Horton

Re: Different compression methods for FPI

Michael Paquier <michael@paquier.xyz>

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From: Michael Paquier <michael@paquier.xyz>
To: Justin Pryzby <pryzby@telsasoft.com>
Cc: Andrey Borodin <x4mmm@yandex-team.ru>, pgsql-hackers@postgresql.org, Thomas Munro <thomas.munro@gmail.com>
Date: 2021-05-25T07:26:42Z
Lists: pgsql-hackers 
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

Commits

  1. Add more error context to RestoreBlockImage() and consume it

  2. Add support for LZ4 with compression of full-page writes in WAL

  3. Extended statistics on expressions

  4. Be clear about whether a recovery pause has taken effect.

  5. Add GUC to enable compression of full page images stored in WAL.