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Re: [HACKERS] Custom compression methods

Ildar Musin <i.musin@postgrespro.ru>

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From: Ildar Musin <i.musin@postgrespro.ru>
To: Ildus Kurbangaliev <i.kurbangaliev@postgrespro.ru>, Robert Haas <robertmhaas@gmail.com>
Cc: Alexander Korotkov <a.korotkov@postgrespro.ru>, Tomas Vondra <tomas.vondra@2ndquadrant.com>, Alvaro Herrera <alvherre@2ndquadrant.com>, Евгений Шишкин <itparanoia@gmail.com>, Andres Freund <andres@anarazel.de>, Oleg Bartunov <obartunov@gmail.com>, Craig Ringer <craig@2ndquadrant.com>, Peter Eisentraut <peter.eisentraut@2ndquadrant.com>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>, Chapman Flack <chap@anastigmatix.net>
Date: 2018-01-22T20:26:31Z
Lists: pgsql-hackers 
Hello Ildus,


15/01/2018 00:49, Ildus Kurbangaliev пишет:
> Attached a new version of the patch. Main changes:
>
> * compression as an access method
> * pglz as default compression access method.
> * PRESERVE syntax for tables rewrite control.
> * pg_upgrade fixes
> * support partitioned tables.
> * more tests.
>
You need to rebase to the latest master, there are some conflicts. I've
applied it to the three days old master to try it.

As I can see the documentation is not yet complete. For example, there
is no section for ALTER COLUMN ... SET COMPRESSION in ddl.sgml; and
section "Compression Access Method Functions" in compression-am.sgml
hasn't been finished.

I've implemented an extension [1] to understand the way developer would
go to work with new infrastructure. And for me it seems clear. (Except
that it took me some effort to wrap my mind around varlena macros but it
is probably a different topic).

I noticed that you haven't cover 'cmdrop' in the regression tests and I
saw the previous discussion about it. Have you considered using event
triggers to handle the drop of column compression instead of 'cmdrop'
function? This way you would kill two birds with one stone: it still
provides sufficient infrastructure to catch those events (and it
something postgres already has for different kinds of ddl commands) and
it would be easier to test.

Thanks!

[1] https://github.com/zilder/pg_lz4

-- 
Ildar Musin
Postgres Professional: http://www.postgrespro.com
Russian Postgres 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.