IDS Forum

Re: Increasing shared memory

Posted By: George_Palmer@aotx.uscourts.gov
Date: Friday, 17 February 2012, at 8:15 a.m.

In Response To: Increasing shared memory (SUSHANT KODE)

Hi,

>Instead of improving, the server performance has degraded. The processes
are
>taking longer time. Also the IDS shuts downs in between with the following

>error:
>Fatal error in ADM VP at mt.c:13388
>Unexpected virtual processor termination, pid = 1825, exit = 0x9
>PANIC: Attempting to bring system down

In other Linux implementations I have worked with the above error is
indicative the OOM ( out of Memory ) has come to life and killed the ADM VP
with a signal 9 ( exit = 0x9 )

Check you message log to see if that has happened. ADM VP is often the
victim as it does not reference the shared memory often but is attached to
it and remains idle much of the time it is running. This causes the OOM
calculation, on who to kill, to score this process very high.

It would be nice to see some utilization of the buffer pools ( onstat -g
buf ) as it is possible you have a great deal too many 8K buffers ( they
can only be used by 8K dbspaces did you change all dbspace to 8k except
root and logical logs ? )

George.

From: "SUSHANT KODE" <ksushants@gmail.com>
To: ids@iiug.org
Date: 02/16/2012 11:42 PM
Subject: Increasing shared memory [26263]
Sent by: ids-bounces@iiug.org

Hi All,

We have Informix 11.10.FC2 on SUSE Linux 10,RAM 24GB with shared memory of
19190788 Kbytes. The bufferpool is as follows:
BUFFERPOOL
default,buffers=102400,lrus=32,lru_min_dirty=1.000000,lru_max_dirty=2.000000

BUFFERPOOL
size=2K,buffers=204800,lrus=32,lru_min_dirty=1.000000,lru_max_dirty=2.000000

BUFFERPOOL
size=8K,buffers=1700000,lrus=128,lru_min_dirty=1.000000,lru_max_dirty=2.000000

We added 24GB more RAM to system and tried doubling the shared memory due
to
performance issues by setting the buffers as follows:
BUFFERPOOL
default,buffers=204800,lrus=32,lru_min_dirty=1.000000,lru_max_dirty=2.000000

BUFFERPOOL
size=2K,buffers=409600,lrus=32,lru_min_dirty=1.000000,lru_max_dirty=2.000000

BUFFERPOOL
size=8K,buffers=3400000,lrus=128,lru_min_dirty=1.000000,lru_max_dirty=2.000000

Instead of improving, the server perfromance has degraded. The processes
are
taking longer time. Also the IDS shuts downs in between with the following
error:
Fatal error in ADM VP at mt.c:13388
Unexpected virtual processor termination, pid = 1825, exit = 0x9
PANIC: Attempting to bring system down

We had the followng advisory in the online.log
09:45:31 WARNING! Logical log layout may cause Dynamic Server to get into

a locked state. Recommended smallest logical log size

is 16 times maximum concurrent user threads.

09:59:56 Performance Advisory: Logical log file size might be too small for
a

checkpoint to complete.
09:59:56 Results: The size of individual logical log files is too small for

the current workload, resulting in each log file filling very

quickly. If log files fill in less than 30 seconds, the checkpoint

might remain blocked because the last log file fills during the time

needed to perform the checkpoint.
09:59:56 Action: Increase the size of the individual logical log files so

that it takes at least 30 seconds to fill each one. Look at the

online log to determine how quickly the log files are filling, and

then increase the size of the files proportionately.

10:53:13 Performance Advisory: Based on the current workload, the physical
log
might be too small to
accommodate the time it takes to flush the buffer pool.
10:53:13 Results: The server might block transactions during checkpoints.
10:53:13 Action: If transactions are blocked during the checkpoint,
increase
the size of the
physical log to at least 739760 KB.

Also when checked the swap memory was completely utilised. So we had to
rollback the buffer changes and get it back to the old setting of the
buffer.

I would like to know the following after increasing the shared memory:
1) If the shared memory is to be increased, what are the other parameters
(LGOBUFF, PHYBUFF)to increase along with buffers, lrus, lru_min_dirty,
lru_max_dirty?
2) What are areas we need to look into apart from increasing the shared
memory? What are the utilies (eg. onstat -g con) that will help us analyze
the
performance?

Do let me know if any details are required.
thanks in advance.

Regards,
Sushant

*******************************************************************************

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Messages In This Thread

• Increasing shared memory
  SUSHANT KODE -- Friday, 17 February 2012, at 12:42 a.m.
  • Re: Increasing shared memory
    Art Kagel -- Friday, 17 February 2012, at 6:04 a.m.
    • Re: Increasing shared memory
      Paul Watson -- Friday, 17 February 2012, at 8:12 a.m.
  • Re: Increasing shared memory
    George_Palmer@aotx.uscourts.gov -- Friday, 17 February 2012, at 8:15 a.m.

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