@Override
  public MetadataStore getMetadataStore(String namespace, Config config, MetricsRegistry metricsRegistry) {
    NAMESPACED_STORES.putIfAbsent(namespace, new InMemoryMetadataStore());
    return NAMESPACED_STORES.get(namespace);
  }
Factory for an in-memory {@link MetadataStore}. Data is not persisted outside of memory and will be cleared on
subsequent restarts.
samza-api/src/main/java/org/apache/samza/metadatastore/InMemoryMetadataStoreFactory.java