From: Tim Kane <tim.kane@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-performance@postgresql.org <pgsql-performance@postgresql.org>
Subject: Re: Constraint exclusion won't exclude parent table
Date: Tue, 13 May 2014 21:57:10 +0100
Message-ID: <CF9840D4.7F03D%tim.kane@gmail.com> (raw)
In-Reply-To: <27718.1400012679@sss.pgh.pa.us>
References: <CF9838D8.7EF3D%tim.kane@gmail.com>
<27718.1400012679@sss.pgh.pa.us>
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>
>
> Yeah, it's not expected that that's going to cost much. I am suspicious
> that what you are looking at is mostly measurement overhead: during
> EXPLAIN ANALYZE, each plan node has to do two gettimeofday() calls per
> call, and there are lots of platforms where that is significant relative
> to the actual work done per node.
>
> You might try comparing the overall times for select count(*) from ...
> rather than EXPLAIN ANALYZE for these two cases. If those times are
> much closer together than what you're getting from EXPLAIN ANALYZE,
> then you've got a machine with expensive gettimeofday() and you have
> to take your measurements with an appropriate quantum of salt.
>
> regards, tom lane
Interesting..
Direct query:
Time: 374336.514 ms
Indirect query:
Time: 387114.059 ms
Mystery solved. Thanks again Tom.
For what it’s worth: Linux 3.2.0-4-amd64 Debian 3.2.46-1+deb7u1 x86_64
>
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To: pgsql-performance@postgresql.org
Cc: tim.kane@gmail.com, tgl@sss.pgh.pa.us
Subject: Re: Constraint exclusion won't exclude parent table
In-Reply-To: <CF9840D4.7F03D%tim.kane@gmail.com>
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