Oracle Unleashed- P8: When I first started using Oracle many years ago, it was possible to know the database and the tools available. With the rash of recent releases of different options for the database and the spate of new tools, only people who wear their underpants over their trousers will be able to know everything there is to know about the Oracle products. | _If the structure of a database table is changed using an alter table command for example the programs that create the SQL Loader readable files must be changed. If this is not done proper backups of all data within the database object will not be taken. For some sites however this type of backup is practical despite the obvious constraints. For a more detailed discussion of the implementation of SQL Loader refer to the Oracle7Server Utilities User s Guide. Types of Database Failure Every DBA experiences a database failure at some point. It might be a minor failure in which the users never even know that they lost service or it might be a severe loss that lasts for several days. Most failures fall somewhere in the middle. Most failures result primarily from the loss or corruption of a physical data file. Of course many other factors can cause database problems. Indeed problems can occur in the memory structures the SGA the system hardware or even the Oracle software that prevent the DBA from starting up the database. The following sections describe the most common types of failures. Tablespace If a loss or corruption takes place in any of the database files that make up a tablespace media recovery is required. The extent of the media recovery needed depends largely on the extent of the data file loss or corruption. The three types of recovery available for this type of recovery are Database recovery Tablespace recovery Data file recovery The database recovery method is generally chosen if the SYSTEM tablespace has been damaged in which case it syncs all the data files within the database during the recovery procedure. The tablespace recovery method is used if recovery is needed for multiple tablespaces that had become damaged such as from the loss of a disk drive. The data file recovery method is performed if only a single database file has been damaged. The commands used to implement these methods are recover database recover tablespace users recover .
