AFAICS this patch does nothing to consider parallel safety -- that is,
as things stand, a variable is allowed in a query that may be
parallelised, but its value is not copied to workers, leading to
incorrect results. For example:
create table foo(a int);
insert into foo select * from generate_series(1,1000000);
create variable zero int;
let zero = 0;
explain (costs off) select count(*) from foo where a%10 = zero;
QUERY PLAN
-----------------------------------------------
Finalize Aggregate
-> Gather
Workers Planned: 2
-> Partial Aggregate
-> Parallel Seq Scan on foo
Filter: ((a % 10) = zero)
(6 rows)
select count(*) from foo where a%10 = zero;
count
-------
38037 -- Different random result each time, should be 100,000
(1 row)
Thoughts?
Regards,
Dean
