Re: slow query, different plans
От | Tom Lane |
---|---|
Тема | Re: slow query, different plans |
Дата | |
Msg-id | 25289.1344061602@sss.pgh.pa.us обсуждение исходный текст |
Ответ на | slow query, different plans ("Midge Brown" <midgems@sbcglobal.net>) |
Список | pgsql-performance |
"Midge Brown" <midgems@sbcglobal.net> writes: > I'm having a problem with a query on our production server, but not on a laptop running a similar postgres version witha recent backup copy of the same table. I tried reindexing the table on the production server, but it didn't make anydifference. Other queries on the same table are plenty fast. Reindexing won't help that. The problem is a bad statistical estimate; it thinks there are about 700 rows with applies2 = 256, when there's really only one. That means the "fast" plan is a lot faster than the planner gives it credit for, and conversely the "slow" plan is a lot slower than the planner is expecting. Their estimated costs end up nearly the same, which makes it a bit of a chance matter which one is picked --- but the true costs are a lot different. So you need to fix that rowcount estimate. Raising the stats target for the table might help. regards, tom lane
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