Describe log based recovery, Database Management System

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Describe log based recovery

The most usably structure for recording data base modification is the LOG the log is a sequence of log records recording all the update activities in the data base. There are several types of log records. An update log records describes a single data base write it has these fields

Transaction identifier

Data item identifier

Old value

New value

The various types log records as.

  • < Ti start >. Transaction Ti has started
  • < Ti , Tx v1,v2 > .Transaction Ti has performed a right on data item
  • < Ti commit > Transaction Ti has committed
  • < Ti about > Transaction Ti has aborted

Ø  Deferred data base modification

Ø  Immediate data base modification

Ø  Check point

Ø  Shadow paging

 


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