| From: | Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com> |
|---|---|
| To: | David Rowley <david(dot)rowley(at)2ndquadrant(dot)com>, scrawford(at)pinpointresearch(dot)com |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, John Naylor <jcnaylor(at)gmail(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: PostgreSQL Limits and lack of documentation about them. |
| Date: | 2018-11-29 13:01:18 |
| Message-ID: | cbce34de-9e56-3636-9eec-2efb25c5f6be@2ndquadrant.com |
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| Lists: | pgsql-hackers |
On 29/11/2018 00:04, David Rowley wrote:
> On Thu, 29 Nov 2018 at 08:17, Steve Crawford
> <scrawford(at)pinpointresearch(dot)com> wrote:
>> 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?
>
> 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
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