Re: PostgreSQL Limits and lack of documentation about them.

On 29/11/2018 00:04, David Rowley wrote:
> On Thu, 29 Nov 2018 at 08:17, Steve Crawford
> <scrawford@pinpointresearch.com> wrote:
>> Both for my edification and as a potentially important documentation detail, do operations that rebuild the table
suchas CLUSTER or pg_repack reclaim the column space?
 
> 
> I've never used pg_repack, but CLUSTER will reform the tuples so that
> they no longer store the actual value for the Datums belonging to the
> dropped column. They'll still contain the null bitmap to mention that
> the dropped column's value is NULL.  The row won't disappear from
> pg_attribute, so the attnums are not resequenced, therefore we must
> maintain the dropped column with the NULL marking.

committed

-- 
Peter Eisentraut              http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services