregion VARCHAR2(30), customer CUSTOMER_TYP, paymentmethod VARCHAR2(30), items ORDERITEMLIST_VARTYP, total NUMBER);
SYS.XMLType payload.Use the dbexecutesql interface from the database for this functionality.
After creating the types, use JPublisher to generate Java classes that map to the SQL types.
TYPE boladm.customer_typ as Customer TYPE boladm.book_typ as Book TYPE boladm.orderitem_typ AS OrderItem TYPE boladm.orderitemlist_vartyp AS OrderItemList TYPE boladm.order_typ AS Order
jpub -input=jaqbol.typ -user=boladm/boladm -case=mixed -methods=false -compatible=CustomDatum
This will create Java classes Customer, Book, OrderItem and OrderItemList that map to the SQL object types created earlier:
public static Connection loadDriver(String user, String passwd) { Connection db_conn = null; try { Class.forName("oracle.jdbc.driver.OracleDriver"); /* your actual hostname, port number, and SID will vary from what follows. Here we use 'dlsun736,' '5521,' and 'test,' respectively: */ db_conn = DriverManager.getConnection( "jdbc:oracle:thin:@dlsun736:5521:test", user, passwd); System.out.println("JDBC Connection opened "); db_conn.setAutoCommit(false); /* Load the Oracle8i AQ driver: */ Class.forName("oracle.AQ.AQOracleDriver"); System.out.println("Successfully loaded AQ driver "); } catch (Exception ex) { System.out.println("Exception: " + ex); ex.printStackTrace(); } return db_conn;
You can create queues with XMLType payloads. These can be used for transmitting and storing messages that contain XML documents. By defining Oracle objects with XMLType attributes, you can do the following:
XMLType.existsNode(), XMLType.extract(), and so on.
| See Also:
Oracle9i XML Database Developer's Guide - Oracle XML DB for details on XMLType operations |
XMLType.existsNode() and XMLType.extract().In the BooksOnline application, assume that the Overseas Shipping site represents the order as SYS.XMLType. The Order Entry site represents the order as an Oracle object, ORDER_TYP.
The Overseas queue table and queue are created as follows:
BEGIN dbms_aqadm.create_queue_table( queue_table => 'OS_orders_pr_mqtab', comment => 'Overseas Shipping MultiConsumer Orders queue table', multiple_consumers => TRUE, queue_payload_type => 'SYS.XMLTtype', compatible => '8.1'); END; BEGIN dbms_aqadm.create_queue ( queue_name => 'OS_bookedorders_que', queue_table => 'OS_orders_pr_mqtab'); END;
Since the representation of orders at the Overseas Shipping site is different from the representation of orders at the Order Entry site, a transformation is applied before messages are propagated from the Order Entry site to the Overseas Shipping site.
/* Add a rule-based subscriber (for Overseas Shipping) to the Booked orders queues with Transformation. Overseas Shipping handles all non-US orders: */ DECLARE subscriber aq$_agent; BEGIN subscriber := aq$_agent('Overseas_Shipping','OS.OS_bookedorders_que',null); dbms_aqadm.add_subscriber( queue_name => 'OE.OE_bookedorders_que', subscriber => subscriber, rule => 'tab.user_data.orderregion = ''INTERNATIONAL''', transformation => 'OS.OE2XML'); END;
For more details on defining transformations that convert the type used by the Order Entry application to the type used by Overseas shipping, see "Creating Transformations".
Assume that an application processes orders for customers in Canada. This application can dequeue messages using the following procedure:
/* Create procedures to enqueue into single-consumer queues: */ create or replace procedure get_canada_orders() as deq_msgid RAW(16); dopt dbms_aq.dequeue_options_t; mprop dbms_aq.message_properties_t; deq_order_data SYS.XMLTtype; no_messages exception; pragma exception_init (no_messages, -25228); new_orders BOOLEAN := TRUE; begin dopt.wait := 1; /* Specify dequeue condition to select Orders for Canada */ dopt.deq_condition := 'tab.user_data.extract(
''/ORDER_TYP/CUSTOMER/COUNTRY/text()'').getStringVal()=''CANADA'''; dopt.consumer_name : = 'Overseas_Shipping'; WHILE (new_orders) LOOP BEGIN dbms_aq.dequeue( queue_name => 'OS.OS_bookedorders_que', dequeue_options => dopt, message_properties => mprop, payload => deq_order_data, msgid => deq_msgid); commit; dbms_output.put_line(' Order for Canada - Order: ' || deq_order_data.getStringVal()); EXCEPTION WHEN no_messages THEN dbms_output.put_line (' ---- NO MORE ORDERS ---- '); new_orders := FALSE; END; END LOOP; end;
A message in a nonpersistent queue is not stored in a database table. You create a nonpersistent queue, which can be either a single-consumer or multiconsumer type. These queues are created in a system-created queue table (AQ$_MEM_SC for single-consumer queues and AQ$_MEM_MC for multiconsumer queues) in the schema specified by the create_np_queue command. Subscribers can be added to the multiconsumer queues (see "Creating a Nonpersistent Queue"). Nonpersistent queues can be destinations for propagation.
You use the enqueue interface to enqueue messages into a nonpersistent queue in the normal way. You can enqueue RAW and Object Type (ADT) messages into a nonpersistent queue. You retrieve messages from a nonpersistent queue through the asynchronous notification mechanism, registering for the notification (using LNOCISubcriptionRegister or DBMS_AQADM.REGISTER) for the queues you are interested in (see "Registering for Notification").
When a message is enqueued into a queue, it is delivered to clients with active registrations for the queue. The messages are published to the interested clients without incurring the overhead of storing them in the database.
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See Also: Documentation on |
Assume that there are three application processes servicing user requests at the Order Entry system. The connection dispatcher shares out connection requests from the application processes. It attempts to maintain a count of the number of users logged on to the Order Entry system and the number of users for each application process. The application processes are named APP_1, APP_2, APP_3. (Application process failures are not considered in this example.)
Using nonpersistent queues meets the requirements in this scenario. When a user logs on to the database, the application process enqueues to the multiconsumer nonpersistent queue, LOGIN_LOGOUT, with the application name as the consumer name. The same process occurs when a user logs out. To distinguish between the two events, the correlation of the message is LOGIN for logins and LOGOUT for logouts.
The callback function counts the login/logout events for each application process. Note that the dispatcher process needs to connect to the database for registering the subscriptions only. The notifications themselves can be received while the process is disconnected from the database.
CONNECT oe/oe; /* Create the Object Type/ADT adtmsg */ CREATE OR REPLACE TYPE adtmsg AS OBJECT (id NUMBER, data VARCHAR2(4000)); /* Create the multiconsumer nonpersistent queue in OE schema: */ EXECUTE dbms_aqadm.create_np_queue(queue_name => 'LOGON_LOGOFF', multiple_consumers => TRUE); /* Enable the queue for enqueue and dequeue: */ EXECUTE dbms_aqadm.start_queue(queue_name => 'LOGON_LOGOFF'); /* Nonpersistent Queue Scenario - procedure to be executed upon logon: */ CREATE OR REPLACE PROCEDURE User_Logon(app_process IN VARCHAR2) AS msgprop dbms_aq.message_properties_t; enqopt dbms_aq.enqueue_options_t; enq_msgid RAW(16); payload RAW(1); BEGIN /* visibility must always be immediate for NonPersistent queues */ enqopt.visibility:=dbms_aq.IMMEDIATE; msgprop.correlation:= 'LOGON'; msgprop.recipient_list(0) := aq$_agent(app_process, NULL, NULL); /* payload is NULL */ dbms_aq.enqueue( queue_name => 'LOGON_LOGOFF', enqueue_options => enqopt, message_properties => msgprop, payload => payload, msgid => enq_msgid); END; /* Nonpersistent queue scenario - procedure to be executed upon logoff: */ CREATE OR REPLACE PROCEDURE User_Logoff(app_process IN VARCHAR2) AS msgprop dbms_aq.message_properties_t; enqopt dbms_aq.enqueue_options_t; enq_msgid RAW(16); payload adtmsg; BEGIN /* Visibility must always be immediate for NonPersistent queues: */ enqopt.visibility:=dbms_aq.IMMEDIATE; msgprop.correlation:= 'LOGOFF'; msgprop.recipient_list(0) := aq$_agent(app_process, NULL, NULL); /* Payload is NOT NULL: */ payload := adtmsg(1, 'Logging Off'); dbms_aq.enqueue( queue_name => 'LOGON_LOGOFF', enqueue_options => enqopt, message_properties => msgprop, payload => payload, msgid => enq_msgid); END; / /* If there is a login at APP1, enqueue a message into 'login_logoff' with correlation 'LOGIN': */ EXECUTE User_logon('APP1'); /* If there is a logout at APP3, enqueue a message into 'login_logoff' with correlation 'LOGOFF' and payload adtmsg(1, 'Logging Off'): */ EXECUTE User_logoff('App3'); /* The OCI program which waits for notifications: */ #include <stdio.h> #include <stdlib.h> #include <string.h> #include <oci.h> #ifdef WIN32COMMON #define sleep(x) Sleep(1000*(x)) #endif /* LOGON / password: */ static text *username = (text *) "OE"; static text *password = (text *) "OE"; /* The correlation strings of messages: */ static char *logon = "LOGON"; static char *logoff = "LOGOFF"; /* The possible consumer names of queues: */ static char *applist[] = {"APP1", "APP2","APP3"}; static OCIEnv *envhp; static OCIServer *srvhp; static OCIError *errhp; static OCISvcCtx *svchp; static void checkerr(/*_ OCIError *errhp, sword status _*/); struct process_statistics { ub4 logon; ub4 logoff; }; typedef struct process_statistics process_statistics; int main(/*_ int argc, char *argv[] _*/); /* Notify Callback: */ ub4 notifyCB(ctx, subscrhp, pay, payl, desc, mode) dvoid *ctx; LNOCISubscription *subscrhp; dvoid *pay; ub4 payl; dvoid *desc; ub4 mode; { text *subname; /* subscription name */ ub4 lsub; /* length of subscription name */ text *queue; /* queue name */ ub4 *lqueue; /* queue name */ text *consumer; /* consumer name */ ub4 lconsumer; text *correlation; ub4 lcorrelation; ub4 size; ub4 appno; OCIRaw *msgid; OCIAQMsgProperties *msgprop; /* message properties descriptor */ process_statistics *user_count = (process_statistics *)ctx; OCIAttrGet((dvoid *)subscrhp, OCI_HTYPE_SUBSCRIPTION, (dvoid *)&subname, &lsub, OCI_ATTR_SUBSCR_NAME, errhp); /* Extract the attributes from the AQ descriptor: */ /* Queue name: */ OCIAttrGet(desc, OCI_DTYPE_AQNFY_DESCRIPTOR, (dvoid *)&queue, &size, OCI_ATTR_QUEUE_NAME, errhp); /* Consumer name: */ OCIAttrGet(desc, OCI_DTYPE_AQNFY_DESCRIPTOR, (dvoid *)&consumer, &lconsumer, OCI_ATTR_CONSUMER_NAME, errhp); /* Message properties: */ OCIAttrGet(desc, OCI_DTYPE_AQNFY_DESCRIPTOR, (dvoid *)&msgprop, &size, OCI_ATTR_MSG_PROP, errhp); /* Get correlation from message properties: */ checkerr(errhp, OCIAttrGet(msgprop, OCI_DTYPE_AQMSG_PROPERTIES, (dvoid *)&correlation, &lcorrelation, OCI_ATTR_CORRELATION, errhp)); if (lconsumer == strlen(applist[0])) { if (!memcmp((dvoid *)consumer, (dvoid *)applist[0], strlen(applist[0]))) appno = 0; else if (!memcmp((dvoid *)consumer, (dvoid *)applist[1], strlen(applist[1]))) appno = 1; else if (!memcmp((dvoid *)consumer, (dvoid *)applist[2], strlen(applist[2]))) appno = 2; else { printf("Wrong consumer in notification"); return; } } else { /* consumer name must be "APP1", "APP2" or "APP3" */ printf("Wrong consumer in notification"); return; } if (lcorrelation == strlen(logon) && /* logon event */ !memcmp((dvoid *)correlation, (dvoid *)logon, strlen(logon))) { user_count[appno].logon++; /* increment logon count for the app process */ printf("Logon by APP%d \n", (appno+1)); printf("Logon Payload length = %d \n", pay1); } else if (lcorrelation == strlen(logoff) && /* logoff event */ !memcmp((dvoid *)correlation,(dvoid *)logoff, strlen(logoff))) { user_count[appno].logoff++; /* increment logoff count for the app process */ printf("Logoff by APP%d \n", (appno+1)); printf("Logoff Payload length = %d \n", pay1); } else /* correlation is "LOGON" or "LOGOFF" */ printf("Wrong correlation in notification"); printf("Total : \n"); printf("App1 : %d \n", user_count[0].logon-user_count[0].logoff); printf("App2 : %d \n", user_count[1].logon-user_count[1].logoff); printf("App3 : %d \n", user_count[2].logon-user_count[2].logoff); } int main(argc, argv) int argc; char *argv[]; { OCISession *authp = (OCISession *) 0; OCISubscription *subscrhp[3]; ub4 namespace = OCI_SUBSCR_NAMESPACE_AQ; process_statistics ctx[3] = {{0,0}, {0,0}, {0,0}}; ub4 sleep_time = 0; printf("Initializing OCI Process\n"); /* Initialize OCI environment with OCI_EVENTS flag set: */ (void) OCIInitialize((ub4) OCI_EVENTS|OCI_OBJECT, (dvoid *)0, (dvoid * (*)(dvoid *, size_t)) 0, (dvoid * (*)(dvoid *, dvoid *, size_t))0, (void (*)(dvoid *, dvoid *)) 0 ); printf("Initialization successful\n"); printf("Initializing OCI Env\n"); (void) OCIEnvInit( (OCIEnv **) &envhp, OCI_DEFAULT, (size_t) 0, (dvoid **) 0 ); printf("Initialization successful\n"); checkerr(errhp, OCIHandleAlloc( (dvoid *) envhp, (dvoid **) &errhp, LNOCI_HTYPE_ERROR, (size_t) 0, (dvoid **) 0)); checkerr(errhp, OCIHandleAlloc( (dvoid *) envhp, (dvoid **) &srvhp, LNOCI_HTYPE_SERVER, (size_t) 0, (dvoid **) 0)); checkerr(errhp, OCIHandleAlloc( (dvoid *) envhp, (dvoid **) &svchp, LNOCI_HTYPE_SVCCTX, (size_t) 0, (dvoid **) 0)); printf("connecting to server\n"); checkerr(errhp, OCIServerAttach( srvhp, errhp, (text *)"inst1_alias", strlen("inst1_alias"), (ub4) OCI_DEFAULT)); printf("connect successful\n"); /* Set attribute server context in the service context: */ checkerr(errhp, OCIAttrSet( (dvoid *) svchp, OCI_HTYPE_SVCCTX, (dvoid *)srvhp, (ub4) 0, OCI_ATTR_SERVER, (OCIError *) errhp)); checkerr(errhp, OCIHandleAlloc((dvoid *) envhp, (dvoid **)&authp, (ub4) OCI_HTYPE_SESSION, (size_t) 0, (dvoid **) 0)); /* Set username and password in the session handle: */ checkerr(errhp, OCIAttrSet((dvoid *) authp, (ub4) OCI_HTYPE_SESSION, (dvoid *) username, (ub4) strlen((char *)username), (ub4) OCI_ATTR_USERNAME, errhp)); checkerr(errhp, OCIAttrSet((dvoid *) authp, (ub4) OCI_HTYPE_SESSION, (dvoid *) password, (ub4) strlen((char *)password), (ub4) OCI_ATTR_PASSWORD, errhp)); /* Begin session: */ checkerr(errhp, OCISessionBegin ( svchp, errhp, authp, OCI_CRED_RDBMS, (ub4) OCI_DEFAULT)); (void) OCIAttrSet((dvoid *) svchp, (ub4) OCI_HTYPE_SVCCTX, (dvoid *) authp, (ub4) 0, (ub4) OCI_ATTR_SESSION, errhp); /* Register for notification: */ printf("allocating subscription handle\n"); subscrhp[0] = (OCISubscription *)0; (void) OCIHandleAlloc((dvoid *) envhp, (dvoid **)&subscrhp[0], (ub4) OCI_HTYPE_SUBSCRIPTION, (size_t) 0, (dvoid **) 0); /* For application process APP1: */ printf("setting subscription name\n"); (void) OCIAttrSet((dvoid *) subscrhp[0], (ub4) OCI_HTYPE_SUBSCRIPTION, (dvoid *) "OE.LOGON_LOGOFF:APP1", (ub4) strlen("OE.LOGON_LOGOFF:APP1"), (ub4) OCI_ATTR_SUBSCR_NAME, errhp); printf("setting subscription callback\n"); (void) OCIAttrSet((dvoid *) subscrhp[0], (ub4) OCI_HTYPE_SUBSCRIPTION, (dvoid *) notifyCB, (ub4) 0, (ub4) OCI_ATTR_SUBSCR_CALLBACK, errhp); (void) OCIAttrSet((dvoid *) subscrhp[0], (ub4) OCI_HTYPE_SUBSCRIPTION, (dvoid *)&ctx, (ub4)sizeof(ctx), (ub4) OCI_ATTR_SUBSCR_CTX, errhp); printf("setting subscription namespace\n"); (void) OCIAttrSet((dvoid *) subscrhp[0], (ub4) OCI_HTYPE_SUBSCRIPTION, (dvoid *) &namespace, (ub4) 0, (ub4) OCI_ATTR_SUBSCR_NAMESPACE, errhp); printf("allocating subscription handle\n"); subscrhp[1] = (OCISubscription *)0; (void) OCIHandleAlloc((dvoid *) envhp, (dvoid **)&subscrhp[1], (ub4) OCI_HTYPE_SUBSCRIPTION, (size_t) 0, (dvoid **) 0); /* For application process APP2: */ printf("setting subscription name\n"); (void) OCIAttrSet((dvoid *) subscrhp[1], (ub4) OCI_HTYPE_SUBSCRIPTION, (dvoid *) "OE.LOGON_LOGOFF:APP2", (ub4) strlen("OE.LOGON_LOGOFF:APP2"), (ub4) OCI_ATTR_SUBSCR_NAME, errhp); printf("setting subscription callback\n"); (void) OCIAttrSet((dvoid *) subscrhp[1], (ub4) OCI_HTYPE_SUBSCRIPTION, (dvoid *) notifyCB, (ub4) 0, (ub4) OCI_ATTR_SUBSCR_CALLBACK, errhp); (void) OCIAttrSet((dvoid *) subscrhp[1], (ub4) OCI_HTYPE_SUBSCRIPTION, (dvoid *)&ctx, (ub4)sizeof(ctx), (ub4) OCI_ATTR_SUBSCR_CTX, errhp); printf("setting subscription namespace\n"); (void) OCIAttrSet((dvoid *) subscrhp[1], (ub4) OCI_HTYPE_SUBSCRIPTION, (dvoid *) &namespace, (ub4) 0, (ub4) OCI_ATTR_SUBSCR_NAMESPACE, errhp); printf("allocating subscription handle\n"); subscrhp[2] = (OCISubscription *)0; (void) OCIHandleAlloc((dvoid *) envhp, (dvoid **)&subscrhp[2], (ub4) OCI_HTYPE_SUBSCRIPTION, (size_t) 0, (dvoid **) 0); /* For application process APP3: */ printf("setting subscription name\n"); (void) OCIAttrSet((dvoid *) subscrhp[2], (ub4) OCI_HTYPE_SUBSCRIPTION, (dvoid *) "OE.LOGON_LOGOFF:APP3", (ub4) strlen("OE.LOGON_LOGOFF:APP3"), (ub4) OCI_ATTR_SUBSCR_NAME, errhp); printf("setting subscription callback\n"); (void) OCIAttrSet((dvoid *) subscrhp[2], (ub4) OCI_HTYPE_SUBSCRIPTION, (dvoid *) notifyCB, (ub4) 0, (ub4) OCI_ATTR_SUBSCR_CALLBACK, errhp); (void) OCIAttrSet((dvoid *) subscrhp[2], (ub4) OCI_HTYPE_SUBSCRIPTION, (dvoid *)&ctx, (ub4)sizeof(ctx), (ub4) OCI_ATTR_SUBSCR_CTX, errhp); printf("setting subscription namespace\n"); (void) OCIAttrSet((dvoid *) subscrhp[2], (ub4) OCI_HTYPE_SUBSCRIPTION, (dvoid *) &namespace, (ub4) 0, (ub4) OCI_ATTR_SUBSCR_NAMESPACE, errhp); printf("Registering fornotifications \n"); checkerr(errhp, OCISubscriptionRegister(svchp, subscrhp, 3, errhp, OCI_DEFAULT)); sleep_time = (ub4)atoi(argv[1]); printf ("waiting for %d s \n", sleep_time); sleep(sleep_time); printf("Exiting"); exit(0); } void checkerr(errhp, status) LNOCIError *errhp; sword status; { text errbuf[512]; sb4 errcode = 0; switch (status) { case OCI_SUCCESS: break; case OCI_SUCCESS_WITH_INFO: (void) printf("Error - OCI_SUCCESS_WITH_INFO\n"); break; case OCI_NEED_DATA: (void) printf("Error - OCI_NEED_DATA\n"); break; case OCI_NO_DATA: (void) printf("Error - OCI_NODATA\n"); break; case OCI_ERROR: (void) OCIErrorGet((dvoid *)errhp, (ub4) 1, (text *) NULL, &errcode, errbuf, (ub4) sizeof(errbuf), OCI_HTYPE_ERROR); (void) printf("Error - %.*s\n", 512, errbuf); break; case OCI_INVALID_HANDLE: (void) printf("Error - OCI_INVALID_HANDLE\n"); break; case OCI_STILL_EXECUTING: (void) printf("Error - OCI_STILL_EXECUTE\n"); break; case OCI_CONTINUE: (void) printf("Error - OCI_CONTINUE\n"); break; default: break; } } /* End of file tkaqdocn.c */
This feature is not supported currently.
