Comment 10 for bug 1696739

With the presence pinger, it does this:

 session := p.pings.Database.Session.Copy()
 defer session.Close()

 pings := p.pings.With(session)
 _, err = pings.UpsertId(...)

That *appears* to want to regularly cause a sasl login.

The lease client does this:

 collection, closer := client.config.Mongo.GetCollection(client.config.Collection)
 defer closer()
 entries, err := client.readEntries(collection)

which ultimately uses a state.database struct and that doesn't appear to copy a session; it just does a mgo.Database.C("collname")

So if we optimise presence pings, that may help.