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