Database backup and recovery

Database backup and recovery

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  Advanced Database Systems TheNeed for Database Backup Backup can be performed in any of the several ways: Use SQL to create backup tables and copy data into them. Use an implementation-defined mechanism that backs up the * Property of STI Page 1 of 8 Database Backup and Recovery mechanism that backs up the whole database or portions of it. Using DBMS installation
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  Advanced Database Systems LogFile The DBMS maintains a special file called log file to keep track of database transactions. It may contain the following: Transaction identifier Type of log record * Property of STI Page 2 of 8 Database Backup and Recovery Type of log record Identifier of data item affected by the database action Before-image of the data item which means its value before change. After-image of the data item which means the value after change Log management information
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  Advanced Database Systems Checkpointing Checkpointingis the point of synchronization between the database and the transaction log file. Checkpoints involve the following operations: * Property of STI Page 3 of 8 Database Backup and Recovery operations: Writing all log records in main memory to secondary storage Writing the modified blocks in the database buffers to secondary storage Writing a checkpoint record to the log file.
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  Advanced Database Systems TheNeed for Recovery There are many different types of failure that can affect database processing. Some causes of failures are as follows: System crashes * Property of STI Page 4 of 8 Database Backup and Recovery System crashes Media failures Application software errors Natural physical disasters Carelessness Sabotage
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  Advanced Database Systems TheNeed for Recovery A DBMS should provide the following facilities to assist with recovery: A backup mechanism A logging facilities * Property of STI Page 5 of 8 Database Backup and Recovery A logging facilities A checkpoint facility A recovery manager
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  Advanced Database Systems RecoveryTechniques The recovery technique that must be selected is dependent on the extent of the damage that has occurred to the database. If the database has been extensively damaged, for * Property of STI Page 6 of 8 Database Backup and Recovery extensively damaged, for example a disk head crash has occurred and destroyed the database. If the database has not been physically damaged but has become inconsistent.
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  Advanced Database Systems RecoveryTechniques Using the Deferred Update In the deferred update protocol, the updates are not written to the database until after a transaction has reached its commit point. In this protocol, the log file is used as follows: * Property of STI Page 7 of 8 Database Backup and Recovery follows: Write the transaction start record to the log. Write a log record containing the entire log data specified previously. Write a transaction commit log record. If the transaction aborts, ignore the log records for the transaction and do not perform the writes.
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  Advanced Database Systems RecoveryTechniques Using the Immediate Update In the immediate update protocol, the updates are applied to the database as they occur without waiting to reach the commit point. In this protocol, the log file is used as follows: * Property of STI Page 8 of 8 Database Backup and Recovery follows: Write the transaction start record to the log. Write a record containing the necessary data to the log file. Write the update to the database buffers. Write a transaction commit record to the log