Crash Recovery

DEFINITION In contrast to transaction aborts, a crash is typically a major failure by which the state of the current database is lost or parts of storage media are unrecoverable (destroyed). Based on log data from a stable log, also called temporary log file, and the inconsistent and/or outdated state of the permanent database, system recovery has to reconstruct the most recent transaction-consistent database state. Because DBMS restart may take too long to be masked for the user, a denial of service can be observed. Recovery from media failures relies on the availability of (several) backup or archive copies of earlier DB states – organized according to the generation principle – and archive logs (often duplexed) covering the processing intervals from the points of time the backup copies were created. Archive recovery usually causes much longer outages than system recovery.