Hi 2018-09-04 9:21 GMT+02:00 Dean Rasheed <dean.a.rash...@gmail.com>:
> 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? > The query use copy of values of variables now - but unfortunately, these values are not passed to workers. Should be fixed. Thank you for test case. Pavel > Regards, > Dean >
