System z Platform Test

Recovery for DB2 group buffer pool

ICF recovery considerations for DB2 group buffer pool duplexing

This topic describes recovery for DB2 group buffer pool duplexing in an internal coupling facility (ICF) environment. DB2 group buffer pools (GBPs) allow us to share data between members of a DB2 data sharing group, while duplexing creates another instance of a GBP structure in another coupling facility; in the event of structure damage or connectivity loss to a primary GBP structure, the system can switch to the secondary structure.

Currently, our DB2 data sharing group consists of 12 members. All of our group buffer pools are enabled for duplexing (DUPLEX(ENABLED)), and all have three CFs designated in their preference list. We have two coupling facilities using ICF CPs on the same CPCs as two of the DB2 members, and our third coupling facility is a stand-alone model. For information on how group buffer pools were initially implemented in our environment, please refer to "DB2 Group Buffer Pool Duplexing", of the December 1999 edition of our test report.

Note that the following coupling facility failure and recovery example assumes the failure occurs on an ICF in a 2 CF environment, the second CF being a stand-alone; messages shown may be issued repeatedly.


Messages issued when the ICF fails

If the system with the ICF housing the primary GBP structure fails, you'll receive messages similar to the following:

IXL158I PATH 72 IS NOW NOT-OPERATIONAL TO CUID: FFF4
        COUPLING FACILITY 009672.IBM.02.000000046781
        PARTITION: 1  CPCID: 00
 
IXC518I SYSTEM JB0 NOT USING
         COUPLING FACILITY  009672.IBM.02.000000046781
         PARTITION: 1    CPCID: 00
         NAMED CF2
         REASON: CONNECTIVITY LOST.
         REASON FLAG: 13300002.
 
DSNB228I @DBZ1 DSNB5STS GROUP BUFFER POOL GBP8
         CANNOT BE ACCESSED FOR READ_STGSTATS
         MVS IXLCACHE REASON CODE=X'0C1C0C06'
 
 
IXC522I REBUILD FOR STRUCTURE DSNDB1G_GBP0 IS BEING STOPPED
        TO SWITCH TO THE NEW STRUCTURE DUE TO
        LOSS OF CONNECTIVITY TO THE STRUCTURE
 
 
DSNB303E @DBG1 DSNB1REE A LOSS OF CONNECTIVITY WAS
         DETECTED
         TO GROUP BUFFER POOL GBP0
 
 
DSNB744I @DBG1 DSNB1GBR DUPLEXING IS BEING STOPPED
         FOR GROUP BUFFER POOL GBP0
         SWITCHING TO SECONDARY
         REASON = LOSSCONNPRI
         DB2 REASON CODE = 00000000
 
IXC101I SYSPLEX PARTITIONING IN PROGRESS FOR J90 REQUESTED BY 
        XCFAS. 
        REASON: SFM STARTED DUE TO STATUS UPDATE MISSING

Messages issued after the ICF system is partitioned from the sysplex

After the failing system that housed the ICF is partitioned out of the sysplex, the group buffer pools transition from duplex to simplex mode:

IXC105I SYSPLEX PARTITIONING HAS COMPLETED FOR J90
        - PRIMARY REASON: SYSTEM REMOVED
        BY SYSPLEX FAILURE MANAGEMENT BECAUSE
        ITS STATUS UPDATE WAS MISSING
         - REASON FLAGS: 000100
 
DSNB745I @DBG1 DSNB1GBR THE TRANSITION BACK TO
          SIMPLEX MODE HAS COMPLETED FOR
          GROUP BUFFER POOL GBP0
 

IXL014I IXLCONN REBUILD REQUEST FOR STRUCTURE DSNDB1G_GBP0
        WAS SUCCESSFUL.  JOBNAME: DBG1DBM1 ASID: 00FD
        CONNECTOR NAME: DB2_DBG1 CFNAME: CF2
 
IXC538I DUPLEXING REBUILD OF STRUCTURE DSNDB1G_GBP0
        WAS NOT INITIATED BY MVS.
        REASON: NO COUPLING FACILITY PROVIDED BETTER OR 
                EQUIVALENT CONNECTIVITY

Messages issued when the secondary GBP structure becomes available

Since we specify DUPLEX(ENABLED) for our group buffer pools in our CFRM policy, our group buffer pools are automatically rebuilt in duplex mode when the secondary coupling facility structure becomes available. You'll see messages similar to the following as this occurs:

IXC517I SYSTEM Z1 ABLE TO USE
         COUPLING FACILITY  009672.IBM.02.000000046781
         PARTITION: 1    CPCID: 00
          NAMED CF2
 
IXC536I DUPLEXING REBUILD OF STRUCTURE DSNDB1G_GBP0
        INITIATED.
        REASON: GAINED CONNECTIVITY TO A COUPLING FACILITY
 
DSNB740I @DBH1 DSNB1RBQ ATTEMPTING TO ESTABLISH
         DUPLEXING FOR
         GROUP BUFFER POOL GBP0
         REASON = POLICY
 
IXC529I DUPLEX REBUILD NEW STRUCTURE DSNDB1G_GBP0
        IS BEING ALLOCATED IN COUPLING FACILITY CF2.
        OLD STRUCTURE IS ALLOCATED IN COUPLING FACILITY CF1.
        REBUILD START REASON: MVS INITIATED BASED ON POLICY
 
 
IXL015I REBUILD NEW STRUCTURE ALLOCATION INFORMATION FOR
        STRUCTURE DSNDB1G_GBP0, CONNECTOR NAME DB2_DBG1
         CFNAME     ALLOCATION STATUS/FAILURE REASON
         --------   ---------------------------------
           CF1        RESTRICTED BY REBUILD OTHER
           CF2        STRUCTURE ALLOCATED
 
IXC521I REBUILD FOR STRUCTURE DSNDB1G_GBP0
        HAS REACHED THE DUPLEXING ESTABLISHED PHASE
 
DSNB742I @DBH1 DSNB1GBR DUPLEXING HAS BEEN
         SUCCESSFULLY ESTABLISHED FOR
         GROUP BUFFER POOL GBP0

Recovery completes

Now, because we specified DUPLEX(ENABLED) in our CFRM policy, our group buffer pools are automatically allocated once the failing ICF comes back online.

Note that table spaces do not require manual recovery when you have group buffer pools set up in duplex mode.