public Criteria getCriteria(PerformanceIndex performanceIndex) {
    return perfIndicesAndCriteria.get(performanceIndex);
  }
Get the {@link Criteria} associated with the specified {@link PerformanceIndex}
@param performanceIndex to which the criteria is related
@return the criteria or null if it doesn't exist
ambry-api/src/main/java/com/github/ambry/commons/Thresholds.java