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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Віталій Тимчишин <tivv00@gmail.com>
Cc: Richard Huxton <dev@archonet.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: PostgreSQL OR performance
Date: Sat, 15 Nov 2008 12:07:31 -0500
Message-ID: <7426.1226768851@sss.pgh.pa.us> (raw)
In-Reply-To: <331e40660811150557s50e54c54m974645e31e30a612@mail.gmail.com>
References: <331e40660811050312u552cab53ifa88e493e1c4f7ac@mail.gmail.com>
	<1225902700.1432.53.camel@jdavis>
	<331e40660811060246m51df553egd4e2ba91f08d1434@mail.gmail.com>
	<29e3942f0811060426k5fe34b1av401a2dba62e4ae3c@mail.gmail.com>
	<331e40660811060833l49bf837em41ca88d4b2061ea1@mail.gmail.com>
	<49131ED5.80307@archonet.com>
	<331e40660811060937q460e6f9fvf336455200d31f56@mail.gmail.com>
	<331e40660811070114rd70cf0dy194020a9f9ea8802@mail.gmail.com>
	<49141C5E.2010404@archonet.com>
	<331e40660811150557s50e54c54m974645e31e30a612@mail.gmail.com>

"=?ISO-8859-5?B?svbi0Nv22SDC2Nzn2OjY3Q==?=" <tivv00@gmail.com> writes:
> I am not. I can't see how materialize can multiply number of rows it gets
> from sort by 100.

Is it the right-hand input of a merge join?  If so you're looking at
mark/restore rescans, ie, repeated fetches of the same tuples.  There
must be a huge number of duplicate join keys in that relation to make
for such an increase though.  Normally the planner avoids putting a
table with lots of duplicates as the RHS of a merge, but if it doesn't
have good statistics for the join key then it might not realize the
problem.

			regards, tom lane



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