Robert Haas <robertmhaas@gmail.com> writes:
> On Mon, Jun 13, 2016 at 11:02 AM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> BTW, decent regression tests could be written without the need to create
>> enormous tables if the minimum rel size in create_plain_partial_paths()
>> could be configured to something less than 1000 blocks. I think it's
>> fairly crazy that that arbitrary constant is hard-wired anyway. Should
>> we make it a GUC?
> That was proposed before, and I didn't do it mostly because I couldn't
> think of a name for it that didn't sound unbelievably corny.
min_parallel_relation_size, or min_parallelizable_relation_size, or
something like that?
> Also,
> the whole way that algorithm works is kind of a hack and probably
> needs to be overhauled entirely in some future release. I'm worried
> about having the words "backward compatibility" thrown in my face when
> it's time to improve this logic. But aside from those two issues I'm
> OK with exposing a knob.
I agree it's a hack, and I don't want to expose anything about the
number-of-workers scaling behavior, for precisely that reason. But a
threshold on the size of a table to consider parallel scans for at all
doesn't seem unreasonable.
regards, tom lane