plan - the OperatorPlan to look for matches to the pattern
A list of all matched sub-plans. The returned plans are
partial views of the original OperatorPlan. Each is a
sub-set of the original plan and represents the same
topology as the pattern, but operators in the returned plan
are the same objects as the original plan. Therefore,
a call getPlan() from any node in the return plan would
return the original plan.