Oracle Database Administrator
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.
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
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
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
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
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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