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

Explain the types of synonyms?
There are two types of synonyms private and public.

Explain a private synonym?
Only its owner can access a private synonym.

Explain a public synonym?
Any database user can access a public synonym..

Explain synonyms used for?
- 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 

Explain an Oracle 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 the index updates?
Indexes are automatically maintained and used by Oracle. Changes to table data are automatically incorporated into all relevant indexes.

Explain clusters?
Clusters are groups of one or more tables physically stores together to share common columns and are often used together.

Explain cluster key?
The related columns of the tables in a cluster are called the cluster key.

Explain index cluster?
A cluster with an index on the cluster key.

Explain hash cluster
A row is stored in a hash cluster based on the result of applying a hash function to the row's cluster key value. All rows with the same hash key value are stores together on disk.

When can hash cluster used?
Hash clusters are better choice when a table is often queried with equality queries. For such queries the specified cluster key value is hashed. The resulting hash key value points directly to the area on disk that stores the specified rows.

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

Explain the types of database links?
Private database link, public database link & network database link.

Explain 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.

Explain 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.

Explain network database link?

Network database link is created and managed by a network domain service. A network database link can be used when any user of any database in the network specifies a global object name in a SQL statement or object definition.

Explain data block?
Oracle database's data is stored in data blocks. One data block corresponds to a specific number of bytes of physical database space on disk.

How to define data block size?
A data block size is specified for each Oracle database when the database is created. A database users and allocated free database space in Oracle data blocks. Block size is specified in init.ora file and cannot be changed latter.

Explain 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.

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