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Re: EXPLAIN ANALYZE total runtime != walltime

From: Jon Lapham <lapham(at)jandr(dot)org>
To: Stephan Szabo <sszabo(at)megazone(dot)bigpanda(dot)com>
Cc: pgsql-general(at)postgresql(dot)org
Subject: Re: EXPLAIN ANALYZE total runtime != walltime
Date: 2004-08-26 03:11:24
Message-ID: 412D54DC.7070307@jandr.org (view raw or flat)
Thread:
Lists: pgsql-general
Stephan Szabo wrote:
> On Wed, 25 Aug 2004, Jon Lapham wrote:
> 
> 
>>I have been using the EXPLAIN ANALYZE command to debug some performance
>>bottlenecks in my database.  In doing so, I have found an oddity (to me
>>anyway).  The "19ms" total runtime reported below actually takes 25
>>seconds on my computer (no other CPU intensive processes running).  Is
>>this normal for EXPLAIN ANALYZE to report a total runtime so vastly
>>different from wall clock time?
>>
>>During the "explain ANALYZE delete from msgid;" the CPU is pegged at
>>100% for the postmaster process, and the HD light only flashes
>>intermittently, so I do not think it is HD I/O.
>>
>>I tossed in a "EXPLAIN ANALYZE VERBOSE" at the end of this email, in
>>case that helps anyone.
> 
> 
> I think EXPLAIN ANALYZE time doesn't include after trigger time (for
> example for foreign keys).  Do any tables reference this one?

Yup, I have a referencing table, that is indeed the performance problem. 
  I'm just surprised that the "total runtime" is not the.. well... total 
runtime.  :)

Thanks,
Jon

-- 
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  Jon Lapham  <lapham(at)jandr(dot)org>                Rio de Janeiro, Brasil
  Personal: http://www.jandr.org/
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