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Fix the execution of Drools rules when using streaming (CEP, Temporal Reasoning)

Description

Normally, the event processing mode defaults to cloud. This works when using a "discrete" triggering method (i.e. for example, trigger the execution of the rules when an OpenNMS events comes in).

In order to use built-in feature of Drools to advanced and complex event processing (i.e. Drools Fusion, CEP, Temporal Reasoning), you have to use stream for the event processing mode. Then, instead of calling fireAllRules to trigger the execution of the rules, it is advised to have a dedicated thread that runs fireUnitHalt.

This thread will be running until the halt method is called from the session. In theory, as the session lives while OpenNMS is running there is no need to call it (for the same reason we don't need to call dispose). These methods are useful if we want, for example, persist the current state of the working memory on disk.

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Alejandro Galue March 8, 2017 at 11:31 AM

The PR was merged into foundation-2017, and I manually ported the solution to foundation-2016.

Alejandro Galue March 2, 2017 at 10:24 AM

I was able to verify that the solution works for foundation-2016, the problem is that the patch has to be a little bit different. So, after merging the PR, I can cherry-pick it on that branch and manually fix it to make it work.

Alejandro Galue March 1, 2017 at 3:37 PM

Alejandro Galue March 1, 2017 at 3:31 PM
Edited

Here is a good reading about the internals for firing rules:

http://blog.athico.com/2015/12/drools-detailed-description-of-internal.html

An example of how to use Drools Fusion:

http://planet.jboss.org/post/getting_started_with_drools_fusion

Alejandro Galue March 1, 2017 at 3:25 PM

Note: In theory, this solution can be ported to older versions of Meridian, but instead of keeping an instance of the WorkingMemory, we need an instance of the Session. I'm not sure if this is possible with Drools 6.0.1 (for Meridian 2016), and Drools 5.x (for Meridian 2015); but if it is possible, then we can use the solution for 19 (which already has a reference to the session inside the DroolsCorrelationEngine).

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PagerDuty

Created March 1, 2017 at 3:23 PM
Updated March 8, 2017 at 4:11 PM
Resolved March 8, 2017 at 11:31 AM