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DBST 652 – Lecture 8 – Part 1. Transactions. Transaction Processing. Logical units of database processing Examples - banking, reservations, stock markets ATM - transfer $100 from savings to checking. Transaction Processing.

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transaction processing
Transaction Processing
  • Logical units of database processing
  • Examples - banking, reservations, stock markets
  • ATM - transfer $100 from savings to checking
transaction processing1
Transaction Processing
  • Multiuser systems - job A gets some time, then job B, then job A and so on.
  • Could also have parallel processing. Job A runs while job B runs.
  • See p. 611 - figure 17.1
transaction processing2
Transaction Processing
  • Transaction - logical unit of work
  • Could involve inserts, updates, deletes
  • see steps for reads and writes on p. 555
transaction processing3
Transaction Processing
  • Problems with concurrency - if not controlled:
  • 1. Lost update
  • 2. Dirty read (temporary update)
  • 3. Incorrect summary
transaction processing4
Transaction Processing
  • Transaction - either all completes or no change to the database remains
  • COMMIT or ROLLBACK
transaction processing5
Transaction Processing
  • Easier said than done - what could keep from completing transaction?
  • Computer crash
  • system error
  • local errors
  • deadlock
  • disk failure
  • p. 616 has list
transaction processing6
Transaction Processing
  • Need to keep track of transactions so can recover to a consistent point in time
  • Tracks begin, read/write/delete, end, commit, rollback
  • look at diagram on p. 618
transaction processing7
Transaction Processing
  • A log keeps track of transactions
  • Has before and after data
  • Used to recover database

See Part 1b next