public int fetchMessageMaxBytes() {
    String fetchSize = (String) get("fetch.message.max.bytes");
    if (StringUtils.isBlank(fetchSize)) {
      return FETCH_MAX_BYTES;
    } else  {
      return Integer.valueOf(fetchSize);
    }
  }
Create kafka consumer configs, based on the subset of global configs.
@param config application config
@param systemName system name
@param clientId client id provided by the caller
@return KafkaConsumerConfig
samza-kafka/src/main/java/org/apache/samza/config/KafkaConsumerConfig.java