Re: parallel.c is not marked as test covered

On Wed, May 11, 2016 at 12:34 AM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> Hmm, that is strange.  I would have expected that to stuff a Gather on
>> top of the Aggregate.  I wonder why it's not doing that.
>
> The reason is that create_plain_partial_paths() contains a hard-wired
> decision not to generate any partial paths for relations smaller than
> 1000 blocks, which means that no partial path will ever be generated
> for *any* relation in the standard regression tests, force_parallel_mode
> or no.

Well that's an interesting theory, except that you've completely
missed the point of force_parallel_mode.  force_parallel_mode pushes a
special Gather node on top of any plan that is not already parallel in
some way but which is parallel-safe.   That special Gather node runs
only in the worker, not the leader, and always uses just one worker.