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: Oleg Bartunov <obartunov@gmail.com>, Craig Ringer <craig@2ndquadrant.com>, Peter Eisentraut <peter.eisentraut@2ndquadrant.com>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>, Andres Freund <andres@anarazel.de>
Date: 2017-11-15T09:09:28Z
Lists: pgsql-hackers 
On Sun, 5 Nov 2017 17:34:23 -0500
Robert Haas <robertmhaas@gmail.com> wrote:

> 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).

In the patch I use separate table for compresssion options (because
each attribute can have additional options for compression). So basicly
compressed attribute linked to compression options, not the compression
method and this method can be safely dropped.

So in the next version of the patch I can just unlink the options from
compression methods and dropping compression method will not affect
already compressed tuples. They still could be decompressed.

-- 
---
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.