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

Get IMS/ESA Shared Queues: A Planning Guide now with O’Reilly online learning.

O’Reilly members experience live online training, plus books, videos, and digital content from 200+ publishers.