COMPRESS= System Option

Specifies the compression of rows in output tables.

Valid in:	configuration file, SAS invocation, OPTIONS statement, SAS System Options window
Category:	Files: SAS Files
PROC OPTIONS GROUP=	SASFILES
Supports:	SAS data set

Syntax

Syntax Description

Details

Comparisons

Syntax

COMPRESS= NO | YES | CHAR | BINARY

Syntax Description

NO

specifies that the rows in a newly created table be uncompressed (fixed-length records).

YES|CHAR

specifies that the rows in a newly created table be compressed (variable-length records) using RLE (Run Length Encoding). RLE compresses rows by reducing repeated consecutive characters (including blanks) to two-byte or three-byte representations.

Tip	Use this compression algorithm for character data.

BINARY

specifies that the rows in a newly created table be compressed (variable-length records) using RDC (Ross Data Compression). RDC combines run-length encoding and sliding-window compression to compress the file.

Tip	This method is highly effective for compressing medium to large (several hundred bytes or larger) blocks of binary data (numeric columns). 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.

Details

Compressing a file is a process that reduces the number of bytes that are required to represent each observation. Advantages of compressing a file include reduced storage requirements for the file and fewer I/O operations that are necessary to read or write to the data during processing. However, more CPU resources are required to read a compressed file (because of the overhead of uncompressing each observation), and there are situations when the resulting file size might increase rather than decrease.

Use the COMPRESS= system option to compress all output data sets that are created during a SAS session.

After a file is compressed, the setting is a permanent attribute of the file, which means that to change the setting, you must re-create the file. That is, to uncompress a file, specify COMPRESS=NO for a DATA step that copies the compressed file.

Note: For the COPY procedure, the default value CLONE uses the compression attribute from the input data set for the output data set. If the engine for the input data set does not support the compression attribute, then PROC COPY uses the current value of the COMPRESS= system option. For more information about CLONE and NOCLONE, see the COPY statement options, DATASETS procedure, in Base SAS Procedures Guide.

Comparisons

The COMPRESS= system option can be overridden by the COMPRESS= connection string option, the COMPRESS= LIBNAME statement option, and the COMPRESS= data set option.

When you create a compressed file, you can also specify REUSE=YES (as a data set option or system option) in order to track and reuse space. With REUSE=YES, new observations are inserted in space freed when other observations are updated or deleted. When the default REUSE=NO is in effect, new observations are appended to the existing file.