Summary, Cont.

• Checkpointing: A quick way to limit the amount of log to scan on recovery.

• Recovery works in 3 phases:

  • Analysis: Forward from checkpoint.
  • Redo: Forward from oldest recLSN.
  • Undo: Backward from end to first LSN of oldest Xact alive at crash.

• Upon Undo, write CLRs.

• Redo “repeats history”: Simplifies the logic!

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