Hi,

I am investigating performance of a Drools 5.4 stateful knowledge session. This session has about 200 rules, 200k facts and takes about 1 hour to run to completion. Looking at the profile there is a hotspot that consumes almost 65% of the cpu time: java.util.AbstractList.hashCode().

Here is the full stack: 

   com.company.rules.engine.Rule_Set_weights_08b44ce519a74b58ab3f85735b2987cbDefaultConsequenceInvoker.evaluate(KnowledgeHelper, WorkingMemory)

   com.company.rules.engine.Rule_Set_weights_08b44ce519a74b58ab3f85735b2987cbDefaultConsequenceInvokerGenerated.evaluate(KnowledgeHelper, WorkingMemory)

   com.company.rules.engine.Rule_Set_weights_08b44ce519a74b58ab3f85735b2987cb.defaultConsequence(KnowledgeHelper, List, FactHandle, GradingFact, FactHandle, ReportNode, FactHandle, WeightsHolder, FactHandle, Logger)

   org.drools.base.DefaultKnowledgeHelper.update(FactHandle, long)

   org.drools.common.NamedEntryPoint.update(FactHandle, Object, long, Activation)

   org.drools.common.NamedEntryPoint.update(FactHandle, Object, long, Activation)

   org.drools.common.PropagationContextImpl.evaluateActionQueue(InternalWorkingMemory)

   org.drools.reteoo.ReteooWorkingMemory$EvaluateResultConstraints.execute(InternalWorkingMemory)

   org.drools.reteoo.AccumulateNode.evaluateResultConstraints(AccumulateNode$ActivitySource, LeftTuple, PropagationContext, InternalWorkingMemory, AccumulateNode$AccumulateMemory, AccumulateNode$AccumulateContext, boolean)

   org.drools.common.DefaultFactHandle.setObject(Object)

   java.util.AbstractList.hashCode()

I believe the following clues can be extracted:

- "Rule_Set_weights" was fired and a fact was modified (confirmed by examining the rule definition)

- The fact modification caused the pre-conditions for other rules to be computed.

- One of these rules has an accumulate condition that accumulates into an AbstractList.

- This list is very very large. So large that looping through the elements in the list and aggregating the hashCode of individual elements dominates execution time (the individual element hashCode doesn't even show up in the profile… either its very fast or maybe its identify hashCode which the profiler might filter?). 

- Accumulate is either working on a large set of data or the same accumulate is evaluated many many times.  

Is my analysis correct? Are there clues that I am missing? 

I have 15 rules that use accumulate… However none accumulate with a result of List. Most accumulate using sum() and count() (result of Number). A few use collectSet(). A few more aggregate into a result with a custom type.

A few other notes: 

- All accumulate conditions are the last condition in the WHEN clause. 

- I use agenda groups to separate fact processing into phases. Rules that accumulate are in a separate agenda group from rules that modify/insert facts that are used in accumulation. I hope this prevents the accumulate condition from being evaluated until all the rules that modify the facts accumulate needs are done firing. I suspect this may not be working as I expect. I haven't put together an example to investigate. 

- When accumulating into a set, the rule condition looks like this:

    $factName : Set() from accumulate( FactMatch( $field : field ), collectionSet( $field ) )

How can I narrow down this further? 

Are there any general rules to follow to optimize use of accumulate in conditions? 

Thanks,

Ryan