Horton

Re: [HACKERS] Custom compression methods

Justin Pryzby <pryzby@telsasoft.com>

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From: Justin Pryzby <pryzby@telsasoft.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Andrew Dunstan <andrew@dunslane.net>, 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>, pgsql-hackers@lists.postgresql.org
Date: 2021-03-24T17:58:15Z
Lists: pgsql-hackers 
On Wed, Mar 24, 2021 at 01:30:26PM -0400, Robert Haas wrote:
> On Wed, Mar 24, 2021 at 1:24 PM Justin Pryzby <pryzby@telsasoft.com> wrote:
> > I think it's not specific to pg_upgrade, but any pg_dump |pg_restore.
> >
> > The analogy with tablespaces is restoring from a cluster where the tablespace
> > is named "vast" to one where it's named "huge".  I do this by running
> > PGOPTIONS=-cdefault_tablespace=huge pg_restore --no-tablespaces
> >
> > So I thinks as long as --no-toast-compression does the corresponding thing, the
> > "restore with alternate compression" case is handled fine.
> 
> I think you might be missing the point. If you're using pg_dump and
> pg_restore, you can pass --no-toast-compression if you want. But if

Actually, I forgot that pg_restore doesn't (can't) have --no-toast-compression.
So my analogy is broken.

> you're using pg_upgrade, and it's internally calling pg_dump
> --binary-upgrade, then you don't have control over what options get
> passed. So --no-toast-compression is just fine for people who are
> dumping and restoring, but it's no help at all if you want to switch
> TOAST compression methods while doing a pg_upgrade. However, what does
> help with that is sticking with what Tom committed before rather than
> changing to what he's proposing now.

I don't know what/any other cases support using pg_upgrade to change stuff like
the example (changing to lz4).  The way to do it is to make the changes either
before or after.  It seems weird to think that pg_upgrade would handle that.

I'm going to risk making the analogy that it's not supported to pass
--no-tablespaces from pg_upgrade to pg_dump/restore.  It certainly can't work
for --link (except in the weird case that the dirs are on the same filesystem).  

-- 
Justin

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.