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From: Віталій Тимчишин <tivv00@gmail.com>
To: Richard Huxton <dev@archonet.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: PostgreSQL OR performance
Date: Sat, 15 Nov 2008 15:57:03 +0200
Message-ID: <331e40660811150557s50e54c54m974645e31e30a612@mail.gmail.com> (raw)
In-Reply-To: <49141C5E.2010404@archonet.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>

2008/11/7 Richard Huxton <dev@archonet.com>

> But it's this materialize that's taking the biggest piece of the time.
>
> > "  ->  Materialize  (cost=469981.13..498937.42 rows=2316503 width=30)
> > (actual time=15915.639..391938.338 rows=242752539 loops=1)"
>
> 15.9 seconds to 391.9 seconds. That's half your time right there. The
> fact that it's ending up with 242 million rows isn't promising - are you
> sure the query is doing what you think it is?


I am not. I can't see how materialize can multiply number of rows it gets
from sort by 100.


>
> > "        ->  Sort  (cost=469981.13..475772.39 rows=2316503 width=30)
> (actual
> > time=15915.599..19920.912 rows=2316503 loops=1)"
> > "              Sort Key: production.company.run_id"
> > "              Sort Method:  external merge  Disk: 104896kB"
>
> By constrast, this on-disk sort of 104MB is comparatively fast.
>

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