3. Log-based Recovery

• Logging is the most popular mechanism for implementing recovery algorithms.

• The recovery manager implements

  • Commit - by writing a commit record to the log and flushing the log (satisfies the Redo Rule)
  • Abort - by using the transaction’s log records to restore before-images
  • Restart - by scanning the log and undoing and redoing operations as necessary

• The algorithms are fast since they use sequential log I/O in place of random database I/O. They greatly affect TP and Restart performance.

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