Sounds like, maybe, your .Net connections are being duplicated without waiting for the old connection to be torn down. When this kind of thing happens, you should still be able to get in as a superuser. Once in, have you checked pg_stat_activity? Between that and process list you ought to see if you've got old, dead connections taking up valuable connection space. --
I'm having strange problem with one of our PG servers.
We're running legacy application (written in .NET) on several servers, it creates large number of connections to a PG cluster (9.3.10), running on CentOS 6. Lately the app team changed the deployment strategy in a way, that in peaks it generated almost twice as much connections as before.
Strange thing is, that the connections filled all the way up to max_connections and started to block the new connections with:
It surprised me, that it didn't kept the reserved connections for the superuser, as the application user is not superuser (got the Create DB though). So I couldn't connect to the server to find out, what is going on. I have verified that no superuser connections were on the server running in that time.
In the process list majority of processes was in "authentication" state and they were not shown in the numbackends of the pg_stat_database view (collectd have had connections already established, so metrics were gathered)