Some (most) of the parameters mentioned above relate to Reads(&Writes), and only some relate to Subscriptions. It is my understanding that the customers is only interested in subscriptions. In such case, he can ignore the Slowdown/Speedup weights, abandonment intervals, automatic rates for read/write. We can get into their explanation but only if they are truly using explicit Reads a lot – let me know.
For Subscriptions, we are left mainly with these parameters:
- Percent deadband buckets/decade, Update rate deadband buckets/decade: These are meant to limit the number of OPC groups created in the server, in case that different percent deadband or update values are specified that are fairly close to each other. For example, it makes little sense to create 3 groups with update rates of 1000, 1001, 1002 milliseconds; and it makes little sense to create 3 group with percent deadband of 10.0%, 10.1% and 10.2%. The component therefore only creates OPC groups with certain update rates and percent deadband, and uses them even if the specified update rate or percent deadband is not precise. For example, with the above examples, we would only create a single OPC group with an update rate of 1000 milliseconds, and with a percent deadband of 10%, and all items will go into this group. The group parameters we choose are the “buckets” we put the items into. Saying that there are e.g. 6 buckets per decade means that there are six of them between 10 and 100 milliseconds, 6 of them between 100 and 1000 milliseconds, 6 of them between 1000 and 10000 milliseconds and so on – it is on a logarithmic scale. With 6 buckets per decade, the update rates for the possible buckets will be roughly 10, 15, 22, 33, 47, 68, then 100, 150, 220, 330, 470, 680, then 1000, 1500, 2200, 3300, 4700, 6800 milliseconds, and so on.
- The downside of the above approach is that you do not necessarily get what you have asked for. You may ask for update rate = 500 milliseconds, but we will use the bucket with 470 milliseconds update rate (we always choose the same or faster; similarly, for percent deadband, we always use the same or lower). If this behavior is not appropriate for the specific app, you can set ExactManualGroupMatch = true and the whole “bucketing” thing will be disabled (for explicit Subscriptions).
