In general, backup and recovery refers to the process and procedures used to protecting your Database System like Oracle against data loss and reconstructing the database after any kind of data loss. A backup is a copy of data from your database that can be used to reconstruct that data.

When an Oracle database is abruptly crashed or stopped using the shutdown abort command, Oracle performs a crash recovery during the startup operation.  The crash recovery process is a special form of recovery, which happens the first time an Oracle database instance is started.In crash recovery, the goal is to bring the datafiles to a transaction-consistent state, preserving all committed changes up to the point when the instance failed.

When building applications, designers and architects should aim for as close to perfect scalability as possible. This is sometimes called linear scalability, where system throughput is directly proportional to the number of CPUs.This discussion applies to Oracle, SQL Server, IBM DB2 or anyother system that uses the various components mentioned below.

In real life, linear scalability is impossible for reasons beyond a designer's control. However, making the application design and implementation as scalable as possible should ensure that current and future performance objectives can be achieved through expansion of hardware components and the evolution of CPU technology.

The Oracle 10g Database introduces a new component called Active Session History (ASH) which can be used to identify blocker and waiter session identities and their associated transaction identifiers and SQL for a specified duration of the report. This data for the sample session activity in the instance is provided by V$ACTIVE_SESSION_HISTORY view. A circular buffer in the SGA contains the sampled data of the active sessions. All sessions that are connected to the db and are waiting for an non-idle class event is considered an active session. This includes any session that was running on the CPU at the time of sampling. Sampling is done every second and contains a lot of useful information for Oracle Performance Tuning

The Oracle Database control file supports the startup and operations of an Oracle Database and is a very small binary file that is absolutely necessary for the Operation of the Oracle Database. A control file is updated continuously by Oracle during database use, so it must be available for writing whenever the database is open. If for some reason the control file is not accessible, then the database cannot function properly.