Best practises and troubleshooting

CEP statements and Esper scripts

Symptom: Your event processing rules are disabled automatically

Cumulocity monitors the memory usage and workload generated by event processing rules, as well as any errors that are occurring while running those rules. If an event processing rule consumes too much memory or generates too many errors, Cumulocity automatically disables this rule.

Troubleshoot from having rules disabled due to memory consumption:

Make sure that your event processing rules do not keep too many events in windows. For example, if you use “win:keepall()” and many events enter the rule, it will be disabled within a short time. Instead of using “win:keepall()“, try using statements such as “std:lastevent()” that consumes less memory.

Troubleshoot from getting disabled due to too high amount of errors:

Monitor the amount of statements for errors. To see errors you will need to read through the details. In case of an error, correct the statement. An example of a wrong statement: “insert into UpdateAlarm select “CLEARED” as status from…” is regarded as an error statement. An example of a corrected statement is: “insert into UpdateAlarm select “10201” as ID, “CLEARED” as status from…”

Naming statements

The @Name annotation gives you the possibility to name your statements in the module. A name needs to be unique within a single module. This will have a direct effect on the channels in the realtime notifications. It will also help to debug the module in administration UI because the channel name (and therefore the statement name) is printed in the list. If you do not name a statement it will automatically be named “statement_{number of statement}“.

Using device contexts

If you need a device context, it is usually not necessary to put every statement into context. If you use aggregation of measurements most of the time you only need the context in the statement that executes the actual aggregation. It is a useful concept to develop the module completely without the context first and add it at the end to those statements where the context applies.

Splitting modules

If your module gets really big it might be helpful to split it into multiple modules. If you declare schematas or functions they will be available in all modules of your tenant. A good approach can be:

Keep in mind that this will create dependencies within the modules (e.g. module 2 needs a schema defined in module 1). You must avoid circular dependencies.

Number formats

When interacting with measurements the values will be in BigDecimal (if you use getNumber()). When calculating with BigDecimal there will be an error if the result is a repeating decimal. This will result into a null return from built-in functions like avg(). There are two ways to prevent this issue:

  1. If you are using built-in functions the easiest way is to cast the BigDecimal to a double value

    avg(cast(getNumber(e, “c8y_TemperatureMeasurement.T.value”), double))

  2. If you are calculating yourself (e.g. in a expression) make sure to round or cut the number if you want to stay with BigDecimal.

    getNumber(e, “c8y_TemperatureMeasurement.T.value”).divide(new BigDecimal(3), 5, RoundingMode.HALF_UP)