Hello,

The maximum value for the MaxMonitoredItemsPerSubscription parameter is the maximum value of int (2147483647) so there are no other limits besides that.

What is a reasonable value for the parameter depends on the bigger picture of your solution. This includes factors such as hardware the Server is running on, how many Clients it is expected to be serving at the same time, how often the Values of the monitored Variables would be changing and how often these changes would be reported to Clients via DataChangeNotifications. If the Server is running on hardware with lots of computing power and it is serving only a few Clients at the same time, you could consider using a higher value for the MaxMonitoredItemsPerSubscription parameter. In the opposite situation, you could consider using a lower value for the parameter. You could also look at configuring MaxMonitoredItemsPerSubscription parameter from the point of view of Client applications connecting to your Server and set it to suit their needs.

Also, the default value of MaxMonitoredItemsPerSubscription was previously 1000, but it has been increased to 10000 since version 4.6.0 of the Prosys OPC UA SDK for Java. If you’re using an older version of the SDK, I would recommend updating to the latest version of the SDK, which at the moment is version 4.9.0.

We do not have any exact metrics on how increasing this parameter would affect the performance of the Server. Increasing it would allow Subscriptions to contain more MonitoredItems, which would effectively mean that methods that process all MonitoredItems of a Subscription would take longer to execute. How much longer processing more MonitoredItems would actually take depends on your hardware.