16-01-2014, 01:14 PM
DATABASE MANAGEMENT SYSTEMS QUESTION ANSWERS
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1) What is a log-file group?
Ans: A log-file group is a set of log files that is used to store system redo information. By having a group of log files, Oracle will automatically mirror redo information to the log files in the groups.
2) How many I/Os per second per disk drive can a standard disk drive service?
Ans: You should not run more than 60-70 I/Os per disk drive on a standard SCSI disk drive. Pushing more I/Os than this can cause disk latencies to increase beyond recommended limits.
3) What is an SID?
Ans: The SID is the system identifier. This environment variable is used to determine which database to connect to.
4) How many databases can you create with one SID?
Ans: Each SID uniquely identifies one database; therefore you can only create one database per SID.
5) How many databases can you create on one system?
Ans: There is no firm limit to the number of databases that can be created on one system. The system resources that each database consumes will be the limiting factor.
6) What is a tablespace used for?
Ans: The tablespace is used to create schema objects. Tables, indexes, views, and clusters all are created within tablespaces.
7) What is an extent?
Ans: An extent is the unit of space that a schema object allocates when it is created or grows. As a table increases in size and fills up all its space, another extent is allocated. An extent is a contiguous group of blocks.
8) What states can a tablespace be in?
Ans: tablespace can be online or offline.
9) Name the four types of segments.
Ans: The four types of segments are data, index, rollback, and temporary.
10) What DBMS object is used for recovery operations?
Ans: The redo log files and the archive log files are used for database recovery.
11) What DBMS object is used for read consistency?
Ans: The rollback segments are used for read consistency.
12) What is read consistency?
Ans: Read consistency allows a long-running transaction to always obtain the same data within the query.
13) How many redo log files do you need?
Ans: Oracle requires at least two redo log files. This allows the log switch to occur and archiving to happen while logging is also happening.
14) What is a control file used for?
Ans: The control file is used to keep information about the structure of the database. When the instance is started, the control file is used to identify the database files.
15) Can the instance be started without a control file?
Ans: Without the control file, DBMS will not know which datafiles to open. Oracle cannot start without a control file.
16) What can you do to help re-create the control file?
Ans: The ALTER DATABASE database BACKUP CONTROLFILE command is used to back up the control file. Using the TO TRACE qualifier generates the SQL statements necessary to reproduce the control file.
18) What is a rollback segment used for?
Ans: Just as the name indicates, a rollback segment is used to store change information that can be used in the event of a rollback. It is also used for read consistency.
19) How big is a rollback segment?
Ans: The rollback segment dynamically allocates and deallocates space. If the OPTIMAL value is set, the rollback segment will try to stay that size.
20) Should more than one user share a user account?
Ans: No, the user accounts are individual. Sometimes the DBA might be auditing the system and will be able to tell what users have been active and when. If many people use the same account, the DBA cannot tell who is using the system.
21) What are the server processes?
Ans: The server processes are the background processes or threads that perform tasks on behalf of DBMS.
22) What is a dedicated server process?
Ans: A dedicated server process has a one-to-one correlation between the user process and the server process. Each user process gets one server process.
23) What is a shared server process?
Ans: The shared server process handles more than one user process. The dispatcher queues the job and the shared server process executes it.
24) What are tables used for?
Ans: A table is the DBMS object that actually holds the data that is entered into the database. A table consists of rows of data that are defined by table columns.
25) What is a partitioned table?
Ans: A partitioned table uses the new Oracle feature, range partitioning. Data is stored in a location based on a range of data you have defined. This range can be numeric or a data format.