Checkpoints Log could become long, and recovery could take long Checkpoints shorten log and recovery time. Checkpoint scheme: all log records currently in volatile storage to stable storage 1.Output all modified data from volatile to stable storage 2.Output a log record <checkpoint> to the log on stable storage 3.Output Now recovery only includes Ti, such that Ti started executing before the most recent checkpoint, and all transactions after Ti All other transactions already on stable storage Concurrent Transactions Must be equivalent to serial execution serializability – Could perform all transactions in critical section Inefficient, too restrictive Concurrency-control algorithms provide serializability
Checkpoints Log could become long, and recovery could take long Checkpoints shorten log and recovery time. Checkpoint scheme: 1.Output all log records currently in volatile storage to stable storage 2.Output all modified data from volatile to stable storage 3.Output a log record <checkpoint> to the log on stable storage Now recovery only includes Ti, such that Ti started executing before the most recent checkpoint, and all transactions after Ti All other transactions already on stable storage Concurrent Transactions Must be equivalent to serial execution – serializability Could perform all transactions in critical section Inefficient, too restrictive Concurrency-control algorithms provide serializability
OS-UNIT-3.docx