Date: Mon, 11 May 2020 21:23:30 -0400
From: Bruce Momjian <bruce@momjian.us>
To: Peter Geoghegan <pg@bowt.ie>
Cc: PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: PG 13 release notes, first draft
Message-ID: <20200512012330.GS4666@momjian.us>
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On Mon, May 11, 2020 at 09:15:43PM -0400, Bruce Momjian wrote:
> On Mon, May 11, 2020 at 05:33:40PM -0700, Peter Geoghegan wrote:
> > On Mon, May 11, 2020 at 5:14 PM Bruce Momjian <bruce@momjian.us> wrote:
> > > Agreed.  How is this?
> > >
> > >         This allows efficient btree indexing of low cardinality columns.
> > >         Users upgrading with pg_upgrade will need to use REINDEX to make use of
> > >         this feature.
> > 
> > I still think that the release notes should say that the key is only
> > stored once, while TIDs that identify table rows are stored together
> > as an array. Everything that's helpful (or harmful) about the feature
> > happens as a consequence of that. This isn't hard to grasp
> > intuitively, and is totally in line with how things like Oracle bitmap
> > indexes are presented to ordinary users.
> 
> I still don't think these details belong in the release notes.

OK, I was able to add some of it cleanly:

	This allows efficient btree indexing of low cardinality columns by
	storing duplicate keys only once.  Users upgrading with pg_upgrade
	will need to use REINDEX to make use of this feature.

-- 
  Bruce Momjian  <bruce@momjian.us>        https://momjian.us
  EnterpriseDB                             https://enterprisedb.com

+ As you are, so once was I.  As I am, so you will be. +
+                      Ancient Roman grave inscription +