Horton

Re: [HACKERS] Custom compression methods

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Cc: Dilip Kumar <dilipbalaut@gmail.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: 2020-10-21T15:20:59Z
Lists: pgsql-hackers 
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.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL 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.