On serializability of multidatabase transactions through forced local conflicts

A multidatabase transaction management mechanism called the optimistic ticket method (OTM) is introduced for enforcing global serializability. It permits the commitment of multidatabase transactions only if their relative serialization order is the same in all participating local database systems (LDBSs). OTM requires the LDBSs to guarantee only local serializability. The basic idea in OTM is to create direct conflicts between multidatabase transactions at each LDBS in order to determine the relative serialization order of their subtransactions. A refinement of OTM, called the implicit ticket method (ITM), is also introduced that uses implicit tickets and eliminates ticket conflicts but works only when the participating LDBSs use rigorous transaction scheduling mechanisms. ITM uses the local commitment order of each subtransaction to determine its implicit ticket value. It achieves global serializability by controlling the commitment (execution order) and thus the serialization order of multidatabase transactions. Both OTM and ITM do not violate the autonomy of the LDBSs and can be combined in a single comprehensive mechanism.<<ETX>>