Re: [HACKERS] Custom compression methods

On Tue, Mar 9, 2021 at 2:45 AM Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>
> On Mon, Mar 8, 2021 at 3:59 PM Justin Pryzby <pryzby(at)telsasoft(dot)com> wrote:
> > > It would be nice to have a way to force
> > > anything compressed with the old method to be re-compressed with the
> > > new method, but not having that doesn't preclude allowing the
> > > parameter to be changed.
> >
> > Doesn't vacuum full/cluster/dump+restore do that ?
>
> Well, dump and restore will do it, certainly, but I don't think VACUUM
> FULL or CLUSTER will. I haven't tested it, though, so maybe I'm wrong.

Yeah, vacuum full or cluster will not re-compress the data. How about
providing syntax ALTER TABLE <tab-name> ALTER COLUMN <col_name> SET
COMPRESSION <com_name> REWRITE? So if we have given a rewrite then we
will always rewrite the table and in an attempt to rewrite we will
re-compress the data. If REWRITE is given and the compression method
is the same as the existing then also we can not skip the rewrite
because we don't know the history, the user might alter the
compression method multiple times without rewrite.

--
Regards,
Dilip Kumar
EnterpriseDB: http://www.enterprisedb.com