Re: [COMMITTERS] pgsql: Install some slightly realistic cost estimation - Mailing list pgsql-hackers

From Tom Lane
Subject Re: [COMMITTERS] pgsql: Install some slightly realistic cost estimation
Date
Msg-id 15397.1114095477@sss.pgh.pa.us
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In response to Re: [COMMITTERS] pgsql: Install some slightly realistic cost estimation  (Mike Rylander <mrylander@gmail.com>)
List pgsql-hackers
Mike Rylander <mrylander@gmail.com> writes:
> unrelated indexes?  Could this bitmapping code be used to combine
> indexes from different tables, say in a large UNION or inherited table
> setup?
> should be true when the implementation is complete.

No, it's only for combining indexes on a single table --- the bitmaps
only store TIDs, which are relative to a particular table.  I don't
think there'd be any advantage to extending the technique to handle
multiple tables; the real win comes when you AND or OR overlapping
bitmaps, and there could never be any overlap between two different
tables.

If we had multi-table indexes it'd be a different story of course.
        regards, tom lane


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