presto-main/src/main/java/io/prestosql/operator/WorkProcessorPipelineSourceOperator.java/WorkProcessorPipelineSourceOperator/workProcessorOperatorEntryMonitor
class WorkProcessorPipelineSourceOperator:    private void workProcessorOperatorEntryMonitor(int operatorIndex)
    {
        if (isLastOperator(operatorIndex)) {
            // this is the top operator so timer needs to be reset
            timer.resetInterval();
        }
        else {
            // report timing for downstream operator
            timer.recordOperationComplete(workProcessorOperatorContexts.get(operatorIndex + 1).operatorTiming);
        }
    }