Re: BUG #15324: Non-deterministic behaviour from parallelised sub-query

On Tue, Aug 14, 2018 at 7:10 AM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>
wrote:

> Yeah, one idea could be that we detect this in
> max_parallel_hazard_walker during the very first pass it performs on
> query-tree. Basically, in the SubLink node check, we can detect
> whether the subselect has Limit/Offset clause and if so, then we can
> treat it as parallel_unsafe. I have tried that way and it prohibits
> the parallel plan for the reported queries. However, I think more
> analysis and verification is required to see if it can happen in any
> other related cases.
>

This seems broken as well:

create table qwr(a int not null, b int not null, c text not null);
insert into qwr select i, i, (select prosrc from pg_proc where
oid=11734) from generate_series(1, 128000) i;
set parallel_setup_cost to 0;
analyze qwr;
select count(*) from qwr where (a, b) in (select a, row_number() over()
from qwr);

.m