From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
---|---|
To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
Cc: | PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, Bruce Momjian <bruce(at)momjian(dot)us> |
Subject: | Re: release notes: tids & self-joins |
Date: | 2019-06-13 17:22:16 |
Message-ID: | 8478.1560446536@sss.pgh.pa.us |
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Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> The release notes say:
> <listitem>
> <!--
> Author: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
> 2018-12-30 [b5415e3c2] Support parameterized TidPaths.
> Author: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
> 2018-12-30 [0a6ea4001] Add a hash opclass for type "tid".
> -->
> <para>
> Improve optimization of self-joins (Tom Lane)
> </para>
> </listitem>
> I don't think that's an accurate summary of those two items. It's
> true that they could make self-joins more efficient, but my reading is
> that it would only do so if the self-join happened to use the ctid
> column.
Yeah. I think Bruce misread the commit messages, which commented that
joining on TID is only likely to be useful in a self-join.
> So I think that this should probably be changed to say something like
> "Improve optimization of self-joins on ctid columns" or "Improve
> optimization of joins involving columns of type tid."
The latter seems fine to me.
regards, tom lane
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