Re: URGENT HELP about 'duration' stats

From: Alvaro Herrera <alvherre(at)commandprompt(dot)com>
To: Camilo Porto <camiloporto(at)hotmail(dot)com>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: URGENT HELP about 'duration' stats
Date: 2007-10-30 21:04:00
Message-ID: 20071030210400.GA2568@alvh.no-ip.org
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Camilo Porto wrote:

> In some tests I have done, I have found these results:
> - Total Time interval which BenchmarkSQL submitted queries = 30 seconds
>
> - sum of executor's duration time during this period of time = 2
> minutes and 36 seconds!! (5x longer than total time)

Are you sure you're not confusing the units? The log you posted shows
milliseconds ...

Another thought is that some queries may count the time more than once.
For example if you submit an UPDATE that acts on a table with foreign
keys, and then the SELECT FOR UPDATE that the FK code does internally is
also logged, I think the UPDATE would include the time consumed in the
SELECT FOR UPDATE. So if you just sum both, the total obtained would
include the SELECT FOR UPDATE twice. This is just a wild guess; I'm not
sure if the queries for FKs checking are logged.

--
Alvaro Herrera Valdivia, Chile ICBM: S 39º 49' 18.1", W 73º 13' 56.4"
"Everybody understands Mickey Mouse. Few understand Hermann Hesse.
Hardly anybody understands Einstein. And nobody understands Emperor Norton."

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