public static Map<String, SystemConsumer> createSystemConsumers(Set<String> storeSystems,
      Map<String, SystemFactory> systemFactories, MetricsRegistry registry, Config config) {
    // Create one consumer for each system in use, map with one entry for each such system
    Map<String, SystemConsumer> consumers = new HashMap<>();

    // Iterate over the list of storeSystems and create one sysConsumer per system
    for (String storeSystemName : storeSystems) {
      SystemFactory systemFactory = systemFactories.get(storeSystemName);
      if (systemFactory == null) {
        throw new SamzaException("System " + storeSystemName + " does not exist in config");
      }
      consumers.put(storeSystemName, systemFactory.getConsumer(storeSystemName, config, registry));
    }

    return consumers;
  }
Creates SystemConsumers for store restore, one consumer per system.
@return map of system name to its system consumer.
samza-core/src/main/scala/org/apache/samza/storage/ContainerStorageManagerUtil.java