CL:453219 was pushed by the CQ at 2017/3/12 at 10:36 PM.

Your PreCQ builder started at Sun, 2017-03-12 10:34:49 PM

I think that if the PreCQ builder had just started a little later, everything would have worked out okay.

Thanks, but I'm still a bit confused. These two changes depended on each other, which I thought meant they're atomically committed (to the extent that that's possible when multiple repositories are involved).

The "Change has been successfully pushed" messages came in 16 seconds apart (10:36:38 vs. 10:36:54). Is it possible for syncs, pre-CQ runs, etc. to pick up a partial set of all the changes that went in in a single CQ run? Are the exact guarantees that CQ-DEPEND makes documented anywhere? https://www.chromium.org/developers/tree-sheriffs/sheriff-details-chromium-os/commit-queue-overview says "Atomic transactions are supported."

Oh, I was assuming that the two CLs the PreCQ was testing:

kernel | gwendal | 452705
kernel | gwendal | 453287

(neither of which contains a dependency on your CLs) actually depended on your CLs.

If that's not the case, then yes. Your CLs did cause the breakage, but you did nothing wrong.

Gerrit supports atomic submits in the same git repository, but not between git repositories. Your two CLs (and the accompanying auto-generated overlay uprev) are in different git repositories.

The PreCQ build must have caught the bad window. Note, until about a year ago, that window was commonly much bigger (worst case could be around 45 minutes), but phobbs@ worked with the GoB team and revised the submission process to use git push, which sped things up a lot, and allowed atomicity inside a git repository.

There is a strong desire from many teams for atomic commits across repositories. GoB has considered it, and may eventually come up with a solution. If they do, we'll take advantage.

Should we update the Sheriff docs?

Thanks for the details!

I've changed it to the following: "Atomic transactions within a single repository are supported. If changes across multiple repositories depend on each other, there is a small window where syncs may pull a partial set of the dependent changes."

Feel free to make "a small window" more precise. :-)

I can't really, it mostly depends on how many git repos contain a submission, and how GoB is feeling that day.