Re: COUNT(*) and index-only scans - Mailing list pgsql-hackers

From Tom Lane
Subject Re: COUNT(*) and index-only scans
Date
Msg-id 13771.1318432683@sss.pgh.pa.us
Whole thread Raw
In response to Re: COUNT(*) and index-only scans  (Greg Stark <stark@mit.edu>)
List pgsql-hackers
Greg Stark <stark@mit.edu> writes:
> On Wed, Oct 12, 2011 at 3:29 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> The problem is precisely that the pages a query is going to read are
>> likely to *not* be a random sample, but to be correlated with
>> recently-dirtied pages.

> Sure, but I was suggesting aiming for the nth percentile rather than a
> linear factor which I don't know has any concrete meaning.

Well, I have no problem with using a more complicated estimation
equation, but it might be nice to get some field experience with the
thing before we start complicating matters.
        regards, tom lane


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