This feature is not supported through the Java API.
Advanced Queuing allows the retention of the message history after consumption. The messages and their histories can be queried using SQL. This allows business analysis of the integrated system. In certain cases, messages need to be tracked. For example, if a message is produced as a result of the consumption of another message, the two are related. As the application designer, you may want to keep track of such relationships. Taken together, retention, message identifiers, and SQL queries make it possible to build powerful message warehouses.
Assume that you need to determine the average order processing time. This includes the time the order has to wait in the backed_order queue. You want to know the average wait time in the backed_order queue. SQL queries can determine the wait time for orders in the shipping application. Specify the retention as TRUE for the shipping queues and specify the order number in the correlation field of the message.
For simplicity, only orders that have already been processed are analyzed. The processing time for an order in the shipping application is the difference between the enqueue time in the WS_bookedorders_que and the enqueue time in the WS_shipped_orders_que (see "tkaqdoca.sql: Script to Create Users, Objects, Queue Tables, Queues & Subscribers" of Appendix C, "Scripts for Implementing BooksOnLine".
SELECT SUM(SO.enq_time - BO.enq_time) / count (*) AVG_PRCS_TIME FROM WS.AQ$WS_orders_pr_mqtab BO , WS.AQ$WS_orders_mqtab SO WHERE SO.msg_state = 'PROCESSED' and BO.msg_state = 'PROCESSED' AND SO.corr_id = BO.corr_id and SO.queue = 'WS_shippedorders_que'; /* Average waiting time in the backed order queue: */ SELECT SUM(BACK.deq_time - BACK.enq_time)/count (*) AVG_BACK_TIME FROM WS.AQ$WS_orders_mqtab BACK WHERE BACK.msg_state = 'PROCESSED' AND BACK.queue = 'WS_backorders_que';
Use the dbexecutesql interface from the database for this functionality.
No example is provided with this release.
Advanced Queuing supports the publish-subscribe model of application integration. In the model, publishing applications put the message in the queue. The subscribing applications subscribe to the message in the queue. More publishing and subscribing applications can be dynamically added without changing the existing publishing and subscribing applications. Advanced Queuing also supports content-based subscriptions. The subscriber can subscribe to a subset of messages in the queue based on the message properties and the contents of the messages. A subscriber to a queue can also be another queue or a consumer on another queue.
You can implement a publish-subscribe model of communication using Advanced Queuing as follows:
The BooksOnLine application illustrates the use of a publish-subscribe model for communicating between applications. The following subsections give some examples.
The Order Entry application defines a queue (OE_booked_orders_que) to communicate orders that are booked to various applications. The Order Entry application is not aware of the various subscriber applications and thus, a new subscriber application can be added without disrupting any setup or logic in the Order Entry (publisher) application.
The various shipping applications and the customer service application (that is, Eastern region shipping, Western region shipping, Overseas shipping and Customer Service) are defined as subscribers to the booked_orders queue of the Order Entry application. Rules are used to route messages of interest to the various subscribers. Thus, Eastern Region shipping, which handles shipment of all orders for the East coast and all rush U.S. orders, expresses the subscription rule as follows:
rule => 'tab.user_data.orderregion = ''EASTERN'' OR (tab.user_data.ordertype = ''RUSH'' AND tab.user_data.customer.country = ''USA'') '
Each subscriber can specify a local queue where messages are to be delivered. The Eastern region shipping application specifies a local queue (ES_booked_orders_que) for message delivery by specifying the subscriber address as follows:
subscriber := aq$_agent('East_Shipping', 'ES.ES_bookedorders_que', null);
Enable propagation from each publisher application queue. To allow subscribed messages to be delivered to remote queues, the Order Entry application enables propagation by means of the following statement:
execute dbms_aqadm.schedule_propagation(queue_name => 'OE.OE_bookedorders_que');
Booked orders are published by the Order Entry application when it enqueues orders (into the OE_booked_order_que) that have been validated and are ready for shipping. These messages are then routed to each of the subscribing applications. Messages are delivered to local queues (if specified) at each of the subscriber applications.
Each of the shipping applications and the Customer Service application will then receive these messages in their local queues. For example, Eastern Region Shipping only receives booked orders that are for East Coast addresses or any U.S. order that is marked RUSH. This application then dequeues messages and processes its orders for shipping.
Real Application Clusters can be used to improve AQ performance by allowing different queues to be managed by different instances. You do this by specifying different instance affinities (preferences) for the queue tables that store the queues. This allows queue operations (enqueue and dequeue) on different queues to occur in parallel.
The AQ queue monitor process continuously monitors the instance affinities of the queue tables. The queue monitor assigns ownership of a queue table to the specified primary instance if it is available, failing which it assigns it to the specified secondary instance.
If the owner instance of a queue table terminates, the queue monitor changes ownership to a suitable instance such as the secondary instance.
AQ propagation is able to make use of Real Application Clusters, although it is transparent to the user. The affinities for jobs submitted on behalf of the propagation schedules are set to the same values as that of the affinities of the respective queue tables. Thus a job_queue_process associated with the owner instance of a queue table will be handling the propagation from queues stored in that queue table, thereby minimizing pinging. Additional discussion on this topic can be found under AQ propagation scheduling (see "Scheduling a Queue Propagation" in Chapter 9, "Administrative Interface").
In the BooksOnLine example, operations on the new_orders_queue and booked_order_queue at the order entry (OE) site can be made faster if the two queues are associated with different instances. This is done by creating the queues in different queue tables and specifying different affinities for the queue tables in the create_queue_table() command.
In the example, the queue table OE_orders_sqtab stores queue new_orders_queue and the primary and secondary are instances 1 and 2 respectively. Queue table OE_orders_mqtab stores queue booked_order_queue and the primary and secondary are instances 2 and 1 respectively. The objective is to let instances 1 and 2 manage the two queues in parallel. By default, only one instance is available, in which case the owner instances of both queue tables will be set to instance 1. However, if Real Application Clusters are set up correctly and both instances 1 and 2 are available, then queue table OE_orders_sqtab will be owned by instance 1 and the other queue table will be owned by instance 2. The primary and secondary instance specification of a queue table can be changed dynamically using the alter_queue_table() command as shown in the following example. Information about the primary, secondary and owner instance of a queue table can be obtained by querying the view USER_QUEUE_TABLES (see "Selecting Queue Tables in User Schema" in "Administrative Interface: Views").
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Note: Queue names and queue table names are converted to upper case. Mixed case (upper and lower case together) is not supported for queue names and queue table names. |
/* Create queue tables, queues for OE */ CONNECT OE/OE; EXECUTE dbms_aqadm.create_queue_table( \ queue_table => 'OE_orders_sqtab',\ comment => 'Order Entry Single-Consumer Orders queue table',\ queue_payload_type => 'BOLADM.order_typ',\ compatible => '8.1',\ primary_instance => 1,\ secondary_instance => 2); EXECUTE dbms_aqadm.create_queue_table(\ queue_table => 'OE_orders_mqtab',\ comment => 'Order Entry Multi Consumer Orders queue table',\ multiple_consumers => TRUE,\ queue_payload_type => 'BOLADM.order_typ',\ compatible => '8.1',\ primary_instance => 2,\ secondary_instance => 1); EXECUTE dbms_aqadm.create_queue ( \ queue_name => 'OE_neworders_que',\ queue_table => 'OE_orders_sqtab'); EXECUTE dbms_aqadm.create_queue ( \ queue_name => 'OE_bookedorders_que',\ queue_table => 'OE_orders_mqtab'); /* Check instance affinity of OE queue tables from AQ administrative view: */ SELECT queue_table, primary_instance, secondary_instance, owner_instance FROM user_queue_tables; /* Alter instance affinity of OE queue tables: */ EXECUTE dbms_aqadm.alter_queue_table( \ queue_table => 'OE.OE_orders_sqtab',\ primary_instance => 2,\ secondary_instance => 1); EXECUTE dbms_aqadm.alter_queue_table( \ queue_table => 'OE.OE_orders_mqtab', \ primary_instance => 1,\ secondary_instance => 2); /* Check instance affinity of OE queue tables from AQ administrative view: */ SELECT queue_table, primary_instance, secondary_instance, owner_instance FROM user_queue_tables;
This feature currently not supported.
public static void createQueueTablesAndQueues(Connection db_conn) { AQSession aq_sess; AQQueueTableProperty sqt_prop; AQQueueTableProperty mqt_prop; AQQueueTable sq_table; AQQueueTable mq_table; AQQueueProperty q_prop; AQQueue neworders_q; AQQueue bookedorders_q; try { /* Create an AQ Session: */ aq_sess = AQDriverManager.createAQSession(db_conn); /* Create a single-consumer orders queue table */ sqt_prop = new AQQueueTableProperty("BOLADM.order_typ"); sqt_prop.setComment("Order Entry Single-Consumer Orders queue table"); sqt_prop.setCompatible("8.1"); sqt_prop.setPrimaryInstance(1); sqt_prop.setSecondaryInstance(2); sq_table = aq_sess.createQueueTable("OE", "OE_orders_sqtab", sqt_prop); /* Create a multiconsumer orders queue table */ mqt_prop = new AQQueueTableProperty("BOLADM.order_typ"); mqt_prop.setComment("Order Entry Multi Consumer Orders queue table"); mqt_prop.setCompatible("8.1"); mqt_prop.setMultiConsumer(true); mqt_prop.setPrimaryInstance(2); mqt_prop.setSecondaryInstance(1); mq_table = aq_sess.createQueueTable("OE", "OE_orders_mqtab", mqt_prop); /* Create Queues in these queue tables */ q_prop = new AQQueueProperty(); neworders_q = aq_sess.createQueue(sq_table, "OE_neworders_que", q_prop); bookedorders_q = aq_sess.createQueue(mq_table, "OE_bookedorders_que", q_prop); } catch (AQException ex) { System.out.println("AQ Exception: " + ex); } } public static void alterInstanceAffinity(Connection db_conn) { AQSession aq_sess; AQQueueTableProperty sqt_prop; AQQueueTableProperty mqt_prop; AQQueueTable sq_table; AQQueueTable mq_table; AQQueueProperty q_prop; try { /* Create an AQ Session: */ aq_sess = AQDriverManager.createAQSession(db_conn); /* Check instance affinities */ sq_table = aq_sess.getQueueTable("OE", "OE_orders_sqtab"); sqt_prop = sq_table.getProperty(); System.out.println("Current primary instance for OE_orders_sqtab: " + sqt_prop.getPrimaryInstance()); mq_table = aq_sess.getQueueTable("OE", "OE_orders_mqtab"); mqt_prop = mq_table.getProperty(); System.out.println("Current primary instance for OE_orders_mqtab: " + mqt_prop.getPrimaryInstance()); /* Alter queue table affinities */ sq_table.alter(null, 2, 1); mq_table.alter(null, 1, 2); sqt_prop = sq_table.getProperty(); System.out.println("Current primary instance for OE_orders_sqtab: " + sqt_prop.getPrimaryInstance()); mq_table = aq_sess.getQueueTable("OE", "OE_orders_mqtab"); mqt_prop = mq_table.getProperty(); System.out.println("Current primary instance for OE_orders_mqtab: " + mqt_prop.getPrimaryInstance()); } catch (AQException ex) { System.out.println("AQ Exception: " + ex); } }
Each instance keeps its own AQ statistics information in its own SGA, and does not have knowledge of the statistics gathered by other instances. When a GV$AQ view is queried by an instance, all other instances funnel their AQ statistics information to the instance issuing the query.
The gv$ view can be queried at any time to see the number of messages in waiting, ready or expired state. The view also displays the average number of seconds messages have been waiting to be processed. The order processing application can use this to dynamically tune the number of order processing processes (see "Selecting the Number of Messages in Different States for the Whole Database" in Chapter 10, "Administrative Interface: Views").
CONNECT oe/oe /* Count the number as messages and the average time for which the messages have been waiting: */ SELECT READY, AVERAGE_WAIT FROM gv$aq Stats, user_queues Qs WHERE Stats.qid = Qs.qid and Qs.Name = 'OE_neworders_que';
Use the dbexecutesql interface from the database for this functionality.
No example is provided with this release.
See Chapter 17, "Internet Access to Advanced Queuing" for information on Internet access to Advanced Queuing features.
In this section, the following topics are discussed:
After consumption by dequeue, messages are retained for the time specified in retention_time. When retention_time expires, messages are removed by the time manager process.
After processing, the message is removed if the retention_time of the queue is 0, or retained for the specified retention time. While the message is retained the message can either be queried using SQL on the queue table view or by dequeuing using the BROWSE mode and specifying the message ID of the processed message.
Advanced Queuing allows a single message to be processed and consumed by more than one consumer. To use this feature, you must create multiconsumer queues and enqueue the messages into these multiconsumer queues. Advanced Queuing allows two methods of identifying the list of consumers for a message: subscriptions and recipient lists.
You can add a subscription to a queue by using the DBMS_AQADM.ADD_SUBSCRIBER PL/SQL procedure (see "Adding a Subscriber" in Chapter 9, "Administrative Interface"). This lets you specify a consumer by means of the AQ$_AGENT parameter for enqueued messages. You can add more subscribers by repeatedly using the DBMS_AQADM.ADD_SUBSCRIBER procedure up to a maximum of 1024 subscribers for a multiconsumer queue.
All consumers that are added as subscribers to a multiconsumer queue must have unique values for the AQ$_AGENT parameter. This means that two subscribers cannot have the same values for the NAME, ADDRESS and PROTOCOL attributes for the AQ$_AGENT type. At least one of the three attributes must be different for two subscribers (see "Agent Type (aq$_agent)" for formal description of this data structure).
You cannot add subscriptions to single-consumer queues or exception queues. A consumer that is added as a subscriber to a queue will only be able to dequeue messages that are enqueued after the DBMS_AQADM.ADD_SUBSCRIBER procedure is completed. In other words, messages that had been enqueued before this procedure is executed will not be available for dequeue by this consumer.
You can remove a subscription by using the DBMS_AQADM.REMOVE_SUBSCRIBER procedure (see "Removing a Subscriber" in Chapter 9, "Administrative Interface"). AQ will automatically remove from the queue all data corresponding to the consumer identified by the AQ$_AGENT parameter. In other words, it is not an error to execute the REMOVE_SUBSCRIBER procedure even when there are pending messages that are available for dequeue by the consumer. These messages will be automatically made unavailable for dequeue after the REMOVE_SUBSCRIBER procedure is executed. In a queue table that is created with the compatible parameter set to '8.1' or higher, such messages that were not dequeued by the consumer will be shown as "UNDELIVERABLE" in the AQ$<queue_table> view. Note that a multiconsumer queue table created without the compatible parameter, or with the compatible parameter set to '8.0', does not display the state of a message on a consumer basis, but only displays the global state of the message.
You do not need to specify subscriptions for a multiconsumer queue if the producers of messages for enqueue supply a recipient list of consumers. In some situations it may be desirable to enqueue a message that is targeted to a specific set of consumers rather than the default list of subscribers. You accomplish this by specifying a recipient list at the time of enqueuing the message.
recipient_list field of the message_properties record.LNOCISetAttr procedure to specify an array of LNOCI_DTYPE_AQAGENT descriptors as the recipient list (LNOCI_ATTR_RECIPIENT_LIST attribute) of an LNOCI_DTYPE_AQMSG_PROPERTIES message properties descriptor.If a recipient list is specified during enqueue, it overrides the subscription list. In other words, messages that have a specified recipient list will not be available for dequeue by the subscribers of the queue. The consumers specified in the recipient list may or may not be subscribers for the queue. It is an error if the queue does not have any subscribers and the enqueue does not specify a recipient list (see "Enqueuing a Message" in Chapter 11, "Operational Interface: Basic Operations").
