As far as I understand the bug that Jesus Garcia mentioned appears when the number of transactions started after sweeper begins to work is bigger than than sweep interval. But in this database users have to work few days for 20K transactions so I don't think that this is the case with my database. The gap of 300K transactions I thing is coming from an application that was not closed for more than 2 weeks and kept an active transaction. I'll send this problem to the software team to investigate.