Re: Better estimates of index correlation

On 3/14/11 5:51 PM, Tom Lane wrote:
> Josh Berkus <josh@agliodbs.com> writes:
>>> I'm not convinced you can get a sufficiently good estimate from a small
>>> subset of pages.
> 
>> Note that if this requires VACUUM rather than ANALYZE, it introduces a
>> problem for data warehousing users, who can go years between vacuums of
>> their largest tables.
> 
> It's likely that the default estimate of zero index correlation will
> work just fine for such users ...

No, it isn't.  In fact, users with very large tables are the ones
hardest hit by our lack of correlation stats.

--                                  -- Josh Berkus                                    PostgreSQL Experts Inc.
                        http://www.pgexperts.com