[ovirt-devel] Gerrit parallel patch handling and CI (Or, why did my code fail post-merge)

[Barak Korren]

On 30 November 2016 at 19:12, Vojtech Szocs <vszocs at redhat.com> wrote:
>
> So before we adopt auto-submit-after-ci-pass (e.g. using Zuul, as Eyal
> mentioned in that thread), we should be able to manually trigger heavy
> CI (check-merged) job from Gerrit web interface, is that correct?

We could make it a two-step operation where you indicate you want to
submit, wait for the CI output and then click submit - but why not
just let the system submit for you?

One road I don't think we should go down is to have 3 CI stages:
"light" check_patch, "heavy" check_patch and "pre-merge", this looks
like a design smell to me.

WRT Zuul:

Unless you are using a strict policy like ff-only (which so far seems
no to scale, because it is essentially a GIL on merging), Zuul is
essential in order to test the right code in CI (even just for basic
check_patch testing). So we are working to bring it in (See OVIRT-734
[1] and OVIRT-882 [2]).

WRT merge gating - Zuul tries to make the process "fire and forget" as
far as maintainers are concerned - if failures are found, it actually
tries out different combinations of patches to see if, from a set of
patches that were asked to be merged, some could be merged even when
others could not.

> If so, it would be the patch owner's responsibility to submit (merge)
> only after heavy CI (check-merged) pass?

The question hiding here is wither a maintainer could submit _without_
passing the "heavy" CI. I'm guessing some maintainers will demand
that, but I'm hoping in the long run this will not be needed and you
will know that once submitted, a patch will be eventually merged
unless it has real issues in it.

> So we could actually write Gerrit plugin using MergeValidationListener
> that would operate in the following way:
> ...snip...

Just because something could be written doesn't mean it should - we
are already stretched too thinly over too much code in the CI system,
we do not want to maintain any more of it, certainly not in a core
component like Gerrit.

Then again, this is a prioritization question - it not up to me to decide.

[1]: https://ovirt-jira.atlassian.net/browse/OVIRT-734
[2]: https://ovirt-jira.atlassian.net/browse/OVIRT-882

-- 
Barak Korren
bkorren at redhat.com
RHCE, RHCi, RHV-DevOps Team
https://ifireball.wordpress.com/