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Need clarification on DataChange Notification behavior
May 6, 2019
12:20, EEST
Forum Posts: 12
Member Since:
December 6, 2018
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Hi Experts,

While testing the behavior of dataChange notifications by using prosys simulation server and prosys opc ua client I have noticed that if I set the publishing interval of subscription settings to 1000 ms and sampling interval of monitoredDataItem to 20000ms and queue size to 1 with discard oldest to true, I’m getting messages/notifications on each second which basically seems like it is not honoring the sampling interval at all .

As per my understanding from documentation(correct me if I’m wrong) sampling interval specifies the polling interval on which server samples the data from source and pushes it to queue and finally on publish interval flushes the queue and deliver the notifications to the client. Now as per the above scenario , since the polling or sampling interval in 20000 server should poll on that interval and because of which we should not get any updates or notifications during the time gap of the sampling and publish interval.

Kindly help me clear the above doubt.
Thanks in advance.Smile


May 6, 2019
14:27, EEST
Bjarne Boström
Forum Posts: 382
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April 3, 2012
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Your observation is correct. To put it shortly we don’t yet support that scenario very well in our SDK. The plan is to eventually support that, but it requires some internal changes to do actual sampling that way. I can go into more SDK details if needed, but basically in the typical scenario we (only) simulate sampling whenever new values are detected on the UaNodes, which is the case with SimulationServer.

Do you have a use-case, in which it would be useful and simply using a larger publishinginterval wouldn’t work?

It is doable, see the MyBigNodeManager SDK sample, assuming you manually limit MonitoredDataItems by your code to only get updates on the sampling rate. However it is a bit more lower-level API to work with.

May 6, 2019
15:26, EEST
Forum Posts: 12
Member Since:
December 6, 2018
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Thanks Bjarne for the response. It was very helpful. Smile
Currently we don’t have such scenario. Came to this scenario while testing our prosys opc ua compliant product for different possibilities.

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