Method for enforcing the serialization of global multidatabase transactions through committing only on consistent subtransaction serialization by the local database managers

摘要

Our invention guarantees global serializability by preventing multidatabase transactions from being serialized in different ways at the participating local database systems (LDBS). In one embodiment tickets are used to inform the MDBS of the relative serialization order of the subtransactions of each global transactions at each LDBS. A ticket is a (logical) timestamp whose value is stored as a regular data item in each LDBS. Each substransaction of a global transaction is required to issue the take-a-ticket operations which consists of reading the value of the ticket (i.e., read ticket) and incrementing it (i.e., write (ticket+1)) through regular data manipulation operations. Only the subtransactions of global transactions take tickets. When different global transactions issue subtransactions at a local database, each subtransaction will include the take-a-ticket operations. Therefore, the ticket values associated with each global subtransaction at the MDBS reflect the local serialization order at each LDBS. The MDBS in accordance with our invention examines the ticket values to determine the local serialization order at the different LDBS's and only authorizes the transactions to commit if the serialization order of the global transactions is the same at each LDBS. In another embodiment, the LDBSs employ rigorous schedulers and the prepared-to-commit messages for each subtransaction are used by the MDBS to ensure global serializability.