Re: parallel.c is not marked as test covered

On Mon, May 9, 2016 at 4:50 PM Andres Freund <andres(at)anarazel(dot)de> wrote:

> I think it's a good idea to run a force-parallel run on some buildfarm
> members. But I'm rather convinced that the core tests run by all animals
> need some minimal coverage of parallel queries. Both because otherwise
> it'll be hard to get some coverage of unusual platforms, and because
> it's imo something rather relevant to test during development.
>
Good point.

After some experiments, I found out that, for my setup (9b7bfc3a88ef7b), a
parallel seq scan is used given both parallel_setup_cost
and parallel_tuple_cost are set to 0 and given that the table is at least 3
times as large as the biggest test table tenk1.

The attached patch is a regression test using this method that is
reasonably small and fast to run. I also hid the workers count from the
explain output when costs are disabled as suggested by Tom Lane and Robert
Haas on this same thread (
http://www.postgresql.org/message-id/CA+TgmobBQS4ss3+CwoZOKgbsBqKfRndwc=hLiALAep5aXQCTDA@mail.gmail.com
).

Testing under these conditions does not test the planner job at all but at
least some parallel code can be run on the build farm and the test suite
gets 2643 more lines and 188 more function covered.

I don't know however if this test will be reliable on other platforms, some
more feedback is needed here.