Algorithms for Recovery and Isolation Exploiting Semantics: Difference between revisions

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Revision as of 14:05, 27 April 2017

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Every transaction implicitly begins with the first "Update" type of entry for the given TransactionID, and is committed with "End Of Log" entry for the transaction.

During a recovery or while undoing the actions of an aborted transaction a special kind of log record is written, the Compensation Log Record (CLR), to record that the action has already been undone. CLRs are of the form (Sequence Number, Transaction ID, Page ID, Redo, Previous Sequence Number, Next Undo Sequence Number). The UndoRedo field iscontains omittedapplication becauseof thatUndo informationfield isof alreadyreverted storedaction, inand the originalUndo logfield recordis foromitted because CLR is thosenever actionsreverted.

== Recovery ==