| From: | Jeff Davis <pgsql(at)j-davis(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | pgsql-hackers(at)postgreSQL(dot)org |
| Subject: | Re: Better estimates of index correlation |
| Date: | 2011-03-16 00:32:01 |
| Message-ID: | 1300235521.3102.2.camel@jdavis-ux.asterdata.local |
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| Lists: | pgsql-hackers |
On Sun, 2011-03-13 at 19:40 -0400, Tom Lane wrote:
> It strikes me that it'd be possible to have btvacuumcleanup directly
> measure order correlation when it's processing a btree index, yielding a
> reliable answer for any btree index regardless of number of columns.
> We could do that by comparing the heap block numbers of adjacent
> index entries' TIDs and counting the number of up-transitions (block
> number larger than previous index entry) versus down-transitions (block
> number smaller than previous).
Link to previous discussion:
http://archives.postgresql.org/pgsql-hackers/2008-10/msg01279.php
Regards,
Jeff Davis
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