Before compressing data, you can use the DSN1COMP stand-alone
utility to estimate how well the data can be compressed.
About this task
After data is compressed, you can use compression reports
and catalog statistics to determine how effectively it was compressed.
Procedure
To find the effectiveness of data compression:
- Use the DSN1COMP stand-alone utility to find out how much
space can be saved and how much processing the compression of your
data requires. Run DSN1COMP on a data set that contains a table space,
a table space partition, or an image copy. DSN1COMP
generates a report of compression statistics but does not compress
the data.
- Examine the compression reports after you use REORG or
LOAD to build the compression dictionary and compress the data. Both utilities issue a report message (DSNU234I or DSNU244I).
The report message gives information about how well the data is compressed
and how much space is saved. (REORG with the KEEPDICTIONARY option
does not produce the report.)
- Query catalog tables to find information about data compression
- PAGESAVE column of the SYSIBM.SYSTABLEPART tells you the percentage
of pages that are saved by compressing the data.
- PCTROWCOMP columns of SYSIBM.SYSTABLES and SYSIBM.SYSTABSTATS
tells you the percentage of the rows that were compressed in the table
or partition the last time RUNSTATS was run. Use the RUNSTATS utility
to update these catalog columns.