Performance down after upgrade from 11.10 to 11.50 in Linux platform

Technote (troubleshooting)


Problem(Abstract)

If the server used raw devices and upgrade from 11.10 to 11.50 in Linux the performance maybe down.

Symptom

In 11.50 when using 'iostat -x to' monitor the system IO the following phenomenon maybe observed.

1. r/s is high
2. rrqm/s is very low or '0'
3. avgrq-sz is low

      time
      Device:
      rrqm/s
      wrqm/s
      r/s
      w/s
      rkB/s
      wkB/s
      avgrq-sz
      avgqu-sz
      await
      svctm
      %util
10:35:19
      rawdev
0.18
0
911.02
0.07
1822.57
0.23
4
16.86
18.51
1.04
94.6
10:35:21
      rawdev
0
0
203.5
0
407
0
4
0.51
2.5
1.94
39.4
10:35:23
      rawdev
0
0
203
0
406
0
4
0.57
2.81
1.96
39.8
10:35:25
      rawdev
0
0
205
0
410
0
4
0.39
1.92
1.55
31.8
10:35:27
      rawdev
0
0
201.5
0
403
0
4
0.42
2.09
1.52
30.6


Cause

In 11.10 the KAIO is off by default and in 11.50 KAIO is on by default, which lead to the IO performance difference.

Resolving the problem

If "iostat -x" showed the above symptom the server should not use KAIO. Please set environment KAIOOF to 1 and restart the server.

export KAIOOF=1

After that the follow information can be seen with 'iostat -x'

1. r/s becomes lower

2. rrqm/s becomes higher

3. avgrq-sz becomes higher

device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s avgrq-sz avgqu-sz await svctm %util
raw1
0
0
5.5
0
22
0
8
0.09
15.64
3.64
2
raw2
0
0
0
0
0
0
0
0
0
0
0
raw3
1427
0
774
0
8796
0
22.73
13.46
17.36
0.46
35.8
raw4
0
0
0
0
0
0
0
0
0
0
0
raw5
0
0
0
0
0
0
0
0
0
0
0
raw6
0
0
0
0
0
0
0
0
0
0
0
raw7
0
0
0
0
0
0
0
0
0
0
0

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Document information


More support for:

Informix Servers

Software version:

11.5

Operating system(s):

Linux

Reference #:

1641917

Modified date:

2013-06-25

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