| From: | Matthew Wakeling <matthew(at)flymine(dot)org> |
|---|---|
| To: | Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-performance(at)postgresql(dot)org |
| Subject: | Re: merge join killing performance |
| Date: | 2010-05-20 01:46:29 |
| Message-ID: | alpine.DEB.2.00.1005192143570.6090@aragorn.flymine.org |
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| Lists: | pgsql-hackers pgsql-performance |
On Wed, 19 May 2010, Scott Marlowe wrote:
>> It's apparently estimating (wrongly) that the merge join won't have to
>> scan very much of "files" before it can stop because it finds an eid
>> value larger than any eid in the other table. So the issue here is an
>> inexact stats value for the max eid.
I wandered if it could be something like that, but I rejected that idea,
as it obviously wasn't the real world case, and statistics should at least
get that right, if they are up to date.
> I changed stats target to 1000 for that field and still get the bad plan.
What do the stats say the max values are?
Matthew
--
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O'Brien: I didn't know things were going so badly.
Nog: Frightening, isn't it?
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