From: | Dimitri Fontaine <dimitri(at)2ndQuadrant(dot)fr> |
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To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Greg Stark <gsstark(at)mit(dot)edu>, Itagaki Takahiro <itagaki(dot)takahiro(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: UNION ALL has higher cost than inheritance |
Date: | 2010-11-08 20:14:20 |
Message-ID: | m2r5ev4lpf.fsf@2ndQuadrant.fr |
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Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:
> But this all looks like a pretty substantial amount of work, and
> given the low level of user demand for improving the performance of
> set operations, it seems to belong fairly far down the to-do list.
Whatever you say, that's your own todo list after all. I just wanted to
chime in and say that it could well be a chicken-and-eggs problem.
Other than that, the only general way I know of to optimise a WHERE
clause containing OR branches is producing the UNION ALL equivalent.
Now maybe I'm all wet, but your explaining sounded like a very nice
first step towards such an automatic optimisation.
Regards,
--
Dimitri Fontaine
http://2ndQuadrant.fr PostgreSQL : Expertise, Formation et Support
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