IDS Forum

AW: Does "onmode -F" always work?

Posted By: Model-Bosch, Tilman
Date: Thursday, 5 January 2006, at 7:15 a.m.

In Response To: Does "onmode -F" always work? (KERN DO)

Hi,

onmode -F does two things:

1) It searches all memory pools and tries to free any freeblks in each

memory pool. Those freeblks belong to the memory pool, but are unused.

When 'onmode -F succeeds, it returns the memory to the the the free memory

in the segment. You should see that the number of blkferee increases and the

number of blkused decreases after running 'onmode -F' .

2) It attempts to return any segment that is completley free to the operating

system. This is possible only, if the segment has only 1 blkused , as this

first block of memory contains the segment header structure.

If any other blk is in use, the segment can't be returned to the OS.

Unfortunatley, any SHM segment will almost everytime have some blocks allocated
by some user or internal pools. So you will often see that onmode -F frees memory
inside a segment, but is not able to return a segment memory to the OS.

Apart from that, in IDS 9.x pools are usually drained by default, i.e. the
engine attempts constantly to return freeblks in pools to the the global free
memory inside a SHM segment. So 'onmode -F' will not be that usefull , as memory
managment of the IDS engine is more efficient anyway.

The downturn of this is, that the constant attempt to free memory from
pools requires latching, which in turn may cause busy waits by other
threads. This can lead to waste of CPU cycles.
If you are experiencing CPU resource bottlenecks (long ready queues)
you may! be hitting this issue. (may have other reasons).

To turn off the new memory managment in IDS , you may set the environment
variable DONTDRAINPOOLS to 1 , before you start IDS (in the environment of
the user who starts IDS).
To avoid the increased usage of memory after setting DONTDRAINPOOLS you
may choose to run 'onmdoe -F' again at intervals of your choice.

One last issue to consider: in IDS 9.40 there is a defect 173929 which
may cause an 'ASSERT FAILURE' when onnmode -F is run.

173929 ONMODE -F MAY CAUSE ASSERT FAIL IN MT_SET_POOL

The defect will cause an assertion failure , but the engine will stay online.
This is fixed in 9.40.UC8 .

Best regards
Tilman

-----Ursprüngliche Nachricht-----
Von: ids-bounces@iiug.org [mailto:ids-bounces@iiug.org] Im Auftrag von KERN DO
Gesendet: 04 January 2006 02:25
An: ids@iiug.org
Betreff: Does "onmode -F" always work? [6161]

Hi,
Has anyone experienced this similar problem? I'm running IDS 9.40.FC5X3 on the
HP-UX 11.11 -- I always have a hard time freeing unused virtual shared memory
segments -- As you can see, the 2nd virtual segment doesn't seem to contain
anything.
Thanks for any feedback.
Kern --

onstat -g seg

IBM Informix Dynamic Server Version 9.40.FC5X3 -- On-Line -- Up 18 days
00:29:36 -- 1672960 Kbytes

Segment Summary:
id key addr size ovhd class blkused blkfree
1378386 1382041601 c000000260000000 974913536 453600 R* 237990 26
171091 1382041602 c0000002a0000000 603979776 19104 V 67951 79505
679386217 1382041603 c000000344000000 134217728 4768 V 7 32761
Total: - - 1713111040 - - 305948 112292

(* segment locked in memory)

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

• Does "onmode -F" always work?
  KERN DO -- Tuesday, 3 January 2006, at 8:25 p.m.
  • RE: Does "onmode -F" always work?
    Robert Roussey\(MIS\) -- Wednesday, 4 January 2006, at 8:51 a.m.
    • RE: Does "onmode -F" always work?
      John_Caron@mab.uscourts.gov -- Wednesday, 4 January 2006, at 9:08 a.m.
      • RE: Does "onmode -F" always work?
        Schmitz, Rob B [IBM Contractor for Sprint] -- Wednesday, 4 January 2006, at 9:25 a.m.
  • RE: Does "onmode -F" always work?
    Schmitz, Rob B [IBM Contractor for Sprint] -- Wednesday, 4 January 2006, at 9:25 a.m.
  • AW: Does "onmode -F" always work?
    Model-Bosch, Tilman -- Thursday, 5 January 2006, at 7:15 a.m.

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