Previous: MINIREL : Recovery Manager
The Recovery Manager operates in the Normal Mode during normal database operation and the Restart Mode during crash restart. While running in the Normal Mode, the Recovery Manager supports transaction atomicity by supporting rollback for aborted transactions. It also performs checkpoints to assist in recovery from crashes. The Restart Mode is invoked by the system after a crash. It is the task of the Recovery Manager to ensure that the system is brought back to a consistent state. There are three distinct phases when a database system is operating in the Restart Mode. The initial phase is the Analysis Phase, in which the Manager processes the log record from the most recent checkpoint taken. The Redo Phase repeats history : i.e. it performs all logged operations. The final Undo Phase Undo Phase moves backward from the end of the log and removes the effects of those transactions that had not yet committed at the time of the crash.
The Recovery Manager primarily interacts with the Log Manager. One of the functions of the Recovery Manager is to generate records to log different actions ( abort, update, commit ). The Recovery Manager creates the log records which are written to the log file by the Log Manager. The Recovery Manager also interacts to a lesser degree with the Buffer Manager and the Transaction Manager. It is invoked by the Transaction Manager for transaction rollback. It requests the Buffer Manager for the Dirty Page list and the Transaction Manager for the Transaction table. Section 3 describes the relationships in detail.
The remainder of this report is organized as follows. Sections 2 and 3 describe the external and internal interfaces. Sections 4 and 5 summarize the accomplishments and testing methods utilized in this project. Finally Section 6 is the retrospective on the design of the MINIREL project.
Previous: MINIREL : Recovery Manager