Re: BUG #15324: Non-deterministic behaviour from parallelised sub-query - Mailing list pgsql-bugs

From Tom Lane
Subject Re: BUG #15324: Non-deterministic behaviour from parallelised sub-query
Date
Msg-id 22819.1534183487@sss.pgh.pa.us
Whole thread Raw
In response to Re: BUG #15324: Non-deterministic behaviour from parallelised sub-query  (Pavel Stehule <pavel.stehule@gmail.com>)
Responses Re: BUG #15324: Non-deterministic behaviour from parallelised sub-query  ("David G. Johnston" <david.g.johnston@gmail.com>)
List pgsql-bugs
Pavel Stehule <pavel.stehule@gmail.com> writes:
> 2018-08-13 19:26 GMT+02:00 Tom Lane <tgl@sss.pgh.pa.us>:
>> Likely, we need to treat the presence of a LIMIT/OFFSET in a sub-select
>> as making it parallel-unsafe, for exactly the reason that that makes
>> its results non-deterministic.

> Isn't it default behave of LIMIT/OFFSET without ORDER BY clause?

In principle, the planner could prove in some cases that the results
were deterministic even with LIMIT/OFFSET.  BuT I doubt it's worth
the trouble.  I certainly wouldn't advocate for such logic to be
part of a back-patched bug fix.

            regards, tom lane


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