Tuesday, April 12, 2011

DBA (Basic) Part 1

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Level: Intermediate

What are the components of Physical database structure of Oracle Database?.
ORACLE database is comprised of three types of files. One or more Data files, two are more Redo Log files, and one or more Control files.

What are the components of Logical database structure of ORACLE database?
Tablespaces and the Database's Schema Objects.

What is a Tablespace?

A database is divided into Logical Storage Unit called tablespaces. A tablespace is used to grouped related logical structures together.

What is Tablespace Quota ?
The collective amount of disk space available to the objects in a schema on a particular tablespace.

What is SYSTEM tablespace and When is it Created?
Every ORACLE database contains a tablespace named SYSTEM, which is automatically created when the database is created. The SYSTEM tablespace always contains the data dictionary tables for the entire database.

Explain the relationship among Database, Tablespace and Data file.
Each databases logically divided into one or more tablespaces One or more data files are explicitly created for each tablespace.

What is schema?
A schema is collection of database objects of a User.

What are Schema Objects ?
Schema objects are the logical structures that directly refer to the database's data. Schema objects include tables,views,sequences,synonyms, indexes, clusters, database triggers, procedures, functions packages and database links.

Can objects of the same Schema reside in different tablespaces.?

Can a Tablespace hold objects from different Schemes ?

What is a Synonym ?
A synonym is an alias for a table, view,sequence or program unit.

What are the type of Synonyms ?
There are two types of Synonyms Private and Public.

What is a Private Synonyms ?
A Private Synonyms can be accessed only by the owner.

What is a Public Synonyms ?
A Public synonyms can be accessed by any user on the database.

What are synonyms used for ?
Synonyms are used to : Mask the real name and owner of an object.
Provide public access to an object
Provide location transparency for tables,views or program units of a remote database.
Simplify the SQL statements for database users.

What is an Index ?
An Index is an optional structure associated with a table to have direct access to rows,which can be created to increase the performance of data retrieval. Index can be created on one or more columns of a table.

How are Indexes Update ?
Indexes are automatically maintained and used by ORACLE. Changes to table data are automatically incorporated into all relevant indexes.

What is Database Link ?
A database link is a named object that describes a "path" from one database to another.

What are the types of Database Links ?

Private Database Link, Public Database Link & Network Database Link.

What is Private Database Link ?
Private database link is created on behalf of a specific user. A private database link can be used only when the owner of the link specifies a global object name in a SQL statement or in the definition of the owner's views or procedures.

What is Public Database Link ?
Public database link is created for the special user group PUBLIC. A public database link can be used when any user in the associated database specifies a global object name in a SQL statement or object definition.

What is Row Chaining ?
In Circumstances, all of the data for a row in a table may not be able to fit in the same data block. When this occurs , the data for the row is stored in a chain of data block (one or more) reserved for that segment.

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.

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