Horton

Re: [HACKERS] Custom compression methods

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Andrew Dunstan <andrew@dunslane.net>, Justin Pryzby <pryzby@telsasoft.com>, Dilip Kumar <dilipbalaut@gmail.com>, Alvaro Herrera <alvherre@alvh.no-ip.org>, Andres Freund <andres@anarazel.de>, 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: 2021-03-24T16:45:21Z
Lists: pgsql-hackers 
Robert Haas <robertmhaas@gmail.com> writes:
> On Wed, Mar 24, 2021 at 11:42 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> On reflection, though, I wonder if we've made pg_dump do the right
>> thing anyway.  There is a strong case to be made for the idea that
>> when dumping from a pre-14 server, it should emit
>> SET default_toast_compression = 'pglz';
>> rather than omitting any mention of the variable, which is what
>> I made it do in aa25d1089.

> But also ... aren't we just doing this to work around a test case that
> isn't especially good in the first place? Counting the number of lines
> in the diff between A and B is an extremely crude proxy for "they're
> similar enough that we probably haven't broken anything."

I wouldn't be proposing this if the xversion failures were the only
reason; making them go away is just a nice side-effect.  The core
point is that the charter of pg_dump is to reproduce the source
database's state, and as things stand we're failing to ensure we
do that.

(But yeah, we really need a better way of making this check in
the xversion tests.  I don't like the arbitrary "n lines of diff
is probably OK" business one bit.)

			regards, tom lane

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.