Log Based Recovery

• The most widely used structure for recording database modification is the log.
• The log is a sequence of log records, recording all the update activities in the database.
• In short Transaction log is a journal, which contains history of all transaction performed.
• Log contains Start of transaction, trans-id, record-id, type of operation (insert, update, delete), old value, new value, End of transaction that is commit or aborted.

Techniques for recovery

Log Based Crash Recovery

o Deferred update

Complete -> update

o Immediate update

Change -> update

o Checkpoints

Shadow Paging