On green runs, the uncompressed size of the logs is over 49MB. This leaves us very little margin for error given a max size of 50MB. The reason I discovered this is that on timeouts, the attempt at screenshotting is putting us over the limit, causing truncation (and an unusable screenshot). To fix this, we can: 1) Chunk these tests 2) Cut down on what's printed in the logs 3) Increase the max log size Seems to me like the order of preference would be 2, 1, 3. I know that we've done #2 before for spammy tests for this exact reason.
As explained to ahal on IRC, this is going to become a blocker if not addressed soon. If we start hitting the limit on green runs, we'll have no way to know if a run is passing or failing and we'll have no choice but to hide this suite by default.
We may or may not want to block on bug 886570. Once structured logging in mochitest lands, it would be easy to just ignore subtest messages unless there is a failure. Otherwise we'd need to parse the logs and keep track of state to make it work. Not that that would be too complicated.. just ugly.
According to Ryan on irc, this has become more and more frequent. For short term I propose we just chunk the job while we figure out how to make the log smaller. The condition for closing this bug should be solving the problem properly and then moving the mochitests back into one chunk.
This was fixed awhile ago by bug 957768 and subsequently bug 937181.