CS348 Lecture 13: Transaction Execution
10 Jan 2019
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Transaction execution 11. 20/22. 18: recall transactions have acid properties, atomicity all or nothing execution, consistency execution preserves database integrity. If ti and tj are concurrent transactions, then it must appear as if they have been executed sequentially (in some serial order) Ti will appear to precede tj (tj sees all updates made by ti but not vice versa) or ti will appear to follow tj (ti will see all updates made by tj but not vice versa) Transaction tj reads a value ti has written, tj succeeds to commit, and ti tries to abort. To abort ti we need to undo effects of a committed transaction tj: cascadeless schedules (aca) allows no reading of uncommitted data, can only abort ti if tj didn"t commit (may lead to cascading aborts of many transactions) Schedulers can be conservative (favors delaying operations) or aggressive (favors rejecting operations)
