CS405G Midterm review notes supplemental Spring 2021 Four kinds of backup data you can use to recover a damaged database: (this is representative of current industry methods) A full backup image. This is the building block of any recovery strategy, without a full backup image, you can't start to restore. If the backup is taken online (i.e. the database is actively running), you may require the logs of all transactions that transpired while the backup was taking place. Restore a full backup, and optionally replay the logs of all transactions since the backup, and your recovery is complete. An incremental backup. This includes all changes since the last full backup. Restore a full backup, restore the incremental backup, optionally replay the logs since the incremental backup, and your recovery is complete. A delta backup. This includes all changes since the last backup of any kind. If the last backup was a full backup image, it and the delta provide the most complete backup. If a delta is preceded by an incremental backup image, you need the delta, the incremental backup, and the full backup image on which the incremental is based. If a delta is preceded by one or more deltas, you need all deltas until you reach an incremental backup or a full backup image. The logs. The logs contain all transactions since the last backup you were able to restore. DB recovery using the DB2 model requires 1. One full backup image (everything in the DB) 2. Zero or one incremental backups (all changes to DB from last full backup) 3. Zero or more delta backups (all changes since last backup of any type) 4. Zero or more logs (these are records of the transactions conducted as they occurred, allows for fine grain recovery down to the transaction level) Full plus incremental strategy Diagrams and base text sourced (with some modification) from https://www.ibm.com/developerworks/data/library/techarticle/dm0910db2incrementalbackup/index.html##fig1 CS405G Midterm review notes supplemental Spring 2021 Full plus delta strategy Recovery example of mixed use Full, Incremental, and Delta backups along with transactions logs used to restore a system to a point in time on Saturday. You may see a diagram like the above and be asked to indicate what is needed to recover to a specific date on the diagram. For example: Above illustrates recovery to a specific point in time on Saturday before the delta backup occurred. The Full from Sunday was recovered first, then the Incremental from Thursday, then the Delta from Friday, and finally transactions logs from the start of the Delta on Friday to the point in time on Saturday that the was the declared recovery point. Diagrams and base text sourced (with some modification) from https://www.ibm.com/developerworks/data/library/techarticle/dm0910db2incrementalbackup/index.html##fig1
