UTL_COMPRESS

252 UTL_COMPRESS

The UTL_COMPRESS package provides a set of data compression utilities.

This chapter contains the following topics:

252.1 UTL_COMPRESS Constants

The maximum number of handles for piecewise operations can be defined by a constant.

UTLCOMP_MAX_HANDLE   CONSTANT  PLS_INTEGER := 5;

252.2 UTL_COMPRESS Exceptions

This table describes exceptions raised by UTL_COMPRESS subprograms.

Table 252-1 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

252.3 UTL_COMPRESS Operational Notes

Certain operational notes apply to UTL_COMPRESS.

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.

252.4 Summary of UTL_COMPRESS Subprograms

This table lists the UTL_COMPRESS subprograms and briefly describes them.

Table 252-2 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

252.4.1 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 252-3 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;

252.4.2 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 252-4 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.

252.4.3 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 252-5 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.

252.4.4 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 252-6 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.

252.4.5 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 252-7 LZ_COMPRESS_OPEN Function Parameters

Parameter Description

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.

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.

252.4.6 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 252-8 LZ_UNCOMPRESS Function and Procedures Parameters

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

252.4.7 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 252-9 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.

252.4.8 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 252-10 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.

252.4.9 LZ_UNCOMPRESS_CLOSE Procedure

This procedure closes and finishes the piecewise uncompress.

Syntax

UTL_COMPRESS.LZ_UNCOMPRESS_CLOSE(
   handle  IN   BINARY_INTEGER);

Parameters

Table 252-11 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.