WAL Recovery (Redo/Undo)

  • Recovery proves durability
  • Redo applies updates by LSN
  • Undo reverses uncommitted work
1 / 5

Redo

  • Apply if LSN > pageLSN
  • Idempotent replay
2 / 5

Undo

  • Reverse uncommitted updates
  • Use before-images
3 / 5

Analysis

  • Determine committed vs active txns
4 / 5

What you will build

  • Toy recovery routine
5 / 5
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