Comment 1 for bug 1749350

The original issue was determined to not be caused by this, and the code in question is layered in such a way to make it very difficult to change this behavior. Users who might be affected by this can set the oplog size to their desired size directly in agent.conf with MONGO_OPLOG_SIZE.
Unfortunately, we don't seem to expose this as ControllerConfig, so admins can't set it at bootstrap or controller it from the juju client.