@Override
        public String getOldestOffset() {
          throw new NotImplementedException(msg);
        }
Note! This method does not populate SystemStreamMetadata for each stream with real data.
Thus, this method should ONLY be used to get number of partitions for each stream.
It will throw NotImplementedException if anyone tries to access the actual metadata.
@param streamNames set of streams for which get the partitions counts
@param cacheTTL cache TTL if caching the data
@return a map, keyed on stream names. Number of partitions in SystemStreamMetadata is the output of this method.
samza-kafka/src/main/java/org/apache/samza/system/kafka/KafkaSystemAdmin.java