Re: PostgreSQL Limits and lack of documentation about them.

On Wed, Nov 28, 2018 at 10:06 AM Peter Eisentraut <
peter(dot)eisentraut(at)2ndquadrant(dot)com> wrote:

> That last sentence about the dropped columns is confusing to me:
>
> + <para>
> + Columns which have been dropped from the table also contribute to the
> + maximum column limit, although the dropped column values for newly
> + created tuples are internally marked as NULL in the tuple's null
> bitmap,
> + which does occupy space.
> + </para>
>
> So the dropped columns matter, but they are null, but the nulls matter
> too. What are we really trying to say here? Maybe this:
>
> Columns which have been dropped from the table also contribute to the
> maximum column limit. Moreover, although the dropped column values for
> newly created tuples are internally marked as NULL in the tuple's null
> bitmap, the null bitmap also occupies space.
>
>
Both for my edification and as a potentially important documentation
detail, do operations that rebuild the table such as CLUSTER or pg_repack
reclaim the column space?

Cheers,
Steve