architecture faq

8/8/2019 Architecture Faq

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9I ARCHITECTURE FAQ

1. What is an Oracle Server

Oracle server is a database management system which consists of an

oracle instance and an oracle database.

2. What is an Oracle Instance

Instance is a combination of SGA and background processes.

3. What is an Oracle database

Oracle database consists of database files which provides the physicalstorage for database information .

4. What is SGA

System Global Area used to store database information that is shared by database

processes.

5. What are the mandatory background processes

SMON, PMON, DBWR, LGWR, CKPT.

6. What are the components of SGA

Shared pool, Database buffer cache, Redo log buffer, Large pool, Java pool.

7. What does shared pool contain

Shared pool contains most recently executed SQL statementsMost recently used data definitions.

8. What does database buffer cache contain

It contains copies of data blocks that have been retrieved from the datafiles.

9. What does redo log buffer contain

Redo log buffer records all changes made to the data for recovery purpose.

10.What is the function of SMON

SMON performs instance recovery by roll forwarding the committed asWell as uncommitted transactions and rollbacks the uncommitted transactions.Colease free space in datafiles.

11. What is the function of PMON

PMON cleans up after failed processes by rolling back the user’s current transactions,Releases table or row locks, resources held by user processes, restarts the deadDispatchers.

12. What is the function of DBWR

DBWR writes dirty buffers (buffers which are modified but not yet written to



Datafiles.) from buffer cache to datafiles.

13. What is the function of LGWR

LGWR writes the data from redo log buffer to redo log files.

14. What is the purpose of checkpoint Purpose of checkpoint is to make sure that all the buffers in the buffer cache that wereModified prior to point in time have been written to the datafiles.

15. When does DBWR writes dirty buffers from buffer cache to datafiles

When a check point occursWhen dirty buffers reach thresh holdWhen time out occursWhen a tablespace is taken offlineWhen a tablespace is taken to read onlyWhen a tablespace is kept in begin backup mode

When a table is dropped or truncatedWhen the database is shutdown.

16. When does LGWR writes to redo log files

When redo log buffer is one third fullWhen a commit occursBefore DBWR writes to datafilesEvery 3 secondsWhen there is 1MB of redo in redo log buffer

17. What is a parameter file

Parameter file defines the characteristics of the instance

18. What are the types of parameter files

Pfile, spfile

19. What is the difference between pfile and spfile

Pfile is a text file , spfile is a binary fileChanges to entries in pfile take effect on the next startupChanges to entries in spfile are persistent across startup and shutdown

20. What is the default location of pfile

$ORACLE_HOME/dbs

21. What is the use of control file?what information it contain?

Control file is used to maintain the integrity of the database.It contains informationLike database name, timestamp of database creation, tablespace names, location of Datafiles and redo log files, checkpoint information, current redo log sequence Number



22. What are the logical structures of the database

Tablespaces, segments, extente, blocks

23. What is a tablespace

Tablespace is a logical structure of the database that consists of one or more datafiles

24. What is a segment

Segment is a space allocated for a specific object within a tablespace

25. What is an extent

An extent is a set of contiguous oracle blocks

26. What is an oracle block

Block is a smallest unit of storage for read write operations.

27. What is the default standard block size in 9i

8k

28. What are the parameters for sizing the buffer cache,shared pool,redo log buffer

Db_cache_size, shared_pool_size, log_buffer

29. What is a password file

Password file authenticates privileged users to start up and shut down an oracleInstance

30. What is an archived redo log file

Archived redo log files are offline copies of the redo log files that are necessary for Recovery from media failures.

31. What is a session

A session is a specific connection of a user to an oracle server

32. What is PGA

Memory reserved for each user process connecting to an oracle database

33. What Is dedicated server

Server process handles the request of a single user process in dedicated server

34. What is shared server

In shared server, multiple server process handles the requests of several user Processes

35. What is server process

Server process is a program which interacts directly with oracle server

36. What is user process



User process is a program which requestsinteraction with the oracle server

37. How can we control the size of SGA

SGA_MAX_SIZE parameter can control the size of sga.

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