public Map<String, CapacityUnit> getAllQuotaUsage() {
    return Collections.unmodifiableMap(cuUsage);
  }
@return A {@link Map} of quota resource id to {@link CapacityUnit} representing usage for all the resources that
this quota source knows about.
ambry-quota/src/main/java/com/github/ambry/quota/capacityunit/AmbryCUQuotaSource.java