On Fri, Nov 14, 2008 at 10:50 AM, Heikki Linnakangas <[EMAIL PROTECTED]> wrote: >> Oracle already thought of that a long time ago, which is why the plan >> has to come out better for it to take effect. > > Huh? We would never willingly choose a worse plan, of course, but the point > is that what looks like a better plan, with a smaller cost estimate, is > sometimes actually worse.
Oracle bases it on cost and elapsed execution time. >> As for bad plans, you >> obviously haven't used Postgres in production enough to deal with it >> continually changing plans for the worse due to index bloat, data >> skew, phase of the moon, etc. :) > > You're right, I haven't, but yes I know that's a problem. We've chatted > about that with Greg sometimes. It would be nice to have more stable plans. > My favorite idea is to stop using the current relation size in the planner, > and use the value snapshotted at ANALYZE instead. That way, the planner > would be completely deterministic, based on the statistics. Then, we could > have tools to snapshot the statistics, move them to a test system, store > them, revert back to old statistics etc. Yes, plan stability would be a Good Thing(tm) IMO. -- Jonah H. Harris, Senior DBA myYearbook.com -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers