IMS/ESA Shared Queues: A Planning Guide

Chapter 10. Changing Shared-Queue Structure Characteristics

In this chapter, we describe

•

10.1, Structure Resizing

•

10.2, Structure Overflow Tests

•

10.3, Structure Rebuild Tests

10.1 Structure Resizing

The size of a structure can be dynamically altered in the Parallel Sysplex

environment. The CFRM policy is updated by the IXCMIAPU utility with the new

SIZE parameter and then activated with the following command:

SETXCF START,POL,POLNAME=xxx,TYPE=CFRM

The structure is put in change-pending status to make the new SIZE parameter

operational. While the structure is allocated, a rebuild of the structure itself has

to be done:

SETXCF START,REBUILD,STRNAME=yyyyyyy

Structure activity is quiesced during some steps of the rebuilding process. This

will affect any IMS in the sysplex that tries to access the structure.

If the CFRM policy includes an INITSIZE that differs from the SIZE parameter, the

ALTER command can be used to increase the structure size:

SETXCF START,ALTER,STRNAME=yyyyyy,SIZE=zzzz

In the shared-queues environment, the first CQS that connects to a structure

allocates the INITSIZE if there is enough space in the coupling facility.

The primary structure size can be dynamically changed by the CQS itself during

CQS activity. CQS dynamically alters the size of the structure from INITSIZE to

SIZE when the overflow threshold in CQSSGxxx (OVFLWMAX) is reached. The

dynamic alteration by CQS is valid for the primary structure only.

In our environment, the structure sizes were:

Transactions were submitted to IMS and queued to the structures without any

serving MPR available.

When the primary structure IMA0MSGQ reached the overflow threshold, CQS

increased the structure from INITSIZE to SIZE. OVFLWMAX=50% is the value

we specified in CQSSGxxx; 70% is the default if no value is assigned.

Using the dynamic structure-size altering capability allows CQS to avoid the

need for overflow processing.

IMA0MSGQ IMA0MSGQOV

SIZE : 1536 KB

INITSIZE : 1024 KB

OVFLWMAX = 50%

SIZE : 1536 KB

INITSIZE : 1024 KB

 Copyright IBM Corp. 1998 85

The messages issued are these:

CQS0260I CQS CMA1CQS STARTED OVERFLOW THRESHOLD PROCESSING FOR STRUCTURE IMA0MSGQ

CQS0200I STRUCTURE IMA0MSGQ QUIESCED FOR OVERFLOW THRESHOLD PHASE 1

CQS0265I STRUCTURE ALTER REQUEST STARTED FOR STRUCTURE IMA0MSGQ

CQS0266I STRUCTURE ALTER REQUEST COMPLETED FOR STRUCTURE IMA0MSGQ

CQS0264I CQS CMA1CQS TERMINATED OVERFLOW THRESHOLD PROCESSING, ALTER SUCCESSFUL ...

CQS0201I STRUCTURE IMA0MSGQ RESUMED AFTER OVERFLOW THRESHOLD PHASE 1

The same set of messages was obtained by operator command to change the

size without waiting to reach the overflow threshold (OVFLWMAX).

SETXCF START,ALTER,STRNAME=IMA0MSGQ,SIZE=1536

At this point, more transactions were entered to force messages into the

overflow structure, and then we added even more to fill up the overflow structure

as well. When this happened, the overflow structure did not increase from its

INITSIZE to SIZE. Instead, it became full, and the following message was issued:

*CQS0205E STRUCTURE IMA0MSGQOV IS FULL CMA2CQS

A display of the overflow structure is shown in Figure 30.

D XCF,STR,STRNAME=IMA0MSGQOV

IXC360I 16.50.06 DISPLAY XCF 727

STRNAME:IMA0MSGQOV

STATUS:ALLOCATED

POLICY SIZE :1536 K

POLICY INITSIZE:1024 K

REBUILD PERCENT:N/A

PREFERENCE LIST:VC1LA1

EXCLUSION LIST IS EMPTY

ACTIVE STRUCTURE

----------------

ALLOCATION TIME:07/29/1998 14:05:26

CFNAME :VC1LA1

COUPLING FACILITY:009674.IBM.02.000000041826

PARTITION:1 CPCID:00

ACTUAL SIZE :1024 K

STORAGE INCREMENT SIZE:256 K

VERSION :B0D2C982 9CFAD504

XCF GRPNAME :IXCLO018

DISPOSITION :KEEP

ACCESS TIME :NOLIMIT

MAX CONNECTIONS:8

# CONNECTIONS :2

Figure 30. Display of a Structure That is Full

This works as documented; the manual states that the overflow structure does

not dynamically alter from its INITSIZE. It can, however, be altered manually as

shown in Figure 31 on page 87.

86 IMS/ESA Shared Queues Planning Guide