Re: Query much slower when run from postgres function

From: Tom Lane
Subject: Re: Query much slower when run from postgres function
Date: ,
Msg-id: 17869.1236641770@sss.pgh.pa.us
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In response to: Re: Query much slower when run from postgres function  (Mario Splivalo)
List: pgsql-performance

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Query much slower when run from postgres function  (Mario Splivalo, )
 Re: Query much slower when run from postgres function  (Tom Lane, )
  Re: Query much slower when run from postgres function  (Guillaume Cottenceau, )
   Re: [JDBC] Query much slower when run from postgres function  (Guillaume Smet, )
    Re: [JDBC] Query much slower when run from postgres function  (Tom Lane, )
     Re: [JDBC] Query much slower when run from postgres function  (Andreas Wenk, )
     Re: [JDBC] Query much slower when run from postgres function  (Dave Cramer, )
      Re: [JDBC] Query much slower when run from postgres function  (James Mansion, )
    Re: [JDBC] Query much slower when run from postgres function  (Scott Carey, )
   Re: Query much slower when run from postgres function  (Mario Splivalo, )
  Re: Query much slower when run from postgres function  (Mario Splivalo, )
   Re: Query much slower when run from postgres function  (Tom Lane, )
    Re: Query much slower when run from postgres function  (Mario Splivalo, )
     Re: Query much slower when run from postgres function  (Tom Lane, )
  Re: Query much slower when run from postgres function  ( (Frank Ch. Eigler), )
   Re: Query much slower when run from postgres function  (Tom Lane, )
    Re: Query much slower when run from postgres function  (decibel, )
     Re: Query much slower when run from postgres function  (Віталій Тимчишин, )
 Re: Query much slower when run from postgres function  (decibel, )

Mario Splivalo <> 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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Subject: Re: [JDBC] Query much slower when run from postgres function
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