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Date: Tue, 3 Mar 2009 20:05:53 +0100
Message-ID: <cd329af80903031105o754b328aid9c1ecdd60b44278@mail.gmail.com>
Subject: Re: Problems with ordering (can't force query planner to
	use an index)
From: Sebastjan Trepca <trepca@gmail.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: pgsql-performance@postgresql.org
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Still the same :/

I raised the default_statistics_target to 600 (it was already 100). I
then restarted pg, ran analyze through all tables and yet there is not
effect.
This is the output for core_accessor:
INFO:  analyzing "public.core_accessor"
INFO:  "core_accessor": scanned 291230 of 291230 pages, containing
17144315 live rows and 0 dead rows; 300000 rows in sample, 17144315
estimated total rows

It thinks there are even less rows in the set:

---------------------------------------------------------------------------=
---------------------------------------------------------------------------=
---------------
 Limit  (cost=3D30816.49..30816.50 rows=3D5 width=3D855) (actual
time=3D683.907..683.910 rows=3D5 loops=3D1)
   ->  Sort  (cost=3D30816.49..30822.29 rows=3D2321 width=3D855) (actual
time=3D683.906..683.907 rows=3D5 loops=3D1)
         Sort Key: core_accessor.date_posted, core_accessor.nooximity
         Sort Method:  top-N heapsort  Memory: 31kB
         ->  Nested Loop  (cost=3D0.00..30777.94 rows=3D2321 width=3D855)
(actual time=3D0.072..517.970 rows=3D68505 loops=3D1)
               ->  Index Scan using core_accessor_fresh_idx on
core_accessor  (cost=3D0.00..8955.44 rows=3D2440 width=3D92) (actual
time=3D0.056..53.107 rows=3D69312 loops=3D1)
                     Index Cond: ((slot_id =3D 472) AND (slot_type_id =3D
119) AND (label =3D ''::text) AND (user_id =3D 0) AND (role =3D 0) AND
(publish_state >=3D 60))
               ->  Index Scan using core_base_pkey on core_base
(cost=3D0.00..8.93 rows=3D1 width=3D763) (actual time=3D0.004..0.005 rows=
=3D1
loops=3D69312)
                     Index Cond: ((core_base.object_id =3D
core_accessor.object_id) AND (core_base.content_type_id =3D
core_accessor.content_type_id))
 Total runtime: 684.015 ms
(10 rows)


Sebastjan


On Tue, Mar 3, 2009 at 6:40 PM, Robert Haas <robertmhaas@gmail.com> wrote:
> On Tue, Mar 3, 2009 at 12:20 PM, Sebastjan Trepca <trepca@gmail.com> wrot=
e:
>> But it's already attached in the first mail or am I missing something?
>>
>> If you don't see it, check this: http://pastebin.com/d71b996d0
>
> Woops, sorry, I thought you had sent plain EXPLAIN. =C2=A0I see it now.
>
> The lowest level at which I see a problem is here:
>
> -> =C2=A0Index Scan using core_accessor_fresh_idx on core_accessor
> (cost=3D0.00..5460.07 rows=3D2970 width=3D92) (actual time=3D0.068..54.92=
1
> rows=3D69312 loops=3D1)
> =C2=A0 =C2=A0Index Cond: ((slot_id =3D 472) AND (slot_type_id =3D 119) AN=
D (label =3D
> ''::text) AND (user_id =3D 0) AND (role =3D 0) AND (publish_state >=3D 60=
))
>
> For some reason it expect 2970 rows but gets 69312.
>
> A good place to start is to change your default_statistics_target
> value to 100 in postgresql.conf, restart postgresql, and re-ANALYZE.
>
> ...Robert
>