IDS Forum

Re: cpu-vps and number of physical cpus

Posted By: ART KAGEL, BLOOMBERG/ 731 LEXIN
Date: Thursday, 10 August 2006, at 10:57 a.m.

In Response To: cpu-vps and number of physical cpus (JACQUES LAPEIRE)

See below my comments introduced with '-- ':

Art S. Kagel

----- Original Message -----
From: Jacques Lapeire <ids@iiug.org>
At: 8/09 10:54:14

Hi people,

after following some training on Informix and installing some instances, I'm
still confused about the NETTYPE parameter.

Example : NETTYPE ipcshm,1,350,CPU

This means 1 cpu-vp and maximum (hard limit) 350 connections via shared
memory, right ?

-- Not exactly. This means set up a shared memory poll thread in the first CPU
VP and configure enough shared memory communications buffers to support 350
shared memory connections. The actual number of CPU VPs are configured by the
NUMCPUVP parameter or the newer VPCLASS ... CPU parameter which replaced it and
several other older parameters. (Eventually NUMCPUVP will be going away, so one
should start using VPCLASS in 9.40 and later releases).

Now I have a cluster, 1 system has 4 cpu's the failover has only 2 cpu's.
Up to now my opinion was , you can use "physical cpus -1" as cpu-vps
(1 reserved for the system).

-- This is the recommendation in the manuals, yes. However, for cpus faster
than about 450MHZ (or ~700MHZ for Intel processors) you can productively use all
of the CPUS and even configure 2 or more CPU VPs per physical processor core
(yes that means at least 4 CPU VPs for a fast dual core processor). On some
very fast processors like the Intel and AMD 2GHZ and faster processors users
have seen inproved performance using as many as 4 CPU VPs per core.

So in this case I could say NETTYPE ipcshm,3,350,CPU which allows 1050
connections on 3 cpu-vps.

-- Yes or NETTYPE ipcshm,3,120,CPU to allocate 360 connections across 3 CPU VPs,
but again, you first have to configure 3 or more CPU VPs using NUMCPUVPS or
VPCLASS (and don't forget to set SINGLE_CPU_VP 0 and MULTIPROCESSOR 1).

But as the second system has only 2 cpus, 1 only start 1 cpu-vp and once the
instance is online on the main machine, I add 2 cpu-vp dynamically (onmode -p
+2 cpu).

-- If you assign NETTYPE more CPU poll threads than there are CPU VPs, then the
engine will use NET VPs instead for those threads which cannot be assigned to a
CPU VP. When you add the other 2 CPU VPs dynamically those poll threads are not
reassigned. (This is a bad thing, BTW, see below for some recommendations
about configuring NETTYPE, BTW)

Do I have 350 or 1050 possible connections in this case ?

-- You have 1050 with 350 handled by the first CPU VP and the remaining 700
handled by 2 NET VPs. The additional CPU VPs are not polling.

Can I define more cpu-vp's than the number of physical cpu's ?

-- Yes, see above.

-- You should be configuring the 3 CPU VPs in the onconfig file and set up the
backup machine to use a different ONCONFIG file tailored to it (simply have the
startup script detect which machine is running it and set ONCONFIG appropriately
depending on primary or failover). As it stands now you have shared memory
poll threads in NET VPs which is very bad for system throughput. Shared memory
poll threads in NET VPs will spin CPU cycles needlessly reducing the available
timeslices available for the other VPs including the CPU VPs.

Does anyone have a clear explanation ?

-- Read the Informix FAQ for more discussions of these topics.

Any help would be appreciated.

Thanks,
Jacques

*******************************************************************************
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Messages In This Thread

• cpu-vps and number of physical cpus
  JACQUES LAPEIRE -- Wednesday, 9 August 2006, at 10:48 a.m.
  • Re: cpu-vps and number of physical cpus
    Martin Fuerderer -- Wednesday, 9 August 2006, at 11:39 a.m.
    • RE: cpu-vps and number of physical cpus
      Support Informix -- Thursday, 10 August 2006, at 2:16 a.m.
      • RE: cpu-vps and number of physical cpus
        Martin Fuerderer -- Thursday, 10 August 2006, at 3:50 a.m.
  • Re: cpu-vps and number of physical cpus
    ART KAGEL, BLOOMBERG/ 731 LEXIN -- Thursday, 10 August 2006, at 10:57 a.m.
    • RE: cpu-vps and number of physical cpus
      Lapeire, Jacques -- Thursday, 10 August 2006, at 11:13 a.m.
    • Re: cpu-vps and number of physical cpus
      MARK JAMISON -- Monday, 18 September 2006, at 12:50 p.m.
      • Re: cpu-vps and number of physical cpus
        ART KAGEL, BLOOMBERG/ 731 LEXIN -- Monday, 18 September 2006, at 3:03 p.m.
        • Re: cpu-vps and number of physical cpus
          MARK JAMISON -- Monday, 18 September 2006, at 3:22 p.m.
          • Re: cpu-vps and number of physical cpus
            ART KAGEL, BLOOMBERG/ 731 LEXIN -- Monday, 18 September 2006, at 3:35 p.m.

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