High memory issue with RuleTerminalNodeLeftTuple objects occupying most of heap space in Drools 6

Issue

• User faces memory issues while firing rules with 1000 facts (e.g. of type Cheese) in Red Hat JBoss BRMS 6.x . Take an example of the following rule.

rule "CheeseFilter"
when
 $cheese1:Cheese(type == "Soft")
 $cheese2:Cheese(type == "Unprocessed")
eval(compareCheese($cheese1,$cheese2)
then
end

The problem is that it has been observed in some scenarios, when there are more than 1000 number of facts inserted into WorkingMemory , the number of EvalNodeLeftTuple is huge, even though the rules were already fired. Here is how the Heap space histogram looks like after rule was fired.

num     #instances         #bytes  class name
----------------------------------------------
   1:      56636683     6330108496  org.drools.core.reteoo.EvalNodeLeftTuple
   2:       1987952      191283392  org.drools.core.reteoo.FromNodeLeftTuple
   3:       1819342       92748416  java.util.HashMap
   4:       2748121       85519872  java.util.HashMap$Node
...

Since the use of eval() method is discouraged due to similar issues, the same rule has been updated to check if that makes any difference.

rule "CheeseFilterNoEval"
when
 $cheese1:Cheese(type == "Soft")
 $cheese2:Cheese(type == "Unprocessed",compareCheese($cheese1,$cheese2))
then
end

However this time the Heap memory histogram was now showing majority of objects occupying the space was of RuleTerminalNodeLeftTuple . To be precise, now the EvalNodeLeftTuple has now been replaced by RuleTerminalNodeLeftTuple and the memory size was increased.

num     #instances         #bytes  class name
----------------------------------------------
   1:      51540200     7776910400  org.drools.core.reteoo.RuleTerminalNodeLeftTuple
   2:       2130648      184982208  org.drools.core.reteoo.FromNodeLeftTuple
   3:       1814433       92512784  java.util.HashMap
   4:       2889611       89847552  java.util.HashMap$Node
...

• What purpose has RuleTerminalNodeLeftTuple ?
• Why is it seen with so many instances occupying so much of Heap memory , occespecially when the rule has been fired already?
• How to reduce the memory size occupied by the RuleTerminalNodeLeftTuple instances?