Re: refactoring basebackup.c (zstd workers)

On Mon, Mar 14, 2022 at 1:21 PM Robert Haas <robertmhaas@gmail.com> wrote:
> There's some appeal to that, but one downside is that it means that
> the client can't be used to fetch data that is compressed in a way
> that the server knows about and the client doesn't. I don't think
> that's great. Why should, for example, pg_basebackup need to be
> compiled with zstd support in order to request zstd compression on the
> server side? If the server knows about the brand new
> justin-magic-sauce compression algorithm, maybe the client should just
> be able to request it and, when given various .jms files by the
> server, shrug its shoulders and accept them for what they are. That
> doesn't work if -Fp is involved, or similar, but it should work fine
> for simple cases if we set things up right.

Concretely, I propose the attached patch for v15. It renames the
newly-added COMPRESSION_LEVEL option to COMPRESSION_DETAIL, introduces
a flexible syntax for options along the lines you proposed, and
adjusts things so that a client that doesn't support a particular type
of compression can still request that type of compression from the
server.

I think it's important to do this for v15 so that we don't end up with
backward-compatibility problems down the road.

-- 
Robert Haas
EDB: http://www.enterprisedb.com