Transaction is a logical unit of work that comprises one or more SQL statements executed by a single user. 
 

What is Read-Only Transaction? 

Read-Only transaction ensures that the results of each query executed in the transaction are consistant with respect to the same point in time. 
 

What is a deadlock? Explain. 

Two processes wating to update the rows of a table which are locked by the other process then deadlock arises. In a database environment 
this will often happen because of not issuing proper row lock commands. Poor design of front-end application may cause this situation and the performance of server will reduce drastically.  These locks will be released automatically when a commit/rollback operation performed or any one of this processes being killed externally. 
 

What is a Schema? 

The set of objects owned by user account is called the schema. 
 

What is a cluster Key? 

The related columns of the tables are called the cluster key. The cluster key is indexed using a cluster index and its value is stored only once for multiple tables in the cluster. 
 

What is Parallel Server? 

Multiple instances accessing the same database (Only In Multi-CPU environments) 
 

What are the basic element of Base configuration of an oracle Database? 

It consists of one or more data files.  One or more control files.  Two or more redo log files.   

The Database contains multiple users/schemas one or more rollback segments one or more tablespaces, data dictionary tables, user objects (table,indexes,views etc.,).   

The server that access the database consists of SGA (Database buffer, Dictionary Cache Buffers, Redo log buffers, Shared SQL pool)
SMON (System MONito)
PMON (Process MONitor)
LGWR (LoG Write)
DBWR (Data Base Write)
ARCH (ARCHiver)
CKPT (Check Point)
RECO
Dispatcher
User Process with associated PGS 
 

What is clusters? 

Group of tables physically stored together because they share common columns and are often used together is called Cluster. 
 

What is an Index? How it is implemented in Oracle Database? 

An index is a database structure used by the server to have direct access of a row in a table. An index is automatically created when a unique of primary key constraint clause is specified in create table comman (Ver 7.0) 

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