10.3 Structure Rebuild Tests
We performed some tests that required a structure rebuild:
10.3.1, Structure Rebuild after Structure Delete (no Connection)
10.3.2, Structure Rebuild after Structure Delete (Connection to the Structure)
10.3.1 Structure Rebuild after Structure Delete (no Connection)
The full-function and Fast-Path structures used in a shared-queues environment
are persistent structures from a Parallel Sysplex viewpoint; they remain
allocated even if all the CQSs disconnect and all CQSs and IMSs cold start. The
structures are used to keep the data contents of IMS objects (messages), as well
as some other application information.
The contents of the shared-queue structures must be consistent across normal
and abnormal termination and across any hardware or software failure. The
structures can be manually or automatically recovered through the following
actions:
If at least one CQS is running, the recovery can be initiated by the following
command:
SETXCF START,REBUILD,STRNAME=strname,LOCATION=NORMAL/OTHER
CQS initiates a structure rebuild during start-up if it detects an empty
structure and finds an SRDS containing a valid structure checkpoint
MVS initiates a structure rebuild if the rebuild threshold for loss of
connectivity is reached. This specified is by the REBUILD parameter in the
CFRM policy.
When a structure recovery is required, CQS uses the SRDS as a recovery
starting point (comparable to database image copy) and then reads all the log
records since the structure checkpoint was taken. The time needed to recover
the structure depends on the number of log records to be applied. Taking
frequent structure checkpoints makes structure recovery faster; however, no
CQS can access the structure during a structure checkpoint. A structure
checkpoint and a valid SRDS must be available for a structure recovery to be
successful.
A structure checkpoint is taken:
When the MVS log becomes full or approaches full condition
After successful structure rebuild
After successful overflow process
When the command /CQCHKPT SHAREDQ STRUCTURE xxx is issued
During CQS normal termination if the command /CQSET SHUTDOWN SHAREDQ was
entered.
We performed a test to see what happens during structure recovery. The test
started when there were no connections to the structure. CQS and IMS were
down before deleting the structure.
Both CQS and IMS were shut down after leaving twenty messages on the
full-function shared queue, as shown in the following display:
92 IMS/ESA Shared Queues Planning Guide
/DISPLAY QCNT TRANSACTION MSGAGE 0
QUEUENAME QCNT-TOTAL QCNT-AGED TSTMP-OLD TSTMP-NEW
IVTNO 20 20 98213/071253 98213/071316
*98213/071351*
The full-function shared-queue structure, IMA0MSGQ, was deleted to force a
structure rebuild when CQS was started. The following command
/CHECKPOINT FREEZE
shut down both IMSs, which brought down CQSs as well:
SETXCF FORCE,STR,STRNAME=IMA0MSGQ
deleting the full-function shared-queue structure. Once IMA1 started, CQS1
rebuilt the full-function structure as shown in Figure 36.
CQS0200I STRUCTURE IMA0MSGQ QUIESCED FOR STRUCTURE REBUILD CMA1CQS
1 CQS0240I CQS CMA1CQS STARTED STRUCTURE RECOVERY FOR STRUCTURE IMA0MSGQ
1 CQS0241I CQS CMA1CQS COMPLETED STRUCTURE RECOVERY FOR STRUCTURE IMA0MSGQ
CQS0201I STRUCTURE IMA0MSGQ RESUMED AFTER STRUCTURE REBUILD CMA1CQS
2 CQS0030I SYSTEM CHECKPOINT COMPLETE, STRUCTURE IMA0MSGQ, LOGTOKEN ...
CQS0020I CQS READY CMA1CQS
3 CQS0220I CQS CMA1CQS STARTED STRUCTURE CHECKPOINT FOR STRUCTURE IMA0MSGQ
CQS0200I STRUCTURE IMA0MSGQ QUIESCED FOR STRUCTURE CHECKPOINT CMA1CQS
CQS0201I STRUCTURE IMA0MSGQ RESUMED AFTER STRUCTURE CHECKPOINT CMA1CQS
4 CQS0030I SYSTEM CHECKPOINT COMPLETE, STRUCTURE IMA0MSGQ, LOGTOKEN ...
CQS0221I CQS CMA1CQS COMPLETED STRUCTURE CHECKPOINT FOR STRUCTURE IMA0MA1
5 CQS0030I SYSTEM CHECKPOINT COMPLETE, STRUCTURE IMA0MSGQ, LOGTOKEN ...
Figure 36. Messages Issued during a CQS Structure Rebuild
In the sequence of events shown in Figure 36, we saw:
1A structure recovery started and completed.
2A CQS system checkpoint was taken as a result of CQS start-up.
3A structure checkpoint was issued after the completion of the structure
recovery.
4A CQS system checkpoint was taken for each IMS startup and each
IMS/CQS synchronization.
5A CQS system checkpoint was taken after the completion of the structure
checkpoint.
At the completion of the structure recovery, the 20 IVTNO transactions were
successfully recovered:
/DISPLAY QCNT TRANSACTION MSGAGE 0
QUEUENAME QCNT-TOTAL QCNT-AGED TSTMP-OLD TSTMP-NEW
IVTNO 20 20 98213/071253 98213/071316
*98213/072214*
If CQS2 is started before the structure rebuild by CQS1 is completed, the
following messages are received:
Chapter 10. Changing Shared-Queue Structure Characteristics 93

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