Marko Tiikkaja <marko@joh.to> writes: > On Mon, Aug 13, 2018 at 7:35 PM, Andres Freund <andres@anarazel.de> wrote: >> Well, the subselect with thelimit going to return different results from >> run to run. Unless you add an ORDER BY there's no guaranteed order in >> which tuples are returned. So I don't think it's surprising that you're >> getting results that differ between runs.
> While this is true, that's missing the point.
Yeah, I agree. I think probably what's happening is that the sub-select is getting pushed down to the parallel workers and they are not all computing the same set of sub-select results, leading to inconsistent answers at the top level.
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?
If we don't need to solve order of rows, then parallel unsafe is not necessary.
