| From: | Ron Mayer <rm_pg(at)cheapcomplexdevices(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Joshua Tolley <eggyknap(at)gmail(dot)com>, josh(at)agliodbs(dot)com, pgsql-hackers(at)postgresql(dot)org, Martijn van Oosterhout <kleptog(at)svana(dot)org> |
| Subject: | Re: Cross-column statistics revisited |
| Date: | 2008-10-17 17:28:10 |
| Message-ID: | 48F8CB2A.6010805@cheapcomplexdevices.com |
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| Thread: | |
| Lists: | pgsql-hackers |
Tom Lane wrote:
> A bad estimate for physical-position correlation has only limited
> impact,
Ah! This seems very true with 8.3 but much less true with 8.0.
On a legacy 8.0 system I have a hard time avoiding cases where
a query like
"select * from addresses where add_state_or_province = 'CA';"
does a 2-second full-table scan instead of a 300ms index scan
thanks to a poor physical order guess.
I just sucked the table into 8.3 and am pleased to say that
it picks a 200ms bitmap scan even with the misleading correlation.
Thanks for bitmap scans guys!
I'll shut up about this physical ordering stuff now
and try to do better upgrading before posting.
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