@Override
  public String toString() {
    return "MaterializationSnapshot{" +
            "validTxnList='" + validTxnList + '\'' +
            ", tableSnapshots=" + tableSnapshots +
            '}';
  }
Returns the json representation of this object.
@return {@link String} containing a json.
storage-api/src/java/org/apache/hadoop/hive/common/MaterializationSnapshot.java