Straight from the horses mouth - this answer from one of my colleagues who
wrote index support.
- What is the overhead of an index.
Answer: At QMGR restart, each message on each indexed queue must be
examined to rebuild its index entry. There is an option on the CSQ6SYSP
macro in zparms(QINDXBLD) (on V5.3) which controls if the QMGR will wait
until all indices have been rebuilt before applications can connect to it,
or not. Other than that overhead, it is much faster to find a message using
the index, rather than 'trawling' through the queue, looking for your
target message. So there is a cost at restart, and a benefit at MQGET time.
- Where is this overhead.
Answer: see Q1
- Where is the index stored physically, which pageset.
Answer: The index is built and maintained in virtual storage in the queue
managers address space. It is built on restart, and freed at shutdown. We
can see no benefit in hardening the index into a pageset.
- Any do's and don'ts regarding to queue's with indexes?
Answer: Use as broad a mix of MessageIds as possible. The fewest
repetitions of the same MessageId gives the best results. Having all
messages with the same MessageId will produce the worst result, and will be
worse than having no index at all!
Cheers
Morag
Morag Hughson
WebSphere MQ for z/OS Development
Internet: [EMAIL PROTECTED]
----- Forwarded by Morag Hughson/UK/IBM on 17/09/2002 10:33 -----
"Douwe van Sluis,
Infodemic B.V." To: [EMAIL PROTECTED]
<d.b.van.sluis@IN cc:
FODEMIC.NL> Subject: MQ Series OS/390
Sent by: MQSeries
List
<MQSERIES@AKH-WIE
N.AC.AT>
16/09/2002 12:52
Please respond to
MQSeries List
We are using MQ Series on OS/390, persistent queue, messagesize avg
100k and we need an index on the queue on MessageId.
This can be set up, no problem, but:
- What is the overhead of an index.
- Where is this overhead.
- Where is the index stored physically, which pageset.
- Any do's and don'ts regarding to queue's with indexes?
Vriendelijke groet,
Douwe van Sluis, Infodemic B.V.
IT-Specialist
www.infodemic.nl
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