@Override
        public Map<SystemStreamPartition, SystemStreamMetadata.SystemStreamPartitionMetadata> apply() {
          throw new SamzaException("Failed to get SSP metadata");
        }
Given a set of SystemStreamPartition, fetch metadata from Kafka for each
of them, and return a map from ssp to SystemStreamPartitionMetadata for
each of them. This method will return null for oldest and newest offsets
if a given SystemStreamPartition is empty. This method will block and
retry indefinitely until it gets a successful response from Kafka.
@param ssps a set of strings of SSP
@param retryBackoff retry backoff strategy
@return a map from ssp to sspMetadata which has offsets
samza-kafka/src/main/java/org/apache/samza/system/kafka/KafkaSystemAdmin.java