From: Tom Lane <tgl@sss.pgh.pa.us>
To: Justin Pryzby <pryzby@telsasoft.com>
Cc: Dilip Kumar <dilipbalaut@gmail.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 19:11:50 -0400
Message-ID: <504396.1616368310@sss.pgh.pa.us> (raw)
In-Reply-To: <456616.1616360715@sss.pgh.pa.us>
References: <20210319174425.GM11765@telsasoft.com>
<CA+TgmobXnzCRf-UOWnjk+OoCT-mzFR867HvoxM2N9uA7+_V-+g@mail.gmail.com>
<20210320212302.GW11765@telsasoft.com>
<301730.1616276227@sss.pgh.pa.us>
<20210320231957.GX11765@telsasoft.com>
<309337.1616287493@sss.pgh.pa.us>
<311370.1616290403@sss.pgh.pa.us>
<CAFiTN-tN-fi=9VEatyiZyhW28yhhQCmn-egYzbdxBTLkOnVQvg@mail.gmail.com>
<CAFiTN-t0w+Rc2U3S+y=7KWcLuOYNB5MfWeGdNa7+pg0UovVdcQ@mail.gmail.com>
<414943.1616358751@sss.pgh.pa.us>
<20210321204148.GB4203@telsasoft.com>
<456616.1616360715@sss.pgh.pa.us>
I wrote:
> Justin Pryzby <pryzby@telsasoft.com> writes:
>> On Sun, Mar 21, 2021 at 04:32:31PM -0400, Tom Lane wrote:
>>> 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.
>> With what version of LZ4 ?
> RHEL8's, which is
> lz4-1.8.3-2.el8.x86_64
I hate to be the bearer of bad news, but this suggests that
LZ4_decompress_safe_partial is seriously broken in 1.9.2
as well:
https://github.com/lz4/lz4/issues/783
Maybe we cannot rely on that function for a few more years yet.
Also, I don't really understand why this code:
/* slice decompression not supported prior to 1.8.3 */
if (LZ4_versionNumber() < 10803)
return lz4_decompress_datum(value);
It seems likely to me that we'd get a flat out build failure
from library versions lacking LZ4_decompress_safe_partial,
and thus that this run-time test is dead code and we should
better be using a configure probe if we intend to allow old
liblz4 versions. Though that might be moot.
regards, tom lane
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To: pgsql-hackers@postgresql.org
Cc: tgl@sss.pgh.pa.us, pryzby@telsasoft.com, dilipbalaut@gmail.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
Subject: Re: [HACKERS] Custom compression methods (mac+lz4.h)
In-Reply-To: <504396.1616368310@sss.pgh.pa.us>
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