The message ordering dictates the order that messages are dequeued from a queue. The ordering method for a queue is specified when a queue table is created (see "Creating a Queue Table" in Chapter 9, "Administrative Interface").
Priority ordering of messages is achieved by specifying priority, enqueue time as the sort order for the message. If priority ordering is chosen, each message will be assigned a priority at enqueue time by the enqueuer. At dequeue time, the messages will be dequeued in the order of the priorities assigned. If two messages have the same priority, the order in which they are dequeued is determined by the enqueue time. A first-in, first-out (FIFO) priority queue can also be created by specifying the enqueue time, priority as the sort order of the messages.
In the BooksOnLine application, a customer can request:
The Order Entry application uses a priority queue to store booked orders. Booked orders are propagated to the regional booked orders queues. At each region, orders in these regional booked orders queues are processed in the order of the shipping priorities.
The following calls create the priority queues for the Order Entry application.
/* Create a priority queue table for OE: */ EXECUTE dbms_aqadm.create_queue_table( \ queue_table => 'OE_orders_pr_mqtab', \ sort_list =>'priority,enq_time', \ comment => 'Order Entry Priority \ MultiConsumer Orders queue table',\ multiple_consumers => TRUE, \ queue_payload_type => 'BOLADM.order_typ', \ compatible => '8.1', \ primary_instance => 2, \ secondary_instance => 1); EXECUTE dbms_aqadm.create_queue ( \ queue_name => 'OE_bookedorders_que', \ queue_table => 'OE_orders_pr_mqtab'); /* When an order arrives, the order entry application can use the following procedure to enqueue the order into its booked orders queue. A shipping priority is specified for each order: */ CREATE OR REPLACE procedure order_enq(book_title IN VARCHAR2, book_qty IN NUMBER, order_num IN NUMBER, shipping_priority IN NUMBER, cust_state IN VARCHAR2, cust_country IN VARCHAR2, cust_region IN VARCHAR2, cust_ord_typ IN VARCHAR2) AS OE_enq_order_data BOLADM.order_typ; OE_enq_cust_data BOLADM.customer_typ; OE_enq_book_data BOLADM.book_typ; OE_enq_item_data BOLADM.orderitem_typ; OE_enq_item_list BOLADM.orderitemlist_vartyp; enqopt dbms_aq.enqueue_options_t; msgprop dbms_aq.message_properties_t; enq_msgid RAW(16); BEGIN msgprop.correlation := cust_ord_typ; OE_enq_cust_data := BOLADM.customer_typ(NULL, NULL, NULL, NULL, cust_state, NULL, cust_country); OE_enq_book_data := BOLADM.book_typ(book_title, NULL, NULL, NULL); OE_enq_item_data := BOLADM.orderitem_typ(book_qty, OE_enq_book_data, NULL); OE_enq_item_list := BOLADM.orderitemlist_vartyp( BOLADM.orderitem_typ(book_qty, OE_enq_book_data, NULL)); OE_enq_order_data := BOLADM.order_typ(order_num, NULL, cust_ord_typ, cust_region, OE_enq_cust_data, NULL, OE_enq_item_list, NULL); /*Put the shipping priority into message property before enqueuing the message: */ msgprop.priority := shipping_priority; dbms_aq.enqueue('OE.OE_bookedorders_que', enqopt, msgprop, OE_enq_order_data, enq_msgid); COMMIT; END; / /* At each region, similar booked order queues are created. The orders are propagated from the central Order Entry's booked order queues to the regional booked order queues.For example, at the western region, the booked orders queue is created. Create a priority queue table for WS shipping: */ EXECUTE dbms_aqadm.create_queue_table( \ queue_table => 'WS_orders_pr_mqtab', sort_list =>' priority,enq_time', \ comment => 'West Shipping Priority \ MultiConsumer Orders queue table',\ multiple_consumers => TRUE, \ queue_payload_type => 'BOLADM.order_typ', \ compatible => '8.1'); /* Booked orders are stored in the priority queue table: */ EXECUTE dbms_aqadm.create_queue ( \ queue_name => 'WS_bookedorders_que', \ queue_table => 'WS_orders_pr_mqtab'); /* At each region, the shipping application dequeues orders from the regional booked order queue according to the orders' shipping priorities, processes the orders, and enqueues the processed orders into the shipped orders queues or the back orders queues. */
Dim OraSession as object Dim OraDatabase as object Dim OraAq as object Dim OraMsg as Object Dim OraOrder,OraCust,OraBook,OraItem,OraItemList as Object Dim Msgid as String Set OraSession = CreateObject("OracleInProcServer.XOraSession") Set OraDatabase = OraSession.DbOpenDatabase("dbname", "user/pwd", 0&) set oraaq = OraDatabase.CreateAQ("OE.OE_bookedorders_que") Set OraMsg = OraAq.AQMsg(ORATYPE_OBJECT, "BOLADM.order_typ") Set OraOrder = OraDatabase.CreateOraObject("BOLADM.order_typ") Set OraCust = OraDatabase.CreateOraObject("BOLADM.Customer_typ") Set OraBook = OraDatabase.CreateOraObject("BOLADM.book_typ") Set OraItem = OraDatabase.CreateOraObject("BOLADM.orderitem_typ") Set OraItemList = OraDatabase.CreateOraObject("BOLADM.orderitemlist_vartyp") ' Get the values of cust_state,cust_country etc from user(form_based ' input) and then a cmd_click event for Enqueue ' will execute the subroutine order_enq. Private Sub Order_enq() OraMsg.correlation = txt_correlation 'Initialize the customer details OraCust("state") = txt_cust_state OraCust("country") = txt_cust_country OraBook("title") = txt_book_title OraItem("quantity") = txt_book_qty OraItem("item") = OraBook OraItemList(1) = OraItem OraOrder("orderno") = txt_order_num OraOrder("ordertype") = txt_cust_order_typ OraOrder("orderregion") = cust_region OraOrder("customer") = OraCust OraOrder("items") = OraItemList 'Put the shipping priority into message property before enqueuing ' the message: OraMsg.priority = priority OraMsg = OraOrder Msgid = OraAq.enqueue 'Release all allocations End Sub
public static void createPriorityQueueTable(Connection db_conn) { AQSession aq_sess; AQQueueTableProperty mqt_prop; AQQueueTable pr_mq_table; AQQueueProperty q_prop; AQQueue bookedorders_q; try { /* Create an AQ Session: */ aq_sess = AQDriverManager.createAQSession(db_conn); /* Create a priority queue table for OE */ mqt_prop = new AQQueueTableProperty("BOLADM.order_typ"); mqt_prop.setComment("Order Entry Priority " + "MultiConsumer Orders queue table"); mqt_prop.setCompatible("8.1"); mqt_prop.setMultiConsumer(true); mqt_prop.setSortOrder("priority,enq_time"); pr_mq_table = aq_sess.createQueueTable("OE", "OE_orders_pr_mqtab", mqt_prop); /* Create a Queue in this queue table */ q_prop = new AQQueueProperty(); bookedorders_q = aq_sess.createQueue(pr_mq_table, "OE_bookedorders_que", q_prop); /* Enable enqueue and dequeue on the queue */ bookedorders_q.start(true, true); } catch (AQException ex) { System.out.println("AQ Exception: " + ex); } } /* When an order arrives, the order entry application can use the following procedure to enqueue the order into its booked orders queue. A shipping priority is specified for each order */ public static void order_enqueue(Connection db_conn, String book_title, double book_qty, double order_num, int ship_priority, String cust_state, String cust_country, String cust_region, String cust_order_type) { AQSession aq_sess; AQQueue bookedorders_q; Order enq_order; Customer cust_data; Book book_data; OrderItem item_data; OrderItem[] items; OrderItemList item_list; AQEnqueueOption enq_option; AQMessageProperty m_property; AQMessage message; AQObjectPayload obj_payload; byte[] enq_msg_id; try { /* Create an AQ Session: */ aq_sess = AQDriverManager.createAQSession(db_conn); cust_data = new Customer(); cust_data.setCountry(cust_country); cust_data.setState(cust_state); book_data = new Book(); book_data.setTitle(book_title); item_data = new OrderItem(); item_data.setQuantity(new BigDecimal(book_qty)); item_data.setItem(book_data); items = new OrderItem[1]; items[0] = item_data; item_list = new OrderItemList(items); enq_order = new Order(); enq_order.setCustomer(cust_data); enq_order.setItems(item_list); enq_order.setOrderno(new BigDecimal(order_num)); enq_order.setOrdertype(cust_order_type); bookedorders_q = aq_sess.getQueue("OE", "OE_bookedorders_que"); message = bookedorders_q.createMessage(); /* Put the shipping priority into message property before enqueuing */ m_property = message.getMessageProperty(); m_property.setPriority(ship_priority); obj_payload = message.getObjectPayload(); obj_payload.setPayloadData(enq_order); enq_option = new AQEnqueueOption(); /* Enqueue the message */ enq_msg_id = bookedorders_q.enqueue(enq_option, message); db_conn.commit(); } catch (AQException aq_ex) { System.out.println("AQ Exception: " + aq_ex); } catch (SQLException sql_ex) { System.out.println("SQL Exception: " + sql_ex); } } /* At each region, similar booked order queues are created. The orders are propagated from the central Order Entry's booked order queues to the regional booked order queues. For example, at the western region, the booked orders queue is created. Create a priority queue table for WS shipping */ public static void createWesternShippingQueueTable(Connection db_conn) { AQSession aq_sess; AQQueueTableProperty mqt_prop; AQQueueTable mq_table; AQQueueProperty q_prop; AQQueue bookedorders_q; try { /* Create an AQ Session: */ aq_sess = AQDriverManager.createAQSession(db_conn); /* Create a priority queue table for WS */ mqt_prop = new AQQueueTableProperty("BOLADM.order_typ"); mqt_prop.setComment("Western Shipping Priority " + "MultiConsumer Orders queue table"); mqt_prop.setCompatible("8.1"); mqt_prop.setMultiConsumer(true); mqt_prop.setSortOrder("priority,enq_time"); mq_table = aq_sess.createQueueTable("WS", "WS_orders_pr_mqtab", mqt_prop); /* Booked orders are stored in the priority queue table: */ q_prop = new AQQueueProperty(); bookedorders_q = aq_sess.createQueue(mq_table, "WS_bookedorders_que", q_prop); /* Start the queue */ bookedorders_q.start(true, true); } catch (AQException ex) { System.out.println("AQ Exception: " + ex); } /* At each region, the shipping application dequeues orders from the regional booked order queue according to the orders' shipping priorities, processes the orders, and enqueues the processed orders into the shipped orders queues or the back orders queues. */ }
AQ supports delay delivery of messages by letting the enqueuer specify a delay interval on a message when enqueuing the message, that is, the time before that a message cannot be retrieved by a dequeue call. (see "Enqueuing a Message [Specify Message Properties]" in Chapter 11, "Operational Interface: Basic Operations"). The delay interval determines when an enqueued message is marked as available to the dequeuers after the message is enqueued.
When a message is enqueued with a delay time set, the message is marked in a WAIT state. Messages in WAIT state are masked from the default dequeue calls. A background time-manager daemon wakes up periodically, scans an internal index for all WAIT state messages, and marks messages as READY if their delay time has passed. The time-manager will then post to all foreground processes that are waiting on queues for messages that have just been made available.
In the BooksOnLine application, delay can be used to implement deferred billing. A billing application can define a queue where shipped orders that are not billed immediately can be placed in a deferred billing queue with a delay. For example, a certain class of customer accounts, such as those of corporate customers, may not be billed for 15 days. The billing application dequeues incoming shipped order messages (from the shippedorders queue) and if the order is for a corporate customer, this order is enqueued into a deferred billing queue with a delay.
/* Enqueue an order to implement deferred billing so that the order is not made visible again until delay has expired: */ CREATE OR REPLACE PROCEDURE defer_billing(deferred_billing_order order_typ) AS defer_bill_queue_name VARCHAR2(62); enqopt dbms_aq.enqueue_options_t; msgprop dbms_aq.message_properties_t; enq_msgid RAW(16); BEGIN /* Enqueue the order into the deferred billing queue with a delay of 15 days: */ defer_bill_queue_name := 'CBADM.deferbilling_que'; msgprop.delay := 15*60*60*24; dbms_aq.enqueue(defer_bill_queue_name, enqopt, msgprop, deferred_billing_order, enq_msgid); END; /
set oraaq = OraDatabase.CreateAQ("CBADM.deferbilling_que") Set OraMsg = OraAq.AQMsg(ORATYPE_OBJECT, "BOLADM.order_typ") Set OraOrder = OraDatabase.CreateOraObject("BOLADM.order_typ") Private Sub defer_billing OraMsg = OraOrder OraMsg.delay = 15*60*60*24 OraMsg = OraOrder 'OraOrder contains the order details Msgid = OraAq.enqueue End Sub
public static void defer_billing(Connection db_conn, Order deferred_order) { AQSession aq_sess; AQQueue def_bill_q; AQEnqueueOption enq_option; AQMessageProperty m_property; AQMessage message; AQObjectPayload obj_payload; byte[] enq_msg_id; try { /* Create an AQ Session: */ aq_sess = AQDriverManager.createAQSession(db_conn); def_bill_q = aq_sess.getQueue("CBADM", "deferbilling_que"); message = def_bill_q.createMessage(); /* Enqueue the order into the deferred billing queue with a delay of 15 days */ m_property = message.getMessageProperty(); m_property.setDelay(15*60*60*24); obj_payload = message.getObjectPayload(); obj_payload.setPayloadData(deferred_order); enq_option = new AQEnqueueOption(); /* Enqueue the message */ enq_msg_id = def_bill_q.enqueue(enq_option, message); db_conn.commit(); } catch (Exception ex) { System.out.println("Exception " + ex); } }
Messages can be enqueued with an expiration that specifies the interval of time the message is available for dequeuing. Note that expiration processing requires that the queue monitor be running. The producer can also specify the time when a message expires, at which time the message is moved to an exception queue.
In the BooksOnLine application, expiration can be used to control the amount of time that is allowed to process a back order. The shipping application places orders for books that are not available on a back order queue. If the shipping policy is that all back orders must be shipped within a week, then messages can be enqueued into the back order queue with an expiration of 1 week. In this case, any back orders that are not processed within one week are moved to the exception queue with the message state set to EXPIRED. This can be used to flag any orders that have not been shipped according to the back order shipping policy.
CONNECT BOLADM/BOLADM
/* Req-enqueue a back order into a back order queue and set a delay of 7 days;
all back orders must be processed in 7 days or they are moved to the
exception queue: */
CREATE OR REPLACE PROCEDURE requeue_back_order(sale_region varchar2,
backorder order_typ)
AS
back_order_queue_name VARCHAR2(62);
enqopt dbms_aq.enqueue_options_t;
msgprop dbms_aq.message_properties_t;
enq_msgid RAW(16);
BEGIN
/* Look up a back order queue based the the region by means of a directory
service: */
IF sale_region = 'WEST' THEN
back_order_queue_name := 'WS.WS_backorders_que';
ELSIF sale_region = 'EAST' THEN
back_order_queue_name := 'ES.ES_backorders_que';
ELSE
back_order_queue_name := 'OS.OS_backorders_que';
END IF;
/* Enqueue the order with expiration set to 7 days: */
msgprop.expiration := 7*60*60*24;
dbms_aq.enqueue(back_order_queue_name, enqopt, msgprop,
backorder, enq_msgid);
END;
/
set oraaq1 = OraDatabase.CreateAQ("WS.WS_backorders_que") set oraaq2 = OraDatabase.CreateAQ("ES.ES_backorders_que") set oraaq3 = OraDatabase.CreateAQ("CBADM.deferbilling_que") Set OraMsg = OraAq.AQMsg(ORATYPE_OBJECT, "BOLADM.order_typ") Set OraBackOrder = OraDatabase.CreateOraObject("BOLADM.order_typ") Private Sub Requeue_backorder Dim q as oraobject If sale_region = WEST then q = oraaq1 else if sale_region = EAST then q = oraaq2 else q = oraaq3 end if OraMsg.delay = 7*60*60*24 OraMsg = OraBackOrder 'OraOrder contains the order details Msgid = q.enqueue End Sub
/* Re-enqueue a back order into a back order queue and set a delay of 7 days; all back orders must be processed in 7 days or they are moved to the exception queue */ public static void requeue_back_order(Connection db_conn, String sale_region, Order back_order) { AQSession aq_sess; AQQueue back_order_q; AQEnqueueOption enq_option; AQMessageProperty m_property; AQMessage message; AQObjectPayload obj_payload; byte[] enq_msg_id; try { /* Create an AQ Session: */ aq_sess = AQDriverManager.createAQSession(db_conn); /* Look up a back order queue based on the region */ if(sale_region.equals("WEST")) { back_order_q = aq_sess.getQueue("WS", "WS_backorders_que"); } else if(sale_region.equals("EAST")) { back_order_q = aq_sess.getQueue("ES", "ES_backorders_que"); } else { back_order_q = aq_sess.getQueue("OS", "OS_backorders_que"); } message = back_order_q.createMessage(); m_property = message.getMessageProperty(); /* Enqueue the order with expiration set to 7 days: */ m_property.setExpiration(7*60*60*24); obj_payload = message.getObjectPayload(); obj_payload.setPayloadData(back_order); enq_option = new AQEnqueueOption(); /* Enqueue the message */ enq_msg_id = back_order_q.enqueue(enq_option, message); db_conn.commit(); } catch (Exception ex) { System.out.println("Exception :" + ex); } }
Messages belonging to one queue can be grouped to form a set that can only be consumed by one user at a time. This requires that the queue be created in a queue table that is enabled for transactional message grouping (see "Creating a Queue Table" in Chapter 9, "Administrative Interface"). All messages belonging to a group have to be created in the same transaction and all messages created in one transaction belong to the same group. With this feature, you can segment complex messages into simple messages.
For example, messages directed to a queue containing invoices can be constructed as a group of messages starting with the header message, followed by messages representing details, followed by the trailer message. Message grouping is also useful if the message payload contains complex large objects such as images and video that can be segmented into smaller objects.
The general message properties (priority, delay, expiration) for the messages in a group are determined solely by the message properties specified for the first message (head) of the group, irrespective of which properties are specified for subsequent messages in the group.
The message grouping property is preserved across propagation. However, it is important to note that the destination queue where messages have to be propagated must also be enabled for transactional grouping. There are also some restrictions you need to keep in mind if the message grouping property is to be preserved while dequeuing messages from a queue enabled for transactional grouping (see "Dequeue Methods" and "Modes of Dequeuing" for additional information).
In the BooksOnLine application, message grouping can be used to handle new orders. Each order contains a number of books ordered one by one in succession. Items ordered over the Web exhibit similar behavior.
