Hi Helmut,
Thank you very much for the helpful reply. Indeed it is OpenVZ which is the limiting factor. I'm limited to 1360 tcp sockets. Here are the entries from /proc/user_beancounters where failcnt > 0 (the last column):
numtcpsock 1277 1360 1360 1360 99386 tcprcvbuf 9230648 11782776 11720320 12703360 687422 lockedpages 3 4096 4096 4096 47122
Long term, i'll provide use a different provider (with KVM). Short term i'm trying out different options to migitate the problem:
ConstrainedSockets 1
Next up, I'm thinking of reducing the TCP timeout value, or similar.
Greetings, David