----- Original Message -----
From: Tom Lane
To: Midge Brown
Sent: Friday, August 03, 2012 11:26 PM
Subject: Re: [PERFORM] slow query, different plans
"Midge Brown" <midgems(at)sbcglobal(dot)net> writes:
> I'm having a problem with a query on our production server, but not on a laptop running a similar postgres version with a recent backup copy of the same table. I tried reindexing the table on the production server, but it didn't make any difference. 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
regards, tom lane
I added "and ts is not null" to the query and the planner came back with .102 ms. The problem area in production went from a 10 second response to < 1 second.
Thanks for the responses.
In response to
pgsql-performance by date
|Next:||From: Ioannis Anagnostopoulos||Date: 2012-08-06 22:04:10|
|Subject: Re: Sequential scan instead of index scan|
|Previous:||From: Midge Brown||Date: 2012-08-06 17:43:13|
|Subject: Re: slow query, different plans|