Re: index v. seqscan for certain values - Mailing list pgsql-performance

From Tom Lane
Subject Re: index v. seqscan for certain values
Date
Msg-id 24670.1081878949@sss.pgh.pa.us
Whole thread Raw
In response to Re: index v. seqscan for certain values  ("Jeremy Dunn" <jdunn@autorevenue.com>)
Responses Re: index v. seqscan for certain values
configure shmmax on MAC OS X
Re: index v. seqscan for certain values
List pgsql-performance
"Jeremy Dunn" <jdunn@autorevenue.com> writes:
> Interestingly, I tried increasing the stat size for the CID column to
> 2000, analyzing, and checking the accuracy of the stats again.

There's a hard limit of 1000, I believe.  Didn't it give you a warning
saying so?

At 1000 the ANALYZE sample size would be 300000 rows, or about a quarter
of your table.  I would have thought this would give frequency estimates
with much better precision than you seem to be seeing --- but my
statistics are rusty enough that I'm not sure about it.  Possibly the
nonuniform clumping of CID has something to do with the poor results.

Any stats majors on the list?

            regards, tom lane

pgsql-performance by date:

Previous
From: "Jeremy Dunn"
Date:
Subject: Re: index v. seqscan for certain values
Next
From: Robert Treat
Date:
Subject: query slows down with more accurate stats