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Random Disconnect from OPC server

05 Mar 2019 10:34 #7165 by Olya
Hi again.

Yes, we use subscriptions also.

Yesterday we managed to reproduce this issue inside the small standalone console application by adding subscriptions and more threads to it.
It is not reproducible in 100% of cases, just sometimes :) and here it does not crash inside the ReadMultipleItems method but still not able to reconnect after being out of network for more than 10 minutes.

Normally our main application does not use so many threads for opc pulling (we were able to reproduce it with just two threads for pulling and one for subscription) but it uses a lot of threads for other tasks.

Attached is the c# code for the console application and the xml document with Matrikon OPC simulation server namespace configuration that we are using.
You can get the server itself here : .
I hope this is helpful.

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03 Mar 2019 06:01 #7157 by admin

In principle, we need a scenario in which we can reproduce the issue on our side, in order to be able to diagnose it. What you have described, however, does not really differ from the tests that we have already performed.

Question: Is your application also using subscriptions?


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02 Mar 2019 22:48 #7156 by Olya
Recently we also encountered a very similar problem. Our company is using OpcLabs.EasyOpcClassic EasyDAClient (version 5.54.453.1) inside WCF service application written in c#.
It is also using ReadMultipleItems method inside some timer from multiple threads and in some cases, after receiving errors it is not able to reconnect again and data flow stops.
The first time we spotted this issue on one of our production servers and we are not sure what was the status of the OPC server when this happened. After this, we tried to reproduce it in our test environment. In our case, it usually happens after we lose the connection between client and server for more than ~5 min and it is much easier to reproduce when the OPC is on the remote machine (we tried to physically disconnect the machine from the network). But in some cases much more rear it happens when the client and the server are both on the same machine (we tried to stop OPC server abruptly).
The symptoms are next:

- after disconnecting from the network we are receiving some errors (usually "The RPC server is unavailable. ") which looks OK;

- then we connect to the network again (after 5-10min) and receive an error again (but in this case timeout for the first call seems to be a little longer);

- then we receive a few more errors.(usually: Read not completed. This error indicates that it could not be verified that the requested read operation was completed during the timeout period. It is possible that the read operation will actually succeed or fail, but later. Increase the timeout period if you want to obtain positive or negative indication of the operation outcome. Other reason for this error may be that under heavy loads, topic request or response queue is overflowing. Check the event log for queue overflow errors (if event logging is supported by the product and enabled).
+ The client method called was 'ReadMultipleItems'.ultipleItems'

- then after some time system doesn't return control from the ReadMultipleItems method;

We also tried to connect with different applications (using EasyDAClient and other OPC clients) while getting this errors from our main application and were able to connect succesfully.
It may be worth to mention that we also have created very small application that does the same job related to EasyDAClient but uses much less resorces, only 3 threads, and with less aggressive garbage collecting and on this application we were not able to reproduce the issue in the same environment.

It is really important for our company to make it work ASAP. Please advice how can we troubleshoot the issue if possible.

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