Dist connection problem

[sanikval]

Hi,

we had the following problem:

Within a few days time between dist-systems 14 and 15 was not synchronized, and system 14 repeated attempts to connect.
One of the attempts failed with connection error "Operation would block (10035)" and system 15 lost all dist connections.

Log from system 15:
...
WCCILdist (1), 2019.10.20 17:46:58.461, SYS, INFO, 39, Connection lost, MAN: (SYS: 14 Dist -num 1 CONN: 2), Connection closed
WCCILdist (1), 2019.10.20 17:47:19.435, SYS, INFO, 4, Connected to (SYS: 14 Dist -num 1 CONN: 2) @ HOSTNAME (IPADDR)
WCCILdist (1), 2019.10.20 17:47:19.444, SYS, INFO, 39, Connection lost, MAN: (SYS: 14 Dist -num 1 CONN: 2), Connection closed
WCCILdist (1), 2019.10.20 17:47:39.550, SYS, INFO, 4, Connected to (SYS: 14 Dist -num 1 CONN: 2) @ HOSTNAME (IPADDR)
WCCILdist (1), 2019.10.20 17:47:39.560, SYS, INFO, 39, Connection lost, MAN: (SYS: 14 Dist -num 1 CONN: 2), Connection closed
WCCILdist (1), 2019.10.20 17:48:00.534, SYS, INFO, 4, Connected to (SYS: 14 Dist -num 1 CONN: 2) @ HOSTNAME (IPADDR)
WCCILdist (1), 2019.10.20 17:48:00.543, SYS, INFO, 39, Connection lost, MAN: (SYS: 14 Dist -num 1 CONN: 2), Connection closed
WCCILdist (1), 2019.10.20 17:48:20.638, SYS, SEVERE, 63, Connection error, MAN: (SYS: 15 Dist -num 1 CONN: 2), Operation would block (10035)
WCCILdist (1), 2019.10.20 17:48:20.638, SYS, SEVERE, 54, Unexpected state, PeerItcIOHandler, exceptionRaised, Exception raised for (SYS: 11 Dist -num 1 CONN: 1)
WCCILdist (1), 2019.10.20 17:48:20.638, SYS, SEVERE, 54, Unexpected state, PeerItcIOHandler, exceptionRaised, Exception raised for (SYS: 11 Dist -num 1 CONN: 1)
WCCILdist (1), 2019.10.20 17:48:20.639, SYS, SEVERE, 54, Unexpected state, PeerItcIOHandler, exceptionRaised, Exception raised for (SYS: 13 Dist -num 1 CONN: 1)
WCCILdist (1), 2019.10.20 17:48:20.639, SYS, SEVERE, 54, Unexpected state, PeerItcIOHandler, exceptionRaised, Exception raised for (SYS: 14 Dist -num 1 CONN: 1)
WCCILdist (1), 2019.10.20 17:48:20.639, SYS, SEVERE, 54, Unexpected state, PeerItcIOHandler, exceptionRaised, Exception raised for (SYS: 11 Dist -num 1 CONN: 2)
WCCILdist (1), 2019.10.20 17:48:20.639, SYS, SEVERE, 54, Unexpected state, PeerItcIOHandler, exceptionRaised, Exception raised for (SYS: 16 Dist -num 1 CONN: 1)
WCCILdist (1), 2019.10.20 17:48:20.640, SYS, SEVERE, 54, Unexpected state, PeerItcIOHandler, exceptionRaised, Exception raised for (SYS: 12 Dist -num 1 CONN: 2)
WCCILdist (1), 2019.10.20 17:48:20.640, SYS, SEVERE, 54, Unexpected state, PeerItcIOHandler, exceptionRaised, Exception raised for (SYS: 14 Dist -num 1 CONN: 1)
WCCILdist (1), 2019.10.20 17:48:20.640, SYS, SEVERE, 54, Unexpected state, PeerItcIOHandler, exceptionRaised, Exception raised for (SYS: 11 Dist -num 1 CONN: 2)
WCCILdist (1), 2019.10.20 17:48:20.640, SYS, SEVERE, 54, Unexpected state, PeerItcIOHandler, exceptionRaised, Exception raised for (SYS: 12 Dist -num 1 CONN: 2)
WCCILdist (1), 2019.10.20 17:48:20.641, SYS, SEVERE, 54, Unexpected state, PeerItcIOHandler, exceptionRaised, Exception raised for (SYS: 16 Dist -num 1 CONN: 1)
WCCILdist (1), 2019.10.20 17:48:20.641, SYS, SEVERE, 54, Unexpected state, PeerItcIOHandler, exceptionRaised, Exception raised for (SYS: 12 Dist -num 1 CONN: 1)
WCCILdist (1), 2019.10.20 17:48:20.641, SYS, SEVERE, 54, Unexpected state, PeerItcIOHandler, exceptionRaised, Exception raised for (SYS: 13 Dist -num 1 CONN: 1)
WCCILdist (1), 2019.10.20 17:48:20.641, SYS, SEVERE, 54, Unexpected state, PeerItcIOHandler, exceptionRaised, Exception raised for (SYS: 12 Dist -num 1 CONN: 1)
WCCILdist (1), 2019.10.20 17:48:20.642, SYS, SEVERE, 54, Unexpected state, PeerItcIOHandler, exceptionRaised, Exception raised for (SYS: 13 Dist -num 1 CONN: 2)

Connections was restored only after restarting dist manager on system 15.

Why could the error "Operation would block" have occurred?

[leoknipp]

The information "Operation would block (10035)" is a system error code provided by the operating system.
The Dist Manager just adds this information to the log message.

Which WinCC OA version + patch level are you using?

Best Regards
Leopold Knipp
Senior Support Specialist

[sanikval]

Thanks for the answer, we are using WinCC OA 3.15 patch 20.