Storing the expansion dictionary for compressed log records in the compression dictionary data set

When you use IFI calls for IFCID 0306 to read compressed log records for replication applications, you can lessen locking and performance problems by using expansion dictionaries that are stored in the compression dictionary data set.

To prepare a stand-alone Db2 subsystem or a data sharing group to use the compression dictionary data set (CDDS) to store expansion dictionaries, follow these steps:

1. Create the CDDS on the z/OS system that contains the stand-alone Db2 subsystem, or on the z/OS system that contains one of the members of a data sharing group. You need to create only one CDDS for the entire data sharing group.
   1. To minimize the possibility of an out-of-space condition, define an SMS data class for the CDDS with the following attributes enabled:
      • Extended addressability
      • Extended format
      • Extent constraint relief
      • CA reclaim
   2. Issue a DEFINE CLUSTER statement like the one below. For KEYS, RECORDSIZE, SPANNED, SHAREOPTIONS, CONTROLINTERVALSIZE, and REUSE, use the same values that are listed. The CDDS name must be of the form prefix.CDDS.

      
      DEFINE CLUSTER                       -
             (NAME(prefix.CDDS)            -
              KEYS(8 0)                    -
              RECORDSIZE(66560 66560)      -
              SPANNED
              REUSE                      -
              SHAREOPTIONS(3 3) )          -
            DATA                           -
             (CYLINDERS(5000 1000)         -
              CONTROLINTERVALSIZE(16384))  -
            INDEX                          -
             (CYLINDERS(1000 500)             -
              CONTROLINTERVALSIZE(2048))

2. Perform the following steps to modify the stand-alone Db2 subsystem or each member of the data sharing group.
   Recommendation: For a data sharing group, complete all steps on one member before continuing to the next member.
   1. Issue the STOP DB2 command.
   2. Apply all PTFs that support using an expansion dictionary in the CDDS to decompress log records for retrieval through IFI calls for IFCID 0306.
   3. Set the following subsystem parameters:
      • Set CDDS_MODE to SOURCE_ONLY.
      • SET CDDS_PREFIX to the prefix value that you specified when you created the CDDS.
   4. Issue the START DB2 command.
3. Issue the START CDDS command on the non-data sharing member or one of the members in the data sharing group. START CDDS directs all members of a data sharing group to allocate and open the CDDS.
   1. If you activate function level 100* after the CDDS is started in function level 500, you need to issue the STOP CDDS command on the non-data sharing member or one of the members in the data sharing group to stop the CDDS before you activate function level 100*. Then issue the START CDDS command.
4. Run REORG TABLESPACE with the INITCDDS option to populate the CDDS. You can specify the SEARCHTIME option with the INITCDDS option to allow REORG to populate the CDDS with an earlier expansion dictionary than the one that currently resides in the table space.