Checkpointing and Media Recovery

Back to: DATA PROCESSING SS 3

 

Welcome to class! 

In today’s class, we will be talking about checkpointing and media recovery. Enjoy the class!

Checkpointing

Checkpointing basically consists of storing a snapshot of the current application state, and later on, use it for restarting the execution in case of failure. A check point record is written into the log periodically at that point when the system writes out to the database on disk all DBMS buffers that have been modified. This is a periodic operation that can reduce the time for recovery from a crash.

Check points are used to make recovery more efficient and to control the reuse of primary and secondary log files. In the case of a crash, backup files will be used to recover the database to the point of crash.

Media recovery

Media recovery deals with the failure of the storage media holding the permanent database, in particular disk failures. The traditional database approach for media recovery uses archive copies (dumps) of the database as well as archive logs. Archive copies represent snapshots of the database and are periodically taken.

The archive log contains the log records for all committed changes which are not yet reflected in the archive copy. In the event of a media failure, the current database can be reconstructed by using the latest archive copy and redoing all changes in chronological order from the archive log.

Faster recovery from disk failures is supported by disk organizations like RAID (redundant arrays of independent disks) which store data redundantly on several disks. However, they do not eliminate the need for archive based media recovery since they cannot completely rule out the possibility of data loss, e.g when multiple disks fail.

General evaluation

1. Explain crash recovery.
2. Explain the following terms in crash recovery (i) Media recovery (ii) Check point (iii) The Write – Ahead log protocol
3. Discuss the concepts of ARIES in crash recovery.

Reading assignment

Understanding Data Processing for Senior Secondary Schools by Dinehin Victoria Pages 261 – 267

Weekend assignment

1. The process by which a database is moved back to a consistent and usable state is called………. (a) cash recovery (b) crash recovery (c) past recovery (d) undo recovery
2. The recovery algorithm that uses no-force and steals approach is …………..  (a) ARIAS (b) ARIES (c) ARREARS  (d) ARIS
3. ARIES works in ……………. Phases (a) 3 (b) 2 (c) 1 (d) 4
4. Which of these is not a crash recovery type ………… (a) ARIES (b) Media recovery (c) Checkpointing (d) UNDO
5. ………. Crash recovery uses backup files (a) Checkpoint (b) ARIES (c) Media recovery
   (d) Atomicity

Theory

1. Discuss the concept of ARIES in crash recovery.
2. Explain the difference between media recovery and check point.
3. Explain the difference between a system crash and a media failure.

 

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