Horton

Re: [HACKERS] Custom compression methods (mac+lz4.h)

Dilip Kumar <dilipbalaut@gmail.com>

View thread View on postgr.es
From: Dilip Kumar <dilipbalaut@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Justin Pryzby <pryzby@telsasoft.com>, Robert Haas <robertmhaas@gmail.com>, 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>, Andrey Borodin <x4mmm@yandex-team.ru>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2021-03-21T07:37:16Z
Lists: pgsql-hackers 
On Sun, Mar 21, 2021 at 7:03 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Also, I see some diffs in the
> indirect_toast test, which seems perhaps worthy of investigation.
> (The diffs look to be just row ordering, but why?)

I have investigated that,  actually in the below insert, after
compression the data size of (repeat('1234567890',50000)) is 1980
bytes with the lz4 whereas with pglz it is 5737 bytes.  So with lz4,
the compressed data are stored inline whereas with pglz those are
getting externalized.  Due to this for one of the update statements
followed by an insert, there was no space on the first page as data
are stored inline so the new tuple is stored on the next page and that
is what affecting the order.  I hope this makes sense.

INSERT INTO indtoasttest(descr, f1, f2) VALUES('one-toasted,one-null',
NULL, repeat('1234567890',50000));


-- 
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.