Crash Recovery

• Crash recovery mechanisms guard against
  • System crashes
  • Media failures
• A log or journal records all changes before they modify the database
• The log is assumed to survive system crashes and media failures
• After a crash the recovery manager follows the ARIES stretegy

  Analysis

  of changes that have not been written and active transactions

  Redo

  actions that were not written to the database

  Undo

  transactions that were not completed

• The log is also updated during the recovery to guard against repeated crashes
• A checkpoint is periodically recorded to the log to reduce the recovery overhead
• A checkpointing strategy is also used to take backup copies of live databases

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 Last change: Monday, December 1, 2003 1:29 pm
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