private void updateMetrics(long startProcessingNs, long endProcessing) {
      queryInputEvents.inc();
      processingTime.update(endProcessing - startProcessingNs);
    }
Updates the MetricsRegistery of this operator
@param startProcessingNs = begin processing of the message
@param endProcessing = end of processing
samza-sql/src/main/java/org/apache/samza/sql/translator/ScanTranslator.java