Data Base Administration Questions and Answers

51. What is a database instance? Explain.
A database instance (Server) is a set of memory structure and background
processes that access a set of database files. The processes can be shared by all of the users.
The memory structure that is used to store the most queried data from
database. This helps up to improve database performance by decreasing the
amount of I/O performed against data file.

52. What is Parallel Server?
Multiple instances accessing the same database (only in multi-CPU
environments)

53. What is a schema?
The set of objects owned by user account is called the schema.

54. What is an index? How it is implemented in Oracle database?
An index is a database structure used bythe 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 command

55. What are clusters?
Group of tables physically stored together because they share common
columns and are often used together is called cluster.

56. 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.

57. 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

58. What is a deadlock? Explain.
Two processes waiting to update the rows of a table, which are locked by other processes then deadlock arises. In a database environment this will often happen because of not issuing the 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.
Memory Management

59. What is SGA?
The System Global Area in an Oracle database is the area in memory to
facilitate the transfer of information between users. It holds the most recently requested structural information between
users. It holds the most recently requested structural information about
the database. The structure is database buffers, dictionary cache, redo log buffer and shared pool area.

60. What is a shared pool?
The data dictionary cache is stored in an area in SGA called the shared pool. This will allow sharing of parsed SQLstatements among concurrent users.

61. What is mean by Program Global Area (PGA)?
It is area in memory that is used by a single Oracle user process.

62. What is a data segment?
Data segment are the physical areas within a database block in which the
data associated with tables and clusters are stored.

63. What are the factors causing the reparsing of SQL statements in SGA?
Due to insufficient shared pool size.
Monitor the ratio of the reloads takes place while executing SQL statements. If the ratio is greater than 1 then increase
the SHARED_POOL_SIZE.