Re: Reducing the cycle time for CLOBBER_CACHE_ALWAYS buildfarm members

I wrote:
> Andrew Dunstan <andrew@dunslane.net> writes:
>> Seems reasonable. I don't have a CCA animal any more, but I guess I
>> could set up a test.

> I can run a test here --- I'll commandeer sifaka for awhile,
> since that's the fastest animal I have.

Done, and here's the results:

Traditional way (-DCLOBBER_CACHE_ALWAYS): 32:53:24
https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=sifaka&dt=2021-07-01%2018%3A06%3A09

New way: 16:15:43
https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=sifaka&dt=2021-07-03%2004%3A02%3A16

That's running sifaka's full test schedule including TAP tests,
which ordinarily takes it a shade under 10 minutes.  The savings
on a non-TAP run would be a lot less, of course, thanks to
fewer initdb invocations.

Although I lacked the patience to run a full back-branch cycle
with -DCLOBBER_CACHE_ALWAYS, I did verify that the patch
correctly injects that #define when running an old branch.
So I think it's ready to go into the buildfarm, modulo any
cosmetic work you might want to do.

            regards, tom lane