Crash Recovery

• Transactions (or units of work) against a database can be interrupted unexpectedly.
• If a failure occurs before all of the changes that are part of the unit of work are completed and committed, the database is left in an inconsistent and unusable state. Crash recovery is the process by which the database is moved back to a consistent and usable state. This is done by rolling back incomplete transactions and completing committed transactions that were still in memory when the crash occurred.

•  When a database is in a consistent and usable state, it has attained what is known as a "point of consistency".

Reasons for Crash Recovery:

•  A transaction failure results from a severe error or condition that causes the database or the database manager to end abnormally.
• A power failure on the machine, causing the database manager and the database partitions on it to go down
• A hardware failure such as memory corruption, or disk, CPU, or network failure.
• A serious operating system error that causes DB2^(R) to go down
• An application terminating abnormally.