1285259 - autoland causing too many conflicts

Status: RESOLVED WORKSFORME

(Conduit Graveyard :: Transplant, defect)

Description

[Dustin J. Mitchell [:dustin] (he/him)]

Just the examples I know of:

 * https://bugzilla.mozilla.org/show_bug.cgi?id=1284005#c10
 * https://bugzilla.mozilla.org/show_bug.cgi?id=1281004#c108
 * https://bugzilla.mozilla.org/show_bug.cgi?id=1284005#c18
 * https://bugzilla.mozilla.org/show_bug.cgi?id=1284005#c20

In each of these cases, a patch that had landed successfully and been successful in CI was later backed out due to mysterious "merge conflicts".  This never happened -- or at least so infrequently that I've never heard of it -- before the advent of the autoland repo.

The result is that patches take a lot more engineer time to re-land, and even after that they land days after they were intended to land, adding a significant lag to the development process.

Comment 1

[Gregory Szorc [:gps]]

Flagging me to provide a comment.

Comment 2

[Gregory Szorc [:gps]]

To summarize what I've said on the sheriffs email list as far as 2 weeks ago, we knew the autoland repo would likely cause more conflicts. However, I was surprised that the frequency was as high as it was.

To combat this, the sheriffs have started merging repos more frequently. The sheriffs have performed 4 merges in the past ~24 hours. This is up from ~1 merge per day. They reported no merge conflicts in that time period. Obviously a low sample size, but so far promising results.

The sheriffs and I agreed that we should treat the autoland repo as highest priority. It is the future. So the merge strategy is to merge autoland to central first. Then if autoland/central don't merge with inbound or fx-team cleanly, backouts are made in inbound/fx-team as necessary and the patch author needs to rebase.

Frequent merges or diverting landings to the autoland repo is the best way to prevent merge conflicts going forward.

If we're still experiencing merge conflicts with higher merge frequency, we'll consider changing the merge priority to favor inbound/fx-team and do backouts on autoland. However, at some point we need to adopt the future. So I'd prefer we stay the course and favor autoland.

At this time, I think we should see what things look like with 4+ merges a day. I'm optimistic that will help with merge conflicts. If it doesn't, we can revisit.

Comment 3

[Dustin J. Mitchell [:dustin] (he/him)]

I haven't had issues with this recently

Comment 4

[Mark Côté [:mcote]]

WORKSFORME is technically a better resolution since there was no fix specifically in here.