Best practises and troubleshooting

EPL monitors

Symptom: Your event processing rules are disabled automatically

If a monitor throws an exception from onload or a listener and the exception is not caught, then the monitor will be terminated. Catch exceptions or avoid the reason for them occurring.

Similarly, if a monitor completes processing an event and has no listeners left active, then it cannot be triggered again, and will automatically remove itself.

Avoid excessive memory usage per monitor

Make sure that your event processing rules do not leak listeners. For example, when doing request-response operations, ensure that no listeners are left active after the response is processed, or if a timeout occurs and there is no response.

Number formats

Cumulocity measurements use the float type. Note that the timestamps are stored as floats (seconds since 1 Jan 1970, 00:00 UTC).

Subscribing to channels and contexts

A context is a parallel processing unit within Apama. Monitor instances can be deployed to multiple contexts using the spawn...to syntax. When subscribing to a channel, all monitor instances within a context will receive events for that subscription. So it is recommended practice to put different subscriptions in different contexts. The use of contexts can prevent part of the application being overloaded from affecting other parts of the application.

Contexts are created with a user-friendly name, and each individual instance of the context object corresponds to different contexts, even if they have the same name.

For example:

action onload() {
   context subContext := context("Worker");
   spawn worker() to subContext;
}
action worker() {
   monitor.subscribe(Measurement.CHANNEL);
   on all Measurement() as m {
      ...
   }
}  

Apama limitations in Cumulocity IoT

Using Apama within the Cumulocity IoT environment necessarily has some restrictions to the capabilities available when Apama is used standalone.

There are a number of ways that assets may be deployed to Apama within Cumulocity IoT and the restrictions vary according to those mechanisms:

When designing an Apama solution to be deployed within any form of Cumulocity IoT environment, consider the following points.

General Apama limitations when using Apama-epl or a custom microservice

Specific Apama limitations when using the Apama-epl application

All of these restrictions are implemented to ensure the smooth and secure operation of Apama applications within Cumulocity IoT.