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6.4. Event processing modes in the decision engine

The decision engine runs in either cloud mode or stream mode. In cloud mode, the decision engine processes facts as facts with no temporal constraints, independent of time, and in no particular order. In stream mode, the decision engine processes facts as events with strong temporal constraints, in real time or near real time. Stream mode uses synchronization to make event processing possible in Red Hat Decision Manager.

Cloud mode

Cloud mode is the default operating mode of the decision engine. In cloud mode, the decision engine treats events as an unordered cloud. Events still have time stamps, but the decision engine running in cloud mode cannot draw relevance from the time stamp because cloud mode ignores the present time. This mode uses the rule constraints to find the matching tuples to activate and execute rules.

Cloud mode does not impose any kind of additional requirements on facts. However, because the decision engine in this mode has no concept of time, it cannot use temporal features such as sliding windows or automatic life-cycle management. In cloud mode, events must be explicitly retracted when they are no longer needed.

The following requirements are not imposed in cloud mode:

  • No clock synchronization because the decision engine has no notion of time
  • No ordering of events because the decision engine processes events as an unordered cloud, against which the decision engine match rules

You can specify cloud mode either by setting the system property in the relevant configuration files or by using the Java client API:

Set cloud mode using system property

drools.eventProcessingMode=cloud

Set cloud mode using Java client API

import org.kie.api.conf.EventProcessingOption;
import org.kie.api.KieBaseConfiguration;
import org.kie.api.KieServices.Factory;

KieBaseConfiguration config = KieServices.Factory.get().newKieBaseConfiguration();

config.setOption(EventProcessingOption.CLOUD);

You can also specify cloud mode using the eventProcessingMode="<mode>" KIE base attribute in the KIE module descriptor file (kmodule.xml) for a specific Red Hat Decision Manager project:

Set cloud mode using project kmodule.xml file

<kmodule>
  ...
  <kbase name="KBase2" default="false" eventProcessingMode="cloud" packages="org.domain.pkg2, org.domain.pkg3" includes="KBase1">
    ...
  </kbase>
  ...
</kmodule>

Stream mode

Stream mode enables the decision engine to process events chronologically and in real time as they are inserted into the decision engine. In stream mode, the decision engine synchronizes streams of events (so that events in different streams can be processed in chronological order), implements sliding windows of time or length, and enables automatic life-cycle management.

The following requirements apply to stream mode:

  • Events in each stream must be ordered chronologically.
  • A session clock must be present to synchronize event streams.
注記

Your application does not need to enforce ordering events between streams, but using event streams that have not been synchronized may cause unexpected results.

You can specify stream mode either by setting the system property in the relevant configuration files or by using the Java client API:

Set stream mode using system property

drools.eventProcessingMode=stream

Set stream mode using Java client API

import org.kie.api.conf.EventProcessingOption;
import org.kie.api.KieBaseConfiguration;
import org.kie.api.KieServices.Factory;

KieBaseConfiguration config = KieServices.Factory.get().newKieBaseConfiguration();

config.setOption(EventProcessingOption.STREAM);

You can also specify stream mode using the eventProcessingMode="<mode>" KIE base attribute in the KIE module descriptor file (kmodule.xml) for a specific Red Hat Decision Manager project:

Set stream mode using project kmodule.xml file

<kmodule>
  ...
  <kbase name="KBase2" default="false" eventProcessingMode="stream" packages="org.domain.pkg2, org.domain.pkg3" includes="KBase1">
    ...
  </kbase>
  ...
</kmodule>

6.4.1. Negative patterns in decision engine stream mode
リンクのコピー

A negative pattern is a pattern for conditions that are not met. For example, the following DRL rule activates a fire alarm if a fire is detected and the sprinkler is not activated:

Fire alarm rule with a negative pattern

rule "Sound the alarm"
when
  $f : FireDetected()
  not(SprinklerActivated())
then
  // Sound the alarm.
end

In cloud mode, the decision engine assumes all facts (regular facts and events) are known in advance and evaluates negative patterns immediately. In stream mode, the decision engine can support temporal constraints on facts to wait for a set time before activating a rule.

The same example rule in stream mode activates the fire alarm as usual, but applies a 10-second delay.

Fire alarm rule with a negative pattern and time delay (stream mode only)

rule "Sound the alarm"
when
  $f : FireDetected()
  not(SprinklerActivated(this after[0s,10s] $f))
then
  // Sound the alarm.
end

The following modified fire alarm rule expects one Heartbeat event to occur every 10 seconds. If the expected event does not occur, the rule is executed. This rule uses the same type of object in both the first pattern and in the negative pattern. The negative pattern has the temporal constraint to wait 0 to 10 seconds before executing and excludes the Heartbeat event bound to $h so that the rule can be executed. The bound event $h must be explicitly excluded in order for the rule to be executed because the temporal constraint [0s, …​] does not inherently exclude that event from being matched again.

Fire alarm rule excluding a bound event in a negative pattern (stream mode only)

rule "Sound the alarm"
when
  $h: Heartbeat() from entry-point "MonitoringStream"
  not(Heartbeat(this != $h, this after[0s,10s] $h) from entry-point "MonitoringStream")
then
  // Sound the alarm.
end

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