On 6/7/23 07:58, Daniel Verite wrote:
> Thomas Munro wrote:
>
>> > > Also, it does not occur at all if parallel scan is disabled.
>> >
>> > Could this be a clue that it is failing to be transitive?
>>
>> That vaguely rang a bell for me... and then I remembered this thread:
>>
>> https://www.postgresql.org/message-id/flat/20191206063401.GB1629883%40rfd.leadboat.com
>
> Thanks for the pointer, non-transitive comparisons seem a likely cause
> indeed.
>
> The parallel scan appears to imply some randomness in the sequence of
> comparisons, which makes the problem more visible.
> After changing the test to shuffle the rows before each sort,
> non-parallel scans also produce outputs that differ, proving that
> parallelism is not a root cause.
>
> Running the test with all the libc collations with collencoding in
> (-1,6) shows that the only ones not affected are C/POSIX/ucs_basic.
> Otherwise the 569 other pre-created libc collations that can be used
> with UTF-8 are affected, plus the default collation
> (French_France.1252 in my case).
Wow, that sounds pretty horrid
--
Joe Conway
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com