In the following example, each enqueue corresponds to an individual book that is part of an order and the group/transaction represents a complete order. Only the first enqueue contains customer information. Note that the OE_neworders_que is stored in the table OE_orders_sqtab,which has been enabled for transactional grouping. Refer to the example code for descriptions of procedures new_order_enq() and same_order_enq().
|
Note: Queue names and queue table names are converted to upper case. Mixed case (upper and lower case together) is not supported for queue names and queue table names. |
connect OE/OE; /* Create queue table for OE: */ EXECUTE dbms_aqadm.create_queue_table( \ queue_table => 'OE_orders_sqtab',\ comment => 'Order Entry Single-Consumer Orders queue table',\ queue_payload_type => 'BOLADM.order_typ',\ message_grouping => DBMS_AQADM.TRANSACTIONAL, \ compatible => '8.1', \ primary_instance => 1,\ secondary_instance => 2); /* Create neworders queue for OE: */ EXECUTE dbms_aqadm.create_queue ( \ queue_name => 'OE_neworders_que', queue_table => 'OE_orders_sqtab'); /* Login into OE account :*/ CONNECT OE/OE; SET serveroutput on; /* Enqueue some orders using message grouping into OE_neworders_que, First Order Group: */ EXECUTE BOLADM.new_order_enq('My First Book', 1, 1001, 'CA'); EXECUTE BOLADM.same_order_enq('My Second Book', 2); COMMIT; / /* Second Order Group: */ EXECUTE BOLADM.new_order_enq('My Third Book', 1, 1002, 'WA'); COMMIT; / /* Third Order Group: */ EXECUTE BOLADM.new_order_enq('My Fourth Book', 1, 1003, 'NV'); EXECUTE BOLADM.same_order_enq('My Fifth Book', 3); EXECUTE BOLADM.same_order_enq('My Sixth Book', 2); COMMIT; / /* Fourth Order Group: */ EXECUTE BOLADM.new_order_enq('My Seventh Book', 1, 1004, 'MA'); EXECUTE BOLADM.same_order_enq('My Eighth Book', 3); EXECUTE BOLADM.same_order_enq('My Ninth Book', 2); COMMIT; /
This functionality is currently not available.
public static void createMsgGroupQueueTable(Connection db_conn) { AQSession aq_sess; AQQueueTableProperty sqt_prop; AQQueueTable sq_table; AQQueueProperty q_prop; AQQueue neworders_q; try { /* Create an AQ Session: */ aq_sess = AQDriverManager.createAQSession(db_conn); /* Create a single-consumer orders queue table */ sqt_prop = new AQQueueTableProperty("BOLADM.order_typ"); sqt_prop.setComment("Order Entry Single-Consumer Orders queue table"); sqt_prop.setCompatible("8.1"); sqt_prop.setMessageGrouping(AQQueueTableProperty.TRANSACTIONAL); sq_table = aq_sess.createQueueTable("OE", "OE_orders_sqtab", sqt_prop); /* Create new orders queue for OE */ q_prop = new AQQueueProperty(); neworders_q = aq_sess.createQueue(sq_table, "OE_neworders_que", q_prop); } catch (AQException ex) { System.out.println("AQ Exception: " + ex); } }
Continuing the scenario introduced in "Message Format Transformation", the Order Entry and Shipping applications have different representations for the order item. The order entry application represents the order item in the form of the ADT OE.order_typ. The Western shipping application represents the order item in the form of the ADT WS.order_typ_sh. Therefore, the queues in the OE schema are of payload type OE.orders_typ and those in the WS schema are of payload type WS.orders_typ_sh.
Message transformation can be used during enqueue. This is especially useful for verification and transformation of messages during enqueue. An application can generate a message based on its own data model. The message can be transformed to the data type of the queue before it is enqueued using the transformation mapping.
At enqueue time, assume that instead of propagating messages from the OE_booked_orders_topic, an application dequeues the order, and, if it is meant for Western Shipping, publishes it to the WS_booked_orders_topic.
The application can use transformations at enqueue time as follows:
CREATE OR REPLACE FUNCTION fwd_message_to_ws_shipping(booked_order OE.order_typ) RETURNS boolean AS enq_opt dbms_aq.enqueue_options_t; msg_prp dbms_aq.message_properties_t; BEGIN IF (booked_order.order_region = 'WESTERN' and booked_order.order_type != 'RUSH') THEN enq_opt.transformation := 'OE.OE2WS'; msg_prp.recipient_list(0) := aq$_agent('West_shipping', null, null); dbms_aq.enqueue('WS.ws_bookedorders_topic', enq_opt, msg_prp, booked_order); RETURN true; ELSE RETURN false; END IF; END;
No example is provided with this release.
No example is provided with this release.
You can perform enqueue requests over the Internet using IDAP. See Chapter 17, "Internet Access to Advanced Queuing" for more information on sending AQ requests using IDAP.
In the BooksOnLine application, a customer can request:
The Order Entry application uses a priority queue to store booked orders. Booked orders are propagated to the regional booked orders queues. At each region, orders in these regional booked orders queues are processed in the order of the shipping priorities.
The following calls create the priority queues for the Order Entry application.
/* Create a priority queue table for OE: */ EXECUTE dbms_aqadm.create_queue_table( \ queue_table => 'OE_orders_pr_mqtab', \ sort_list =>'priority,enq_time', \ comment => 'Order Entry Priority \ MultiConsumer Orders queue table',\ multiple_consumers => TRUE, \ queue_payload_type => 'BOLADM.order_typ', \ compatible => '8.1', \ primary_instance => 2, \ secondary_instance => 1); EXECUTE dbms_aqadm.create_queue ( \ queue_name => 'OE_bookedorders_que', \ queue_table => 'OE_orders_pr_mqtab');
Assume that a customer, John, wants to send an enqueue request using SOAP. The XML message will have the following format.
<?xml version="1.0"?> <Envelope xmlns= "http://schemas.xmlsoap.org/soap/envelope/"> <Body> <AQXmlSend xmlns = "http://ns.oracle.com/AQ/schemas/access"> <producer_options> <destination>OE.OE_bookedorders_que</destination> </producer_options> <message_set> <message_count>1</message_count> <message> <message_number>1</message_number> <message_header> <correlation>ORDER1</correlation> <priority>1</priority> <sender_id> <agent_name>john</agent_name> </sender_id> </message_header> <message_payload> <ORDER_TYP> <ORDERNO>100</ORDERNO> <STATUS>NEW</STATUS> <ORDERTYPE>URGENT</ORDERTYPE> <ORDERREGION>EAST</ORDERREGION> <CUSTOMER> <CUSTNO>1001233</CUSTNO> <CUSTID>JOHN</CUSTID> <NAME>JOHN DASH</NAME> <STREET>100 EXPRESS STREET</STREET> <CITY>REDWOOD CITY</CITY> <STATE>CA</STATE> <ZIP>94065</ZIP> <COUNTRY>USA</COUNTRY> </CUSTOMER> <PAYMENTMETHOD>CREDIT</PAYMENTMETHOD> <ITEMS> <ITEMS_ITEM> <QUANTITY>10</QUANTITY> <ITEM> <TITLE>Perl handbook</TITLE> <AUTHORS>Randal</AUTHORS> <ISBN>345620200</ISBN> <PRICE>19</PRICE> </ITEM> <SUBTOTAL>190</SUBTOTAL> </ITEMS_ITEM> <ITEMS_ITEM> <QUANTITY>10</QUANTITY> <ITEM> <TITLE>JDBC guide</TITLE> <AUTHORS>Taylor</AUTHORS> <ISBN>123420212</ISBN> <PRICE>59</PRICE> </ITEM> <SUBTOTAL>590</SUBTOTAL> </ITEMS_ITEM> </ITEMS> <CCNUMBER>NUMBER01</CCNUMBER> <ORDER_DATE>08/23/2000 12:45:00</ORDER_DATE> </ORDER_TYP> </message_payload> </message> </message_set> <AQXmlCommit/> </AQXmlSend> </Body> </Envelope>
When there are multiple processes dequeuing from a single consumer queue or dequeuing for a single consumer on the multiconsumer queue, different processes skip the messages that are being worked on by a concurrent process. This allows multiple processes to work concurrently on different messages for the same consumer.
In this section, the following topics are discussed:
A message can be dequeued using one of the following dequeue methods:
A correlation identifier is a user-defined message property (of VARCHAR2 datatype) while a message identifier is a system-assigned value (of RAW datatype). Multiple messages with the same correlation identifier can be present in a queue, while only one message with a given message identifier can be present. If there are multiple messages with the same correlation identifier, the ordering (enqueue order) between messages may not be preserved on dequeue calls. The correlation identifier cannot be changed between successive dequeue calls without specifying the first message navigation option.
A dequeue condition is an expression that is similar in syntax to the WHERE clause of a SQL query. Dequeue conditions are expressed in terms of the attributes that represent message properties or message content. The messages in the queue are evaluated against the conditions and a message that satisfies the given condition is returned.
A default dequeue means that the first available message for the consumer of a multiconsumer queue or the first available message in a single-consumer queue is dequeued.
Note that dequeuing with correlation identifier, message identifier, or dequeue condition will not preserve the message grouping property (see "Message Grouping" and "Message Navigation in Dequeue" for more information).
In the BooksOnLine example, rush orders received by the East shipping site are processed first. This is achieved by dequeuing the message using the correlation identifier, which has been defined to contain the order type (rush/normal). For an illustration of dequeuing using a message identifier, refer to the get_northamerican_orders procedure discussed in the example under "Modes of Dequeuing".
CONNECT boladm/boladm; /* Create procedures to dequeue RUSH orders */ create or replace procedure get_rushtitles(consumer in varchar2) as deq_cust_data BOLADM.customer_typ; deq_book_data BOLADM.book_typ; deq_item_data BOLADM.orderitem_typ; deq_msgid RAW(16); dopt dbms_aq.dequeue_options_t; mprop dbms_aq.message_properties_t; deq_order_data BOLADM.order_typ; qname varchar2(30); no_messages exception; pragma exception_init (no_messages, -25228); new_orders BOOLEAN := TRUE; begin dopt.consumer_name := consumer; dopt.wait := 1; dopt.correlation := 'RUSH'; IF (consumer = 'West_Shipping') THEN qname := 'WS.WS_bookedorders_que'; ELSIF (consumer = 'East_Shipping') THEN qname := 'ES.ES_bookedorders_que'; ELSE qname := 'OS.OS_bookedorders_que'; END IF; WHILE (new_orders) LOOP BEGIN dbms_aq.dequeue( queue_name => qname, dequeue_options => dopt, message_properties => mprop, payload => deq_order_data, msgid => deq_msgid); commit; deq_item_data := deq_order_data.items(1); deq_book_data := deq_item_data.item; dbms_output.put_line(' rushorder book_title: ' || deq_book_data.title || ' quantity: ' || deq_item_data.quantity); EXCEPTION WHEN no_messages THEN dbms_output.put_line (' ---- NO MORE RUSH TITLES ---- '); new_orders := FALSE; END; END LOOP; end; / CONNECT EXECUTE on get_rushtitles to ES; /* Dequeue the orders: */ CONNECT ES/ES; /* Dequeue all rush order titles for East_Shipping: */ EXECUTE BOLADM.get_rushtitles('East_Shipping');
set oraaq1 = OraDatabase.CreateAQ("WS.WS_backorders_que") set oraaq2 = OraDatabase.CreateAQ("ES.ES_backorders_que") set oraaq3 = OraDatabase.CreateAQ("CBADM.deferbilling_que") Set OraMsg = OraAq.AQMsg(ORATYPE_OBJECT, "BOLADM.order_typ") Set OraBackOrder = OraDatabase.CreateOraObject("BOLADM.order_typ") Private Sub Requeue_backorder Dim q as oraobject If sale_region = WEST then q = oraaq1 else if sale_region = EAST then q = oraaq2 else q = oraaq3 end if OraMsg.delay = 7*60*60*24 OraMsg = OraBackOrder 'OraOrder contains the order details Msgid = q.enqueue End Sub
public static void getRushTitles(Connection db_conn, String consumer) { AQSession aq_sess; Order deq_order; byte[] deq_msgid; AQDequeueOption deq_option; AQMessageProperty msg_prop; AQQueue bookedorders_q; AQMessage message; AQObjectPayload obj_payload; boolean new_orders = true; try { /* Create an AQ Session: */ aq_sess = AQDriverManager.createAQSession(db_conn); deq_option = new AQDequeueOption(); deq_option.setConsumerName(consumer); deq_option.setWaitTime(1); deq_option.setCorrelation("RUSH"); if(consumer.equals("West_Shipping")) { bookedorders_q = aq_sess.getQueue("WS", "WS_bookedorders_que"); } else if(consumer.equals("East_Shipping")) { bookedorders_q = aq_sess.getQueue("ES", "ES_bookedorders_que"); } else { bookedorders_q = aq_sess.getQueue("OS", "OS_bookedorders_que"); } while(new_orders) { try { /* Dequeue the message */ message = bookedorders_q.dequeue(deq_option, Order.getFactory()); obj_payload = message.getObjectPayload(); deq_order = (Order)(obj_payload.getPayloadData()); System.out.println("Order number " + deq_order.getOrderno() + " is a rush order"); } catch (AQException aqex) { new_orders = false; System.out.println("No more rush titles"); System.out.println("Exception-1: " + aqex); } } } catch (Exception ex) { System.out.println("Exception-2: " + ex); } }
A consumer can dequeue a message from a multiconsumer, normal queue by supplying the name that was used in the AQ$_AGENT type of the DBMS_AQADM.ADD_SUBSCRIBER procedure or the recipient list of the message properties. (See "Adding a Subscriber" or "Enqueuing a Message [Specify Message Properties]" for more information).
consumer_name field of the dequeue_options_t record.LNOCISetAttr procedure to specify a text string as the LNOCI_ATTR_CONSUMER_NAME of an LNOCI_DTYPE_AQDEQ_OPTIONS descriptor.Multiple processes or operating system threads can use the same consumer_name to dequeue concurrently from a queue. In that case AQ will provide the first unlocked message that is at the head of the queue and is intended for the consumer. Unless the message ID of a specific message is specified during dequeue, the consumers can dequeue messages that are in the READY state.
A message is considered PROCESSED only when all intended consumers have successfully dequeued the message. A message is considered EXPIRED if one or more consumers did not dequeue the message before the EXPIRATION time. When a message has expired, it is moved to an exception queue.
The exception queue must also be a multiconsumer queue. Expired messages from multiconsumer queues cannot be dequeued by the intended recipients of the message. However, they can be dequeued in the REMOVE mode exactly once by specifying a NULL consumer name in the dequeue options. Hence, from a dequeue perspective, multiconsumer exception queues behave like single-consumer queues because each expired message can be dequeued only once using a NULL consumer name. Note that expired messages can be dequeued only by specifying a message ID if the multiconsumer exception queue was created in a queue table with the compatible parameter set to '8.0'.
Beginning with release 8.1.6, only the queue monitor removes messages from multiconsumer queues. This allows dequeuers to complete the dequeue operation by not locking the message in the queue table. Since the queue monitor removes messages that have been processed by all consumers from multiconsumer queues approximately once every minute, users may see a delay when the messages have been completely processed and when they are physically removed from the queue.
Consumers of a message in multiconsumer queues (either by virtue of being a subscriber to the queue or because the consumer was a recipient in the enqueuer's recipient list) can be local or remote.
NULL NAME and NULL ADDRESS and PROTOCOL field in the AQ$_AGENT type (see "Agent Type (aq$_agent)" in Chapter 2, "Basic Components").ADDRESS field refers to a queue in the same database. In this case the consumer will dequeue the message from a different queue in the same database. These addresses will be of the form [schema].queue_name where queue_name (optionally qualified by the schema name) is the target queue. If the schema is not specified, the schema of the current user executing the ADD_SUBSCRIBER procedure or the enqueue is used (see "Adding a Subscriber", or "Enqueuing a Message" in Chapter 11, "Operational Interface: Basic Operations"). Use the DBMS_AQADM.SCHEDULE_PROPAGATION command with a NULL destination (which is the default) to schedule propagation to such remote consumers (see "Scheduling a Queue Propagation" in Chapter 9, "Administrative Interface").ADDRESS field refers to a queue in a different database. In this case the database must be reachable using database links and the PROTOCOL must be either NULL or 0. These addresses will be of the form [schema].queue_name@dblink. If the schema is not specified, the schema of the current user executing the ADD_SUBSCRIBER procedure or the enqueue is used. If the database link is not a fully qualified name (does not have a domain name specified), the default domain as specified by the db_domain init.ora parameter will be used. Use the DBMS_AQADM.SCHEDULE_PROPAGATION procedure with the database link as the destination to schedule the propagation. AQ does not support the use of synonyms to refer to queues or database links.ADDRESS field refers to a destination that can be reached by a third party protocol. You will need to refer to the documentation of the third party software to determine how to specify the ADDRESS and the PROTOCOL database link, and on how to schedule propagation.When a consumer is remote, a message will be marked as PROCESSED in the source queue immediately after the message has been propagated, even though the consumer may not have dequeued the message at the remote queue. Similarly, when a propagated message expires at the remote queue, the message is moved to the DEFAULT exception queue of the remote queue's queue table, and not to the exception queue of the local queue. As can be seen in both cases, AQ does not currently propagate the exceptions to the source queue. You can use the MSGID and the ORIGINAL_MSGID columns in the queue table view (AQ$<queue_table>) to chain the propagated messages. When a message with message ID m1 is propagated to a remote queue, m1 is stored in the ORIGINAL_MSGID column of the remote queue.
The DELAY, EXPIRATION and PRIORITY parameters apply identically to both local and remote consumers. AQ accounts for any delay in propagation by adjusting the DELAY and EXPIRATION parameters accordingly. For example, if the EXPIRATION is set to one hour, and the message is propagated after 15 minutes, the expiration at the remote queue will be set to 45 minutes.
Since the database handles message propagation, OO4O does not differentiate between remote and local recipients. The same sequence of calls/steps are required to dequeue a message for local and remote recipients.
You have several options for selecting a message from a queue. You can select the "first message". Alternatively, once you have selected a message and established its position in the queue (for example, as the fourth message), you can then retrieve the "next message".
The first message navigation perfoms a SELECT on the queue. The next message navigation fetches from the results of the SELECT run in the first message navigation. Thus performance is optimized because subsequent dequeues need not run the entire SELECT again.
These selections work in a slightly different way if the queue is enabled for transactional grouping.
Note that the transaction grouping property is negated if a dequeue is performed in one of the following ways: dequeue by specifying a correlation identifier, dequeue by specifying a message identifier, or dequeuing some of the messages of a transaction and committing (see "Dequeue Methods").
In navigating through the queue, if the program reaches the end of the queue while using the "next message" or "next transaction" option, and you have specified a nonzero wait time, then the navigating position is automatically changed to the beginning of the queue. If a zero wait time is specified, you may get an exception when the end of the queue is reached.
The following scenario in the BooksOnLine example continues the message grouping example already discussed with regard to enqueuing (see "Dequeue Methods").
