ZCOMPRESSION Subcommand (SET command)

Note: This command works only if you are connected to the IBM® SPSS® Statistics Server.

ZCOMPRESSION is an override mechanism that works with a setting on the IBM SPSS Statistics Server to determine whether scratch files that are created during a session are in compressed or uncompressed form. Scratch files are created by CACHE, SORT, AGGREGATE, transformations, and any other procedure that adds columns to the data file.

  • The administrator of the IBM SPSS Statistics Server must give you permission to override the IBM SPSS Statistics Server setting. If you don't have permission, a warning message is displayed and the command is ignored.
  • A compressed scratch file reduces the amount of disk I/O compared to an uncompressed scratch file but requires more processing on the IBM SPSS Statistics Server.
  • The extra overhead associated with compression is considerably greater when writing than reading a file. Consider using a higher value for SET CACHE to reduce the frequency of writing new scratch files containing the entire data set. A higher SET CACHE value will also increase the number of times a scratch file is read.
  • If you are working with a very large data file (larger than half of the Server's RAM) and compression is on, you may consider issuing an explicit CACHE command before running other procedures. Doing this will ensure the procedures take full advantage of the disk I/O benefits.
  • The override specification takes effect the next time that a scratch file is written and stays in effect until SET ZCOMPRESSION is specified again or until the end of the session.
  • The default setting for compressing scratch files is set on the IBM SPSS Statistics Server. There is no syntax default.

YES. Compress scratch files.

NO. Do not compress scratch files.