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* slow 'IN' clause
@ 2006-04-10 03:44 FavoYang@gmail.com
0 siblings, 1 reply; 2+ messages in thread
From: FavoYang@gmail.com @ 2006-04-10 03:44 UTC (permalink / raw)
To: pgsql-sql
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)
^ permalink raw reply [nested|flat] 2+ messages in thread
* Re: slow 'IN' clause
@ 2006-04-11 20:21 Bruno Wolff III <bruno@wolff.to>
parent: FavoYang@gmail.com
0 siblings, 0 replies; 2+ messages in thread
From: Bruno Wolff III @ 2006-04-11 20:21 UTC (permalink / raw)
To: FavoYang@gmail.com; +Cc: pgsql-sql
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.
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