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COMPRESS=

Valid in:	configuration file, SAS invocation, OPTIONS statement, Systems Options window
Category:	Files: SAS files
PROC OPTIONS GROUP=	SASFILES

Syntax Description

YES | CHAR

specifies that observations in a newly created SAS output data set are compressed (variable-length records).

Tip:	SAS uses RLE (Run Length Encoding) to compress observations. This compression algorithm (RLE) is better for character data.
Alias:	Y

Note:   COMPRESS=CHAR is accepted by Version 7 and later versions of SAS software.  

NO

specifies that observations in a newly created SAS output data set are uncompressed (fixed-length records).

Alias:

N

BINARY

specifies that observations in a newly created SAS output data set are compressed.

Tip:

SAS uses RDC (Ross Data Compression) for this setting. This method is highly effective for compressing medium to large (several hundred bytes or larger) blocks of binary data (that is, numeric variables). Because the compression function operates on a single record at a time, the record length needs to be several hundred bytes or larger for effective compression.

Note:   COMPRESS=BINARY is accepted by Version 7 and later versions of SAS software.  

Operating Environment Information:   The syntax that is shown here applies to the OPTIONS statement. On the command line or in a configuration file, the syntax is specific to your operating environment. For details, see the SAS documentation for your operating environment.  

Details

When COMPRESS=YES or COMPRESS=CHAR, SAS compresses the size of the data set with run-length encoding. Run-length encoding compresses the data set by reducing repeated consecutive characters to two- or three-byte representations.

When COMPRESS=BINARY, SAS uses Ross Data Compression, which combines run-length encoding and sliding-window compression to compress the data set.

Use SAS/Toolkit software to specify your own compression method.

Note:   Compression of observations is not supported by all engines.   

In Version 8, data sets created with engines that were available in earlier versions of SAS, such as the TAPE and XPORT engines, are still accessed by those engines. Therefore, if compression was unable for those engines, it is also not available when you access those data sets in Version 8.

The advantages that are gained by using the COMPRESS= system option include:

• reduced storage requirements for the data set

• fewer input and output operations necessary to read from or write to the data set during processing.

The disadvantages of using the COMPRESS= system option are that

• it may not compress the file at all (and may actually make the file larger), but a message that details the amount of compression is provided

• more CPU resources are required.

Comparisons

The COMPRESS= system option can be overridden by the COMPRESS= data set option.

PERFORMANCE NOTE: Using this option increases the CPU time for reading a data set because of the overhead of uncompressing the record. In addition, some engines do not support compression of observations. When using COMPRESS=YES and REUSE=YES system option settings, observations cannot be addressed by observation number. For additional details, see the COMPRESS= data set option in "SAS Data Set Options."

Note that REUSE=YES takes precedence over the POINTOBS=YES data set option setting.

See Also

	Data Set Options: COMPRESS= REUSE=
	System Option: REUSE=

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