| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Justin Pryzby <pryzby(at)telsasoft(dot)com> |
| Cc: | Dilip Kumar <dilipbalaut(at)gmail(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, Alexander Korotkov <a(dot)korotkov(at)postgrespro(dot)ru>, David Steele <david(at)pgmasters(dot)net>, Ildus Kurbangaliev <i(dot)kurbangaliev(at)gmail(dot)com>, Dmitry Dolgov <9erthalion6(at)gmail(dot)com>, Andrey Borodin <x4mmm(at)yandex-team(dot)ru>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: [HACKERS] Custom compression methods (mac+lz4.h) |
| Date: | 2021-03-21 23:11:50 |
| Message-ID: | 504396.1616368310@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
I wrote:
> Justin Pryzby <pryzby(at)telsasoft(dot)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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