The get_orders() procedure dequeues orders from the OE_neworders_que. Recall that each transaction refers to an order and each message corresponds to an individual book in the order. The get_orders() procedure loops through the messages to dequeue the book orders. It resets the position to the beginning of the queue using the first message option before the first dequeues. It then uses the next message navigation option to retrieve the next book (message) of an order (transaction). If it gets an error message indicating all message in the current group/transaction have been fetched, it changes the navigation option to next transaction and gets the first book of the next order. It then changes the navigation option back to next message for fetching subsequent messages in the same transaction. This is repeated until all orders (transactions) have been fetched.
CONNECT boladm/boladm; create or replace procedure get_new_orders as deq_cust_data BOLADM.customer_typ; deq_book_data BOLADM.book_typ; deq_item_data BOLADM.orderitem_typ; deq_msgid RAW(16); dopt dbms_aq.dequeue_options_t; mprop dbms_aq.message_properties_t; deq_order_data BOLADM.order_typ; qname VARCHAR2(30); no_messages exception; end_of_group exception; pragma exception_init (no_messages, -25228); pragma exception_init (end_of_group, -25235); new_orders BOOLEAN := TRUE; BEGIN dopt.wait := 1; dopt.navigation := DBMS_AQ.FIRST_MESSAGE; qname := 'OE.OE_neworders_que'; WHILE (new_orders) LOOP BEGIN LOOP BEGIN dbms_aq.dequeue( queue_name => qname, dequeue_options => dopt, message_properties => mprop, payload => deq_order_data, msgid => deq_msgid); deq_item_data := deq_order_data.items(1); deq_book_data := deq_item_data.item; deq_cust_data := deq_order_data.customer; IF (deq_cust_data IS NOT NULL) THEN dbms_output.put_line(' **** NEXT ORDER **** '); dbms_output.put_line('order_num: ' || deq_order_data.orderno); dbms_output.put_line('ship_state: ' || deq_cust_data.state); END IF; dbms_output.put_line(' ---- next book ---- '); dbms_output.put_line(' book_title: ' || deq_book_data.title || ' quantity: ' || deq_item_data.quantity); EXCEPTION WHEN end_of_group THEN dbms_output.put_line ('*** END OF ORDER ***'); commit; dopt.navigation := DBMS_AQ.NEXT_TRANSACTION; END; END LOOP; EXCEPTION WHEN no_messages THEN dbms_output.put_line (' ---- NO MORE NEW ORDERS ---- '); new_orders := FALSE; END; END LOOP; END; / CONNECT EXECUTE ON get_new_orders to OE; /* Dequeue the orders: */ CONNECT OE/OE; EXECUTE BOLADM.get_new_orders;
Dim OraSession as object Dim OraDatabase as object Dim OraAq as object Dim OraMsg as Object Dim OraOrder,OraItemList,OraItem,OraBook,OraCustomer as Object Dim Msgid as String Set OraSession = CreateObject("OracleInProcServer.XOraSession") Set OraDatabase = OraSession.DbOpenDatabase("", "boladm/boladm", 0&) set oraaq = OraDatabase.CreateAQ("OE.OE_neworders_que") Set OraMsg = OraAq.AQMsg(ORATYPE_OBJECT, "BOLADM.order_typ") OraAq.wait = 1 OraAq.Navigation = ORAAQ_DQ_FIRST_MESSAGE private sub get_new_orders Dim MsgIsDequeued as Boolean On Error goto ErrHandler MsgIsDequeued = TRUE msgid = q.Dequeue if MsgIsDequeued then set OraOrder = OraMsg OraItemList = OraOrder("items") OraItem = OraItemList(1) OraBook = OraItem("item") OraCustomer = OraOrder("customer") ' Populate the textboxes with the values if( OraCustomer ) then if OraAq.Navigation <> ORAAQ_DQ_NEXT_MESSAGE then MsgBox " ********* NEXT ORDER *******" end if txt_book_orderno = OraOrder("orderno") txt_book_shipstate = OraCustomer("state") End if OraAq.Navigation = ORAAQ_DQ_NEXT_MESSAGE txt_book_title = OraBook("title") txt_book_qty = OraItem("quantity") Else MsgBox " ********* END OF ORDER *******" End if ErrHandler : 'Handle error case, like no message etc If OraDatabase.LastServerErr = 25228 then OraAq.Navigation = ORAAQ_DQ_NEXT_TRANSACTION MsgIsDequeued = FALSE Resume Next End If 'Process other errors end sub
No example is provided with this release.
A dequeue request can either view a message or delete a message (see "Dequeuing a Message" in Chapter 11, "Operational Interface: Basic Operations").
If a message is browsed, it remains available for further processing. Similarly if a message is locked, it remains available for further processing after the lock is released by performing a transaction commit or rollback. After a message is consumed, using either of the remove modes, it is no longer available for dequeue requests.
When a message is dequeued using REMOVE_NODATA mode, the payload of the message is not retrieved. This mode can be useful when the user has already examined the message payload, possibly by means of a previous BROWSE dequeue. In this way, you can avoid the overhead of payload retrieval that can be substantial for large payloads
A message is retained in the queue table after it has been consumed only if a retention time is specified for a queue. Messages cannot be retained in exception queues (refer to the section on exceptions for further information). Removing a message with no data is generally used if the payload is known (from a previous browse/locked mode dequeue call), or the message will not be used.
Note that after a message has been browsed, there is no guarantee that the message can be dequeued again since a dequeue call from a concurrent user might have removed the message. To prevent a viewed message from being dequeued by a concurrent user, you should view the message in the locked mode.
In general, use care while using the browse mode. The dequeue position is automatically changed to the beginning of the queue if a nonzero wait time is specified and the navigating position reaches the end of the queue. Hence repeating a dequeue call in the browse mode with the "next message" navigation option and a nonzero wait time can dequeue the same message over and over again. We recommend that you use a nonzero wait time for the first dequeue call on a queue in a session, and then use a zero wait time with the next message navigation option for subsequent dequeue calls. If a dequeue call gets an "end of queue" error message, the dequeue position can be explicitly set by the dequeue call to the beginning of the queue using the "first message" navigation option, following which the messages in the queue can be browsed again.
In the following scenario from the BooksOnLine example, international orders destined to Mexico and Canada are to be processed separately due to trade policies and carrier discounts. Hence, a message is viewed in the locked mode (so no other concurrent user removes the message) and the customer country (message payload) is checked. If the customer country is Mexico or Canada, the message is consumed (deleted from the queue) using REMOVE_NODATA (since the payload is already known). Otherwise, the lock on the message is released by the commit call. Note that the remove dequeue call uses the message identifier obtained from the locked mode dequeue call. The shipping_bookedorder_deq (refer to the example code for the description of this procedure) call illustrates the use of the browse mode.
CONNECT boladm/boladm; create or replace procedure get_northamerican_orders as deq_cust_data BOLADM.customer_typ; deq_book_data BOLADM.book_typ; deq_item_data BOLADM.orderitem_typ; deq_msgid RAW(16); dopt dbms_aq.dequeue_options_t; mprop dbms_aq.message_properties_t; deq_order_data BOLADM.order_typ; deq_order_nodata BOLADM.order_typ; qname VARCHAR2(30); no_messages exception; pragma exception_init (no_messages, -25228); new_orders BOOLEAN := TRUE; begin dopt.consumer_name := consumer; dopt.wait := DBMS_AQ.NO_WAIT; dopt.navigation := dbms_aq.FIRST_MESSAGE; dopt.dequeue_mode := DBMS_AQ.LOCKED; qname := 'OS.OS_bookedorders_que'; WHILE (new_orders) LOOP BEGIN dbms_aq.dequeue( queue_name => qname, dequeue_options => dopt, message_properties => mprop, payload => deq_order_data, msgid => deq_msgid); deq_item_data := deq_order_data.items(1); deq_book_data := deq_item_data.item; deq_cust_data := deq_order_data.customer; IF (deq_cust_data.country = 'Canada' OR deq_cust_data.country = 'Mexico' ) THEN dopt.dequeue_mode := dbms_aq.REMOVE_NODATA; dopt.msgid := deq_msgid; dbms_aq.dequeue( queue_name => qname, dequeue_options => dopt, message_properties => mprop, payload => deq_order_nodata, msgid => deq_msgid); commit; dbms_output.put_line(' **** next booked order **** '); dbms_output.put_line('order_no: ' || deq_order_data.orderno || ' book_title: ' || deq_book_data.title || ' quantity: ' || deq_item_data.quantity); dbms_output.put_line('ship_state: ' || deq_cust_data.state || ' ship_country: ' || deq_cust_data.country || ' ship_order_type: ' || deq_order_data.ordertype); END IF; commit; dopt.dequeue_mode := DBMS_AQ.LOCKED; dopt.msgid := NULL; dopt.navigation := dbms_aq.NEXT_MESSAGE; EXCEPTION WHEN no_messages THEN dbms_output.put_line (' ---- NO MORE BOOKED ORDERS ---- '); new_orders := FALSE; END; END LOOP; end; / CONNECT EXECUTE on get_northamerican_orders to OS; CONNECT ES/ES; /* Browse all booked orders for East_Shipping: */ EXECUTE BOLADM.shipping_bookedorder_deq('East_Shipping', DBMS_AQ.BROWSE); CONNECT OS/OS; /* Dequeue all international North American orders for Overseas_Shipping: */ EXECUTE BOLADM.get_northamerican_orders;
OO4O supports all the modes of dequeuing described earlier. Possible values include:
Dim OraSession as object Dim OraDatabase as object Dim OraAq as object Dim OraMsg as Object Dim OraOrder,OraItemList,OraItem,OraBook,OraCustomer as Object Dim Msgid as String Set OraSession = CreateObject("OracleInProcServer.XOraSession") Set OraDatabase = OraSession.DbOpenDatabase("", "boladm/boladm", 0&) set oraaq = OraDatabase.CreateAQ("OE.OE_neworders_que") OraAq.DequeueMode = ORAAQ_DQ_BROWSE
public static void get_northamerican_orders(Connection db_conn) { AQSession aq_sess; Order deq_order; Customer deq_cust; String cust_country; byte[] deq_msgid; AQDequeueOption deq_option; AQMessageProperty msg_prop; AQQueue bookedorders_q; AQMessage message; AQObjectPayload obj_payload; boolean new_orders = true; try { /* Create an AQ Session: */ aq_sess = AQDriverManager.createAQSession(db_conn); deq_option = new AQDequeueOption(); deq_option.setConsumerName("Overseas_Shipping"); deq_option.setWaitTime(AQDequeueOption.WAIT_NONE); deq_option.setNavigationMode(AQDequeueOption.NAVIGATION_FIRST_MESSAGE); deq_option.setDequeueMode(AQDequeueOption.DEQUEUE_LOCKED); bookedorders_q = aq_sess.getQueue("OS", "OS_bookedorders_que"); while(new_orders) { try { /* Dequeue the message - browse with lock */ message = bookedorders_q.dequeue(deq_option, Order.getFactory()); obj_payload = message.getObjectPayload(); deq_msgid = message.getMessageId(); deq_order = (Order)(obj_payload.getPayloadData()); deq_cust = deq_order.getCustomer(); cust_country = deq_cust.getCountry(); if(cust_country.equals("Canada") || cust_country.equals("Mexico")) { deq_option.setDequeueMode( AQDequeueOption.DEQUEUE_REMOVE_NODATA); deq_option.setMessageId(deq_msgid); /* Delete the message */ bookedorders_q.dequeue(deq_option, Order.getFactory()); System.out.println("---- next booked order ------"); System.out.println("Order no: " + deq_order.getOrderno()); System.out.println("Ship state: " + deq_cust.getState()); System.out.println("Ship country: " + deq_cust.getCountry()); System.out.println("Order type: " + deq_order.getOrdertype()); } db_conn.commit(); deq_option.setDequeueMode(AQDequeueOption.DEQUEUE_LOCKED); deq_option.setMessageId(null); deq_option.setNavigationMode( AQDequeueOption.NAVIGATION_NEXT_MESSAGE); } catch (AQException aqex) { new_orders = false; System.out.println("--- No more booked orders ----"); System.out.println("Exception-1: " + aqex); } } } catch (Exception ex) { System.out.println("Exception-2: " + ex); } }
AQ allows applications to block on one or more queues waiting for the arrival of either a newly enqueued message or for a message that becomes ready. You can use the DEQUEUE operation to wait for the arrival of a message in a queue (see "Dequeuing a Message") or the LISTEN operation to wait for the arrival of a message in more than one queue (see "Listening to One or More Single-Consumer Queues".
When the blocking DEQUEUE call returns, it returns the message properties and the message payload. By contrast, when the blocking LISTEN call returns, it discloses only the name of the queue where a message has arrived. A subsequent DEQUEUE operation is needed to dequeue the message.
Applications can optionally specify a timeout of zero or more seconds to indicate the time that AQ must wait for the arrival of a message. The default is to wait forever until a message arrives in the queue. This optimization is important in two ways. It removes the burden of continually polling for messages from the application. And it saves CPU and network resource because the application remains blocked until a new message is enqueued or becomes READY after its DELAY time. Applications can also perform a blocking dequeue on exception queues to wait for arrival of EXPIRED messages.
A process or thread that is blocked on a dequeue is either awakened directly by the enqueuer if the new message has no DELAY or is awakened by the queue monitor process when the DELAY or EXPIRATION time has passed. Applications cannot only wait for the arrival of a message in the queue that an enqueuer enqueues a message, but also on a remote queue, if propagation has been scheduled to the remote queue using DBMS_AQADM.SCHEDULE_PROPAGATION. In this case, the AQ propagator will wake up the blocked dequeuer after a message has been propagated.
In the BooksOnLine example, the get_rushtitles procedure discussed under dequeue methods specifies a wait time of 1 second in the dequeue_options argument for the dequeue call. Wait time can be specified in different ways as illustrated in the following code.
DBMS_AQ.NO_WAIT, a wait time of 0 seconds is implemented. The dequeue call in this case will return immediately even if there are no messages in the queue.DBMS_AQ.FOREVER, the dequeue call is blocked without a time out until a message is available in the queue./* dopt is a variable of type dbms_aq.dequeue_options_t. Set the dequeue wait time to 10 seconds: */ dopt.wait := 10; /* Set the dequeue wait time to 0 seconds: */ dopt.wait := DBMS_AQ.NO_WAIT; /* Set the dequeue wait time to infinite (forever): */ dopt.wait := DBMS_AQ.FOREVER;
OO4O supports asynchronous dequeuing of messages. First, the monitor is started for a particular queue. When messages that fulfil the user criteria are dequeued, the user's callback object is notified.
AQDequeueOption deq-opt;
deq-opt = new AQDequeueOption ();
If the transaction dequeuing the message from a queue fails, it is regarded as an unsuccessful attempt to consume the message. AQ records the number of failed attempts to consume the message in the message history. Applications can query the retry_count column of the queue table view to find out the number of unsuccessful attempts on a message. In addition, AQ allows the application to specify, at the queue level, the maximum number of retries for messages in the queue. If the number of failed attempts to remove a message exceeds this number, the message is moved to the exception queue and is no longer available to applications.
A bad condition can cause the transaction receiving a message to end. AQ allows users to hide the bad message for a prespecified interval. A retry_delay can be specified along with maximum retries. This means that a message that has had a failed attempt will be visible in the queue for dequeue after the retry_delay interval. Until then it will be in the WAITING state. In the AQ background process, the time manager enforces the retry delay property. The default value for maximum retries is 5. The default value for retry delay is 0. Note that maximum retries and retry delay are not available with 8.0-compatible multiconsumer queues.
/* Create a package that enqueue with delay set to one day: /* CONNECT BOLADM/BOLADM > /* queue has max retries = 4 and retry delay = 12 hours */ execute dbms_aqadm.alter_queue(queue_name = 'WS.WS_BOOKED_ORDERS_QUE', max_retr ies = 4, retry_delay = 3600*12); > /* processes the next order available in the booked_order_queue */ CREATE OR REPLACE PROCEDURE process_next_order() AS dqqopt dbms_aq.dequeue_options_t; msgprop dbms_aq.message_properties_t; deq_msgid RAW(16); book BOLADM.book_typ; item BOLADM.orderitem_typ; BOLADM.order_typ order; BEGIN > dqqopt.dequeue_option := DBMS_AQ.FIRST_MESSAGE; dbms_aq.dequeue('WS.WS_BOOKED_ORDERS_QUEUE', dqqopt, msgprop, order, deq_msgid ); > /* for simplicity, assume order has a single item */ item = order.items(1); book = the_orders.item; > /* assume search_inventory searches inventory for the book */ /* if we don't find the book in the warehouse, abort transaction */ IF (search_inventory(book) != TRUE) rollback; ELSE process_order(order); END IF; > END; /
Use the dbexecutesql interface from the database for this functionality.
public static void setup_queue(Connection db_conn) { AQSession aq_sess; AQQueue bookedorders_q; AQQueueProperty q_prop; try { /* Create an AQ Session: */ aq_sess = AQDriverManager.createAQSession(db_conn); bookedorders_q = aq_sess.getQueue("WS", "WS_bookedorders_que"); /* Alter queue - set max retries = 4 and retry delay = 12 hours */ q_prop = new AQQueueProperty(); q_prop.setMaxRetries(4); q_prop.setRetryInterval(3600*12); // specified in seconds bookedorders_q.alterQueue(q_prop); } catch (Exception ex) { System.out.println("Exception: " + ex); } } public static void process_next_order(Connection db_conn) { AQSession aq_sess; Order deq_order; OrderItem order_item; Book book; AQDequeueOption deq_option; AQMessageProperty msg_prop; AQQueue bookedorders_q; AQMessage message; AQObjectPayload obj_payload; try { /* Create an AQ Session: */ aq_sess = AQDriverManager.createAQSession(db_conn); deq_option = new AQDequeueOption(); deq_option.setNavigationMode(AQDequeueOption.NAVIGATION_FIRST_MESSAGE); bookedorders_q = aq_sess.getQueue("WS", "WS_bookedorders_que"); /* Dequeue the message */ message = bookedorders_q.dequeue(deq_option, Order.getFactory()); obj_payload = message.getObjectPayload(); deq_order = (Order)(obj_payload.getPayloadData()); /* for simplicity, assume order has a single item */ order_item = deq_order.getItems().getElement(0); book = order_item.getItem(); /* assume search_inventory searches inventory for the book * if we don't find the book in the warehouse, abort transaction */ if(search_inventory(book) != true) db_conn.rollback(); else process_order(deq_order); } catch (AQException aqex) { System.out.println("Exception-1: " + aqex); } catch (Exception ex) { System.out.println("Exception-2: " + ex); } }
AQ provides four integrated mechanisms to support exception handling in applications: EXCEPTION_QUEUES, EXPIRATION, MAX_RETRIES and RETRY_DELAY.
An exception_queue is a repository for all expired or unserviceable messages. Applications cannot directly enqueue into exception queues. Also, a multiconsumer exception queue cannot have subscribers associated with it. However, an application that intends to handle these expired or unserviceable messages can dequeue from the exception queue. The exception queue created for messages intended for a multiconsumer queue must itself be a multiconsumer queue. Like any other queue, the exception queue must be enabled for dequeue using the DBMS_AQADM.START_QUEUE procedure. You will get an Oracle error if you try to enable an exception queue for enqueue.
