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: Dilip Kumar <dilipbalaut@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: 2021-03-08T20:58:58Z
Lists: pgsql-hackers 
On Mon, Mar 08, 2021 at 03:26:04PM -0500, Robert Haas wrote:
> On Mon, Mar 8, 2021 at 5:02 AM Dilip Kumar <dilipbalaut@gmail.com> wrote:
> > So now only pending point is,  how do we handle the upgrade when you
> > are upgrading from --with-lz4 to --without-lz4 binary and a couple of
> > options discussed here are
> > a) Should we allow table creation with lz4 even if it is compiled
> > --without-lz4?  In case of xml we always allow table creation even if
> > it is compiled --wthout-libxml
> > b) Instead of allowing this always, only allow during binary upgrade.

> 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 ?

> I think the pg_dump argument should be --no-toast-compression, not
> --no-toast-compressions. I agree with Justin that pg_restore should
> have the option also.

I mentioned that this is hard to do, since the compression is stored inside the
text blob that creates the whole table...Unless toast compression is a
per-relation property rather than per-attribute.  I don't think pg_restore
should try to reverse-engineer the text output by pg_dump to elide the
"COMPRESSION lz4".

I think maybe CREATE shouldn't support COMPRESSION at all, and pg_dump/restore
would use ALTER.  That makes this very slightly less of an issue, as one can
use pg_restore -f- |grep -v '^ALTER TABLE .* SET COMPRESSION' |psql -d,
rather than sed 's/COMPRESSION lz4//'

> Man, it would be really nice to be able to set the default for new
> tables, rather than having all these places hard-coded to use
> DefaultCompressionMethod. Surely lotsa people are going to want to set
> toast_compression = lz4 in postgresql.conf and forget about it.

I don't understand - isn't that what 0002 does ?

Subject: [PATCH v32 2/4] Add default_toast_compression GUC                                                                                                                                                                         

-- 
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.