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Transactions and Buffer Pool (cont)

Handling stealing:
  • page P, held by tx T, is output to disk and replaced
  • if T aborts, some of its changes are already "committed"
  • must log changed values in P at "steal-time"
  • use these to UNDO changes in case of failure of T
Handling no forcing:
  • consider: transaction T commits, then system crashes
  • but what if modified page P has not yet been output?
  • must log changed values in P as soon as they change
  • use these to support REDO to restore changes