When a message has expired, it is moved to an exception queue. The exception queue for a message in multiconsumer queue must also be a multiconsumer queue. Expired messages from multiconsumer queues cannot be dequeued by the intended recipients of the message. However, they can be dequeued in the REMOVE mode exactly once by specifying a NULL consumer name in the dequeue options. Hence, from a dequeue perspective multiconsumer exception queues behave like single-consumer queues because each expired message can be dequeued only once using a NULL consumer name. Messages can also be dequeued from the exception queue by specifying the message ID.
The exception queue is a message property that can be specified during enqueue time (see "Enqueuing a Message [Specify Message Properties]" in Chapter 11, "Operational Interface: Basic Operations"). In PL/SQL users can use the exception_queue attribute of the DBMS_AQ.MESSAGE_PROPERTIES_T record to specify the exception queue. In OCI users can use the LNOCISetAttr procedure to set the LNOCI_ATTR_EXCEPTION_QUEUE attribute of the LNOCIAQMsgProperties descriptor.
If an exception queue is not specified, the default exception queue is used. If the queue is created in a queue table, for example, QTAB, the default exception queue will be called AQ$_QTAB_E. The default exception queue is automatically created when the queue table is created. Messages are moved to the exception queues by AQ under the following conditions:
DBMS_AQ.NEVER, meaning the messages will not expire.For messages intended for multiple recipients, each message keeps a separate retry count for each recipient. The message is moved to the exception queue only when retry counts for all recipients of the message have exceeded the specified retry limit. The default retry limit is 5 for single-consumer queues and 8.1-compatible multiconsumer queues. No retry limit is not supported for 8.0- compatible multiconsumer queues.
DBMS_AQ.DEQUEUE. If the dequeue procedure succeeds but the PL/SQL procedure raises an exception, AQ will attempt to increment the RETRY_COUNT of the message returned by the dequeue procedure.Messages intended for 8.1-compatible multiconsumer queues cannot be dequeued by the intended recipients once the messages have been moved to an exception queue. These messages should instead be dequeued in the REMOVE or BROWSE mode exactly once by specifying a NULL consumer name in the dequeue options. The messages can also be dequeued by their message IDs.
Messages intended for single consumer queues, or for 8.0-compatible multiconsumer queues, can only be dequeued by their message IDs once the messages have been moved to an exception queue.
Users can associate a RETRY_DELAY with a queue. The default value for this parameter is 0, meaning that the message will be available for dequeue immediately after the RETRY_COUNT is incremented. Otherwise the message will be unavailable for RETRY_DELAY seconds. After RETRY_DELAY seconds, the queue monitor marks the message as READY.
For a multiconsumer queue, RETRY_DELAY is for each subscriber.
In the BooksOnLine application, the business rule for each shipping region is that an order will be placed in a back order queue if the order cannot be filled immediately. The back order application will try to fill the order once a day. If the order cannot be filled within 5 days, it is placed in an exception queue for special processing. You can implement this process by making use of the retry and exception handling features in AQ.
The following example shows how you can create a queue with specific maximum retry and retry delay interval.
/* Example for creating a back order queue in Western Region which allows a maximum of 5 retries and 1 day delay between each retry. */ CONNECT BOLADM/BOLADM BEGIN dbms_aqadm.create_queue ( queue_name => 'WS.WS_backorders_que', queue_table => 'WS.WS_orders_mqtab', max_retries => 5, retry_delay => 60*60*24); END; / /* Create an exception queue for the back order queue for Western Region. */ CONNECT BOLADM/BOLADM BEGIN dbms_aqadm.create_queue ( queue_name => 'WS.WS_backorders_excpt_que', queue_table => 'WS.WS_orders_mqtab', queue_type => DBMS_AQADM.EXCEPTION_QUEUE); end; / /* Enqueue a message to WS_backorders_que and specify WS_backorders_excpt_que as the exception queue for the message: */ CONNECT BOLADM/BOLADM CREATE OR REPLACE PROCEDURE enqueue_WS_unfilled_order(backorder order_typ) AS back_order_queue_name varchar2(62); enqopt dbms_aq.enqueue_options_t; msgprop dbms_aq.message_properties_t; enq_msgid raw(16); BEGIN /* Set back order queue name for this message: */ back_order_queue_name := 'WS.WS_backorders_que'; /* Set exception queue name for this message: */ msgprop.exception_queue := 'WS.WS_backorders_excpt_que'; dbms_aq.enqueue(back_order_queue_name, enqopt, msgprop, backorder, enq_msgid); END; /
The exception queue is a message property that can be provided at the time of enqueuing a message. If this property is not set, the default exception queue of the queue will be used for any error conditions.
set oraaq = OraDatabase.CreateAQ("CBADM.deferbilling_que") Set OraMsg = OraAq.AQMsg(ORATYPE_OBJECT, "BOLADM.order_typ") Set OraOrder = OraDatabase.CreateOraObject("BOLADM.order_typ") OraMsg = OraOrder OraMsg.delay = 15*60*60*24 OraMsg.ExceptionQueue = "WS.WS_backorders_que" 'Fill up the order values OraMsg = OraOrder 'OraOrder contains the order details Msgid = OraAq.enqueue
public static void createBackOrderQueues(Connection db_conn) { AQSession aq_sess; AQQueue backorders_q; AQQueue backorders_excp_q; AQQueueProperty q_prop; AQQueueProperty q_prop2; AQQueueTable mq_table; try { /* Create an AQ Session: */ aq_sess = AQDriverManager.createAQSession(db_conn); mq_table = aq_sess.getQueueTable("WS", "WS_orders_mqtab"); /* Create a back order queue in Western Region which allows a maximum of 5 retries and 1 day delay between each retry. */ q_prop = new AQQueueProperty(); q_prop.setMaxRetries(5); q_prop.setRetryInterval(60*24*24); backorders_q = aq_sess.createQueue(mq_table, "WS_backorders_que", q_prop); backorders_q.start(true, true); /* Create an exception queue for the back order queue for Western Region. */ q_prop2 = new AQQueueProperty(); q_prop2.setQueueType(AQQueueProperty.EXCEPTION_QUEUE); backorders_excp_q = aq_sess.createQueue(mq_table, "WS_backorders_excpt_que", q_prop2); } catch (Exception ex) { System.out.println("Exception " + ex); } } /* Enqueue a message to WS_backorders_que and specify WS_backorders_excpt_que as the exception queue for the message: */ public static void enqueue_WS_unfilled_order(Connection db_conn, Order back_order) { AQSession aq_sess; AQQueue back_order_q; AQEnqueueOption enq_option; AQMessageProperty m_property; AQMessage message; AQObjectPayload obj_payload; byte[] enq_msg_id; try { /* Create an AQ Session: */ aq_sess = AQDriverManager.createAQSession(db_conn); back_order_q = aq_sess.getQueue("WS", "WS_backorders_que"); message = back_order_q.createMessage(); /* Set exception queue name for this message: */ m_property = message.getMessageProperty(); m_property.setExceptionQueue("WS.WS_backorders_excpt_que"); obj_payload = message.getObjectPayload(); obj_payload.setPayloadData(back_order); enq_option = new AQEnqueueOption(); /* Enqueue the message */ enq_msg_id = back_order_q.enqueue(enq_option, message); db_conn.commit(); } catch (Exception ex) { System.out.println("Exception: " + ex); } }
Messages can be routed to various recipients based on message properties or message content. Users define a rule-based subscription for a given queue to specify interest in receiving messages that meet particular conditions.
Rules are Boolean expressions that evaluate to TRUE or FALSE. Similar in syntax to the WHERE clause of a SQL query, rules are expressed in terms of the attributes that represent message properties or message content. These subscriber rules are evaluated against incoming messages and those rules that match are used to determine message recipients. This feature thus supports the notions of content-based subscriptions and content-based routing of messages.
Subscription rules can also be defined on an attribute of type XMLType using XML operators such as ExistsNode.
For the BooksOnLine application, we illustrate how rule-based subscriptions are used to implement a publish-subscribe paradigm utilizing content-based subscription and content-based routing of messages. The interaction between the Order Entry application and each of the Shipping Applications is modeled as follows:
XMLType attribute to identify special handling.Each shipping application subscribes to the OE booked orders queue. The following rule-based subscriptions are defined by the Order Entry user to handle the routing of booked orders from the Order Entry application to each of the Shipping applications.
CONNECT OE/OE;
Western Region Shipping defines an agent called 'West_Shipping' with the WS booked orders queue as the agent address (destination queue where messages must be delivered). This agent subscribes to the OE booked orders queue using a rule specified on order region and ordertype attributes.
/* Add a rule-based subscriber for West Shipping - West Shipping handles Western region U.S. orders, Rush Western region orders are handled by East Shipping: */ DECLARE subscriber aq$_agent; BEGIN subscriber := aq$_agent('West_Shipping', 'WS.WS_bookedorders_que', null); dbms_aqadm.add_subscriber( queue_name => 'OE.OE_bookedorders_que', subscriber => subscriber, rule => 'tab.user_data.orderregion = ''WESTERN'' AND tab.user_data.ordertype != ''RUSH'''); END; /
Eastern Region Shipping defines an agent called East_Shipping with the ES booked orders queue as the agent address (the destination queue where messages must be delivered). This agent subscribes to the OE booked orders queue using a rule specified on orderregion, ordertype and customer attributes.
/* Add a rule-based subscriber for East Shipping - East shipping handles all Eastern region orders, East shipping also handles all U.S. rush orders: */ DECLARE subscriber aq$_agent; BEGIN subscriber := aq$_agent('East_Shipping', 'ES.ES_bookedorders_que', null); dbms_aqadm.add_subscriber( queue_name => 'OE.OE_bookedorders_que', subscriber => subscriber, rule => 'tab.user_data.orderregion = ''EASTERN'' OR (tab.user_data.ordertype = ''RUSH'' AND tab.user_data.customer.country = ''USA'') '); END;
Overseas Shipping defines an agent called Overseas_Shipping with the OS booked orders queue as the agent address (destination queue to which messages must be delivered). This agent subscribes to the OE booked orders queue using a rule specified on the orderregion attribute. Since the representation of orders at the Overseas Shipping site is different from the representation of orders at the Order Entry site, a transformation is applied before messages are propagated from the Order Entry site to the Overseas Shipping site.
/* Add a rule-based subscriber (for Overseas Shipping) to the Booked orders queues with Transformation. Overseas Shipping handles all non-US orders: */ DECLARE subscriber aq$_agent; BEGIN subscriber := aq$_agent('Overseas_Shipping','OS.OS_bookedorders_que',null); dbms_aqadm.add_subscriber( queue_name => 'OE.OE_bookedorders_que', subscriber => subscriber, rule => 'tab.user_data.orderregion = ''INTERNATIONAL''', transformation => 'OS.OE2XML'); END;
See "Message Format Transformation" for more details on defining transformations.
Assume that the Overseas Shipping site has a subscriber, Overseas_DHL, for handling RUSH orders. Since OS_bookedorders_que has the order details represented as an XMLType, the rule uses XPath syntax.
DECLARE subscriber aq$_agent; BEGIN subscriber := aq$_agent('Overseas_DHL', null, null); dbms_aqadm.add_subscriber( queue_name => 'OS.OS_bookedorders_que', subscriber => subscriber, rule => 'tab.user_data.extract(''/ORDER_TYP/ORDERTYPE/
text()'').getStringVal()=''RUSH'''); END;
This functionality is currently not available.
public static void addRuleBasedSubscribers(Connection db_conn) { AQSession aq_sess; AQQueue bookedorders_q; String rule; AQAgent agt1, agt2, agt3; try { /* Create an AQ Session: */ aq_sess = AQDriverManager.createAQSession(db_conn); bookedorders_q = aq_sess.getQueue("OE", "OE_booked_orders_que"); /* Add a rule-based subscriber for West Shipping - West Shipping handles Western region U.S. orders, Rush Western region orders are handled by East Shipping: */ agt1 = new AQAgent("West_Shipping", "WS.WS_bookedorders_que"); rule = "tab.user_data.orderregion = 'WESTERN' AND " + "tab.user_data.ordertype != 'RUSH'"; bookedorders_q.addSubscriber(agt1, rule); /* Add a rule-based subscriber for East Shipping - East shipping handles all Eastern region orders, East shipping also handles all U.S. rush orders: */ agt2 = new AQAgent("East_Shipping", "ES.ES_bookedorders_que"); rule = "tab.user_data.orderregion = 'EASTERN' OR " + "(tab.user_data.ordertype = 'RUSH' AND " + "tab.user_data.customer.country = 'USA')"; bookedorders_q.addSubscriber(agt2, rule); /* Add a rule-based subscriber for Overseas Shipping Intl Shipping handles all non-U.S. orders: */ agt3 = new AQAgent("Overseas_Shipping", "OS.OS_bookedorders_que"); rule = "tab.user_data.orderregion = 'INTERNATIONAL'"; bookedorders_q.addSubscriber(agt3, rule); } catch (Exception ex) { System.out.println("Exception: " + ex); } }
Advanced Queuing can monitor multiple queues for messages with a single call, LISTEN. An application can use LISTEN to wait for messages for multiple subscriptions. It can also be used by gateway applications to monitor multiple queues. If the LISTEN call returns successfully, a dequeue must be used to retrieve the message (see "Listening to One or More Single-Consumer Queues".
Without the LISTEN call, an application which sought to dequeue from a set of queues would have to continuously poll the queues to determine if there were a message. Alternatively, you could design your application to have a separate dequeue process for each queue. However, if there are long periods with no traffic in any of the queues, these approaches will create unacceptable overhead. The LISTEN call is well suited for such applications.
Note that when there are messages for multiple agents in the agent list, LISTEN returns with the first agent for whom there is a message. In that sense LISTEN is not 'fair' in monitoring the queues. The application designer must keep this in mind when using the call. To prevent one agent from 'starving' other agents for messages, the application can change the order of the agents in the agent list.
In the customer service component of the BooksOnLine example, messages from different databases arrive in the customer service queues, indicating the state of the message. The customer service application monitors the queues and whenever there is a message about a customer order, it updates the order status in the order_status_table. The application uses the listen call to monitor the different queues. Whenever there is a message in any of the queues, it dequeues the message and updates the order status accordingly.
CODE (in tkaqdocd.sql) /* Update the status of the order in the order status table: */ CREATE OR REPLACE PROCEDURE update_status( new_status IN VARCHAR2, order_msg IN BOLADM.ORDER_TYP) IS old_status VARCHAR2(30); dummy NUMBER; BEGIN BEGIN /* Query old status from the table: */ SELECT st.status INTO old_status FROM order_status_table st WHERE st.customer_order.orderno = order_msg.orderno; /* Status can be 'BOOKED_ORDER', 'SHIPPED_ORDER', 'BACK_ORDER' and 'BILLED_ORDER': */ IF new_status = 'SHIPPED_ORDER' THEN IF old_status = 'BILLED_ORDER' THEN return; /* message about a previous state */ END IF; ELSIF new_status = 'BACK_ORDER' THEN IF old_status = 'SHIPPED_ORDER' OR old_status = 'BILLED_ORDER' THEN return; /* message about a previous state */ END IF; END IF; /* Update the order status: */ UPDATE order_status_table st SET st.customer_order = order_msg, st.status = new_status; COMMIT; EXCEPTION WHEN OTHERS THEN /* change to no data found */ /* First update for the order: */ INSERT INTO order_status_table(customer_order, status) VALUES (order_msg, new_status); COMMIT; END; END; / /* Dequeues message from 'QUEUE' for 'CONSUMER': */ CREATE OR REPLACE PROCEDURE DEQUEUE_MESSAGE( queue IN VARCHAR2, consumer IN VARCHAR2, message OUT BOLADM.order_typ) IS dopt dbms_aq.dequeue_options_t; mprop dbms_aq.message_properties_t; deq_msgid RAW(16); BEGIN dopt.dequeue_mode := dbms_aq.REMOVE; dopt.navigation := dbms_aq.FIRST_MESSAGE; dopt.consumer_name := consumer; dbms_aq.dequeue( queue_name => queue, dequeue_options => dopt, message_properties => mprop, payload => message, msgid => deq_msgid); commit; END; / /* Monitor the queues in the customer service databse for 'time' seconds: */ CREATE OR REPLACE PROCEDURE MONITOR_STATUS_QUEUE(time IN NUMBER) IS agent_w_message aq$_agent; agent_list dbms_aq.agent_list_t; wait_time INTEGER := 120; no_message EXCEPTION; pragma EXCEPTION_INIT(no_message, -25254); order_msg boladm.order_typ; new_status VARCHAR2(30); monitor BOOLEAN := TRUE; begin_time NUMBER; end_time NUMBER; BEGIN begin_time := dbms_utility.get_time; WHILE (monitor) LOOP BEGIN /* Construct the waiters list: */ agent_list(1) := aq$_agent('BILLED_ORDER', 'CS_billedorders_que', NULL); agent_list(2) := aq$_agent('SHIPPED_ORDER', 'CS_shippedorders_que', NULL); agent_list(3) := aq$_agent('BACK_ORDER', 'CS_backorders_que', NULL); agent_list(4) := aq$_agent('Booked_ORDER', 'CS_bookedorders_que', NULL); /* Wait for order status messages: */ dbms_aq.listen(agent_list, wait_time, agent_w_message); dbms_output.put_line('Agent' || agent_w_message.name || ' Address '|| agent_w_message.address); /* Dequeue the message from the queue: */ dequeue_message(agent_w_message.address, agent_w_message.name, order_msg); /* Update the status of the order depending on the type of the message, * the name of the agent contains the new state: */ update_status(agent_w_message.name, order_msg); /* Exit if we have been working long enough: */ end_time := dbms_utility.get_time; IF (end_time - begin_time > time) THEN EXIT; END IF; EXCEPTION WHEN no_message THEN dbms_output.put_line('No messages in the past 2 minutes'); end_time := dbms_utility.get_time; /* Exit if we have done enough work: */ IF (end_time - begin_time > time) THEN EXIT; END IF; END; END LOOP; END; /
Feature not currently available.
public static void monitor_status_queue(Connection db_conn) { AQSession aq_sess; AQAgent[] agt_list = null; AQAgent ret_agt = null; Order deq_order; AQDequeueOption deq_option; AQQueue orders_q; AQMessage message; AQObjectPayload obj_payload; String owner = null; String queue_name = null; int idx = 0; try { /* Create an AQ Session: */ aq_sess = AQDriverManager.createAQSession(db_conn); /* Construct the waiters list: */ agt_list = new AQAgent[4]; agt_list[0] = new AQAgent("BILLED_ORDER", "CS_billedorders_que", 0); agt_list[1] = new AQAgent("SHIPPED_ORDER", "CS_shippedorders_que", 0); agt_list[2] = new AQAgent("BACK_ORDER", "CS_backorders_que", 0); agt_list[3] = new AQAgent("BOOKED_ORDER", "CS_bookedorders_que", 0); /* Wait for order status messages for 120 seconds: */ ret_agt = aq_sess.listen(agt_list, 120); System.out.println("Message available for agent: " + ret_agt.getName() + " " + ret_agt.getAddress()); /* Get owner, queue where message is available */ idx = ret_agt.getAddress().indexOf("."); if(idx != -1) { owner = ret_agt.getAddress().substring(0, idx); queue_name = ret_agt.getAddress().substring(idx + 1); /* Dequeue the message */ deq_option = new AQDequeueOption(); deq_option.setConsumerName(ret_agt.getName()); deq_option.setWaitTime(1); orders_q = aq_sess.getQueue(owner, queue_name); /* Dequeue the message */ message = orders_q.dequeue(deq_option, Order.getFactory()); obj_payload = message.getObjectPayload(); deq_order = (Order)(obj_payload.getPayloadData()); System.out.println("Order number " + deq_order.getOrderno() + " retrieved"); } catch (AQException aqex) { System.out.println("Exception-1: " + aqex); } catch (Exception ex) { System.out.println("Exception-2: " + ex); } }
Continuing the scenario introduced in "Message Format Transformation" and "Message Transformation During Enqueue", the queues in the OE schema are of payload type OE.orders_typ and the queues in the WS schema are of payload type WS.orders_typ_sh.
