IDS Forum

RE: Estimate size of virtual portion of shared mem

Posted By: Andrew Ford
Date: Wednesday, 3 April 2013, at 11:40 a.m.

In Response To: Estimate size of virtual portion of shared memory (RAFAEL GOMEZ)

You just need a guesstimate right now based on some basic info, over time
and as your system runs you will be able to fine tune the instance based on
the actual needs.

First question. Is the server dedicated to the Informix instance or is it
used for other applications? Based on the answer to this question, you can
determine what percentage of that 64GB RAM will be used by Informix. If the
server is dedicated to Informix, you can allocated 80-90% or 50 to 58GB or
RAM to Informix. If other apps on this server need memory, figure out what
they need and subtract that from your 50 to 50GB number to get the total
amount of memory the engine needs.

From here you could try and determine how you want to split that 58GB
between the buffers (Resident segment) and Virtual Segment, but in my
opinion 50GB is a lot (all of my engines use < 3.5GB total and my
Innovator-C engines use 2GB total and they all are very busy and perform
very well) so you could just start with a 50/50 split and go from there.

Give 50GB / 2 = 25GB = 13107200 2K buffers or 6553600 4K buffers (depending
on your systems page size, adjust if you are using any configurable page
sizes) and give 25GB to SHMVIRTSIZE.

This should be good enough to start. Monitor the read cache hit % over time
and monitor the amount of virtual segment memory being used.

If your read cache hit % dips below an acceptable level (99%) and you
consistently have virtual memory going unused then you can reconfigure to
give more buffers and less virtual segment.

If the engine is dynamically adding virtual segments and the read cache is
acceptable then lower the number of buffers and increase the SHMVIRTSIZE.

Andrew

-----Original Message-----
From: ids-bounces@iiug.org [mailto:ids-bounces@iiug.org] On Behalf Of RAFAEL
GOMEZ
Sent: Wednesday, April 03, 2013 10:13 AM
To: ids@iiug.org
Subject: Estimate size of virtual portion of shared memory [29961]

Hi,

I´m trying to estimate the size of the initial virtual segment of shared
memory to give an accurate value to SHMVIRTSIZE in my ONCONFIG file.

I´ve found the formula in IDS 11.50 Performance Guide, but in the first step
it is said: "Estimate a value for the thread pool after booting variable.
This variable is partially dependent on the number of virtual processors.",
and I can´t find any information about this estimation or any samples.

Please, could anybody give a little light over this value. Thanks in
advance.

My configuration: IDS 11.50 FC9, RedHat 6.3 x86-64, 16 CPU, 64 Gb RAM

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Messages In This Thread

• Estimate size of virtual portion of shared memory
  RAFAEL GOMEZ -- Wednesday, 3 April 2013, at 11:13 a.m.
  • RE: Estimate size of virtual portion of shared mem
    Andrew Ford -- Wednesday, 3 April 2013, at 11:40 a.m.
    • Re: RE: Estimate size of virtual portion of shared
      RAFAEL GOMEZ -- Thursday, 4 April 2013, at 5:57 a.m.
      • RE: RE: Estimate size of virtual portion of sh....
        Andrew Ford -- Thursday, 4 April 2013, at 9:16 a.m.
        • Re: RE: RE: Estimate size of virtual portion of sh
          RAFAEL GOMEZ -- Thursday, 4 April 2013, at 11:51 a.m.

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