Horton

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

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Dilip Kumar <dilipbalaut@gmail.com>
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: 2021-03-21T20:32:31Z
Lists: pgsql-hackers 
Dilip Kumar <dilipbalaut@gmail.com> writes:
>> Yeah, we need to set the default_toast_compression in the beginning of
>> the test as attached.
> In the last patch, I did not adjust the compression_1.out so fixed
> that in the attached patch.

Pushed that; however, while testing that it works as expected,
I saw a new and far more concerning regression diff:

diff -U3 /home/postgres/pgsql/src/test/regress/expected/strings.out /home/postgres/pgsql/src/test/regress/results/strings.out
--- /home/postgres/pgsql/src/test/regress/expected/strings.out	2021-02-18 10:34:58.190304138 -0500
+++ /home/postgres/pgsql/src/test/regress/results/strings.out	2021-03-21 16:27:22.029402834 -0400
@@ -1443,10 +1443,10 @@
 -- If start plus length is > string length, the result is truncated to
 -- string length
 SELECT substr(f1, 99995, 10) from toasttest;
- substr 
---------
- 567890
- 567890
+         substr         
+------------------------
+ 567890\x7F\x7F\x7F\x7F
+ 567890\x7F\x7F\x7F\x7F
  567890
  567890
 (4 rows)
@@ -1520,10 +1520,10 @@
 -- If start plus length is > string length, the result is truncated to
 -- string length
 SELECT substr(f1, 99995, 10) from toasttest;
- substr 
---------
- 567890
- 567890
+         substr         
+------------------------
+ 567890\177\177\177\177
+ 567890\177\177\177\177
  567890
  567890
 (4 rows)

This seems somewhat repeatable (three identical failures in three
attempts).  Not sure why I did not see it yesterday; but anyway,
there is something wrong with partial detoasting for LZ4.

			regards, tom lane

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.