Horton

Re: [HACKERS] Custom compression methods (mac+lz4.h)

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Dilip Kumar <dilipbalaut@gmail.com>, Justin Pryzby <pryzby@telsasoft.com>, Andres Freund <andres@anarazel.de>, Tomas Vondra <tomas.vondra@2ndquadrant.com>, David Steele <david@pgmasters.net>, Ildus Kurbangaliev <i.kurbangaliev@gmail.com>, Dmitry Dolgov <9erthalion6@gmail.com>, Andrey Borodin <x4mmm@yandex-team.ru>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2021-03-22T15:59:18Z
Lists: pgsql-hackers 
On Mon, Mar 22, 2021 at 11:48 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
> > Anyway, this particular macro name was chosen, it seems, for symmetry
> > with VARDATA_4B_C, but if you want to change it to something else, I'm
> > OK with that, too.
>
> After looking at postgres.h for a bit, I'm thinking that what these
> should have been symmetric with is the considerably-less-terrible
> names used for the corresponding VARATT_EXTERNAL cases.  Thus,
> something like
>
> s/VARRAWSIZE_4B_C/VARDATA_COMPRESSED_GET_RAWSIZE/
> s/VARCOMPRESS_4B_C/VARDATA_COMPRESSED_GET_COMPRESSION/

Works for me.

> Possibly the former names should survive and the latter become
> wrappers around them, not sure.  But we shouldn't be using the "4B"
> terminology anyplace except this part of postgres.h.

I would argue that it shouldn't be used any place at all, and that we
ought to go the other direction and get rid of the existing macros -
e.g. change #define VARATT_IS_1B_E to #define VARATT_IS_EXTERNAL
instead of defining the latter as a no-value-added wrapper around the
former. Maybe at one time somebody thought that the test for
VARATT_IS_EXTERNAL might someday have more cases than just
VARATT_IS_1B_E, but that's not looking like a good bet in 2021.

-- 
Robert Haas
EDB: 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.