204 UTL_COMPRESS

The UTL_COMPRESS package provides a set of data compression utilities.

This chapter contains the following topics:

Using UTL_COMPRESS
- Constants
- Exceptions
- Operational Notes
Summary of UTL_COMPRESS Subprograms

Using UTL_COMPRESS

Constants
Exceptions
Operational Notes

Constants

Define max number of handles for piecewise operations:

UTLCOMP_MAX_HANDLE   CONSTANT  PLS_INTEGER := 5;

Exceptions

Table 204-1 UTL_COMPRESS Exceptions

Exception	Description
`BUFFER_TOO_SMALL`	The compressed representation is too big.
`DATA_ERROR`	The input or output data stream was found to be an invalid format.
`INVALID_ARGUMENT`	One of the arguments was an invalid type or value.
`INVALID_HANDLE`	Invalid handle for piecewise compress or uncompress.
`STREAM_ERROR`	An error occurred during compression or uncompression of the data stream

Operational Notes

It is the caller's responsibility to free the temporary LOB returned by the LZ* functions with DBMS_LOB.FREETEMPORARY call.
A BFILE passed into LZ_COMPRESS* or lZ_UNCOMPRESS* has to be opened by DBMS_LOB.FILEOPEN.
Under special circumstances (especially if the input has already been compressed) the output produced by one of the UTL_COMPRESS subprograms may be the same size, or even slightly larger than, the input.
The output of the UTL_COMPRESS compressed data is compatible with gzip(with -n option)/gunzip on a single file.

Summary of UTL_COMPRESS Subprograms

Table 204-2 UTL_COMPRESS Package Subprograms

Subprogram	Description
ISOPEN Function	Checks to see if the handle to a piecewise (un)compress context is open or closed
LZ_COMPRESS Functions and Procedures	Compresses data using Lempel-Ziv compression algorithm
LZ_COMPRESS_ADD Procedure	Adds a piece of compressed data
LZ_COMPRESS_CLOSE	Closes and finishes piecewise compress operation
LZ_COMPRESS_OPEN	Initializes a piecewise context that maintains the compress state and data
LZ_UNCOMPRESS Functions and Procedures	Accepts compressed input, verifies it to be a valid and uncompresses it
LZ_UNCOMPRESS_EXTRACT Procedure	Extracts a piece of uncompressed data
LZ_UNCOMPRESS_OPEN Function	Initializes a piecewise context that maintains the uncompress state and data
LZ_UNCOMPRESS_CLOSE Procedure	Closes and finishes the piecewise uncompress

ISOPEN Function

This function checks to see if the handle to a piecewise (un)compress context is open or closed.

Syntax

UTL_COMPRESS.ISOPEN(
   handle in binary_integer) 
 RETURN BOOLEAN;

Parameters

Table 204-3 ISOPEN Function Parameters

Parameter	Description
`handle`	The handle to a piecewise uncompress context.

Return Values

TRUE if the given piecewise handle is opened, otherwise FALSE.

Examples

IF (UTL_COMPRESS.ISOPEN(myhandle) = TRUE) then 
   UTL_COMPRESS.LZ_COMPRESS_CLOSE(myhandle, lob_1); 
END IF;

Alternatively:

IF (UTL_COMPRESS.ISOPEN(myhandle) = TRUE) THEN 
   UTL_COMPRESS.LZ_UNCOMPRESS_CLOSE(myhandle); 
END IF;

LZ_COMPRESS Functions and Procedures

These functions and procedures compress data using Lempel-Ziv compression algorithm.

Syntax

This function accept a RAW as input, compress it and return the compressed RAW result and metadata:

UTL_COMPRESS.LZ_COMPRESS (
   src       IN           RAW,
   quality   IN           BINARY_INTEGER DEFAULT 6) 
 RETURN RAW;

This function accept a BLOB as input, compress it and returns a temporary BLOB for the compressed data:

UTL_COMPRESS.LZ_COMPRESS (
  src       IN           BLOB,
  quality   IN           BINARY_INTEGER DEFAULT 6) 
 RETURN BLOB;

This procedure returns the compressed data into the existing BLOB(dst) which is trimmed to the compressed data size:

UTL_COMPRESS.LZ_COMPRESS (
  src      IN            BLOB, 
  dst      IN OUT NOCOPY BLOB, 
  quality  IN            BINARY_INTEGER DEFAULT 6);

This function returns a temporary BLOB for the compressed data:

UTL_COMPRESS.LZ_COMPRESS (
   src     IN            BFILE, 
   quality IN            BINARY_INTEGER DEFAULT 6) 
 RETURN BLOB;

This procedure will return the compressed data into the existing BLOB(dst) which is trimmed to the compressed data size:

UTL_COMPRESS.LZ_COMPRESS (
   src     IN            BFILE, 
   dst     IN OUT NOCOPY BLOB, 
   quality IN            BINARY_INTEGER DEFAULT 6);

Parameters

Table 204-4 LZ_COMPRESS Function and Procedures Parameters

Parameter	Description
`src`	Data (`RAW`, `BLOB or BFILE`) to be compressed.
`dst`	Destination for compressed data
`quality`	An integer in the range 1 to 9, 1=fast compression, 9=best compression, default=6

Usage Notes

quality is an optional compression tuning value. It allows the UTL_COMPRESS user to choose between speed and compression quality, meaning the percentage of reduction in size. A faster compression speed will result in less compression of the data. A slower compression speed will result in more compression of the data. Valid values are [1..9], with 1=fastest and 9=slowest. The default 'quality' value is 6.

LZ_COMPRESS_ADD Procedure

This procedure adds a piece of compressed data.

