Re: Refactoring of compression options in pg_basebackup

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From: Michael Paquier <[email protected]>
To: Robert Haas <[email protected]>
Cc: Georgios Kokolatos <[email protected]>
Cc: Postgres hackers <[email protected]>
Cc: Jeevan Ladhe <[email protected]>
Subject: Re: Refactoring of compression options in pg_basebackup
Date: Fri, 14 Jan 2022 12:23:27 +0900
Message-ID: <[email protected]> (raw)
In-Reply-To: <CA+TgmoZ5+Tis+ow5R=GtwoFkMRvf0CqM=bDUXx+wQioND+coYg@mail.gmail.com>
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On Thu, Jan 13, 2022 at 01:36:00PM -0500, Robert Haas wrote:
> 1. If, as you propose, we add a new flag --compression-method=METHOD
> then how will the user specify server-side compression?

This would require a completely different option switch, which is
basically the same thing as what you are suggesting with
--server-compress.

> 2. If, as we seem to agree, the compression method is more important
> than the compression level, then why is the option to set the
> less-important thing called just --compress, and the option to set the
> more important thing has a longer name?

I agree that the method is more important than the level for most
users, and I would not mind dropping completely --compress in favor of
something else, which is something I implied upthread.

> I proposed to solve both of these problems by using
> --compression-level=NUMBER to set the compression level and
> --compress=METHOD or --server-compress=METHOD to set the algorithm and
> specify on which side it is to be applied. If, instead of doing that,
> we go with what you have proposed here, then I don't understand how to
> fit server-side compression into the framework in a reasonably concise
> way. I think we would end up with something like pg_basebackup
> --compression-method=lz4 --compress-on-server, which seems rather long
> and awkward. Do you have a better idea?

Using --compression-level=NUMBER and --server-compress=METHOD to
specify a server-side compression method with a level is fine by me,
but I find the reuse of --compress to specify a compression method 
confusing as it maps with the past option we have kept in
pg_basebackup for a couple of years now.  Based on your suggested set
of options, we could then have a --client-compress=METHOD and
--compression-level=NUMBER to specify a client-side compression method
with a level.  If we do that, I guess that we should then:
1) Block the combination of --server-compress and --client-compress.
2) Remove the existing -Z/--compress and -z/--gzip.

You have implied 1) upthread as far as I recall, 2) is something I am
adding on top of it.

> I think I understand what the patch is doing. I just think it creates
> a problem for my patch. And I'd like to know whether you have an idea
> how to solve that problem. And if not, then I'd like you to consider
> the solution that I am proposing rather than the patch you've already
> got.

I am fine to drop this thread's patch with its set of options and work
on top of your proposal, aka what's drafted two paragraphs above.
--
Michael


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