Select the actions on this page in order.

This step compares automatic table compression to manual table compression.

Get actual compressed size

The first step collects statistics for the CUSTOMER_ADDRESS_WITH_AUTO_COMPRESSION table and retrieves an estimate of the the table size. The SQL used to collect statistics and determine the table size are:


CALL ADMIN_CMD
  ('RUNSTATS ON TABLE CUSTOMER_ADDRESS_WITH_AUTO_COMPRESSION')

SELECT CAST(CAST(NPAGES AS DOUBLE)/256
  AS DECIMAL(5,3))
  FROM SYSIBM.SYSTABLES
    WHERE CREATOR=?SCHEMA?
      AND NAME='CUSTOMER_ADDRESS_WITH_AUTO_COMPRESSION'

Compare table sizes

The second step plots the current table size, the estimated table size, the actual compressed size, and the automatically compressed size on a bar graph.

Since we don't compress the first one to two MB of data inserted into the table it does not compress as much as a full reorganization would compress the data. This is a small table, so one to two megabytes has a significant impact on the overall compression of this table. If the table was gigabytes in size, not compressing the first couple of megabytes is negligable.