Publishing interval in performance view document

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bhavanca
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Publishing interval in performance view document

Post by bhavanca »

Hello,

I am trying to performance test our OPCUA server. I am using the "Performance View" document . Particularly I am testing the subscription service. On performance view, for a subscribe configuration, I set sampling interval=10ms, Publshing interval=10ms and Queue size=0.

When I start test, in the Log, it shows "UaSession::create Subscription():Revised Publishinginterval = 100". The resulting subscribe graph also shows Time per call(ms) mostly around 100ms.

(Note - The node I am monitoring has been configured with MinimumSamplingInterval = 1ms in the server)

I need help understanding the reason why the Publishing interval is being revised to 100ms.
Is there a setting I need to change to allow publishing interval of say 10ms?
Also may I know what is the minimum publishing interval supported by UA EXpert?

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Support Team
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Re: Publishing interval in performance view document

Post by Support Team »

Hi,

the UA Client (in this case UaExpert) is *requesting* a sampling and a publishing interval, and the server is responding to that with the *revised* sampling and and *revised* publishing interval. The UA technology allowes to do "fast" sampling (and putting the data into a queue) and "slow" publishing. The idear is to allow you to monitor very quick and fast moving signals, but not overloading the bandwith of the communication, by sending bigger blocks of data (the queue) at a slower rate over the wire. Whereas the sampling is the speed the server is collecting the data from the source, and whereas publishing is the speed the server is going to send the (queue) of data over the wire.

If you configure the Node with 1ms sampling (and the server has confirmed by revising same) you MUST configure a queue of 100 values to not loose any data, because you already KNOW that the server has revised a publish interval of 100ms. However, if you configure a queue of "1" instead, you decided to NOT being interested in all the values. From a client perspective there is NO WAY to go below revised publish rate of a server (except you re-program the server-side), however typically the server developer already has considered what performance he wants to achieve (and how much he wants to protect against obtrusive client). So the basic question is not how to tweak the revised publish rate, the question is how many nodes can you put into your subscription, to find the turning point where the server can not deliver the requested amount within the revised 100ms anymore.

If you just want to find out how fast the server can deliver the data, you could use the "read" functionality (including the max-age parameter to decide reading from cache or from source). The Performance View of UaExpert has the ability to "Read" or to "Register" first and Read thereafter, which gives you the maximum performance.
Best regards
Unified Automation Support Team

bhavanca
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Re: Publishing interval in performance view document

Post by bhavanca »

Hello,

Thanks for the prompt response and thank you for the detailed explanation. I understand it much better now.

Kind Regards

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