Re: Joel's Performance Issues WAS : Opteron vs Xeon - Mailing list pgsql-performance

From Josh Berkus
Subject Re: Joel's Performance Issues WAS : Opteron vs Xeon
Date
Msg-id 200504231127.42389.josh@agliodbs.com
Whole thread Raw
In response to Re: Joel's Performance Issues WAS : Opteron vs Xeon  (Kevin Brown <kevin@sysexperts.com>)
Responses Re: Joel's Performance Issues WAS : Opteron vs Xeon
List pgsql-performance
Jim, Kevin,

> > Hrm... I was about to suggest that for timing just the query (and not
> > output/data transfer time) using explain analyze, but then I remembered
> > that explain analyze can incur some non-trivial overhead with the timing
> > calls. Is there a way to run the query but have psql ignore the output?
> > If so, you could use \timing.
>
> Would timing "SELECT COUNT(*) FROM (query)" work?

Just \timing would work fine; PostgreSQL doesn't return anything until it has
the whole result set.  That's why MSSQL vs. PostgreSQL timing comparisons are
deceptive unless you're careful:  MSSQL returns the results on block at a
time, and reports execution time as the time required to return the *first*
block, as opposed to Postgres which reports the time required to return the
whole dataset.

--
Josh Berkus
Aglio Database Solutions
San Francisco

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