From: Ow Mun Heng <Ow.Mun.Heng@wdc.com>
To: Carlo Stonebanks <stonec.register@sympatico.ca>
Cc: pgsql-performance@postgresql.org
Subject: Re: REPOST: Nested loops row estimates always too high
Date: Mon, 24 Sep 2007 14:46:16 +0800
Message-ID: <1190616376.17050.51.camel@neuromancer.home.net> (raw)
In-Reply-To: <fcu215$2em3$1@news.hub.org>
References: <fcu215$2em3$1@news.hub.org>
On Thu, 2007-09-20 at 11:02 -0400, Carlo Stonebanks wrote:
> (SORRY FOR THE REPOST, I DON'T SEE MY ORIGINAL QUESTION OR ANY ANSWERS HERE)
>
> I am noticing that my queries are spending a lot of time in nested loops.
> The table/index row estimates are not bad, but the nested loops can be off
> by a factor of 50. In any case, they are always too high.
>
> Are the over-estimations below significant, and if so, is this an indication
> of a general configuration problem?
Sounds much like the issue I was seeing as well.
>
> Unique (cost=67605.91..67653.18 rows=4727 width=16) (actual
> time=8634.618..8637.918 rows=907 loops=1)
You can to rewrite the queries to individual queries to see it if helps.
In my case, I was doing
select a.a,b.b,c.c from
(select a from x where) a <--- Put as a SRF
left join (
select b from y where ) b <--- Put as a SRF
on a.a = b.a
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To: pgsql-performance@postgresql.org
Cc: Ow.Mun.Heng@wdc.com, stonec.register@sympatico.ca
Subject: Re: REPOST: Nested loops row estimates always too high
In-Reply-To: <1190616376.17050.51.camel@neuromancer.home.net>
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