41⟩ Explain a Data Segment?
Each Non-clustered table has a data segment. All of the tables data is stored in the extents of its data segment. Each cluster has a data segment. The data of every table in the cluster is
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Each Non-clustered table has a data segment. All of the tables data is stored in the extents of its data segment. Each cluster has a data segment. The data of every table in the cluster is
Each Index has an Index segment that stores all of its data.
A Database contains one or more Rollback Segments to temporarily store "undo" information.
Rollback Segments are used : To generate read-consistent database information during database recovery to rollback uncommitted transactions for users.
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.
Every ORACLE database has one or more physical data files. A databases 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.
A data file can be associated with only one database.Once created a data file cant change size.
The set of Redo Log files for a database is collectively known as the databases redo log.
The Primary function of the redo log is to record all changes made to data.
The Information in a redo log file is used only to recover the database from a system or media failure prevents database data from being written to a databases data files.
A Control file records the physical structure of the database. It contains the following information.
Database Name, Names and locations of a databases files and redolog files. ,Time stamp of database creation.
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.
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.
An integrity constraint is a declarative way to define a business rule for a column of a table.
SGA and ORACLE background processes constitute an ORACLE instance. (or) Combination of memory structure and background process.
The System Global Area (SGA) is a shared memory region allocated by ORACLE that contains data and control information for one ORACLE instance.
Database buffers, Redo Log Buffer the Shared Pool and Cursors.
Database buffers store the most recently used blocks of database data. It can also contain modified data that has not yet been permanently written to disk.