At dequeue time, an application can move messages from OE_booked_orders_topic to the WS_booked_orders_topic by using a selection criteria on dequeue to dequeue only orders with order_region "WESTERN" and order_type not equal to "RUSH." At the same time, the transformation is applied and the order in the ws.order_typ_sh type is retrieved. Then the message is enqueued into the WS.ws_booked_orders queue.
CREATE OR REPLACE PROCEDURE fwd_message_to_ws_shipping AS enq_opt dbms_aq.enqueue_options_t; deq_opt dbms_aq.dequeue_options_t; msg_prp dbms_aq.message_properties_t; booked_order WS.order_typ_sh; BEGIN /* First dequeue the message from OE booked orders topic */ deq_opt.transformation := 'OE.OE2WS'; deq_opt.condition := 'tab.user_data.order_region = ''WESTERN'' and tab.user_ data.order_type != ''RUSH'''; dbms_aq.dequeue('OE.oe_bookedorders_topic', deq_opt, msg_prp, booked_order); /* enqueue the message in the WS booked orders topic */ msg_prp.recipient_list(0) := aq$_agent('West_shipping', null, null); dbms_aq.enqueue('WS.ws_bookedorders_topic', enq_opt, msg_prp, booked_order); END;
No example is provided with this release.
No example is provided with this release.
You can perform dequeue requests over the Internet using SOAP. See Chapter 17, "Internet Access to Advanced Queuing" for more information on receiving AQ messages using SOAP.
In the BooksOnline scenario, assume that the East shipping application receives AQ messages with a correlation identifier 'RUSH' over the Internet. The dequeue request will have the following format:
<?xml version="1.0"?> <Envelope xmlns= "http://schemas.xmlsoap.org/soap/envelope/"> <Body> <AQXmlReceive xmlns = "http://ns.oracle.com/AQ/schemas/access"> <consumer_options> <destination>ES_ES_bookedorders_que</destination> <consumer_name>East_Shipping</consumer_name> <wait_time>0</wait_time> <selector> <correlation>RUSH</correlation> </selector> </consumer_options> <AQXmlCommit/> </AQXmlReceive> </Body> </Envelope>
This feature allows clients to receive notifications for messages of interest. It supports multiple mechanisms to receive notifications. Clients can receive notifications procedurally using PL/SQL, JMS, or OCI callback functions, or clients can receive notifications through e-mail or HTTP post.
For persistent queues, notifications contain only the message properties, except for JMS notifications. Clients have to explicitly dequeue to receive the message. In JMS, the dequeue is done as part of the notifications and hence explicit dequeue is not required. For nonpersistent queues, the message is delivered as part of the notification.
Clients can also specify the presentation for notifications as either RAW or XML.
In the BooksOnLine application, a customer can request Fed-Ex shipping (priority 1), priority air shipping (priority 2), or regular ground shipping (priority 3).
The shipping application then ships the orders according to the user's request. It is of interest to BooksOnLine to find out how many requests of each shipping type come in each day. The application uses asynchronous notification facility for this purpose. It registers for notification on the WS.WS_bookedorders_que. When it is notified of new message in the queue, it updates the count for the appropriate shipping type depending on the priority of the message.
Refer to the Visual Basic online help, "Monitoring Messages".
This feature is not supported by the Java API.
This example illustrates the use of OCIRegister. At the shipping site, an OCI client program keeps track of how many orders were made for each of the shipping types, FEDEX, AIR and GROUND. The priority field of the message enables us to determine the type of shipping desired.
#include <stdio.h> #include <stdlib.h> #include <string.h> #include <oci.h> #ifdef WIN32COMMON #define sleep(x) Sleep(1000*(x)) #endif static text *username = (text *) "WS"; static text *password = (text *) "WS"; static OCIEnv *envhp; static OCIServer *srvhp; static OCIError *errhp; static OCISvcCtx *svchp; static void checkerr(/*_ OCIError *errhp, sword status _*/); struct ship_data { ub4 fedex; ub4 air; ub4 ground; }; typedef struct ship_data ship_data; int main(/*_ int argc, char *argv[] _*/); /* Notify callback: */ ub4 notifyCB(ctx, subscrhp, pay, payl, desc, mode) dvoid *ctx; LNOCISubscription *subscrhp; dvoid *pay; ub4 payl; dvoid *desc; ub4 mode; { text *subname; ub4 size; ship_data *ship_stats = (ship_data *)ctx; text *queue; text *consumer; OCIRaw *msgid; ub4 priority; OCIAQMsgProperties *msgprop; OCIAttrGet((dvoid *)subscrhp, OCI_HTYPE_SUBSCRIPTION, (dvoid *)&subname, &size, OCI_ATTR_SUBSCR_NAME, errhp); /* Extract the attributes from the AQ descriptor. Queue name: */ OCIAttrGet(desc, OCI_DTYPE_AQNFY_DESCRIPTOR, (dvoid *)&queue, &size, OCI_ATTR_QUEUE_NAME, errhp); /* Consumer name: */ OCIAttrGet(desc, OCI_DTYPE_AQNFY_DESCRIPTOR, (dvoid *)&consumer, &size, OCI_ATTR_CONSUMER_NAME, errhp); /* Msgid: */ OCIAttrGet(desc, OCI_DTYPE_AQNFY_DESCRIPTOR, (dvoid *)&msgid, &size, OCI_ATTR_NFY_MSGID, errhp); /* Message properties: */ OCIAttrGet(desc, OCI_DTYPE_AQNFY_DESCRIPTOR, (dvoid *)&msgprop, &size, OCI_ATTR_MSG_PROP, errhp); /* Get priority from message properties: */ checkerr(errhp, OCIAttrGet(msgprop, OCI_DTYPE_AQMSG_PROPERTIES, (dvoid *)&priority, 0, OCI_ATTR_PRIORITY, errhp)); switch (priority) { case 1: ship_stats->fedex++; break; case 2 : ship_stats->air++; break; case 3: ship_stats->ground++; break; default: printf(" Error priority %d", priority); } } int main(argc, argv) int argc; char *argv[]; { OCISession *authp = (OCISession *) 0; OCISubscription *subscrhp[8]; ub4 namespace = OCI_SUBSCR_NAMESPACE_AQ; ship_data ctx = {0,0,0}; ub4 sleep_time = 0; printf("Initializing OCI Process\n"); /* Initialize OCI environment with OCI_EVENTS flag set: */ (void) OCIInitialize((ub4) OCI_EVENTS|OCI_OBJECT, (dvoid *)0, (dvoid * (*)(dvoid *, size_t)) 0, (dvoid * (*)(dvoid *, dvoid *, size_t))0, (void (*)(dvoid *, dvoid *)) 0 ); printf("Initialization successful\n"); printf("Initializing OCI Env\n"); (void) OCIEnvInit( (OCIEnv **) &envhp, OCI_DEFAULT, (size_t) 0, (dvoid **) 0 ); printf("Initialization successful\n"); checkerr(errhp, OCIHandleAlloc( (dvoid *) envhp, (dvoid **) &errhp, OCI_HTYPE_ ERROR, (size_t) 0, (dvoid **) 0)); checkerr(errhp, OCIHandleAlloc( (dvoid *) envhp, (dvoid **) &srvhp, OCI_HTYPE_ SERVER, (size_t) 0, (dvoid **) 0)); checkerr(errhp, OCIHandleAlloc( (dvoid *) envhp, (dvoid **) &svchp, OCI_HTYPE_ SVCCTX, (size_t) 0, (dvoid **) 0)); printf("connecting to server\n"); checkerr(errhp, OCIServerAttach( srvhp, errhp, (text *)"inst1_alias", strlen("inst1_alias"), (ub4) OCI_DEFAULT)); printf("connect successful\n"); /* Set attribute server context in the service context: */ checkerr(errhp, OCIAttrSet( (dvoid *) svchp, OCI_HTYPE_SVCCTX, (dvoid *)srvhp, (ub4) 0, OCI_ATTR_SERVER, (OCIError *) errhp)); checkerr(errhp, OCIHandleAlloc((dvoid *) envhp, (dvoid **)&authp, (ub4) OCI_HTYPE_SESSION, (size_t) 0, (dvoid **) 0)); /* Set username and password in the session handle: */ checkerr(errhp, OCIAttrSet((dvoid *) authp, (ub4) OCI_HTYPE_SESSION, (dvoid *) username, (ub4) strlen((char *)username), (ub4) OCI_ATTR_USERNAME, errhp)); checkerr(errhp, OCIAttrSet((dvoid *) authp, (ub4) OCI_HTYPE_SESSION, (dvoid *) password, (ub4) strlen((char *)password), (ub4) OCI_ATTR_PASSWORD, errhp)); /* Begin session: */ checkerr(errhp, OCISessionBegin ( svchp, errhp, authp, OCI_CRED_RDBMS, (ub4) OCI_DEFAULT)); (void) OCIAttrSet((dvoid *) svchp, (ub4) OCI_HTYPE_SVCCTX, (dvoid *) authp, (ub4) 0, (ub4) OCI_ATTR_SESSION, errhp); /* Register for notification: */ printf("allocating subscription handle\n"); subscrhp[0] = (OCISubscription *)0; (void) OCIHandleAlloc((dvoid *) envhp, (dvoid **)&subscrhp[0], (ub4) OCI_HTYPE_SUBSCRIPTION, (size_t) 0, (dvoid **) 0); printf("setting subscription name\n"); (void) OCIAttrSet((dvoid *) subscrhp[0], (ub4) OCI_HTYPE_SUBSCRIPTION, (dvoid *) "WS.WS_BOOKEDORDERS_QUE:BOOKED_ORDERS", (ub4) strlen("WS.WS_BOOKEDORDERS_QUE:BOOKED_ORDERS"), (ub4) OCI_ATTR_SUBSCR_NAME, errhp); printf("setting subscription callback\n"); (void) OCIAttrSet((dvoid *) subscrhp[0], (ub4) OCI_HTYPE_SUBSCRIPTION, (dvoid *) notifyCB, (ub4) 0, (ub4) OCI_ATTR_SUBSCR_CALLBACK, errhp); (void) OCIAttrSet((dvoid *) subscrhp[0], (ub4) OCI_HTYPE_SUBSCRIPTION, (dvoid *)&ctx, (ub4)sizeof(ctx), (ub4) OCI_ATTR_SUBSCR_CTX, errhp); printf("setting subscription namespace\n"); (void) OCIAttrSet((dvoid *) subscrhp[0], (ub4) OCI_HTYPE_SUBSCRIPTION, (dvoid *) &namespace, (ub4) 0, (ub4) OCI_ATTR_SUBSCR_NAMESPACE, errhp); printf("Registering \n"); checkerr(errhp, OCISubscriptionRegister(svchp, subscrhp, 1, errhp, OCI_DEFAULT)); sleep_time = (ub4)atoi(argv[1]); printf ("waiting for %d s", sleep_time); sleep(sleep_time); printf("Exiting"); exit(0); } void checkerr(errhp, status) LNOCIError *errhp; sword status; { text errbuf[512]; sb4 errcode = 0; switch (status) { case OCI_SUCCESS: break; case OCI_SUCCESS_WITH_INFO: (void) printf("Error - OCI_SUCCESS_WITH_INFO\n"); break; case OCI_NEED_DATA: (void) printf("Error - OCI_NEED_DATA\n"); break; case OCI_NO_DATA: (void) printf("Error - OCI_NODATA\n"); break; case OCI_ERROR: (void) OCIErrorGet((dvoid *)errhp, (ub4) 1, (text *) NULL, &errcode, errbuf, (ub4) sizeof(errbuf), OCI_HTYPE_ERROR); (void) printf("Error - %.*s\n", 512, errbuf); break; case OCI_INVALID_HANDLE: (void) printf("Error - OCI_INVALID_HANDLE\n"); break; case OCI_STILL_EXECUTING: (void) printf("Error - OCI_STILL_EXECUTE\n"); break; case OCI_CONTINUE: (void) printf("Error - OCI_CONTINUE\n"); break; default: break; } }
This example illustrates the use of the DBMS_AQ.REGISTER procedure.
In the BooksOnline scenario, assume that we want a PL/SQL callback WS.notifyCB() to be invoked when the subscriber BOOKED_ORDER receives a message in the WS.WS_BOOKED_ORDERS_QUE queue. In addition, we want to send an e-mail to john@company.com when an order is enqueued in the queue for subscriber BOOKED_ORDERS. Also assume that we want to invoke the servlet http://xyz.company.com/servlets/NofifyServlet. This can be done as follows:
First define a PL/SQL procedure that will be invoked on notification.
connect ws/ws; set echo on; set serveroutput on; -- notifyCB callback create or replace procedure notifyCB( context raw, reginfo sys.aq$_reg_info, descr sys.aq$_descriptor, payload raw, payloadl number) AS dequeue_options DBMS_AQ.dequeue_options_t; message_properies DBMS_AQ.message_properties_t; message_handle RAW(16); message BOLADM.order_typ; BEGIN -- get the consumer name and msg_id from the descriptor dequeue_options.msgid := descr.msg_id; dequeue_options.consumer_name := descr.consumer_name; -- Dequeue the message DBMS_AQ.DEQUEUE(queue_name => descr.queue_name, dequeue_options => dequeue_options, message_properties => message_properties, payload => message, msgid => message_handle); commit; DBMS_OUTPUT.PUTLINE('Received Order: ' || message.orderno); END; /
The PL/SQL procedure, e-mail address, and HTTP URL can be registered as follows:
connect ws/ws; set echo on; set serveroutput on; DECLARE reginfo1 sys.aq$_reg_info; reginfo2 sys.aq$_reg_info; reginfo3 sys.aq$_reg_info; reginfolist sys.aq$_reg_info_list; BEGIN -- register for the pl/sql procedure notifyCB to be called on notification reginfo1 := sys.aq$_reg_info('WS.WS_BOOKEDORDERS_QUE:BOOKED_ORDERS', DBMS_AQ.NAMESPACE_AQ, 'plsql://WS.notifyCB', HEXTORAW('FF')); -- register for an e-mail to be sent to john@company.com on notification reginfo2 := sys.aq$_reg_info('WS.WS_BOOKEDORDERS_QUE:BOOKED_ORDERS', DBMS_AQ.NAMESPACE_AQ, 'mailto://john@company.com', HEXTORAW('FF')); -- register for an HTTP servlet to be invoked for notification reginfo3 := sys.aq$_reg_info('WS.WS_BOOKEDORDERS_QUE:BOOKED_ORDERS', DBMS_AQ.NAMESPACE_AQ, 'http://xyz.oracle.com/servlets/NotifyServlet', HEXTORAW('FF')); -- Create the registration info list reginfolist := sys.aq$_reg_info_list(reginfo1); reginfolist.EXTEND; reginfolist(2) := reginfo2; reginfolist.EXTEND; reginfolist(3) := reginfo3; -- do the registration sys.dbms_aq.register(reginfolist, 3); END;
Clients can register for AQ notifications over the Internet. See Chapter 17, "Internet Access to Advanced Queuing" for more information on registering for AQ notifications using SOAP.
The register request has the following format:
?xml version="1.0"?> <Envelope xmlns= "http://schemas.xmlsoap.org/soap/envelope/"> <Body> <AQXmlRegister xmlns = "http://ns.oracle.com/AQ/schemas/access"> <register_options> <destination>WS.WS_BOOKEDORDERS_QUE</destination> <consumer_name>BOOKED_ORDERS</consumer_name> <notify_url>mailto://john@company.com</notify_url> </register_options> <AQXmlCommit/> </AQXmlRegister> </Body> </Envelope>
The e-mail notification sent to john@company.com will have the following format:
<?xml version="1.0"?> <Envelope xmlns="http://www.oracle.com/schemas/IDAP/envelope"> <Body> <AQXmlNotification xmlns="http://www.oracle.com/schemas/AQ/access"> <notification_options> <destination>WS.WS_BOOKEDORDERS_QUE</destination> </notification_options> <message_set> <message> <message_header> <message_id>81128B6AC46D4B15E03408002092AA15</message_id> <correlation>RUSH</correlation> <priority>1</priority> <delivery_count>0</delivery_count> <sender_id> <agent_name>john</agent_name> </sender_id> <message_state>0</message_state> </message_header> </message> </message_set> </AQXmlNotification> </Body> </Envelope>
In this section, the following topics are discussed:
This feature allows applications to communicate with each other without being connected to the same database or to the same queue. Messages can be propagated from one queue to another. The destination queue can be located in the same database or in a remote database. Propagation is performed by job queue background processes. Propagation to the remote queue uses database links over Oracle Net Services or HTTP(S).
The propagation feature is used as follows. First one or more subscribers are defined for the queue from which messages are to be propagated (see "Subscriptions and Recipient Lists"). Second, a schedule is defined for each destination where messages are to be propagated from the queue. Enqueued messages will be propagated and automatically available for dequeuing at the destination queues.
For propagation over the Internet, you must specify the remote Internet user in the database link. The remote Internet user must have privileges to enqueue in the destination queue.
Note that two or more job_queue background processes must be running to use propagation. This is in addition to the number of job_queue background processes needed for handling non-propagation related jobs. Also, if you want to deploy remote propagation, you must ensure that the database link specified for the schedule is valid and have proper privileges for enqueuing into the destination queue. For more information about the administrative commands for managing propagation schedules, see "Propagation Scheduling".
Propagation also has mechanisms for handling failure. For example, if the database link specified is invalid, then the appropriate error message is reported.
Finally, propagation provides detailed statistics about the messages propagated and the schedule itself. This information can be used to properly tune the schedules for best performance. See "Enhanced Propagation Scheduling Capabilities" for a discussion of the failure handling and error reporting facilities of propagation and propagation statistics.
