IDS Forum

Re: shared memory parameters

Posted By: JACQUES RENAUT
Date: Tuesday, 9 February 2010, at 4:17 p.m.

In Response To: shared memory parameters (DOUGLAS MERRILL)

You wrote---------------------------------------------------
Having trouble with share memory parameters.
I am trying to locate each piece of the memory size number reported by "onstat -". So far I have been able to correlate changes in onconfig with changes in that onstat number. However, I haven't been able to get it all and can't seem to find out who knows this.

When oninit -v starts up the engine, I see the resident memory pool number reported there but cannot find the details in that number. It's killing me.

You might ask why I'm doing this. Well, we had an assertion failure that we can't account for and when we killed all memory segments (with IBM's help) and rebooted the RHEL 4 AS box, IDS 10.00 FC4 could not attach to the SHMVIRTSIZE memory cited in the onconfig file. IBM suggested we take that 20gb figure and reduce it. We did and IDS attached and we went with it. We still don't know why we can't start the engine with the same 20gb SHMVIRTSIZE we have had for years.

One thing leads to another. We swopped identically memory from our test box to see if we could isolate the problem. No change was noted. Now I'm trying to get very specific about the shared memory parameters on our test box so that I can define and hopefully understand what is going on with our production box.

Of course both boxes are the same except for memory (prod has more). In fact, test has 24gb of ram with 6gb being used for raid5. The prod box has 32gb of ram with 8gb being used for raid5. Strangely, I can push SHMVIRTSIZE to 21gb on test but can only push prod to about 18.5gb. So now I'm in the middle of it. Seems to me something is going on with hardware or the OS but what? Why does IDS initialize with more virtual shared memory than there is memory on the box? Why can't the prod instance initialize using the same onconfig paramaters that it has for years?

On the other hand, here's an easy question: Where can I find the size of the resident pool, other than in the output from oninit -v ?

Thanks to all!

--------------------------------------------------------------------------------

Response

You can see the size of the resident segment via onstat -g seg. I think there is some formula you can use to calculate the size of the resident pool (possibly in the admin guide) and it depends on a lot of different parameters (probably the largest being the BUFFERPOOL definition then probably LOCKS).

IDS can initialize with more shared memory then real memory on the box if you have a big enough swap space. The amount of shared memory you can create and use on a machine is more dependent on OS kernel parameters then physical memory (provided you have enough swap space defined). Do you know if there was any kernel parameter modifications on the prod server? Or any swap changes? Can you post the exact error you get when you try to bring the server online (from either the MSGPATH file or terminal. The exact error you were getting would probably give some clue as to the limiting resource.

Sometimes it's not a resource limit, but a process address space issue in the sense that a shared memory segment will colide with something else in the address space (like a shared library). You might take a look at pmap output and see if any shared memory segments are getting near anything else in the address space (as the engine generally requires that our shared memory be contiguous). That can be worked around with SHMBASE or I believe commands to modify the shared library to tell it where in the address space to load.

Jacques Renaut
IBM Informix Advanced Support
APD Team

Messages In This Thread

• shared memory parameters
  DOUGLAS MERRILL -- Tuesday, 9 February 2010, at 3:54 p.m.
  • Re: shared memory parameters
    JACQUES RENAUT -- Tuesday, 9 February 2010, at 4:17 p.m.
  • Re: shared memory parameters
    Lennie Jarratt -- Tuesday, 9 February 2010, at 5:52 p.m.
  • AW: shared memory parameters
    Andreas.KUTSCHE@spar.at -- Wednesday, 10 February 2010, at 3:34 a.m.
    • Re: AW: shared memory parameters
      John Miller iii -- Wednesday, 10 February 2010, at 11:30 a.m.
    • RE: shared memory parameters
      Wyza, Jonathon -- Wednesday, 10 February 2010, at 11:36 a.m.
      • AW: shared memory parameters
        Andreas.KUTSCHE@spar.at -- Thursday, 11 February 2010, at 7:33 a.m.

IDS Forum is maintained by Administrator with WebBBS 5.12.