Re: Add LZ4 compression in pg_dump

On Sun, Mar 27, 2022 at 10:13:00AM -0400, Robert Haas wrote:
> On Sat, Mar 26, 2022 at 12:22 PM Justin Pryzby <pryzby@telsasoft.com> wrote:
> > 0002: I wonder if you're able to re-use any of the basebackup parsing stuff
> > from commit ffd53659c.  You're passing both the compression method *and* level.
> > I think there should be a structure which includes both.  In the future, that
> > can also handle additional options.  I hope to re-use these same things for
> > wal_compression=method:level.
> 
> Yeah, we should really try to use that infrastructure instead of
> inventing a bunch of different ways to do it. It might require some
> renaming here and there, and I'm not sure whether we really want to
> try to rush all this into the current release, but I think we should
> find a way to get it done.

It seems like something a whole lot like parse_compress_options() should be in
common/.  Nobody wants to write it again, and I couldn't convince myself to
copy it when I looked at using it for wal_compression.

Maybe it should take an argument which specifies the default algorithm to use
for input of a numeric "level".  And reject such input if not specified, since
wal_compression has never taken a "level", so it's not useful or desirable to
have that default to some new algorithm.

I could write this down if you want, although I'm not sure how/if you intend
other people to use bc_algorithm and bc_algorithm.  I don't think it's
important to do for v15, but it seems like it could be done after featue
freeze.  pg_dump+lz4 is targetting v16, although there's a cleanup patch that
could also go in before branching.

-- 
Justin