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Page history last edited by PBworks 15 years, 10 months ago


  • 1-safe: transactions propigated
  • 2-safe: backup uses commit protocol to commit T synchronously
  • 1-safe has a dependency problem: if T1 depends on T2, but T2 didn't get applied, then T1 is lost, too
  • solution: predeclare dependencies (possible because T has already been committed once) on backup



  • 1-safe backups correctness:
    • internal consistancy on backup site
    • backup will reflect a subset of the committed Ts
  • 2-safe correctness:
    • in sync, but possibly applies transaction before primary is able to respond: COMMIT
  • dependency reconstruction:
    • use locking on backups, BUT we need to ensure locking occurs in the same order
    • solution: assign tickets (local numbers, monotonically increasing) to T
    • modified lock manager waits for the correct ordering of Ts
  • epoch installs:
    • if commit(T) <= X, commit T
    • if prepare(T) <= X, but commit(T) > X
      • if T's primary peer was coordinator, do not commit
      • else check with the backup of T's coordinator B':
        • if B' is commit T in X, then commit
        • else do not
    • otherwise don't commit T (defer to next epoch)
  • UNDERSTAND SCENARIOS! especially bumping

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