Re: Inconsistant query plan

On Tue, 2006-01-24 at 17:15, Daniel Gish wrote:
> Hi,
> We are running Postgresql 8.1, and getting dramatically inconsistant results
> after running VACUUM ANALYZE. Sometimes after analyzing the database, the
> query planner chooses a very efficient plan (15 rows, 4.744 ms), and
> sometimes a terrible one (24 rows, 3536.995 ms). Here's the abbreviated
> query:
>
> SELECT * FROM t1 INNER JOIN (t2 INNER JOIN (t3 INNER JOIN t4 ON t3.gid =
> t4.gid) ON t3.gid = t2.gid) ON t2.eid = t1.eid WHERE ...
>
> In the efficient plan, t2 is joined to t3 & t4 before being joined to t1.
> The inefficient plan joins t1 to t2 before joining to the other tables.
>
> We've experimented with different settings, such as shared_buffers &
> max_fsm_pages, to no avail. Anybody have a suggestion for getting the
> efficient plan to execute consistantly? If you'd like to see the actual
> query & query plans let me know.

Have you adjusted the stats target for that column? See \h alter table
in psql for the syntax for that. Then run analyze again.