Too few data entries

If a group buffer pool does not have enough data entries, castout to disk occurs more frequently.

Begin general-use programming interface information. You can see the number of pages cast out by using the GDETAIL option of the DISPLAY GROUPBUFFERPOOL command.

A more serious data entry shortage is indicated by field E in the DISPLAY GROUPBUFFERPOOL GDETAIL report shown in the following figure.

Figure 1. Example output of group detail statistics

DSNB783I -DB1A CUMULATIVE GROUP DETAIL STATISTICS SINCE 15:35:23 May 17, 2002
DSNB784I -DB1A GROUP DETAIL STATISTICS
                 READS
                   DATA RETURNED A                    = 3845
DSNB785I -DB1A     DATA NOT RETURNED
                     DIRECTORY ENTRY EXISTED B        = 27
                     DIRECTORY ENTRY CREATED C        = 28336
                     DIRECTORY ENTRY NOT CREATED D    = 332, 0
 
DSNB786I -DB1A   WRITES
                   CHANGED PAGES                      = 20909
                   CLEAN PAGES                        = 0
                   FAILED DUE TO LACK OF STORAGE E    = 8
                 CHANGED PAGES SNAPSHOT VALUE         = 974
DSNB787I -DB1A   RECLAIMS
                   FOR DIRECTORY ENTRIES F            = 18281
                   FOR DATA ENTRIES                   = 47
                 CASTOUTS                             = 16073
DSNB788I -DB1A   CROSS INVALIDATIONS
                   DUE TO DIRECTORY RECLAIMS G        = 4489
                   DUE TO WRITES                      = 3624
                   EXPLICIT                           = 0
DSNB762I -DB1A   DUPLEXING STATISTICS FOR GBP0-SEC
                   WRITES
                     CHANGED PAGES                    = 20909
                     FAILED DUE TO LACK OF STORAGE    = 8
                   CHANGED PAGES SNAPSHOT VALUE       = 974
DSNB790I -DB1A DISPLAY FOR GROUP BUFFER POOL GBP0 IS COMPLETE
DSN9022I -DB1A DSNB1CMD 'DISPLAY GROUPBUFFERPOOL' NORMAL COMPLETION

A value in this field indicates that the data page resources of the coupling facility are being consumed faster than the Db2 castout processes can free them.

You can increase the number of data entries in the group buffer pool in one of two ways:

Increase the total size of the group buffer pool.
Use the ALTER GROUPBUFFERPOOL command to adjust the ratio in favor of data entries.

End general-use programming interface information.