COMPRESS= Data Set Option

Specifies the compression of rows in an output table.

Valid in:	DATA and PROC steps
Category:	Data Set Control
Restriction:	Use with output data sets only.
Supports:	SAS data set

Syntax

Details

Comparisons

Syntax

COMPRESS=NO | YES | CHAR | BINARY

Syntax Description

NO: specifies that the rows in a newly created data set are uncompressed (fixed-length records).

YES | CHAR: specifies that the rows in a newly created data set are compressed (variable-length records) by SAS using RLE (Run Length Encoding). RLE compresses rows by reducing repeated consecutive characters (including blanks) to two-byte or three-byte representations.

Alias:ON

Tip:Use this compression algorithm for character data.

BINARY: specifies that the rows in a newly created data set are compressed (variable-length records) by SAS 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 required to represent each row. Advantages of compressing a file include reduced storage requirements for the file and fewer I/O operations 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 row). There are also situations where the resulting file size might increase rather than decrease.

Use the COMPRESS= data set option to compress an individual file. Specify the option for output data sets only, that is, data sets named in the DATA statement of a DATA step or in the OUT= option of a SAS procedure.

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.

Comparisons

The COMPRESS= data set option overrides the COMPRESS= option in the LIBNAME statement, the COMPRESS= connection string option, and the COMPRESS= system option.

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