Horton

Re: [HACKERS] Custom compression methods

Justin Pryzby <pryzby@telsasoft.com>

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From: Justin Pryzby <pryzby@telsasoft.com>
To: Dilip Kumar <dilipbalaut@gmail.com>
Cc: Robert Haas <robertmhaas@gmail.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: 2021-03-09T07:43:13Z
Lists: pgsql-hackers 
On Tue, Mar 09, 2021 at 01:04:10PM +0530, Dilip Kumar wrote:
> On Tue, Mar 9, 2021 at 2:45 AM Robert Haas <robertmhaas@gmail.com> wrote:
> >
> > On Mon, Mar 8, 2021 at 3:59 PM Justin Pryzby <pryzby@telsasoft.com> wrote:
> > > > It would be nice to have a way to force
> > > > anything compressed with the old method to be re-compressed with the
> > > > new method, but not having that doesn't preclude allowing the
> > > > parameter to be changed.
> > >
> > > Doesn't vacuum full/cluster/dump+restore do that ?
> >
> > Well, dump and restore will do it, certainly, but I don't think VACUUM
> > FULL or CLUSTER will. I haven't tested it, though, so maybe I'm wrong.
> 
> Yeah, vacuum full or cluster will not re-compress the data.  How about
> providing syntax ALTER TABLE <tab-name> ALTER COLUMN <col_name> SET
> COMPRESSION <com_name> REWRITE?

It'd be strange to me if "rewrite" were associated with a column.

Depending on what data strucutures you use, you might accidentally fail to
rewrite the table if someone wrote something like:
postgres=# alter table t alter a set compression pglz REWRITE, alter a set compression pglz;

Although I hope that's something to support someday for columnar AMs, I think
table-rewriting now is done in entirety, and the syntax should reflect that.

-- 
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.