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Recoverability

Recoverability. Recoverable sector D 0 D 1 chooser. Larger actions? Commit point. id . begin_ra(). ABORT(). COMMIT(). end_ra(). Version histories. Cell storage Install. Journal storage x. WriteJournal (item x, v, id). ReadJournal (item x, v, id).

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Recoverability

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  1. Recoverability Recoverable sector D0 D1 chooser Larger actions? Commit point

  2. id  begin_ra() ABORT() COMMIT() end_ra()

  3. Version histories Cell storage Install Journal storage x WriteJournal (item x, v, id)

  4. ReadJournal (item x, v, id) Commit record table Bootstrap Slow

  5. Logging: Cell st.: read/write Log: non-volatile+sequential

  6. Plan: 1) Fail  Recover from log • uncommitted  back out (undo) • committed  install (rddo) 2) ABORT ()  undo cur. action (redo)

  7. Append-only: type: UPDATE id: 172 undo: x  old redo: x  new type: OUTCOME id: 174 status: COMMITTED 1) When to write log? 2) How to recover?

  8. Disk-bound DB: write x • WAL protocol • Write ahead logging • Log COMMIT record • before returning from • commit() log update record

  9. Recovery: • Scan log backwards • Winners: COMMITTED or ABORTED • Losers: Everything else • Redo COMM. Winners • Undo Losers

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