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| Making sense of log file size |
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| BergerC |
 Posted: Fri Sep 06, 2002 11:55 am Post subject: Making sense of log file size |
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Novice
Joined: 08 Apr 2002
Posts: 15
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I've read through a LOT of good threads on this site re: logging. I've learned much. However, in the limited testing I've done, and based on what I've seen at several implementations, I have a question on log file size/number and how many persistent messages can actually be held on a queue manager.
Based on the MQ Admin documentation, you can add 750 bytes to a persistent message length, and that's the space required to hold it in a log file. So if I've got a 1 MB message, I'm not really concerned about the 750 bytes - I'll round it off for the discussion.
# Primary logs = 3
# Secondary logs = 2
log file pages = 256k (x4)
With this setup, I would estimate my log capacity at 5 MB. My simplistic reasoning would seem to indicate I can hold 5, 1 MB persistent messages on a queue on this queue manager, but no more (slightly less, with all the other items that must be logged.)
Why is it then that I seem to be able to hold A GREAT DEAL more than that? I can use a test utility to put HUNDREDS of large (500K, 300K) messages, equalling 200 MB, onto a single queue (again, all persistent messages, but not under syncpoint.)
I'm missing something obvious.
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Chris |
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| mgrabinski |
| Posted: Sun Sep 08, 2002 9:59 pm Post subject: |
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Master
Joined: 16 Oct 2001
Posts: 246
Location: Katowice, Poland
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When the active log fills up, its contents goes to archive log
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Marcin Grabinski <>< |
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| nimconsult |
| Posted: Sun Sep 08, 2002 10:20 pm Post subject: |
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Master
Joined: 22 May 2002
Posts: 268
Location: NIMCONSULT - Belgium
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BergerC,
No. 5Mb circular log files does not mean that you are limited to 5Mb in queues. Log files are used to store transactions, not queue content.
With 5Mb log files:
- you cannot put a persistent message of more than 5Mb in a queue.
- you cannot put more than total 5Mb persistent messages in one or multiple queues in a single transaction (or in multiple transactions running simultaneously)
- you can put as many messages as you want in queues.
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Nicolas Maréchal
Senior Architect - Partner
NIMCONSULT Software Architecture Services (Belgium)
http://www.nimconsult.be |
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| BergerC |
| Posted: Mon Sep 09, 2002 5:27 am Post subject: |
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Novice
Joined: 08 Apr 2002
Posts: 15
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Thanks to both cimconsult and mgrabinski. This does change my outlook quite a bit.
Is this aspect of MQ doumented in any of the standard manuals that I've simply overlooked?
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Chris |
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| nimconsult |
| Posted: Mon Sep 09, 2002 10:52 pm Post subject: |
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Master
Joined: 22 May 2002
Posts: 268
Location: NIMCONSULT - Belgium
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I think that most information about log files is in the System Administration manual, in the chapter about Recovery & Restart. I am not quite sure that the explanation is clear about how log files work, but they mention that log files are used to keep track of transactions.
Logging, transaction management, recovery and restart is a common theory, originally found in databases, transaction monitors (CICS, Tuxedo, MTS...), journaled file systems, that you learn in courses or by experience.
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Nicolas Maréchal
Senior Architect - Partner
NIMCONSULT Software Architecture Services (Belgium)
http://www.nimconsult.be |
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| TonyD |
| Posted: Tue Sep 10, 2002 7:51 pm Post subject: |
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Knight
Joined: 15 May 2001
Posts: 540
Location: New Zealand
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| You might find it useful, if you have time, to create a test QM on an NT machine, create a couple of test queues (persistent) and then put and get some messages from the queues. Then shut down the queue manager and run the 'dmpmqlog' utility. With a bit of detective work you will be able to work out what records are written to the log and the information that is held in them. If you have a program that is putting or getting UOWs that will be even more useful in terms of seeing the transaction-ralted information that is written. |
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