Problem: mod-circulation and mod-pubsub when performing timer events "age-to-lost" types introduces a socket leak.
wayne reported 2500 sockets in use between mod-pubsub and Okapi. And 1000 sockets in use between okapi and mod-authtoken (there's a limit of 1000 in Okapi). 2500 is a limit in mod-pubsub likely.
This is probably in issue an mod-circulation, but could also be mod-pubsub.
In order to remedy the situation, Okapi is restarted (which will close all sockets).