Re: [PATCH] Incremental sort (was: PoC: Partial sort)

Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> writes:
> I don't know, I've tried running the tests on a number of machines,
> similar to those failing. Rapsberry Pi, Fedora 31, ... and it worked
> everywhere while the failures seem consistent.

On my machine, it reproduces about one time in six with
force_parallel_mode = regress. It seems possible given your
results that reducing max_parallel_workers would make it more
likely, but I've not tried that.

What I'm seeing, after adding some debug printouts, is that sortMethod is
frequently zero when we reach the EXPLAIN output for a worker. In many of
the tests this happens even though there is no visible failure, because
we've got a filter function hiding the output :-(

So I concur with James' conclusion that the existing code is relying on
sortMethod initializing to zeroes, and that we did the wrong thing by
trying to give SORT_TYPE_STILL_IN_PROGRESS a nonzero representation.
I do not like his patch though, particularly not the type pun with NULL.
I think the correct fix is to change the enum declaration.

I know it's darn late where you are, do you want me to change it?

regards, tom lane