Re: PG 13 release notes, first draft - Mailing list pgsql-hackers

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.

-- 
Peter Geoghegan