Changing group buffer pools

You can change group buffer pool attributes such as the castout threshold values, checkpoint frequency, and size.

Default values of unaltered group buffer pools

When you issue an ALTER GROUPBUFFERPOOL command, it does not change any option that you did not explicitly specify. That is, the default is to leave the values unchanged.

An unaltered group buffer pool has the values shown in the following table for the attributes that you can change with the ALTER GROUPBUFFERPOOL command.
Option Value
GBPCACHE YES
RATIO 10
CLASST 5,0
GBPOOLT 30 (%)
GBPCHKPT 4 (minutes)
When new values take effect
When you issue the ALTER GROUPBUFFERPOOL command, some option specifications become effective only at the next allocation of the group buffer pool. The following table lists each option, when the new value takes effect, and if the option is applicable for a group buffer pool that is specified as GBPCACHE(NO).
Keyword New value takes effect Applicable if GBPCACHE(NO)?
GBPCACHE at next allocation N/A
AUTOREC immediately No
RATIO at next allocation 2 No 3
CLASST immediately No 3
GBPOOLT immediately No 3
GBPCHKPT immediately No 3
Notes:
  1. You can use the z/OS® command SETXCF START,REBUILD to have the change take effect if the group buffer pool is not duplexed. If the group buffer pool is duplexed and you want to change to GBPCACHE(NO), first go back to simplex mode and rebuild. GBPCACHE(NO) is not allowed for duplexed group buffer pools.
  2. You can use the z/OS command SETXCF START,REBUILD to have the change take effect if the group buffer pool is not duplexed. If the group buffer pool is duplexed, first go back to simplex mode and rebuild; then optionally go back to duplex mode. If a group buffer pool is duplexed, both instances of that duplexed group buffer pool use the same RATIO value.
  3. Db2 issues message DSNB761 when you specify this option for a GBPCACHE(NO) group buffer pool. These settings only take effect after the GBPCACHE attribute has been changed to YES.
Trace information for data sharing members
When this command with group scope is issued in a Db2 data sharing member, it also runs on all other active members. IFICID 090 trace records for other group members can show that the same command was issued by the SYSOPR authorization ID from the 016.TLPKN5F correlation ID, in addition to the trace records from the member where the original command was issued.