From: Tom Lane <tgl@sss.pgh.pa.us>
To: Marc Cousin <cousinmarc@gmail.com>
Cc: Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: inheritance: planning time vs children number vs column number
Date: Mon, 28 Feb 2011 10:35:37 -0500
Message-ID: <7266.1298907337@sss.pgh.pa.us> (raw)
In-Reply-To: <201102281409.55827.cousinmarc@gmail.com>
References: <201102281038.04945.cousinmarc@gmail.com>
<4D6B9BC9.1000404@enterprisedb.com>
<201102281409.55827.cousinmarc@gmail.com>
Marc Cousin <cousinmarc@gmail.com> writes:
> The Monday 28 February 2011 13:57:45, Heikki Linnakangas wrote :
>> Testing here with a table with 1000 columns and 100 partitions, about
>> 80% of the planning time is looking up the statistics on attribute
>> width, to calculate average tuple width. I don't see O(n^2) behavior,
>> though, it seems linear.
> It is only based on experimentation, for my part, of course…
> If you measure the planning time, modifying either the columns or the
> partitions number, the square root of the planning time is almost perfectly
> proportional with the parameter you're playing with.
Could we see a concrete example demonstrating that? I agree with Heikki
that it's not obvious what you are testing that would have such behavior.
I can think of places that would have O(N^2) behavior in the length of
the targetlist, but it seems unlikely that they'd come to dominate
runtime at a mere 1000 columns.
regards, tom lane
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To: pgsql-performance@postgresql.org
Cc: tgl@sss.pgh.pa.us, cousinmarc@gmail.com, heikki.linnakangas@enterprisedb.com
Subject: Re: inheritance: planning time vs children number vs column number
In-Reply-To: <7266.1298907337@sss.pgh.pa.us>
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