Horton

Re: [HACKERS] Custom compression methods

Robert Haas <robertmhaas@gmail.com>

View thread View on postgr.es
From: Robert Haas <robertmhaas@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Alvaro Herrera <alvherre@alvh.no-ip.org>, Dilip Kumar <dilipbalaut@gmail.com>, Andres Freund <andres@anarazel.de>, Justin Pryzby <pryzby@telsasoft.com>, Tomas Vondra <tomas.vondra@2ndquadrant.com>, Alexander Korotkov <a.korotkov@postgrespro.ru>, David Steele <david@pgmasters.net>, Ildus Kurbangaliev <i.kurbangaliev@gmail.com>, Dmitry Dolgov <9erthalion6@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2021-03-20T02:41:15Z
Lists: pgsql-hackers 
On Fri, Mar 19, 2021 at 8:25 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Extrapolating from the way we've dealt with similar issues
> in the past, I think the structure of pg_dump's output ought to be:
>
> 1. SET default_toast_compression = 'source system's value'
> in among the existing passel of SETs at the top.  Doesn't
> matter whether or not that is the compiled-in value.
>
> 2. No mention of compression in any CREATE TABLE command.
>
> 3. For any column having a compression option different from
> the default, emit ALTER TABLE SET ... to set that option after
> the CREATE TABLE.  (You did implement such a SET, I trust.)

Actually, *I* didn't implement any of this. But ALTER TABLE sometab
ALTER somecol SET COMPRESSION somealgo works.

This sounds like a reasonable approach.

> There might be scope for a dump option to suppress mention
> of compression altogether (comparable to, eg, --no-tablespaces).
> But I think that's optional.  In any case, we don't want
> to put people in a position where they should have used such
> an option and now they have no good way to recover their
> dump to the system they want to recover to.

The patch already has --no-toast-compression.

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

Commits

  1. docs: Update TOAST storage docs for configurable compression.

  2. Further tweaking of pg_dump's handling of default_toast_compression.

  3. Fix interaction of TOAST compression with expression indexes.

  4. Tidy up more loose ends related to configurable TOAST compression.

  5. Short-circuit slice requests that are for more than the object's size.

  6. Mostly-cosmetic adjustments of TOAST-related macros.

  7. Remove useless configure probe for <lz4/lz4.h>.

  8. Error on invalid TOAST compression in CREATE or ALTER TABLE.

  9. docs: Fix omissions related to configurable TOAST compression.

  10. More code cleanup for configurable TOAST compression.

  11. Bring configure support for LZ4 up to snuff.

  12. Make compression.sql regression test independent of default.

  13. Use valid compression method in brin_form_tuple

  14. Fix up pg_dump's handling of per-attribute compression options.

  15. Allow configurable LZ4 TOAST compression.

  16. Fix inconsistencies in the code

  17. Mostly-cosmetic improvements in memory chunk header alignment coding.

  18. Allow numeric to use a more compact, 2-byte header in many cases.