Discuss how the log file (or journal) is a fundamental feature in any recovery mechanism. Explain what is meant by forward and backward recovery and describe how the log file is used in forward and backward recovery. What is the significance of the write-ahead log protocol? How do checkpoints affect the recovery protocol?
What will be an ideal response?
Log file contains before and after-images of updates to the database. Before images can be used to
undo changes to the database (i.e. perform backward recovery); after-images can be used to redo
changes (i.e. perform forward recovery).
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