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MQSeries.net Forum Index » General IBM MQ Support » Checkpoints in Log

Checkpoints in Log

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greenhorn

Posted: Sat Mar 09, 2002 2:15 am Post subject:

Novice

Joined: 04 Mar 2002
Posts: 10

Could anybody let me know the advantage of using checkpoints in Logs ?
Does it anyway help reduce the restart time of the Q manager and does it help reduce the disk space consumption ?
Cheers
Greenhorn

Coz

Posted: Mon Mar 11, 2002 5:12 am Post subject:

Apprentice

Joined: 20 Feb 2002
Posts: 44
Location: Basel CH

If you're referring to the use of rcdmqimg with linear logging then the answer is simply that the number of logs that have to be kept to recover from a media failure is drastically reduced. Once messages have been committed they are'nt really needed anymore hence the rolling log files but the MQ Objects are written to the logfiles only at startup I believe (maybe checkpointed automatically but I beleive that the gap is relatively huge).
Using rcdmqimg will 'move' the obeject definition to a newer logfile thus allowing older logfiles to be deleted.

Coz

jhalstead

Posted: Mon Mar 11, 2002 9:28 am Post subject:

Master

Joined: 16 Aug 2001
Posts: 258
Location: London

I guess there are two things being discussed here, check points and media images. I'm going to answer assuming you did meant checkpoints!

Checkpoint are controlled by the queue manager they are not directly of use to the user (apart from the fact that they keep data consistent between logs and object files!).

As far as I understand checkpoints are taken automatically by the queue manager every 1000 operations along with at startup and shutdown (although I think this may now be 10,000 on v5.2). At this point MQSeries ensures that the log and object files are synchronised.
If you are using circular logging this is the point at which the logs can be recycled. So for circular logging your primary and secondary log files should be able to accomodate those thousand operations along with the message data.
With linear logging the checkpoint process has no impact on the size/use of the logs.
I don't think checkpointing provides any direct log space saving, rather it dictates the size of your logs (if you're using circular logging).

You are correct in that checkpoints are meant to aid the efficiency of recovery.

A good place to review this would be the MQSeries system administration guide.

http://www-3.ibm.com/software/ts/mqseries/library/manualsa/index.html

Cheers

Jamie

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