very high CPU usage in "top", but not in "mpstat" - Mailing list pgsql-performance

From Cyrille Bonnet
Subject very high CPU usage in "top", but not in "mpstat"
Date
Msg-id 47E18B2A3472@3months.com
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Responses Re: very high CPU usage in "top", but not in "mpstat"
List pgsql-performance

Hello all,

 

We are using Postgres 7.3 with JBoss 3.2.3 on a Linux Fedora 1.0 box.

 

When I am looking at CPU activity with “top”, I often see something like:

 

  PID USER     PRI  NI  SIZE  RSS SHARE STAT %CPU %MEM   TIME CPU COMMAND

14154 postgres  25   0  3592 3592  2924        R    99.1      0.3        93:53   0 postmaster

 

At the same time, “mpstat” gives me something like:

 

11:27:21 AM  CPU   %user   %nice %system   %idle    intr/s

11:27:21 AM  all       2.99      0.00   18.94         78.08    105.94

 

The system is not visibly slow and response time is satisfactory. Sometimes, the CPU usage drops to 1 or 2%, but not for long usually. Also I have checked the number of open connections to Postgres and there are only 5 (maximum is set to the default: 32).

 

Should I be worried that Postgres is eating up 99% of my CPU??? Or is this *expected* behaviour?

 

Please note that I am a developer, not a system administrator, so maybe I misunderstand the usage of “top” here.

 

Any help will be appreciated.

 

Cyrille.

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