On Wed, Nov 28, 2018 at 10:06 AM Peter Eisentraut < peter.eisentr...@2ndquadrant.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
