How to merge your patch

[Ben Gamari]

tl;dr. Our beloved @marge-bot is behaving much more reliably now thanks
       to improvements in CI reliability and build batching. To merge
       an (accepted) merge request simply designate @marge-bot as its
       assignee. Marge will handle the rest. If things go awry let me
       know.


Hi everyone,

As you may have noticed, over the last weeks we have been feeling out
how best to leverage our new CI infrastructure, particularly when it
comes to merging patches.

As mentioned a few weeks ago, we have introduced a bot, Marge, to help
us work around some temporary limitations of GitLab's merge workflow.
Unfortunately, Marge had her own set of quirks which have taken a while
to sort out. In particular, fragile tests tended to result in repeated
merge attempts which tended to clog up CI, leading to an avalanche of
waiting, build failures, and general despair.

However, we have been working to improve this situation in three ways:

 * provisioning more builder capacity to reduce wait times

 * fixing or disabling fragile tests to reduce the need for retries

 * enable Marge's batched merge functionality, reducing the number of
   builds necessary per merged patch [1]

In light of this I just wanted to reiterate the previous guidance on
merging patches. If you have a merge request you would like to merge
simply do the following:

 1. make sure that it has at least one approval. This should
    happen in the course of code review but do ping if this was
    forgotten.

 2. assign the merge request to @marge-bot using the assignee field in
    the right-hand sidebar of the merge request page.

 3. next time Marge does a batch of merges she will fold in your MR
    (leaving a helpful comment to let you know) and, if the batch passes
    CI, merge it. If not she will leave a comment letting you know there
    was an issue. I will try to step in to sort out the mess when this
    happens.

Do let me know if you have any questions.

Cheers,

- Ben


[1] thanks to Matthew Pickering for picking this up
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