Horton

Re: Custom compression methods

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Oleg Bartunov <obartunov@gmail.com>
Cc: Craig Ringer <craig@2ndquadrant.com>, Ildus Kurbangaliev <i.kurbangaliev@postgrespro.ru>, Peter Eisentraut <peter.eisentraut@2ndquadrant.com>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>, Andres Freund <andres@anarazel.de>
Date: 2017-11-05T22:34:23Z
Lists: pgsql-hackers 
On Sun, Nov 5, 2017 at 2:22 PM, Oleg Bartunov <obartunov@gmail.com> wrote:
>> IIRC there were some concerns about what happened with pg_upgrade,
>> with consuming precious toast bits, and a few other things.
>
> yes, pg_upgrade may be a problem.

A basic problem here is that, as proposed, DROP COMPRESSION METHOD may
break your database irretrievably.  If there's no data compressed
using the compression method you dropped, everything is cool -
otherwise everything is broken and there's no way to recover.  The
only obvious alternative is to disallow DROP altogether (or make it
not really DROP).

Both of those alternatives sound fairly unpleasant to me, but I'm not
exactly sure what to recommend in terms of how to make it better.
Ideally anything we expose as an SQL command should have a DROP
command that undoes whatever CREATE did and leaves the database in an
intact state, but that seems hard to achieve in this case.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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.