@Override
  public List<SQLPrimaryKey> addPrimaryKeys(List<SQLPrimaryKey> pks) throws InvalidObjectException,
    MetaException {
    return addPrimaryKeys(pks, true);
  }
Called right before an action that would drop a storage descriptor.
This function makes the SD's reference to a CD null, and then deletes the CD
if it no longer is referenced in the table.
@param msd the storage descriptor to drop
standalone-metastore/metastore-server/src/main/java/org/apache/hadoop/hive/metastore/ObjectStore.java