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| PeterPotkay |
 Posted: Thu May 19, 2005 5:12 pm Post subject: /var/mqm and large files option |
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Poobah
Joined: 15 May 2001
Posts: 7722
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In most of the UNIX Quick Beginnings, you will find the comment:
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If you want to use individual queues that will hold more than 2 GB of data, you must enable /var/mqm to use large files.
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What error would you get if you tried to put more than 2 GIG of data to a queue?
What is the drawback to setting that option for var/mqm?
Once it is set, how much data can a queue hold? Until your disk fills, or MaxQDepth is hit?
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Peter Potkay
Keep Calm and MQ On |
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| sebastianhirt |
| Posted: Fri May 20, 2005 2:14 am Post subject: |
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Yatiri
Joined: 07 Jun 2004
Posts: 620
Location: Germany
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Hi Peter,
From the MQ Admin II workshop:
The maximum size of a queue file can be 1GB.
The cost of that is that MQ is using more shared memory ressources.
My thoughts about that:
If the queue file can only be 1 GB, why can a queue hold (at least) 2 GB of data? I mean if you put 2 GB of persistent messages to a queue, then all of them are written to the queue file.
They say support pac MP01 is giving information about the tuning of queue limits. I would guess, that there are also limits mentioned. If I find some time in the afternoon, I think I'll read it up.
If you can put until your filesystem is full, and you have a 3 TB filesystem.... How long can your system handle that? I guess some of the filesystems would have a hard time addressing a 3TB file. (OK my example might be a bit over the top, but anyway  )
my 2 cents
Sebastian |
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| jefflowrey |
| Posted: Fri May 20, 2005 3:09 am Post subject: |
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Grand Poobah
Joined: 16 Oct 2002
Posts: 19981
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I think that "enable /var/mqm to use large files" means "configure the OS to allow the queue files to be larger than 1GB".
I don't know the performance impacts of doing this.
I do know that I would prefer to do this for all systems, rather than find out what happens to the OS when MQ tries to write a file that's bigger than the OS allows it to be.
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I am *not* the model of the modern major general. |
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| PGoodhart |
| Posted: Fri May 20, 2005 3:36 am Post subject: |
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Master
Joined: 17 Jun 2004
Posts: 278
Location: Harrisburg PA
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I believe they are refering to the hard and soft limits set on the user id by the OS. This is really an OS setting, and may be different from UNIX to UNIX. On AIX the commands to view the settings are:
"Soft limits"
ulimit -Sa
"Hard limits"
ulimit -Ha
These should be run as the user that runs mq.
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Patrick Goodhart
MQ Admin/Web Developer/Consultant
WebSphere Application Server Admin |
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| sjensen |
| Posted: Fri May 20, 2005 3:43 am Post subject: |
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Centurion
Joined: 18 Dec 2003
Posts: 134
Location: London
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Hi,
I beleive on Solaris you must mount the /var/mqm/qmgrs/$QMGR_name subdirectories with the largefiles option.
Cheers
Stefan |
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| markt |
| Posted: Fri May 20, 2005 3:47 am Post subject: |
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Knight
Joined: 14 May 2002
Posts: 508
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>> I think that "enable /var/mqm to use large files" means "configure the OS to allow the queue files to be larger than 1GB".
Yes it means exactly this.
Performance aspects are going to vary by OS, but I know on AIX it's not significant. It's a config option on the OS because it normally affects things like block size and inode allocations on the filesystem. So a filesystem supporting large files might not be as efficient if you were to try to have very very many small files. But that's not a normal pattern for MQ storage so it doesn't matter there.
MQ will generate an immediate MQRC value and/or an FDC when it recognises it cannot write a larger file - much the same as if it ran out of space on the disk.
Once enabled you can get 1TB in a queue. |
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| PeterPotkay |
| Posted: Fri May 20, 2005 7:42 am Post subject: |
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Poobah
Joined: 15 May 2001
Posts: 7722
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I got some new Linux servers coming, with 100GB allocated to /var/mqm.
I think I will ask the SA to turn this option on.
20,000 100K messages are going to hit the 2 GB limit, and nowadays, for some batch processing, that is not a lot of messages. I would rather limit the # of messages on a queue by specifically setting the Max queue attributes, versus having the OS complain about the q being to deep.
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Peter Potkay
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