Date: Tue, 11 Apr 2006 15:21:06 -0500
From: Bruno Wolff III <bruno@wolff.to>
To: FavoYang@gmail.com
Cc: pgsql-sql@postgresql.org
Subject: Re: slow 'IN' clause
Message-ID: <20060411202106.GA17919@wolff.to>
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	pgsql-sql@postgresql.org
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On Sun, Apr 09, 2006 at 20:44:34 -0700,
  FavoYang@gmail.com wrote:
> I have a slow sql:
> SELECT * FROM mytable WHERE id IN (1,3,5,7,....3k here...);
> mytable is about 10k rows.
> 
> if don't use the "IN" clause, it will cost 0,11 second, otherwise it
> will cost 2.x second
> I guess pg use linear search to deal with IN clause, is there any way
> to let pg use other search method with IN clause? (ex.Binary Search or
> hash Search)

It would help if you told us what version of Postgres you are running
and showed EXPLAIN ANALYZE results for the two queries.

I have heard of people getting better speed by loading the constant list
into a temp table and then doing a join.

Some older versions of Postgres also had problems with large constant lists,
so if you are using an old version of Postgres upgrading might help.