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| svmmq |
 Posted: Mon Jun 01, 2015 4:53 am Post subject: MQ log file size on Linux |
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Newbie
Joined: 19 Mar 2015
Posts: 6
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Hi,
We are creating queue managers on Linux and IBM pointed us to a document that says the following with respect to sizing the logs, 'As long as you have the disk space you are recommended to allocate the maximum size'. Are there any disadvantages of sizing the files at the maximum size that would make us reconsider sizing this big?
Thanks
Shannon |
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| mqjeff |
| Posted: Mon Jun 01, 2015 4:59 am Post subject: |
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Grand Master
Joined: 25 Jun 2008
Posts: 17447
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What things have you considered?
What things are you concerned about?
Perhaps, hopefully, obviously the speed of the disk in question is a significant factor.
Also hopefully obvious, the expected size of your transactions is a factor, as is the unexpected size of your transactions.
You should also consider what is more important to allow to fail - the queue manager or the application. |
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| exerk |
| Posted: Mon Jun 01, 2015 5:12 am Post subject: |
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Jedi Council
Joined: 02 Nov 2006
Posts: 6339
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Also, bearing in mind if using linear logging, it is easier to manage a small number of large files than a large number of small files.
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It's puzzling, I don't think I've ever seen anything quite like this before...and it's hard to soar like an eagle when you're surrounded by turkeys. |
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| svmmq |
| Posted: Mon Jun 01, 2015 7:22 am Post subject: |
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Newbie
Joined: 19 Mar 2015
Posts: 6
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| I am wondering if the large files will have an impact on the process to archive the file when it is no longer required or the time it would take to dynamically allocate a secondary file if one was required and if anyone has experienced problems due to large files. We are using linear logging. |
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| Andyh |
| Posted: Mon Jun 01, 2015 7:22 am Post subject: |
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Master
Joined: 29 Jul 2010
Posts: 239
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Generic starting advice is to use a small number of large log extents.
There's a small performance cost associated with switching extents, and once the queue manager has been created there's no supported means to increase the extent size, hence a small number of large extents generally makes a good starting point.
It is NOT good generic advice to use the maximum total log size. The total log space should be based upon the duration of your longest running transaction, and the peak message throughput.
If you were to create a queue manager with a 100GB+ recovery log, then you'd have to consider the potential impact (albeit with a small possibility) of replaying 100GB+ of recovery log at queue manager restart.
In very general terms, a queue manager with a huge recovery log is very often a sign that the creator of the queue manager did not properly understand the factors involved in sizing the log, it should certainly ring alarm bells in any MQ system review. |
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| exerk |
| Posted: Mon Jun 01, 2015 8:50 am Post subject: |
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Jedi Council
Joined: 02 Nov 2006
Posts: 6339
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| Andyh wrote: |
| ...It is NOT good generic advice to use the maximum total log size. The total log space should be based upon the duration of your longest running transaction, and the peak message throughput... |
I am in full agreement, and when I get an application developer/owner that actually gives me that (accurate) information, I'll act on it 
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It's puzzling, I don't think I've ever seen anything quite like this before...and it's hard to soar like an eagle when you're surrounded by turkeys. |
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| mqjeff |
| Posted: Mon Jun 01, 2015 9:41 am Post subject: |
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Grand Master
Joined: 25 Jun 2008
Posts: 17447
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| exerk wrote: |
| Andyh wrote: |
| ...It is NOT good generic advice to use the maximum total log size. The total log space should be based upon the duration of your longest running transaction, and the peak message throughput... |
I am in full agreement, and when I get an application developer/owner that actually gives me that (accurate) information, I'll act on it |
Also, again, you need to make at least some allowance for unexpected transaction sizes. |
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| svmmq |
| Posted: Mon Jun 01, 2015 10:37 am Post subject: |
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Newbie
Joined: 19 Mar 2015
Posts: 6
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| Thanks. Can you offer a size that would be considered an acceptable size for a 'large log extents'? We have increased our infrastructure to accept messages up to 30meg maximum and like was written in a previous post it is near impossible to get the developers to accurately provide volumetrics. |
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