Re: More efficient build farm animal wakeup?

On Mon, Nov 21, 2022 at 10:31 AM Magnus Hagander <magnus@hagander.net> wrote:
> Um, branches of interest will only pick up when it gets a new *branch*, not a new *commit*, so I think that would be
avery different problem to solve. And I don't think we have new branche *that* often...
 

Sure, could be done with an extra different request you make from time
to time or keeping the existing list.  No strong opinions on that, I
was just observing that it could also be combined, something like:

Client: I have 14@1234, 15@1234, HEAD@1234; what should I do now, boss?
Server: You should fetch 14 (it has a new commit) and 16 (it's a new
branch you didn't mention).

> I'd imagine something like a
> GET https://git.postgresql.org/buildfarm-branchtips
> X-branch-master: a4adc31f69
> X-branch-REL_14_STABLE: b33283cbd3
> X-longpoll: 120
>
> For that one it would check branch master and rel 14, and if either branchtip doesn't match what was in the header,
it'dreturn immediately with a textfile that's basically
 
> master:<whateveritis>
>
> if master has changed and not REL_14.
>
> If nothing has changed, go into longpoll for 120 seconds based on the header, and if nothing at all has changed in
thattime, return a 304.
 

LGTM, that's exactly the sort of thing I was imagining.

> We could also use something like a websocket to just stream the changes out over.

True.  The reason I started on about long polling instead of
websockets is that I was imagining that the simpler, dumber protocol
where the client doesn't even really know it's participating a new
kind of magic would be more cromulent in ye olde perl script (no new
cpan dependencies).

> In either case it would also need to change the buildfarm client to run as a daemon rather than a cronjob I think?
(obviouslyoptional, we don't have to remove the current abilities)
 

Given that the point of the build farm is (these days) to test on
weird computers and operating systems, I expect that proper 'run like
a service' support would be painful or not get done.  It'd be nice if
there were some way to make this work with simple crontab entries...