Horton

Re: [HACKERS] Custom compression methods

Dilip Kumar <dilipbalaut@gmail.com>

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From: Dilip Kumar <dilipbalaut@gmail.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Justin Pryzby <pryzby@telsasoft.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: 2021-03-09T09:14:41Z
Lists: pgsql-hackers 
On Tue, Mar 9, 2021 at 1:56 AM Robert Haas <robertmhaas@gmail.com> wrote:
>
> With this design, we can support changing the compression method on a
> column quite easily. It's just a hint, like the STORAGE parameter. It
> has no bearing on what can be present in the table, but just controls
> how new values are stored. 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.

So you mean if we are not able to decompress the old data because the
binary was not compiled with lz4 then don't give error and continue.
I think that depends upon how we are going to support this option for
example suppose we are setting as ALTER COLUMN f1 SET COMPRESSION pglz
REWRITE, then maybe it make sense that even we are not able to rewrite
because it was not compiled with lz4 we can successfully set the new
compression method to pglz.

Another thing is that if the table has some rowtype column then we
will have to process that and decompress any compressed field inside
that right?  I haven't yet thought how complex it will be to
decompress the data stored inside an already formed composite type but
I will analyze this.

-- 
Regards,
Dilip Kumar
EnterpriseDB: 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.