Horton

Re: [HACKERS] Custom compression methods

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>, Andres Freund <andres@anarazel.de>, Justin Pryzby <pryzby@telsasoft.com>, 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 Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2021-03-19T21:49:37Z
Lists: pgsql-hackers

Attachments

On Fri, Mar 19, 2021 at 4:38 PM Robert Haas <robertmhaas@gmail.com> wrote:
> Yes, and prion's got this concerning diff:
>
>   Column |  Type   | Collation | Nullable | Default | Storage |
> Compression | Stats target | Description
>  --------+---------+-----------+----------+---------+---------+-------------+--------------+-------------
> - f1     | integer |           |          |         | plain   |
>      |              |
> + f1     | integer |           |          |         | plain   | pglz
>      |              |
>
> Since the column is not a varlena, it shouldn't have a compression
> method configured, yet on that machine it does, possibly because that
> machine uses -DRELCACHE_FORCE_RELEASE -DCATCACHE_FORCE_RELEASE.

I could reproduce the problem with those flags. I pushed a fix.

> Regarding your point, that does look like clutter. We don't annotate
> the dump with a storage clause unless it's non-default, so probably we
> should do the same thing here. I think I gave Dilip bad advice here...

Here's a patch for that. It's a little strange because you're going to
skip dumping the toast compression based on the default value on the
source system, but that might not be the default on the system where
the dump is being restored, so you could fail to recreate the state
you had. That is avoidable if you understand how things work, but some
people might not. I don't have a better idea, though, so let me know
what you think of this.

-- 
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.