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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Dilip Kumar <dilipbalaut@gmail.com>
Cc: Justin Pryzby <pryzby@telsasoft.com>
Cc: Robert Haas <robertmhaas@gmail.com>
Cc: Andres Freund <andres@anarazel.de>
Cc: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Cc: Alexander Korotkov <a.korotkov@postgrespro.ru>
Cc: David Steele <david@pgmasters.net>
Cc: Ildus Kurbangaliev <i.kurbangaliev@gmail.com>
Cc: Dmitry Dolgov <9erthalion6@gmail.com>
Cc: Andrey Borodin <x4mmm@yandex-team.ru>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: [HACKERS] Custom compression methods (mac+lz4.h)
Date: Sun, 21 Mar 2021 16:32:31 -0400
Message-ID: <414943.1616358751@sss.pgh.pa.us> (raw)
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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





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  Cc: tgl@sss.pgh.pa.us, dilipbalaut@gmail.com, pryzby@telsasoft.com, robertmhaas@gmail.com, andres@anarazel.de, tomas.vondra@2ndquadrant.com, a.korotkov@postgrespro.ru, david@pgmasters.net, i.kurbangaliev@gmail.com, 9erthalion6@gmail.com, x4mmm@yandex-team.ru, pgsql-hackers@lists.postgresql.org
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