Syntax

UTL_COMPRESS.LZ_COMPRESS_ADD (
   handle IN             BINARY_INTEGER, 
   dst    IN OUT NOCOPY  BLOB, 
   src    IN             RAW);

Parameters

Table 204-5 LZ_COMPRESS_ADD Procedure Parameters

Parameter	Description
`handle`	The handle to a piecewise compress context.
`dst`	The opened `LOB` from `LZ_COMPRESS_OPEN` to store compressed data.
`src`	The input data to be compressed.

Exceptions

invalid_handle - out of range invalid or unopened handle.
invalid_argument - NULL handle, src, dst, or invalid dst.

LZ_COMPRESS_CLOSE

This procedure closes and finishes piecewise compress operation.

Syntax

UTL_COMPRESS.LZ_COMPRESS_CLOSE (
   handle IN             BINARY_INTEGER, 
   dst    IN OUT NOCOPY  BLOB);

Parameters

Table 204-6 LZ_COMPRESS_CLOSE Procedure Parameters

Parameter	Description
`handle`	The handle to a piecewise compress context.
`dst`	The opened `LOB` from `LZ_COMPRESS_OPEN` to store compressed data.

Exceptions

invalid_handle - out of range invalid or uninitialized handle.
invalid_argument - NULL handle, dst, or invalid dst.

LZ_COMPRESS_OPEN

This function initializes a piecewise context that maintains the compress state and data.

Syntax

UTL_COMPRESS.LZ_COMPRESS_OPEN (
   dst       IN OUT NOCOPY BLOB, 
   quality   IN            BINARY_INTEGER DEFAULT 6) 
 RETURN BINARY_INTEGER;

Parameters

Table 204-7 LZ_COMPRESS_OPEN Function Parameters

Parameter	Description
`dst`	User supplied LOB to store compressed data.
`quality`	Speed versus efficiency of resulting compressed output. Valid values are the range 1..9, with a default value of 6. 1=fastest compression, 9=slowest compression and best compressed file size.

Return Values

A handle to an initialized piecewise compress context.

Exceptions

invalid_handle - invalid handle, too many open handles.
invalid_argument - NULL dst or invalid quality specified.

Usage Notes

Close the opened handle with LZ_COMPRESS_CLOSE

once the piecewise compress is completed
in the event of an exception in the middle of process

because lack of doing so will cause these handles to leak.

LZ_UNCOMPRESS Functions and Procedures

This procedure accepts as input a RAW, BLOB or BFILE compressed string, verifies it to be a valid compressed value, uncompresses it using Lempel-Ziv compression algorithm, and returns the uncompressed RAW or BLOB result.

Syntax

This function returns uncompressed data as RAW:

UTL_COMPRESS.LZ_UNCOMPRESS(
   src  IN  RAW)
  RETURN RAW;

This function returns uncompressed data as a temporary BLOB:

UTL_COMPRESS.LZ_UNCOMPRESS(
   src  IN  BLOB)
  RETURN BLOB;

This procedure returns the uncompressed data into the existing BLOB(dst), which will be trimmed to the uncompressed data size:

UTL_COMPRESS.LZ_UNCOMPRESS(
   src  IN  BLOB,
   dst  IN OUT NOCOPY BLOB);

This function returns a temporary BLOB for the uncompressed data:

UTL_COMPRESS.LZ_UNCOMPRESS(
   src  IN BFILE) 
 RETURN BLOB;

This procedure returns the uncompressed data into the existing BLOB(dst). The original dst data will be overwritten.

UTL_COMPRESS.LZ_UNCOMPRESS(
   src  IN  BFILE,
   dst  IN OUT NOCOPY BLOB);

Parameters

Table 204-8 LZ_UNCOMPRESS Function and Procedures Parameters

Parameter	Description
`src`	Compressed data.
`dst`	Destination for uncompressed data.

LZ_UNCOMPRESS_EXTRACT Procedure

This procedure extracts a piece of uncompressed data.

Syntax

UTL_COMPRESS.LZ_UNCOMPRESS_EXTRACT(
   handle  IN          BINARY_INTEGER, 
   dst     OUT NOCOPY  RAW);

Parameters

Table 204-9 LZ_UNCOMPRESS_EXTRACT Function Parameters

Parameter	Description
`handle`	The handle to a piecewise uncompress context.
`dst`	The uncompressed data.

Exceptions

no_data_found - finished uncompress.
invalid_handle - out of range invalid or uninitialized handle.
invalid_argument - NULL handle.

LZ_UNCOMPRESS_OPEN Function

This function initializes a piecewise context that maintains the uncompress state and data.

Syntax

UTL_COMPRESS.LZ_UNCOMPRESS_OPEN(
   src  IN  BLOB)
  RETURN BINARY_INTEGER;

Parameters

Table 204-10 LZ_UNCOMPRESS_OPEN Function Parameters

Parameter	Description
`src`	The input data to be uncompressed.

Return Values

A handle to an initialized piecewise compress context.

Exceptions

invalid_handle - invalid handle, too many open handles.
invalid_argument - NULL src.

Usage Notes

Close the opened handle with LZ_UNCOMPRESS_CLOSE

once the piecewise uncompress is completed
in the event of an exception in the middle of process

because lack of doing so will cause these handles to leak.

LZ_UNCOMPRESS_CLOSE Procedure

This procedure closes and finishes the piecewise uncompress.

Syntax

UTL_COMPRESS.LZ_UNCOMPRESS_CLOSE(
   handle  IN   BINARY_INTEGER);

Parameters

Table 204-11 LZ_UNCOMPRESS_CLOSE Procedure Parameters

Parameter	Description
`handle`	The handle to a piecewise uncompress context.

Exceptions

invalid_handle - out of range invalid or uninitialized handle.
invalid_argument - NULL handle.