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Subscriptions and Reads/Writes creating separate connections to the OPC Server

13 May 2015 18:38 #3136 by support
I can confirm this behavior. Although it "kind of" works, it is a bug; I wonder how it could go unnoticed.

Will fix; I will send you an email with more information.

Best regards

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13 May 2015 13:26 #3135 by cdunlap

Thank you for the help.

It is actually 2 separate connections to the server, not just 2 separate groups.

In the OPC Analyzer trace, I see two calls to CoCreateInstance before any Release is called. I have attached the trace so you can take a look and give your input. Please ignore the first few lines, as they were done before the behavior happened. You can start looking at time 08:36:42.532.

The trace is interacting with a custom OPC Server we developed, but I have also seen this occur when connecting to a TOP Server, and could see the server's UI that displays the number of clients increase by two.

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12 May 2015 18:59 #3130 by support

do you mean truly two connections (technically, that would be two OPCServer objects), or just two OPC groups under the same connection/OPCServer object?

The expected behavior (under the default settings) would be one connection/OPCServer, and one or two OPCGroup-s beneath it.

If this is not what is happening that I would have to investigate. Please let me know.

Best regards

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12 May 2015 14:39 #3129 by cdunlap

I am using build 5.33.1152.1 and have a question about the internal optimizations that are going on regarding connecting to the OPC Server.

I have noticed that if I have a subscription to a tag and then perform a read or write operation (of the same tag), there will be 2 separate client connections to the OPC Server. If I do all subscriptions, or all read/writes (of different tags), I seem to only have 1 connection to the OPC Server.

I have tried this using the Demo .NET application and saw these results as well. I have used multiple servers and saw the behavior by using the OPC Analyzer to see multiple connections being created. Some of the servers also had diagnostics that proved that more than one connection was being made.

Can you give some input on the benefit of this or if it is expected?

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