COMP 9243 — Week 5 ( 17 s 1 )

Synchronisation and Coordination (Part 2) Transactions A transaction can be regarded as a set of server operations that are guaranteed to appear atomic in the presence of multiple clients and partial failure. The concept of a transaction originates from the database community as a mechanism to maintain the consistency of databases. Transaction management is build around two basic operations: BeginTransaction, EndTransaction. An EndTransaction operations causes the whole transaction to either Commit or Abort. For this discussion, the operations performed in a transaction are Read and Write. Transactions have the ACID property: Atomic: all-or-nothing, once committed the full transaction is performed, if aborted, there is no trace left; Consistent: concurrent transactions will not produce inconsistent results; Isolated: transactions do not interfere with each other, i.e., no intermediate state of a transaction is visible outside; (this is also called the serialisable property) Durable: all-or-nothing property must hold even if server or hardware fails.