// table sm:
//      sector_nr bigint(16) not null,
//      hash varchar(128) not null,
//      primary key(sector_nr),
//      index(hash)

// table dm:
//      hash varchar(128) not null,
//      count bigint(16) not null,
//      data blob not null,
//      primary key(hash)

// function put_block(long sectornr_in, byte [] data_in, byte [] hash_in)
// {
//      SELECT count AS prev_count, hash AS previous_hash FROM sm, dm WHERE sm.hash=dm.hash AND sectornr=sectornr_in (*1)

//      if (previous_hash == null || previous_hash != hash_in) {
//              if prev_count == 1
//                      DELETE from dm WHERE hash=previous_hash                                 (*2)
//
//              SELECT new_count FROM dm WHERE hash=hash_in;                                    (*3)
//              if (new_count == null)
//                      INSERT INTO dm(hash, count, data) VALUES(hash_in, 1, data_in)           (*4)
//              else
//                      UPDATE dm SET count=count+1 WHERE hash=hash_in;                         (*5)
//      }

//      if previous_count == null
//              INSERT INTO sm(sectornr, hash) VALUES(sectornr_in, hash_in);                    (*6)
//      else
//              UPDATE sm SET hash=hash_in WHERE sectornr=sectornr_in                           (*7)
// }