From: Tom Lane <tgl@sss.pgh.pa.us>
To: Mario Splivalo <mario.splivalo@megafon.hr>
Cc: pgsql-performance@postgresql.org
Subject: Re: Query much slower when run from postgres function
Date: Mon, 09 Mar 2009 19:36:10 -0400
Message-ID: <17869.1236641770@sss.pgh.pa.us> (raw)
In-Reply-To: <49B5948C.3050800@megafon.hr>
References: <49B51B60.6030600@megafon.hr>
<27649.1236616294@sss.pgh.pa.us>
<49B56A3D.8000100@megafon.hr>
<14317.1236628318@sss.pgh.pa.us>
<49B5948C.3050800@megafon.hr>
Mario Splivalo <mario.splivalo@megafon.hr> writes:
> So, it is the same. When I do EXPLAIN ANALYZE EXECUTE I get completely
> different execution plan:
> ...
> -> Bitmap Heap Scan on messages
> (cost=287.98..21192.42 rows=12848 width=4) (actual time=0.049..0.169
> rows=62 loops=1)
> Recheck Cond: (service_id = $1)
> -> Bitmap Index Scan on
> messages_uq__service_id__tan (cost=0.00..284.77 rows=12848 width=0)
> (actual time=0.038..0.038 rows=62 loops=1)
> Index Cond: (service_id = $1)
Well, there's the problem: without knowing what the specific service_id
is, the planner is estimating 12848 matching rows, which is evidently
off by a couple of orders of magnitude. And that's pushing it to adopt
a hash join instead of a nestloop. Are you sure the stats on this
table are up to date? Maybe you need to increase the stats target?
regards, tom lane
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To: pgsql-performance@postgresql.org
Cc: tgl@sss.pgh.pa.us, mario.splivalo@megafon.hr
Subject: Re: Query much slower when run from postgres function
In-Reply-To: <17869.1236641770@sss.pgh.pa.us>
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