IMS/ESA Shared Queues: A Planning Guide

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:

1A structure recovery started and completed.

2A CQS system checkpoint was taken as a result of CQS start-up.

3A structure checkpoint was issued after the completion of the structure

recovery.

4A CQS system checkpoint was taken for each IMS startup and each

IMS/CQS synchronization.

5A 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