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Chapter 20

Chapter 20. Transaction Management. Agenda. Transaction Concurrent Processing Backup and Recovery. Transaction - I. Definition An action or actions to read or update the contents of the database Types Committed Aborted Compensating. Transaction - II. Property of Transactions (ACID)

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Chapter 20

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  1. Chapter 20 Transaction Management

  2. Agenda • Transaction • Concurrent Processing • Backup and Recovery

  3. Transaction - I • Definition • An action or actions to read or update the contents of the database • Types • Committed • Aborted • Compensating

  4. Transaction - II • Property of Transactions (ACID) • Atomicity (all or nothing) • Consistency (state by database constraints and applications) • Isolation (independent) • Durability (permanent)

  5. Concurrent Processing • Definition • Problems • Control

  6. Concurrent Processing • Multiprogramming • Interleaved between two transactions • CPU • I/O • Logical unit of work

  7. Concurrent Processing Problem • No problem • Write different data • Update different data • Read the same data • Problem • Write the same data • Update the same data

  8. Concurrent Processing Problems • Lost update • Two transactions simultaneously update the same files • Uncommitted update • Transaction 2 uses the result updated by transaction 1 • Transaction 1 aborts and rolls back • Transaction 2 commits • Inconsistent Analysis • Transaction 1 reads • Transaction 2 reads and uses for calculation • Transaction 1 updates and commits • Transaction 2 updates and commits

  9. SERIALIZABILITY • Transaction results form concurrent processing are the same as if stand-alone sequential processing was used • Ensure no anomalies arise from concurrent processing

  10. Concurrency Control • Locking • Deadlock • Two-phase locking • Timestamping • Optimistic technique

  11. Locking • Types • Shared Locks vs. Exclusive Locks • Read Locks vs. Write Locks • Upgrade vs. Downgrade • Granularity • Database • file • page • record • field

  12. Deadlock • Definition • Tow or more transactions each wait for locks held by other transaction • Livelock • Control • Wait-Die • Wound-wait • Time out • Conservative 2PL

  13. Two-phase Locking • Growing phase • Get all locks • Upgrade locks • Shrinking phase • Downgrade locks • Once starting to release a lock - no more new locks

  14. Timestamping • Timestamp • unique identifier as relative starting time of a transaction • Read-timestamp & write timestamp • Timestamp protocol • Transactions with smaller timestamps get priority in the event of conflict • Transaction is only allowed on the item with smaller read-timestamp or write timestamp

  15. Optimistic Technique • Read phase • Validate phase • Write phase

  16. Database Recovery • Definition • Restoring the database to its correct state in the event of a failure • Reasons • Physical (fire, flood, etc.) • Sabotage • Carelessness • Hardware • Software (application/system)

  17. Database Backup • Backup • Copy of the database • Transaction log • Transaction ID, time, operation, object, before image, after image, prior pointer, next pointer • Checkpoint • Synchronize transaction log and the database • Write data from buffers to database on the disk • Write checkpoint to log identify current transaction(s)

  18. Recovery Methods • Reprocessing • Record all transactions since last backup and replay the following transactions • Rollfoward • Use the transaction log to change any committed transactions on the database or since last checkpoint • Rollback • Use transaction log to undo any aborted transactions

  19. Shadow Paging Method • Current page table vs. Shadow page table • Pros & cons • Faster • Less overhead • Data fragmentation • Reclaim inaccessible blocks

  20. Points To Remember • Properties of Transaction • Concurrent Processing • Backup and Recovery

  21. Assignments • Review chapters 5-6, 11-14, and 19-20 • Read chapter • Exam 3 • Date: 5/17/07 • Project • Due date: 5/22/07 • Place: Tahoe 2090 • Time: 12 noon

  22. End of MIS150 • Study! Study! Study! • There is no easy way out! • Have a happy and safe summer!!

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