Horton

Re: [HACKERS] Custom compression methods

Ildus Kurbangaliev <i.kurbangaliev@postgrespro.ru>

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From: Ildus Kurbangaliev <i.kurbangaliev@postgrespro.ru>
To: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Cc: Alvaro Herrera <alvherre@2ndquadrant.com>, Евгений Шишкин <itparanoia@gmail.com>, Andres Freund <andres@anarazel.de>, Robert Haas <robertmhaas@gmail.com>, Oleg Bartunov <obartunov@gmail.com>, Craig Ringer <craig@2ndquadrant.com>, Peter Eisentraut <peter.eisentraut@2ndquadrant.com>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Date: 2017-12-06T15:07:16Z
Lists: pgsql-hackers 
On Fri, 1 Dec 2017 21:47:43 +0100
Tomas Vondra <tomas.vondra@2ndquadrant.com> wrote:
 
> 
> +1 to do the rewrite, just like for other similar ALTER TABLE commands

Ok. What about the following syntax:

ALTER COLUMN DROP COMPRESSION - removes compression from the column
with the rewrite and removes related compression options, so the user
can drop compression method.

ALTER COLUMN SET COMPRESSION NONE for the cases when
the users want to just disable compression for future tuples. After
that they can keep compressed tuples, or in the case when they have a
large table they can decompress tuples partially using e.g. UPDATE,
and then use ALTER COLUMN DROP COMPRESSION which will be much faster
then.

ALTER COLUMN SET COMPRESSION <cm> WITH <cmoptions> will change
compression for new tuples but will not touch old ones. If the users
want the recompression they can use DROP/SET COMPRESSION combination.

I don't think that SET COMPRESSION with the rewrite of the whole table
will be useful enough on any somewhat big tables and same time big
tables is where the user needs compression the most.

I understand that ALTER with the rewrite sounds logical and much easier
to implement (and it doesn't require Oids in tuples), but it could be
unusable.

-- 
----
Regards,
Ildus Kurbangaliev

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.