One of our dovecot backend servers ran into a problem with it's auth process a few days ago. This doesn't appear to be the error logged when dovecot hits its internal limit so I'm not sure what is going on here.
auth: Error: malloc: 58012: Cannot allocate memory auth: Error: Unable to allocate memory for mutexes from the region auth: Error: PANIC: Cannot allocate memory auth: passwd(test,1.1.1.1,<8HTlNHzNIQBAjhKC>): unknown user pop3: Error: Authenticated user not found from userdb, auth lookup +id=2509111297 (client-pid=4781 client-id=1) pop3-login: Internal login failure (pid=4781 id=1) (internal failure, 1 +succesful auths): user=<test>...
There was at least 10+GB free RAM on the server and no indication of a system level issue at the same time. The server is running 2.1.9. There were about 3,200 active sessions, with something like 12 new sessions/sec. The other identical servers are/were handling virtually identical load with the same service uptime and haven't had any issues so far. (Crash happened 7 days ago.)
-- Kelsey Cummings - kgc@corp.sonic.net sonic.net, inc. System Architect 2260 Apollo Way 707.522.1000 Santa Rosa, CA 95407