数据库系统的故障恢复（理论）

Recovery:

1.Failure types: 

              transaction failure, system failure, disk failure.
2.Log-based recovery

1. log record structures
2. Deferred database modification: redo logs

                1) .Log record structures

                2).Write rules:
                3).How to recovery

3.Immediate database modification: undo logs

1. Log record structures
2. Write rules:
3. How to recovery

4.Check-points: why?how?

1. Nonquiescen