A propagation schedule is defined for a pair of source and destination queues. If a queue has messages to be propagated to several queues, a schedule has to be defined for each of the destination queues. A schedule indicates the time frame during which messages can be propagated from the source queue. This time frame may depend on a number of factors such as network traffic, load at source database, load at destination database, and so on. The schedule therefore has to be tailored for the specific source and destination. When a schedule is created, a job is automatically submitted to the job_queue facility to handle propagation.
The administrative calls for propagation scheduling provide flexibility for managing the schedules (see "Scheduling a Queue Propagation" in Chapter 9, "Administrative Interface"). The duration or propagation window parameter of a schedule specifies the time frame during which propagation has to take place. If the duration is unspecified, the time frame is an infinite single window. If a window has to be repeated periodically, a finite duration is specified along with a next_time function that defines the periodic interval between successive windows.
The latency parameter for a schedule is relevant only when a queue does not have any messages to be propagated. This parameter specifies the time interval within which a queue has to be rechecked for messages. Note that if the latency is less than 5 seconds, then the job_queue_interval parameter for the job queue processes should be less than or equal to the latency parameter.
The propagation schedules defined for a queue can be changed or dropped at anytime during the life of the queue. In addition there are calls for temporarily disabling a schedule (instead of dropping the schedule) and enabling a disabled schedule. A schedule is active when messages are being propagated in that schedule. All the administrative calls can be made irrespective of whether the schedule is active or not. If a schedule is active, it will take a few seconds for the calls to be executed.
In the BooksOnLine example, messages in the OE_bookedorders_que are propagated to different shipping sites. The following example code illustrates the various administrative calls available for specifying and managing schedules. It also shows the calls for enqueuing messages into the source queue and for dequeuing the messages at the destination site. The catalog view USER_QUEUE_SCHEDULES provides all information relevant to a schedule (see "Selecting Propagation Schedules in User Schema" in Chapter 10, "Administrative Interface: Views").
CONNECT OE/OE; /* Schedule Propagation from bookedorders_que to shipping: */ EXECUTE dbms_aqadm.schedule_propagation( \ queue_name => 'OE.OE_bookedorders_que'); /* Check if a schedule has been created: */ SELECT * FROM user_queue_schedules; /* Enqueue some orders into OE_bookedorders_que: */ EXECUTE BOLADM.order_enq('My First Book', 1, 1001, 'CA', 'USA', \ 'WESTERN', 'NORMAL'); EXECUTE BOLADM.order_enq('My Second Book', 2, 1002, 'NY', 'USA', \ 'EASTERN', 'NORMAL'); EXECUTE BOLADM.order_enq('My Third Book', 3, 1003, '', 'Canada', \ 'INTERNATIONAL', 'NORMAL'); EXECUTE BOLADM.order_enq('My Fourth Book', 4, 1004, 'NV', 'USA', \ 'WESTERN', 'RUSH'); EXECUTE BOLADM.order_enq('My Fifth Book', 5, 1005, 'MA', 'USA', \ 'EASTERN', 'RUSH'); EXECUTE BOLADM.order_enq('My Sixth Book', 6, 1006, '' , 'UK', \ 'INTERNATIONAL', 'NORMAL'); EXECUTE BOLADM.order_enq('My Seventh Book', 7, 1007, '', 'Canada', \ 'INTERNATIONAL', 'RUSH'); EXECUTE BOLADM.order_enq('My Eighth Book', 8, 1008, '', 'Mexico', \ 'INTERNATIONAL', 'NORMAL'); EXECUTE BOLADM.order_enq('My Ninth Book', 9, 1009, 'CA', 'USA', \ 'WESTERN', 'RUSH'); EXECUTE BOLADM.order_enq('My Tenth Book', 8, 1010, '' , 'UK', \ 'INTERNATIONAL', 'NORMAL'); EXECUTE BOLADM.order_enq('My Last Book', 7, 1011, '' , 'Mexico', \ 'INTERNATIONAL', 'NORMAL'); /* Wait for propagation to happen: */ EXECUTE dbms_lock.sleep(100); /* Connect to shipping sites and check propagated messages: */ CONNECT WS/WS; set serveroutput on; /* Dequeue all booked orders for West_Shipping: */ EXECUTE BOLADM.shipping_bookedorder_deq('West_Shipping', DBMS_AQ.REMOVE); CONNECT ES/ES; SET SERVEROUTPUT ON; /* Dequeue all remaining booked orders (normal order) for East_Shipping: */ EXECUTE BOLADM.shipping_bookedorder_deq('East_Shipping', DBMS_AQ.REMOVE); CONNECT OS/OS; SET SERVEROUTPUT ON; /* Dequeue all international North American orders for Overseas_Shipping: */ EXECUTE BOLADM.get_northamerican_orders('Overseas_Shipping'); /* Dequeue rest of the booked orders for Overseas_Shipping: */ EXECUTE BOLADM.shipping_bookedorder_deq('Overseas_Shipping', DBMS_AQ.REMOVE); /* Disable propagation schedule for booked orders EXECUTE dbms_aqadm.disable_propagation_schedule( \ queue_name => 'OE_bookedorders_que'); /* Wait for some time for call to be effected: */ EXECUTE dbms_lock.sleep(30); /* Check if the schedule has been disabled: */ SELECT schedule_disabled FROM user_queue_schedules; /* Alter propagation schedule for booked orders to execute every 15 mins (900 seconds) for a window duration of 300 seconds: */ EXECUTE dbms_aqadm.alter_propagation_schedule( \ queue_name => 'OE_bookedorders_que', \ duration => 300, \ next_time => 'SYSDATE + 900/86400',\ latency => 25); /* Wait for some time for call to be effected: */ EXECUTE dbms_lock.sleep(30); /* Check if the schedule parameters have changed: */ SELECT next_time, latency, propagation_window FROM user_queue_schedules; /* Enable propagation schedule for booked orders: EXECUTE dbms_aqadm.enable_propagation_schedule( \ queue_name => 'OE_bookedorders_que'); /* Wait for some time for call to be effected: */ EXECUTE dbms_lock.sleep(30); /* Check if the schedule has been enabled: */ SELECT schedule_disabled FROM user_queue_schedules; /* Unschedule propagation for booked orders: */ EXECUTE dbms_aqadm.unschedule_propagation( \ queue_name => 'OE.OE_bookedorders_que'); /* Wait for some time for call to be effected: */ EXECUTE dbms_lock.sleep(30); /* Check if the schedule has been dropped SELECT * FROM user_queue_schedules;
This functionality is currently not available.
No example is provided with this release.
Large Objects can be propagated using AQ using two methods:
RAW queues. In RAW queues the message payload is stored as a Binary Large Object (BLOB). This allows users to store up to 32KB of data when using the PL/SQL interface and as much data as can be contiguously allocated by the client when using OCI. This method is supported by all releases after 8.0.4 inclusive.LOB attributes. The user can populate the LOB and read from the LOB using Oracle's LOB handling routines. The LOB attributes can be BLOBs or CLOBs (not NCLOBs). If the attribute is a CLOB AQ will automatically perform any necessary characterset conversion between the source queue and the destination queue. This method is supported by all releases from 8.1.3 inclusive.
Note that AQ does not support propagation from Object queues that have BFILE or REF attributes in the payload.
In the BooksOnLine application, the company may wish to send promotional coupons along with the book orders. These coupons are generated depending on the content of the order, and other customer preferences. The coupons are images generated from some multimedia database, and are stored as LOBs.
When the order information is sent to the shipping warehouses, the coupon contents are also sent to the warehouses. In the following code, order_typ is enhanced to contain a coupon attribute of LOB type. The code demonstrates how the LOB contents are inserted into the message that is enqueued into OE_bookedorders_que when an order is placed. The message payload is first constructed with an empty LOB. The place holder (LOB locator) information is obtained from the queue table and is then used in conjunction with the LOB manipulation routines, such as DBMS_LOB.WRITE(), to fill the LOB contents. The example has additional examples regarding for enqueue and dequeue of messages with LOBs as part the payload.
A COMMIT is issued only after the LOB contents are filled in with the appropriate image data. Propagation automatically takes care of moving the LOB contents along with the rest of the message contents. The following code also shows a dequeue at the destination queue for reading the LOB contents from the propagated message. The LOB contents are read into a buffer that can be sent to a printer for printing the coupon.
/* Enhance the type order_typ to contain coupon field (lob field): */ CREATE OR REPLACE TYPE order_typ AS OBJECT ( orderno NUMBER, status VARCHAR2(30), ordertype VARCHAR2(30), orderregion VARCHAR2(30), customer customer_typ, paymentmethod VARCHAR2(30), items orderitemlist_vartyp, total NUMBER, coupon BLOB); / /* lob_loc is a variable of type BLOB, buffer is a variable of type RAW, length is a variable of type NUMBER. */ /* Complete the order data and perform the enqueue using the order_enq() procedure: */ dbms_aq.enqueue('OE.OE_bookedorders_que', enqopt, msgprop, OE_enq_order_data, enq_msgid); /* Get the lob locator in the queue table after enqueue: */ SELECT t.user_data.coupon INTO lob_loc FROM OE.OE_orders_pr_mqtab t WHERE t.msgid = enq_msgid; /* Generate a sample LOB of 100 bytes: */ buffer := hextoraw(rpad('FF',100,'FF')); /* Fill in the lob using LOB routines in the dbms_lob package: */ dbms_lob.write(lob_loc, 90, 1, buffer); /* Issue a commit only after filling in lob contents: */ COMMIT; /* Sleep until propagation is complete: */ /* Perform dequeue at the Western Shipping warehouse: */ dbms_aq.dequeue( queue_name => qname, dequeue_options => dopt, message_properties => mprop, payload => deq_order_data, msgid => deq_msgid); /* Get the LOB locator after dequeue: */ lob_loc := deq_order_data.coupon; /* Get the length of the LOB: */ length := dbms_lob.getlength(lob_loc); /* Read the LOB contents into the buffer: */ dbms_lob.read(lob_loc, length, 1, buffer);
This functionality is not available currently.
No example is provided with this release.
Detailed information about the schedules can be obtained from the catalog views defined for propagation. Information about active schedules--such as the name of the background process handling that schedule, the SID (session, serial number) for the session handling the propagation and the Oracle instance handling a schedule (relevant if Real Application Clusters are being used)--can be obtained from the catalog views. The same catalog views also provide information about the previous successful execution of a schedule (last successful propagation of message) and the next execution of the schedule.
For each schedule, detailed propagation statistics are maintained:
This includes the total number of messages propagated in a schedule, total number of bytes propagated in a schedule, maximum number of messages propagated in a window, maximum number of bytes propagated in a window, average number of messages propagated in a window, average size of propagated messages and the average time to propagated a message. These statistics have been designed to provide useful information to the queue administrators for tuning the schedules such that maximum efficiency can be achieved.
Propagation has built-in support for handling failures and reporting errors. For example, if the specified database link is invalid, the remote database is unavailable, or if the remote queue is not enabled for enqueuing, then the appropriate error message is reported. Propagation uses an exponential backoff scheme for retrying propagation from a schedule that encountered a failure.
If a schedule continuously encounters failures, the first retry happens after 30 seconds, the second after 60 seconds, the third after 120 seconds and so forth. If the retry time is beyond the expiration time of the current window, the next retry is attempted at the start time of the next window. A maximum of 16 retry attempts is made, after which the schedule is automatically disabled. When a schedule is disabled automatically due to failures, the relevant information is written into the alert log.
A check for scheduling failures indicates:
By examining this information, a queue administrator can fix the failure and enable the schedule. During a retry, if propagation is successful, the number of failures is reset to 0.
Propagation has support built-in for Oracle Real Application Clusters and is transparent to the user and the queue administrator. The job that handles propagation is submitted to the same instance as the owner of the queue table where the queue resides.
If there is a failure at an instance and the queue table that stores the queue is migrated to a different instance, the propagation job is also migrated to the new instance. This will minimize pinging between instances and thus offer better performance. Propagation has been designed to handle any number of concurrent schedules. Note that the number of job queue processes is limited to a maximum of 1000, and some of these may be used to handle nonpropagation-related jobs. Hence, propagation has built-in support for multitasking and load balancing.
The propagation algorithms are designed such that multiple schedules can be handled by a single snapshot (job_queue) process. The propagation load on a job_queue process can be skewed based on the arrival rate of messages in the different source queues.
If one process is overburdened with several active schedules while another is less loaded with many passive schedules, propagation automatically re-distributes the schedules so they are loaded uniformly.
In the BooksOnLine example, the OE_bookedorders_que is a busy queue since messages in it are propagated to different shipping sites. The following example code illustrates the calls supported by enhanced propagation scheduling for error checking and schedule monitoring.
CONNECT OE/OE; /* get averages select avg_time, avg_number, avg_size from user_queue_schedules; /* get totals select total_time, total_number, total_bytes from user_queue_schedules; /* get maximums for a window select max_number, max_bytes from user_queue_schedules; /* get current status information of schedule select process_name, session_id, instance, schedule_disabled from user_queue_schedules; /* get information about last and next execution select last_run_date, last_run_time, next_run_date, next_run_time from user_queue_schedules; /* get last error information if any select failures, last_error_msg, last_error_date, last_error_time from user_queue_schedules;
This functionality is currently not available.
No example is provided with this release.
When system errors such as a network failure occur, Advanced Queuing continues to attempt to propagate messages using an exponential backoff algorithm. In some situations that indicate application errors, AQ will mark messages as UNDELIVERABLE if there is an error in propagating the message.
Examples of such errors are when the remote queue does not exist or when there is a type mismatch between the source queue and the remote queue. In such situations users must query the DBA_SCHEDULES view to determine the last error that occurred during propagation to a particular destination. The trace files in the $ORACLE_HOME/log directory can provide additional information about the error.
In the BooksOnLine example, the ES_bookedorders_que in the Eastern Shipping region is stopped intentionally using the stop_queue() call. After a short while the propagation schedule for OE_bookedorders_que will display an error indicating that the remote queue ES_bookedorders_que is disabled for enqueuing. When the ES_bookedorders_que is started using the start_queue() call, propagation to that queue resumes and there is no error message associated with schedule for OE_bookedorders_que.
/* Intentionally stop the eastern shipping queue : */connect BOLADM/BOLADM EXECUTE dbms_aqadm.stop_queue(queue_name => 'ES.ES_bookedorders_que');/* Wait for some time before error shows up in dba_queue_schedules: */EXECUTE dbms_lock.sleep(100);/* This query will return an ORA-25207 enqueue failed error: */SELECT qname, last_error_msg from dba_queue_schedules; /* Start the eastern shipping queue: */ EXECUTE dbms_aqadm.start_queue(queue_name => 'ES.ES_bookedorders_que');/* Wait for Propagation to resume for eastern shipping queue: */EXECUTE dbms_lock.sleep(100); /* This query will indicate that there are no errors with propagation: SELECT qname, last_error_msg from dba_queue_schedules;
This functionality is handled by the database.
No example is provided with this release.
At propagation time, a transformation can be specified when adding a rule-based subscriber to OE_bookedorders_topic for Western shipping orders. The transformation is applied to the orders, transforming them to the WS.order_typ_sh type before propagating them to WS_bookedorders_topic.
declare subscriber sys.aq$_agent; begin subscriber :=sys.aq$_agent('West_Shipping','WS.WS_bookedorders_topic',null); dbms_aqadm.add_subscriber(queue_name => 'OE.OE_bookedorders_topic', subscriber => subscriber, rule => 'tab.user_data.orderregion =''WESTERN'' AND tab.user_data.ordertype != ''RUSH''', transformation => 'OE.OE2WS'); end;
No example is provided with this release.
No example is provided with this release.
In Oracle9i, you can set up Advanced Queuing propagation over HTTP and HTTPS (HTTP over SSL). HTTP propagation uses the Internet access infrastructure and requires that the AQ servlet that connects to the destination database be deployed. The database link must be created with the connect string indicating the Web server address and port and indicating HTTP as the protocol. The source database must be created for running Java and XML. Otherwise, the setup for HTTP propagation is more or less the same as Oracle Net Services (formerly Net8) propagation.
In the BooksOnLine example, messages in the OE_bookedorders_que are propagated to different shipping sites. For the purpose of this scenario, the Western Shipping application is running on another database, 'dest-db' and we will propagate to WS_bookedorders_que.
HTTP propagation depends on Internet access to the destination database. Create a class AQPropServlet that extends the AQxmlServlet.
import java.io.*; import javax.servlet.*; import javax.servlet.http.*; import oracle.AQ.*; import oracle.AQ.xml.*; import java.sql.*; import oracle.jms.*; import javax.jms.*; import java.io.*; import oracle.jdbc.pool.*; /* This is an AQ Propagation Servlet. */ public class AQPropServlet extends oracle.AQ.xml.AQxmlServlet /* getDBDrv - specify the database to which the servlet will connect */ public AQxmlDataSource createAQDataSource() throws AQxmlException { AQxmlDataSource db_drv = null; db_drv = new AQxmlDataSource("aqadm", "aqadm", "dest-db", "dest-host", 5521); return db_drv; } public void init() { try { AQxmlDataSource axds = this.createAQDataSource(); setAQDataSource(axds) ; setSessionMaxInactiveTime(180) ; } catch (Exception e) { System.err.println("Error in init : " +e) ; } } }
This servlet must connect to the destination database. The servlet must be deployed on the Web server in the path aqserv/servlet. In Oracle9i, the propagation servlet name and deployment path are fixed; that is, they must be AQPropServlet and aqserv/servlet, respectively.
Assume that the Web server host and port are webdest.oracle.com and 8081, respectively.
For this example, the connect string of the database link should be as follows:
(DESCRIPTION=(ADDRESS=(PROTOCOL=http)(HOST=webdest.oracle.com)(PORT=8081))
If SSL is used, then specify HTTPS as the protocol in the connect string.
Create the database link as follows:
create public database link dba connect to john identified by welcome using '(DESCRIPTION=(ADDRESS=(PROTOCOL=http)(HOST=webdest.oracle.com)(PORT=8081))' ;
If SSL is used, then specify HTTPS as the protocol in the connect string.
Create the database link as follows:
create public database link dba connect to john identified by welcome using '(DESCRIPTION=(ADDRESS=(PROTOCOL=http)(HOST=webdest.oracle.com)(PORT=8081))' ;
Here john is the AQ HTTP agent used to access the AQ (propagation) servlet. Welcome is the password used to authenticate with the Web server.
OE.OE_bookedorders_que.
execute dbms_aqadm.add_subscriber('OE.OE_bookedorders_que', aq$_agent(null, 'WS.WS_bookedorders_que', null));
dbms_aqdm.schedule_propagation at the source database.
dbms_aqadm.schedule_propagation('OE.OE_bookedorders_que', 'dba');
All other propagation administration APIs work the same for HTTP propagation. Use the propagation view, DBA_QUEUE_SCHEDULES, to check the propagation statistics for propagation schedules using HTTP.
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