Reference Work Entry

Encyclopedia of Database Systems

pp 1644-1645

Logging/Recovery Subsystem

  • Andreas ReuterAffiliated withEML Research gGmbH Villa Bosch, Heidelberg, Germany

Synonyms

Audit trail; Log component; Log manager; Recovery manager

Definition

The logging/recovery subsystem (LRS) of a DBMS is responsible for implementing the fault tolerance mechanisms needed to support database transactions. The log component stores the information needed to undo the updates performed by a transaction in case it has to be rolled back, either to an internal save point or to the beginning. It also stores information needed to re-apply the updates of committed transactions to the database in case they are (partially) lost due to a system crash or after a storage media failure. In addition, the log component keeps track of all relevant state transitions such as begin-transaction, prepare, commit, abort, checkpoint, etc. The log is the first resource that is activated when restarting the database after a crash [1]. The recovery component orchestrates the activities needed to repair the database, depending on the situation. For example, after a crash, it f ...

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