Horton

Re: [HACKERS] Custom compression methods

Dilip Kumar <dilipbalaut@gmail.com>

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From: Dilip Kumar <dilipbalaut@gmail.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Tomas Vondra <tomas.vondra@2ndquadrant.com>, Alexander Korotkov <a.korotkov@postgrespro.ru>, David Steele <david@pgmasters.net>, Ildus Kurbangaliev <i.kurbangaliev@gmail.com>, Dmitry Dolgov <9erthalion6@gmail.com>, PostgreSQL Developers <pgsql-hackers@lists.postgresql.org>
Date: 2020-10-22T11:40:27Z
Lists: pgsql-hackers 
On Wed, Oct 21, 2020 at 8:51 PM Robert Haas <robertmhaas@gmail.com> wrote:
>
> On Thu, Oct 8, 2020 at 5:54 PM Tomas Vondra
> <tomas.vondra@2ndquadrant.com> wrote:
> > And is the oidvector actually needed? If we have the extra catalog,
> > can't we track this simply using the regular dependencies? So we'd have
> > the attcompression OID of the current compression method, and the
> > preserved values would be tracked in pg_depend.
>
> If we go that route, we have to be sure that no such dependencies can
> exist for any other reason. Otherwise, there would be confusion about
> whether the dependency was there because values of that type were
> being preserved in the table, or whether it was for the hypothetical
> other reason. Now, admittedly, I can't quite think how that would
> happen. For example, if the attribute default expression somehow
> embedded a reference to a compression AM, that wouldn't cause this
> problem, because the dependency would be on the attribute default
> rather than the attribute itself. So maybe it's fine.

Yeah, and moreover in the new patchset, we are storing the compression
methods in the new catalog 'pg_compression' instead of merging with
the pg_am.  So I think only for the preserve purpose we will maintain
the attribute -> pg_compression dependency so it should be fine.

-- 
Regards,
Dilip Kumar
EnterpriseDB: http://www.enterprisedb.com

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.