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High context switches occurring

From: "Anjan Dave" <adave(at)vantage(dot)com>
To: <pgsql-performance(at)postgresql(dot)org>
Subject: High context switches occurring
Date: 2005-11-22 16:59:54
Message-ID: 4BAFBB6B9CC46F41B2AD7D9F4BBAF785098E73@vt-pe2550-001.vantage.vantage.com (view raw or flat)
Thread:
Lists: pgsql-performance
Hi,

 

One of our PG server is experiencing extreme slowness and there are
hundreds of SELECTS building up. I am not sure if heavy context
switching is the cause of this or something else is causing it.

 

Is this pretty much the final word on this issue?

http://archives.postgresql.org/pgsql-performance/2004-04/msg00249.php

 

procs                      memory      swap          io     system
cpu

 r  b   swpd   free   buff  cache              si   so   bi    bo   in
cs       us sy id wa

 2  0     20 2860544 124816 8042544    0    0     0     0    0     0  0
0  0  0

 2  0     20 2860376 124816 8042552    0    0     0    24  157 115322 13
10 76  0

 3  0     20 2860364 124840 8042540    0    0     0   228  172 120003 12
10 77  0

 2  0     20 2860364 124840 8042540    0    0     0    20  158 118816 15
10 75  0

 2  0     20 2860080 124840 8042540    0    0     0    10  152 117858 12
11 77  0

 1  0     20 2860080 124848 8042572    0    0     0   210  202 114724 14
10 76  0

 2  0     20 2860080 124848 8042572    0    0     0    20  169 114843 13
10 77  0

 3  0     20 2859908 124860 8042576    0    0     0   188  180 115134 14
11 75  0

 3  0     20 2859848 124860 8042576    0    0     0    20  173 113470 13
10 77  0

 2  0     20 2859836 124860 8042576    0    0     0    10  157 112839 14
11 75  0

 

The system seems to be fine on iowait/memory side, except the CPU being
busy with the CS. Here's the top output:

 

11:54:57  up 59 days, 14:11,  2 users,  load average: 1.13, 1.66, 1.52

282 processes: 281 sleeping, 1 running, 0 zombie, 0 stopped

CPU states:  cpu    user    nice  system    irq  softirq  iowait    idle

           total   13.8%    0.0%    9.7%   0.0%     0.0%    0.0%   76.2%

           cpu00   12.3%    0.0%   10.5%   0.0%     0.0%    0.1%   76.8%

           cpu01   12.1%    0.0%    6.1%   0.0%     0.0%    0.1%   81.5%

           cpu02   10.9%    0.0%    9.1%   0.0%     0.0%    0.0%   79.9%

           cpu03   19.4%    0.0%   14.9%   0.0%     0.0%    0.0%   65.6%

           cpu04   13.9%    0.0%   11.1%   0.0%     0.0%    0.0%   74.9%

           cpu05   14.9%    0.0%    9.1%   0.0%     0.0%    0.0%   75.9%

           cpu06   12.9%    0.0%    8.9%   0.0%     0.0%    0.0%   78.1%

           cpu07   14.3%    0.0%    8.1%   0.0%     0.1%    0.0%   77.3%

Mem:  12081720k av, 9273304k used, 2808416k free,       0k shrd,
126048k buff

                   4686808k actv, 3211872k in_d,  170240k in_c

Swap: 4096532k av,      20k used, 4096512k free                 8044072k
cached

 

 

PostgreSQL 7.4.7 on i686-redhat-linux-gnu

Red Hat Enterprise Linux AS release 3 (Taroon Update 5)

Linux vl-pe6650-004 2.4.21-32.0.1.ELsmp

 

This is a Dell Quad XEON. Hyperthreading is turned on, and I am planning
to turn it off as soon as I get a chance to bring it down.

 

WAL is on separate drives from the OS and database.

 

Appreciate any inputs please....

 

Thanks,
Anjan

 

 

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Next:From: Vivek KheraDate: 2005-11-22 17:14:54
Subject: Re: High context switches occurring
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Subject: Re: System queue

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