@Override
  public boolean equals(Object o) {
    if (this == o) return true;
    if (o == null || getClass() != o.getClass()) return false;

    MetadataUpdateEvent that = (MetadataUpdateEvent) o;

    return metadataClusters != null ? metadataClusters.equals(that.metadataClusters) : that.metadataClusters == null;
  }
Map of metadatas for each cluster by cluster ids.
ambari-server/src/main/java/org/apache/ambari/server/events/MetadataUpdateEvent.java