From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | "Julian Scarfe" <julian(at)avbrief(dot)com> |
Cc: | pgsql-performance(at)postgresql(dot)org |
Subject: | Re: Inheritance, unique keys and performance |
Date: | 2008-01-13 20:47:50 |
Message-ID: | 8606.1200257270@sss.pgh.pa.us |
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Lists: | pgsql-performance |
"Julian Scarfe" <julian(at)avbrief(dot)com> writes:
> From: "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us>
>> The
>> problem you've got is that you need a nestloop-with-inner-indexscan
>> plan type, where the inner side is an Append group (that is, an
>> inheritance tree) --- and 8.1 doesn't know how to create such a plan.
>> If you can update to 8.2 or later it should get better.
> Isn't test 3 (scalar subqueries) also a nestloop-with-inner-indexscan with
> an inner Append?
No. The subquery is planned separately and sees the upper query's
variable as a pseudo-constant Param. In neither query does the
planner think that a join is happening.
regards, tom lane
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