private Put createPutForStartBackupSession() {
    Put put = new Put(ACTIVE_SESSION_ROW);
    put.addColumn(SESSIONS_FAMILY, ACTIVE_SESSION_COL, ACTIVE_SESSION_YES);
    return put;
  }
Exclusive operations are: create, delete, merge
@throws IOException if a table operation fails or an active backup exclusive operation is
                    already underway
hbase-backup/src/main/java/org/apache/hadoop/hbase/backup/impl/BackupSystemTable.java