Horton

Re: [HACKERS] Custom compression methods

Robert Haas <robertmhaas@gmail.com>

View thread View on postgr.es
From: Robert Haas <robertmhaas@gmail.com>
To: Justin Pryzby <pryzby@telsasoft.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Alvaro Herrera <alvherre@alvh.no-ip.org>, Dilip Kumar <dilipbalaut@gmail.com>, Andres Freund <andres@anarazel.de>, Tomas Vondra <tomas.vondra@2ndquadrant.com>, David Steele <david@pgmasters.net>, Ildus Kurbangaliev <i.kurbangaliev@gmail.com>, Dmitry Dolgov <9erthalion6@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2021-03-22T17:38:36Z
Lists: pgsql-hackers

Attachments

On Mon, Mar 22, 2021 at 12:16 PM Robert Haas <robertmhaas@gmail.com> wrote:
> But, what about giving the default_toast_compression_method GUC an
> assign hook that sets a global variable of type "char" to the
> appropriate value? Then GetDefaultToastCompression() goes away
> entirely. That might be worth exploring.

Actually, we can do even better. We should just make the values
actually assigned to the GUC be TOAST_PGLZ_COMPRESSION etc. rather
than TOAST_PGLZ_COMPRESSION_ID etc. Then a whole lot of complexity
just goes away. I added some comments explaining why using
TOAST_PGLZ_COMPRESSION is the wrong thing anyway. Then I got hacking
and rearranged a few other things. So the attached patch does these
thing:

- Changes default_toast_compression to an enum, as in your patch, but
now with values that are the same as what ultimately gets stored in
attcompression.
- Adds a comment warning against incautious use of
TOAST_PGLZ_COMPRESSION_ID, etc.
- Moves default_toast_compression_options to guc.c.
- After doing the above two things, we can remove the #include of
utils/guc.h into access/toast_compression.h, so the patch does that.
- Moves NO_LZ4_SUPPORT, GetCompressionMethodName, and
CompressionNameToMethod to guc.c. Making these inline functions
doesn't save anything meaningful; it's more important not to export a
bunch of random identifiers.
- Removes an unnecessary cast to bool from the definition of
CompressionMethodIsValid.

I think this is significantly cleaner than what we have now, and I
also prefer it to your proposal.

Comments?

-- 
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.