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Published byEdwin Bridges Modified over 9 years ago
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Recovery and Concurrency Recovery Transaction Sync Point Commit Rollback Failure System Media Tran 1 Tran 2Tran 3 Tran 4 Journal(log file)
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Time tctf Checkpoint System failure T1 T2 T3 T4 T5 T2T3T4 T2 T5 T4 Undo List Redo List
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Concurrency The Lost Update problem The Uncommitted Dependency problem The Inconsistent analysis problem
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Transaction ATransaction B t1 Retrieve p t2 Retrieve p --- Update p --- Update p --- t3 t4 Lost update problem
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Transaction ATransaction B t1 Retrieve p t2 Update p --- Rollback --- t3 t4 Uncommitted dependency problem ---
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Transaction ATransaction B t1 Update p t2 Update p --- Rollback --- t3 t4 Uncommitted dependency problem ---
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Transaction ATransaction B t1 t2 Update ACC 3 30 -> 20 --- Retrieve ACC 1 Sum = 40 --- t3 t4 Inconsistent analysis problem --- Retrieve ACC 2 Sum = 90 Retrieve ACC 3 Sum = 40 Retrieve ACC 1 t5 --- Update ACC 1 40 -> 50 t6 t7 t8 Commit Retrieve ACC 3 sum = 110 ACC 1ACC 2ACC 3 40 50 30
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Locking XS- XNNY SNYY -YYY Shared Locks (S locks) Exclusive Locks (X locks)
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Transaction ATransaction B t1 Retrieve p (acquire S lock on p) t2 Retrieve p (acquire S lock on p) --- Update p (request X lock on p) --- waitUpdate p (request X lock on p) t3 t4 Lost update problem wait ---
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Transaction ATransaction B t1 Update p (request X lock on p) t2 Update p (acquire X lock on p) --- Commit / Rollback (release X lock on p) --- t3 t4 Uncommitted dependency problem wait --- wait Resume:Update p (acquire X lock on p)
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Transaction ATransaction B t1 t2 Update ACC 3 (acquire X lock on ACC 3) 30 -> 20 --- Retrieve ACC 1 (acquire S lock on ACC 1) Sum = 40 --- t3 t4 --- Retrieve ACC 2: (acquire S lock on ACC 2) Sum = 90 Retrieve ACC 3 (acquire S lock on ACC 3) Retrieve ACC 1 (acquire S lock on ACC 1) t5 --- Update ACC 1 Request X lock on ACC 3) t6 t7 t8 wait Retrieve ACC 3 (request S lock on ACC 3) ACC 1ACC 2ACC 3 40 50 30 --- wait
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