From: Tom Lane <tgl@sss.pgh.pa.us>
To: Valentine Gogichashvili <valgog@gmail.com>
Cc: Oleg Bartunov <oleg@sai.msu.su>
Cc: pgsql-performance@postgresql.org
Cc: pgsql-hackers@postgresql.org
Subject: Re: [PERFORM] Cannot make GIN intarray index be used by the planner
Date: Wed, 09 May 2007 15:18:12 -0400
Message-ID: <29856.1178738292@sss.pgh.pa.us> (raw)
In-Reply-To: <3ce9822f0705091141m227697d7h4b7f2b5b723cfbd7@mail.gmail.com>
References: <3ce9822f0705090612nd6198a2xd06da85f1accbae9@mail.gmail.com>
<Pine.LNX.4.64.0705091728560.12152@sn.sai.msu.ru>
<3ce9822f0705090636s46b71c48mafb6ba7d64781fbf@mail.gmail.com>
<Pine.LNX.4.64.0705091744470.12152@sn.sai.msu.ru>
<3ce9822f0705091141m227697d7h4b7f2b5b723cfbd7@mail.gmail.com>
[cc'ing to pgsql-hackers since this is looking like a contrib/intarray bug]
"Valentine Gogichashvili" <valgog@gmail.com> writes:
> here is the DT
That works fine for me in 8.2:
regression=# explain SELECT id, (myintarray_int4)
FROM myintarray_table_nonulls
WHERE ARRAY[8] <@ myintarray_int4;
QUERY PLAN
------------------------------------------------------------------------------------------------------------------
Index Scan using idx_nonnulls_myintarray_int4_gin on myintarray_table_nonulls (cost=0.00..8.27 rows=1 width=36)
Index Cond: ('{8}'::integer[] <@ myintarray_int4)
(2 rows)
What I am betting is that you've installed contrib/intarray in this
database and that's bollixed things up somehow. In particular, intarray
tries to take over the position of "default" gin opclass for int4[],
and the opclass that it installs as default has operators named just
like the built-in ones. If somehow your query is using pg_catalog.<@
instead of intarray's public.<@, then the planner wouldn't think the
index is relevant.
In a quick test your example still works with intarray installed, because
what it's really created is public.<@ (integer[], integer[]) which is
an exact match and therefore takes precedence over the built-in
pg_catalog.<@ (anyarray, anyarray). But if for example you don't have
public in your search_path then the wrong operator would be chosen.
Please look at the pg_index entry for your index, eg
select * from pg_index where indexrelid =
'"versionA".idx_nonnulls_myintarray_int4_gin'::regclass;
and see whether the index opclass is the built-in one or not.
Note to hackers: we've already discussed that intarray shouldn't be
trying to take over the default gin opclass, but I am beginning to
wonder if it still has a reason to live at all. We should at least
consider removing the redundant operators to avoid risks like this one.
regards, tom lane
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To: pgsql-performance@postgresql.org
Cc: tgl@sss.pgh.pa.us, valgog@gmail.com, oleg@sai.msu.su, pgsql-hackers@postgresql.org
Subject: Re: [PERFORM] Cannot make GIN intarray index be used by the planner
In-Reply-To: <29856.1178738292@sss.pgh.pa.us>
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