Re: Different compression methods for FPI

On Mon, May 24, 2021 at 11:44:45PM -0500, Justin Pryzby wrote:
> The goal is to support 2+ "methods" (including "none"), which takes 4 bits, so
> may as well support 3 methods.
>
> - uncompressed
> - pglz
> - lz4
> - zlib or zstd or ??

Let's make a proper study of all that and make a choice, the only
thing I am rather sure of is that pglz is bad compared to all the
others. There is no point to argue as long as we don't know if any of
those candidates are suited for the job.

> This version:
> 0) repurposes the pre-existing GUC as an enum;
> 1) saves a bit (until zstd is included);
> 2) shows the compression in pg_waldump;
>
> To support different compression levels, I think I'd change from an enum to
> string and an assign hook, which sets a pair of ints.

Hmm. I am not really sure what you mean here, but let's keep that
in mind until we get more performance numbers.
--
Michael