Howdy!
Mathieu Othacehe <othacehe@gnu.org> skribis:
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>> Seems to me that ‘BuildSteps’ is an orthogonal concern that has little>> to do with Cuirass’ job and with its data model. In Hydra I saw that as>> a (necessary) kludge.>> I'm not sure to follow you here. Cuirass and Hydra have an almost> identical database schema and are now working very similarly from what I> understand.>> In Hydra, a JobSet (Specification in Cuirass) has several Builds. Each> Build can be broken in several BuildSteps, corresponding to transitive> derivation inputs that must be built.>> Hydra manages to get those BuildSteps to be built in a topological> order, in the same way as the Guix Build Coordinator.>> This makes me think that we could implement this exact same mechanism in> Cuirass but I'm maybe missing something.
When Cuirass was started, I wanted to avoid what I perceived as ashortcoming of Hydra’s design: one daemon connection per job and buildsteps, which kinda replicate what the daemon is doing.
So I suggested going for one connection for all the jobs and passing allthe derivations to the daemon so that the daemon can see the big picture,make better scheduling decisions, and so we don’t have to re-implement“build steps”.
But as you know, this strategy didn’t work out as expected because ofscalability issues in the daemon.
Regardless, it seems to me that ‘BuildSteps’ is a low-level thingcompared to the rest of the Cuirass database: it reifies part of thederivation graph whereas the rest of the database is all about “jobs”and “builds” thereof. It’s not the same abstraction level.
I realize it’s somewhat subjective though and I don’t want to impedeprogress!
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>> If Cuirass would instead delegate derivation build requests to a>> Coordinator/daemon-like thing, it wouldn’t have to worry about those>> details. That would better separate concerns.>> I think that having Cuirass delegating its builds to the Coordinator is> not the right move. That would mean doubling the size of the CI code> base, doubling the number of databases, for a feature that we could> implement in Cuirass, just by making it catch-up on Hydra.
I see. Generally speaking, I think better separation of concerns maysometimes be worth extra code, insomuch as it makes it easier to reasonabout things, to debug, and to add new features. Of course it’s atradeoff; adding too much code just for the beauty of abstractions isn’treasonable either.
I wonder if having two databases instead of single one (which wouldessentially be the union of those two databases) is a problem. I guessone problem is if that makes it hard to make commonly-needed “joins”across the two databases.
Regarding features, one thing I like about the Coordinator is itssupport for retrying builds, which could serve to detect flaky builds orbuild processes that are kernel- or hardware-dependent. I think it’s afeature we’d want eventually, but I wonder if it should be Cuirass’sjob.
It’d be nice to focus on a single code base for “distributed builds” ingeneral, and I was hoping for a Coordinator/Cuirass convergence on thisaspect. But at the end of the day, what matters most is what weachieve. Cuirass has been doing so much better on many fronts over thelast few weeks, including reliability, build throughput, and monitoring.At the same time, the Coordinator proves useful and easy to deploy inmore experimental setups; I think Chris’s instance now aggregatesresults from a variety of machines, including POWER and GNU/Hurd, andthat seemed quite easy to do. I’m not going to complain aboutover-success in this area! :-)
Ludo’.