SPD Engine System Options

COMPRESS= System Option

Specifies to compress SPD Engine data sets on disk as they are being created.

Valid in:	configuration file, SAS invocation, OPTIONS statement, System Options window
Restriction:	cannot be used with ENCRYPT=YES or ENCRYPT=RC4
Default:	NO

Syntax
Details

Syntax

COMPRESS= NO | YES | CHAR | BINARY

NO: performs no data set compression.
YES | CHAR: performs the Run Length Compression (SPDSRLC2) on the data set.
BINARY: performs the Ross Data Compression (SPDSRDC) on the data set.

Details

When you specify COMPRESS=YES|BINARY|CHAR, the SPD Engine compresses, by blocks, the data component file as it is created. To specify the size of the compressed blocks, use the IOBLOCKSIZE= Data Set Option when you create the data set. To add padding to the newly compressed blocks, specify PADCOMPRESS= Data Set Option when creating or updating the data set. For more information, see Compressing SPD Engine Data Sets.

The SPD Engine does not support user-specified compression. If you are migrating a default Base SAS engine data set that is both compressed and encrypted, the encryption is retained, but the compression is dropped.

The CONTENTS procedure prints information about the compression. The following example explains the compressed info fields in the CONTENTS procedure output:

                         -          Compressed Info      -                                 
                         Number of compressed blocks     202                               
                         Raw data blocksize              32736                             
                         Number of blocks with overflow  5                               
                         Max overflow chain length       3                                 
                         Block number for max chain      80                                 
                         Min overflow area               87                              
                         Max overflow area               181

Number of compressed blocks	number of compressed blocks that are required to store data.
Raw data blocksize	compressed block size in bytes calculated from the size specified in the IOBLOCKSIZE= data set option.
Number of blocks with overflow	number of compressed blocks that needed more space. When data is updated and the compressed new block is larger than the compressed old block, an overflow block fragment is created.
Max overflow chain length	largest number of overflows for a single block. For example, the maximum overflow chain length would be 2 if a compressed block was updated and became larger, and then updated again to a larger size.
Block number for max chain	number of the block containing the largest number of overflow blocks.
Min overflow area	minimum amount of disk space that an overflow requires.
Max overflow area	maximum amount of disk space that an overflow requires.

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