Databases are the technical basis of most data repositories of today’s world! Downtime in transaction processing systems is so critical that can shutdown whole organizations with a high possibility of going out of business. DataBase Management Systems (DBMS) must be able to recover from failures without any data loss and preferably in a short period of time. Therefore, the database needs to be restored to the state it was in just before a problem stopped any database processing.
Database backups occur frequently; however, they always lack interim data that update the database between backup jobs’ intervals! As shown in the image below, a completed transaction must be copied both to the active database and to a transaction journal. When a database backup is performed the transaction journal is marked with a date stamp as to refer to it in case a restore is required.
The recovery process starts with the last complete backup plus a journal listing of all the transactions since the last backup. The recovery process reruns all the transactions up to the one when the system crashed. Therefore, the transaction journal is critical to the database integrity as it brings it back to its operational state without any loss of transactions.
