public String getMetaInfo(String metaInfoKey) {
    return getMessageValues().get(metaInfoKey);
  }
The Set is used to store the migrations that have been performed
The structure looks like:
{
Key: migration-info
Type: set-migration-info
Source: ContainerID
MessageMap:
 {
    "0910checkpointmigration" : true
 }
}
samza-core/src/main/java/org/apache/samza/coordinator/stream/messages/SetMigrationMetaMessage.java