Using Tickets to Enforce the Serializability of

To enforce global serializability in a multi database environment the multidatabase transaction man ager must take into account the indirect transitive con icts between multidatabase transactions caused by local transactions Such con icts are di cult to resolve because the behavior or even the existence of local transactions is not known to the multidatabase system To overcome these di culties we propose to incorporate additional data ma nipulation operations in the subtransactions of each mul tidatabase transaction We show that if these operations create direct con icts between subtransactions at each par ticipating local database system indirect con icts can be resolved even if the multidatabase system is not aware of their existence Based on this approach we introduce opti mistic and conservative multidatabase transaction manage ment methods that require the local database systems to assure only local serializability The proposed methods do not violate the autonomy of the local database systems and guarantee global serializability by preventing multidatabase transactions from being serialized in di erent ways at the participating database systems Re nements of these meth ods are also proposed for multidatabase environments where the participating database systems allow schedules that are cascadeless or transactions have analogous execution and se rialization orders In particular we show that forced local con icts can be eliminated in rigorous local systems local cascadelessness simpli es the design of a global scheduler and that local strictness o ers no signi cant advantages over cascadelessness