CRASH RECOVERY
CONTENT
- Crash Recovery
- ARIES (Analysis, Redo and Undo)
- Other Recovery-Related Data Structures
Crash Recovery in Databases
Definition of Crash Recovery
Crash recovery is a critical process in database management systems (DBMS) that ensures the restoration of a consistent and usable state following a system crash. This complex operation involves rolling back incomplete transactions and applying committed transactions that were still in memory when the crash occurred. To achieve this, the DBMS relies on a crucial component known as the Log.
The Log: A Chronicle of Actions
The Log serves as a historical record of all actions executed by the DBMS. Physically, the log is stored as a file of records in stable storage, which is assumed to remain intact even in the face of system crashes.
For recovery purposes, each page in the database contains the LSN (Log Sequence Number) of the most recent log record that describes a change to that specific page. This identifier is referred to as pageLSN. Furthermore, every log record is assigned a unique LSN.
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