Message-ID: <45E8B209.1040209@commandprompt.com>
Date: Fri, 02 Mar 2007 15:23:53 -0800
From: "Joshua D. Drake" <jd@commandprompt.com>
Organization: Command Prompt, Inc.
User-Agent: Thunderbird 1.5.0.9 (X11/20070103)
MIME-Version: 1.0
To: Bruce Momjian <bruce@momjian.us>
CC: Tom Lane <tgl@sss.pgh.pa.us>, Benjamin Minshall <minshall@intellicon.biz>,
	pgsql-performance@postgresql.org
Subject: Re: stats collector process high CPU utilization
References: <200703022306.l22N6dc21565@momjian.us>
In-Reply-To: <200703022306.l22N6dc21565@momjian.us>
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Bruce Momjian wrote:
> Sorry, I introduced this bug.

To the gallows with you! :) Don't feel bad, there were several hackers
that missed the math on that one.

Joshua D. Drake


> 
> ---------------------------------------------------------------------------
> 
> Tom Lane wrote:
>> Benjamin Minshall <minshall@intellicon.biz> writes:
>>> Tom Lane wrote:
>>>> It's sounding like what you had was just transient bloat, in which case
>>>> it might be useful to inquire whether anything out-of-the-ordinary had
>>>> been done to the database right before the excessive-CPU-usage problem
>>>> started.
>>> I don't believe that there was any unusual activity on the server, but I 
>>> have set up some more detailed logging to hopefully identify a pattern 
>>> if the problem resurfaces.
>> A further report led us to realize that 8.2.x in fact has a nasty bug
>> here: the stats collector is supposed to dump its stats to a file at
>> most every 500 milliseconds, but the code was actually waiting only
>> 500 microseconds :-(.  The larger the stats file, the more obvious
>> this problem gets.
>>
>> If you want to patch this before 8.2.4, try this...
>>
>> Index: pgstat.c
>> ===================================================================
>> RCS file: /cvsroot/pgsql/src/backend/postmaster/pgstat.c,v
>> retrieving revision 1.140.2.2
>> diff -c -r1.140.2.2 pgstat.c
>> *** pgstat.c	26 Jan 2007 20:07:01 -0000	1.140.2.2
>> --- pgstat.c	1 Mar 2007 20:04:50 -0000
>> ***************
>> *** 1689,1695 ****
>>   	/* Preset the delay between status file writes */
>>   	MemSet(&write_timeout, 0, sizeof(struct itimerval));
>>   	write_timeout.it_value.tv_sec = PGSTAT_STAT_INTERVAL / 1000;
>> ! 	write_timeout.it_value.tv_usec = PGSTAT_STAT_INTERVAL % 1000;
>>   
>>   	/*
>>   	 * Read in an existing statistics stats file or initialize the stats to
>> --- 1689,1695 ----
>>   	/* Preset the delay between status file writes */
>>   	MemSet(&write_timeout, 0, sizeof(struct itimerval));
>>   	write_timeout.it_value.tv_sec = PGSTAT_STAT_INTERVAL / 1000;
>> ! 	write_timeout.it_value.tv_usec = (PGSTAT_STAT_INTERVAL % 1000) * 1000;
>>   
>>   	/*
>>   	 * Read in an existing statistics stats file or initialize the stats to
>>
>>
>> 			regards, tom lane
>>
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> 


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