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MQSeries.net Forum IndexIBM MQ Installation/Configuration SupportAltering circular log sizes

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bduncan
PostPosted: Wed Apr 18, 2001 3:37 pm Post subject: Reply with quote

Padawan

Joined: 11 Apr 2001
Posts: 1554
Location: Silicon Valley

Problem Description:
When processing large groups of messages, our queue managers would run out of log space. The queue manager logs persistent messages, such as those coming from feeds, to disk in order to be able to recover in case of a failure. These logs are circular, but if a single unit of work is initiated that spans a greater amount of disk space than the logs are capable, the application initiating the unit of work dies.

Problem Solution:
The only boxes we have encountered this problem on are those handling large groups of messages. In order to increase the log size, a configuration file must be altered BEFORE the queue manager is created on the box. This means that at some point after installing MQSeries, but before issuing the crtmqm command, a file in /var/mqm must be changed. The name of this file is mqs.ini. Near the bottom, you should see a section called LogDefaults: and three lines that look like this:
LogPrimaryFiles=3
LogSecondaryFiles=2
LogFilePages=1024
LogPrimaryFiles indicates the number of circular log files that MQSeries will maintain at all times. LogSecondaryFiles indicates the total number of circular log files that MQSeries will add as necessary. LogFilePages indicates the size of each log file, and this can be misleading because it is in 4K chucks, so 1024 really means 4096K or 4Mb log file sizes. So, by default, the queue manager allocates 3 4096K log files at startup, and will create up to 2 more 4Mb log files if needed. This means only a total of 20Mb of circular logs. If we move more than 20Mb of data within a single unit of work, our queue manager will break. For our purposes, the following attributes should suffice:
LogPrimaryFiles=10
LogSecondaryFiles=5
LogFilePages=16384
So this means that we will allocate 10 64Mb log files at startup, or 640Mb, and allocate up to 320Mb of additional logs as necessary.


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NeilCasey
PostPosted: Mon Jun 25, 2001 9:46 pm Post subject: Reply with quote

Newbie

Joined: 24 Jun 2001
Posts: 4

This is one way of specifying these values, but they can also be provided on the crtmqm command line, which removes the need to edit the defaults stanza. It is after all just a list of defaults, not a proscription of how the queue manager is built.

Neil Casey
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Tom Hogan
PostPosted: Thu Aug 16, 2001 9:35 am Post subject: Reply with quote

Novice

Joined: 15 Aug 2001
Posts: 10

I am also investigating an issue with regard to log sizes. I thought the default log files were big enough for my needs, but now I guess not. I tried using the dmpmqlog command to see if the messages on the log were larger than I thought, but all I ever see are system entries (like start, stop, and checkpoint). Is there any tool that can report the number and size of logged messages, preferably when the queue manager is still running? dmpmqlog seems to only work when the queue manager is not running.
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jhalstead
PostPosted: Thu Oct 04, 2001 8:51 am Post subject: Reply with quote

Master

Joined: 16 Aug 2001
Posts: 258
Location: London

Couple of quickies to do with Logging on AIX.

Is there a maximum number of pages which can be allocated to a log file? If not a maximum is there an optimal size?

Secondly in the system admin guide there is a checkpoint overhead for 'active units of work' (200 bytes per active unit), I'd have thought that this implies un-commited units of work, however it's not really clear... Anyone know for definate?

Many Thanks

Jamie
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venkat kurra
PostPosted: Thu Nov 01, 2001 10:09 am Post subject: Reply with quote

Master

Joined: 18 Oct 2001
Posts: 245
Location: Bloomington , IL

Hi,
I would like to use Circular log.We are getting 10,000 messages/day and each message has 4mb length.We plan to use 50 to 100 as batch size and all messages are persistence.
I think the unit of work need 200mb to 400mb.
so i plan to take
Log Primary files =10
Log secondary files =5
Log File size =16384
so each file has 64mb.
is this sufficient or shell i increase file size?
I don't have experience in this set up.i saw "Calculating the size of the log" from mqadmin reference book.still i have some confusition.
correct it...
Thanks,
Venkat
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bduncan
PostPosted: Thu Nov 01, 2001 11:07 am Post subject: Reply with quote

Padawan

Joined: 11 Apr 2001
Posts: 1554
Location: Silicon Valley

Venkat,
I had to recently deal with a problem where our queue managers were using up their circular log files, and causing the queue manager to crash. The problem is that we calculated the circular log size based on the parameters that IBM specifies in the System Administration Guide. Unfortunately these weren't sufficient. Basically IBM support could only say, "make them bigger" without giving us any guidance as to how much bigger they needed to be. Granted, our setup was much larger than yours - we had a single queue manager handling about 700 persistent messages per second, under syncpointed batches of 100, and this was pretty constant throughout the day, so we had several million messages per day. These messages were tiny though (under 1K) and we calculated that we only needed 150Mb logs (being VERY generous with the overhead). So to sum it up, since disk space is so cheap these days, I'd make the logs as big as you can get away with. Make these extra logs in the form of secondaries so that they won't be allocated unless necessary....


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venkat kurra
PostPosted: Thu Nov 01, 2001 11:36 am Post subject: Reply with quote

Master

Joined: 18 Oct 2001
Posts: 245
Location: Bloomington , IL

Thanque very much
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