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  1. #1
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    Wink Unanswered: AIX - VMO - Strict_maxperm

    Does anyone use this ? It seems that one would only use this if real memory is scarce. I have not read anything good about this. I was thinking about using mount option RBRW or Dio(avoid dbl caching) for DB2 instead of restricting memory using strict-maxperm.

    respectfully,
    Perfman

  2. #2
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    I'm going to kind of "hijack" your thread from Chit-Chat to the DB2 Forum. My guess is that you'll get a lot more useful responses there!

    For what my two cents are worth, VMO uses disk as "surrogate RAM" like most virtual memory systems do... This is a two-edged sword in that it gives you more address space, but the performance is normally sorely handicapped (comparing disk performance versus RAM performance).

    Judicious use of virtual memory can allow you to run much more than you could without using virtual memory, and at relatively low performance cost... However, there is always some cost, and if you mis-use the virtual memory that cost can be horrific! My advice is to use virtual memory carefully, and test, test, test performance before you go to production!

    -PatP

  3. #3
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    Hey Pat. The way this whole thing began with Strict_maxperm is that someone had this turned on. I did not agree. The system is scanning for fre pages like a one armed paper hanger and LRUD is using 5-25% cpu because he hit the hard maxpermlimit of 25%(maxperm). The system only has 24 gb to run a huge DB2 warehouse. I am trying to figure out how much more real memory the P570 would need to turn off strict maxperm. Like you said this was done as a cost avoidance that came back and bit him.

    respectfully,
    Perfman
    Last edited by Perfman; 07-06-06 at 15:45.

  4. #4
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    I can see one using strict maxperm if you are sharing the server with other applications; if I remember right, CIO is preferrable to DIO.
    mota

  5. #5
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    Quote Originally Posted by Perfman
    I am trying to figure out how much more real memory the P570 would need to turn off strict maxperm.
    DB2 and AIX are not my long suit, but can you give us a better idea of the size of the db versus the size of the machine? Is this a mouse swinging an elephant, or an 800 pound gorilla in a straight jacket trying to eat a banana? If the machine is dreadfully underpowered, you probably can't just RAM your way to performance. If it is dreadfully mis-configured, you may not need more RAM to fix the performance problems.

    My guess is that you are somewhere between the extremes, but so far I don't have enough information to even offer a guess.

    -PatP

  6. #6
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    Quote Originally Posted by dbamota
    I can see one using strict maxperm if you are sharing the server with other applications; if I remember right, CIO is preferrable to DIO.
    I believe CIO needs JFS2, I am still using JFS.

  7. #7
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    Quote Originally Posted by Pat Phelan
    DB2 and AIX are not my long suit, but can you give us a better idea of the size of the db versus the size of the machine? Is this a mouse swinging an elephant, or an 800 pound gorilla in a straight jacket trying to eat a banana? If the machine is dreadfully underpowered, you probably can't just RAM your way to performance. If it is dreadfully mis-configured, you may not need more RAM to fix the performance problems.

    My guess is that you are somewhere between the extremes, but so far I don't have enough information to even offer a guess.

    -PatP
    900gb EIM warehouse db on a p570 - 6 CPUs - 24 gb real. I am looking at adding an additional 24-32gb of real and turning off strict-maxperm. I believe performance is suffering because of strict max_perm being turned on.
    respectfully,
    George

  8. #8
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    Keep in mind that my guesstimates are just that, educated guesses... Your circumstances may dictate your options, or may "encourage" you to make other decisions.

    With a 900 Gb database, I'd be comfortable running 48 Gb of RAM in a four CPU configuration. Since you are running six CPUs, I'd be inclined to push for more RAM... Because the P570 uses orthagonal memory addressing, I'd stay with multiples of 16 Gb, so I'd push for 64 Gb RAM based on the information that you've provided so far.

    I don't configure these boxes regularly, so I'd be quite willing to defer to folks that do if they have an opinion.

    -PatP

  9. #9
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    Quote Originally Posted by Pat Phelan
    Keep in mind that my guesstimates are just that, educated guesses... Your circumstances may dictate your options, or may "encourage" you to make other decisions.

    With a 900 Gb database, I'd be comfortable running 48 Gb of RAM in a four CPU configuration. Since you are running six CPUs, I'd be inclined to push for more RAM... Because the P570 uses orthagonal memory addressing, I'd stay with multiples of 16 Gb, so I'd push for 64 Gb RAM based on the information that you've provided so far.

    I don't configure these boxes regularly, so I'd be quite willing to defer to folks that do if they have an opinion.

    -PatP
    Thanks for getting back to me.
    The cpu isn't the bottleneck. The CPUs are not over worked by any means. It is the real memory that is constrained. I agree that 64gb would be the way to go. Thanks for your help.
    George

  10. #10
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    What is Orthogonal memory addressing? TIA

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