KAIO error or warning（讨论线索，2010-01）

KAIO error or warning

Neil Truby posted on Wednesday, January 20, 2010 7:52 PM

IDS 11.5FC6 on RHEL 5.2.

We're getting a warning, or maybe error, each time we start one of the many
instances on this server.

requested number of KAIO events (16384) exceeds limit (8448). using 8448.

Although the "limit" number varies; sometimes as low as 128.

Any ideas what this is or if it is a worry?

IBM Service Request Number 81212 019 866 refers.

thanks

Sandor Szabo - 21 Jan 2010 08:42 GMT - Sandor 的回答

Neil,
I would not worry too much but you should check the following two kernel
parameters:

"/proc/sys/fs/aio-max-nr"
"/proc/sys/fs/aio-nr"

Ids would like to use  half of remaining system wide AIO requests... and
not getting it
Do you have other IDS instances running on the same machine or different SW
using also the AIO interface ?

Kind regards

Sandor
Neil Truby - 21 Jan 2010 17:10 GMT - Neil 观察后再问 

If I look at what it was:
cat /proc/sys/fs/aio-max-nr
65536

Then increase it twenty-fold:
echo 1280000 > /proc/sys/fs/aio-max-nr

First instance
OK
Second instance
10:46:27  IBM Informix Dynamic Server Version 11.50.FC6     Software Serial
Number AAA#B000000
10:46:28  requested number of KAIO events (320000) exceeds limit (160000).
using 160000.
10:46:29  IBM Informix Dynamic Server Initialized -- Shared Memory
Initialized.
Third instance
10:47:57  requested number of KAIO events (320000) exceeds limit (40000).
using 40000.
10:47:58  Physical Recovery Complete: 0 Pages Examined, 0 Pages Restored.
Fourth instance
10:49:36  Physical Recovery Started at Page (2:2775).
10:49:36  requested number of KAIO events (320000) exceeds limit (10000).
using 10000.
10:49:37  Physical Recovery Complete: 0 Pages Examined, 0 Pages Restored.

etc.

I cannot see a pattern to this that will tell me what would be a suitable
setting.

Art Kagel replied to Neil Truby on Thursday, January 21, 2010 12:48 PM - Art Kagel 的回答

You can control how much KAIO resource each instance requests with the
KAIOON environment variable.  If you set:

export KAIOON=20000

then that instance will only request 20000 concurrent IO blocks from the
OS.  With the default, 65535, the first server would have requested 32767,
so if you want each server to get that many KAIO blocks, set KAIOON to 32767
and set aio_max_ar to 32767 * 2 * <# instances> or greater.

Art

Art S. Kagel
Advanced DataTools (www.advancedatatools.com)
IIUG Board of Directors (art@iiug.org)

See you at the 2010 IIUG Informix Conference
April 25-28, 2010
Overland Park (Kansas City), KS
www.iiug.org/conf