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Re: Bad plan for nested loop + limit

From: David Wilson <david(dot)t(dot)wilson(at)gmail(dot)com>
To: Alexander Staubo <alex(at)bengler(dot)no>
Cc: pgsql-performance <pgsql-performance(at)postgresql(dot)org>
Subject: Re: Bad plan for nested loop + limit
Date: 2009-02-15 04:29:52
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Lists: pgsql-performance
On Sat, Feb 14, 2009 at 5:25 PM, Alexander Staubo <alex(at)bengler(dot)no> wrote:
> Output from "explain analyze":
>  Limit  (cost=0.00..973.63 rows=4 width=48) (actual
> time=61.554..4039.704 rows=1 loops=1)
>   ->  Nested Loop  (cost=0.00..70101.65 rows=288 width=48) (actual
> time=61.552..4039.700 rows=1 loops=1)
>         ->  Nested Loop  (cost=0.00..68247.77 rows=297 width=52)
> (actual time=61.535..4039.682 rows=1 loops=1)

Those estimates are pretty far off. Did you try increasing the
statistics target? Also, is the first query repeatable (that is, is it
already in cache when you do the test, or alternately, are all queries
*out* of cache when you test?)
- David T. Wilson

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