Horton

Re: [HACKERS] Custom compression methods

Ildus Kurbangaliev <i.kurbangaliev@postgrespro.ru>

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From: Ildus Kurbangaliev <i.kurbangaliev@postgrespro.ru>
To: 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: 2017-12-18T08:54:31Z
Lists: pgsql-hackers 
On Thu, 14 Dec 2017 10:29:10 -0500
Robert Haas <robertmhaas@gmail.com> wrote:

> On Wed, Dec 13, 2017 at 7:18 AM, Ildus Kurbangaliev
> <i.kurbangaliev@postgrespro.ru> wrote:
> > Since we agreed on ALTER syntax, i want to clear things about
> > CREATE. Should it be CREATE ACCESS METHOD .. TYPE СOMPRESSION or
> > CREATE COMPRESSION METHOD? I like the access method approach, and it
> > simplifies the code, but I'm just not sure a compression is an
> > access method or not.  
> 
> +1 for ACCESS METHOD.

An access method then.

> 
> > Current implementation
> > ----------------------
> >
> > To avoid extra patches I also want to clear things about current
> > implementation. Right now there are two tables, "pg_compression" and
> > "pg_compression_opt". When compression method is linked to a column
> > it creates a record in pg_compression_opt. This record's Oid is
> > stored in the varlena. These Oids kept in first column so I can
> > move them in pg_upgrade but in all other aspects they behave like
> > usual Oids. Also it's easy to restore them.  
> 
> pg_compression_opt -> pg_attr_compression, maybe.
> 
> > Compression options linked to a specific column. When tuple is
> > moved between relations it will be decompressed.  
> 
> Can we do this only if the compression method isn't OK for the new
> column?  For example, if the old column is COMPRESS foo PRESERVE bar
> and the new column is COMPRESS bar PRESERVE foo, we don't need to
> force decompression in any case.

Thanks, sounds right, i will add it to the patch.

-- 
---
Ildus Kurbangaliev
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.