Queue size for opc-ua client items subscription

For ignition tag exposed with the ignition opc ua server, opc-ua client subscribe items with parameters:

  • Subscription Rate
  • Revised Rate (= sampling rate ?)

Those information are available on gateway wab page server statistics.

But we don’t see the value of the “Queue size” parameters.

Ignition opc-ua server support this parameter provided by the client or this parameter is forced to 1 ?

The queue size Ignition’s UA client uses is not configurable. This is something we’re hoping to change in 7.9.

So the Queue size is 1 in 7.8.2 ?

Yes, I believe it’s been 1 in every version.

On an 8.1.7 Ignition version, would it be possible to set the “Queue” property to, for example, 10 to obtain the 10 last events that appeared in between 2 refreshes of the tag? Or is your previous answer from 2016 still relevant?

Yes, but it’s not between refreshes of the tag, it’s between publish intervals for the OPC UA subscription. You need to set it appropriately in combination with the Sampling Interval (Tag Group rate) and the Publishing Interval.

For example… Tag Group (Sampling Interval) = 1s, Publishing Interval = 10s, Queue Size = 10, you could possibly have 10 different sampled values all queued published together every 10s.

OPC UA subscriptions “execute” periodically at their Publishing Interval, sending any queued data change notifications for any Monitored Items belonging to the Subscription to the client at that time.

Actually I am developing an OPC-UA driver based on the SDK example, I noticed that some datavalue changes are much too fast. Consequently IGN is not to be notified of all value changes (valueChanged tag).
From what I understand, it would be possible to solve this problem by adjusting the publish interval and the queue size.
Or my problem would only come from using a java “ConcurrentMap” (as in the ValueSimulator example) as a reference for the tag’s dataValue.
“node.getFilterChain (). addLast (AttributeFilters.getValue …”