Comment 4 for bug 1852502

Dropping in some notes on voice and chat conversations so that they don't get lost down the line:

- We are working on migrating to Mongo 4 in the Juju 3.0 release. Per upstream, Mongo 4 probably doesn't have this issue.

- For Mongo 3, upstream has recommended that we "Consider using a TTL index to limit data size instead of a capped collection". We can look into that option if we aren't able to do the mongo upgrade for some reason.

- There do not seem to be workarounds in the meantime, other than doing the mongodb dump separately, without the collection that's causing trouble. Everything *should* work when you restore this mongodb to a fresh controller, but you won't be able to use the Juju backup tools in order to orchestrate, and we're not 100% certain that there won't be ill effects from losing the collection.