Oracle Database(DBA) Interview Questions and Answers

What is Rollback Segment?
A Database contains one or more Rollback Segments to temporarily store undo information.
What are the uses of Rollback Segment?
Rollback Segments are used: To generate read-consistent database information during database recovery to rollback uncommitted transactions for users.
What is a Temporary Segment?
Temporary segments are created by ORACLE when a SQL statement needs a temporary work area to complete execution. When the statement finishes execution, the temporary segment extents are released to the system for future use.
What is a Data File?
Every ORACLE database has one or more physical data files. A database's data files contain all the database data. The data of logical database structures such as tables and indexes is physically stored in the data files allocated for a database.
What are the Characteristics of Data Files?
A data file can be associated with only one database.Once created a data file can't change size.One or more data files form a logical unit of database storage called a tablespace.
What is a Redo Log?
The set of Redo Log files for a database is collectively known as the database's redo log.
What is the function of Redo Log?
The Primary function of the redo log is to record all changes made to data.
What is the use of Redo Log Information?
The Information in a redo log file is used only to recover the database from a system or media failure the prevents database data from being written to a database's data files.
What does a Control file Contain?

A Control file records the physical structure of the database. It contains the following information Database Name ,Names and locations of a database's files ,redolog files and  Time stamp of database creation.

What is the use of Control File?
When an instance of an ORACLE database is started, its control file is used to identify the database and redo log files that must be opened for database operation to proceed. It is also used in database recovery.
What is a Data Dictionary?
The data dictionary of an ORACLE database is a set of tables and views that are used as a read-only reference about the database. It stores information about both the logical and physical structure of the database, the valid users of an ORACLE database, integrity constraints defined for tables in the database and space allocated for a schema object and how much of it is being used.

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