UNIX Interview Questions/FAQs for Oracle DBAs

1. What’s the difference between soft link and hard link?
Ans:
A symbolic (soft) linked file and the targeted file can be located on the same or different file system while for a hard link they must be located on the same file system, because they share same inode number and an inode table is unique to a file system, both must be on the same file system.

2. How you will read a file from shell script?
Ans:
while read line
do
echo $line
done < file_name

3. What’s the use of umask?
Will decide the default permissions for files.

4. What is crontab and what are the arguments?
Ans:
The entries have the following elements:
field             allowed values
—–             ————–
minute            0-59
hour                0-23
day of month   1-31
month             1-12
day of week     0-7 (both 0 and 7 are Sunday)
user                 Valid OS user
command         Valid command or script

? ? ? ? ? command
|  | |  | |_________day of the week (0-6, 0=Sunday)
|  | |  |___________month (1-12)
|  | |_____________day of the month (1-31)
|  |_______________hour (0-23)
|_________________minute (0-59)

5. How to find operating system (OS) version?
Ans:
uname –a

6. How to find out the run level of the user?
Ans:
uname –r

7. How to delete 7 days old trace files?
Ans:
find ./trace –name *.trc –mtime +7 –exec rm {} \;

8. How to get 10th line of a file (by using grep)?

9. (In Solaris) how to find out whether it’s 32bit or 64bit?

10. What is paging?

11. What is top command?
Ans:
top is a operating system command, it will display top processes which are taking high cpu and memory.

12. How to find out the status of last command executed?
Ans:
$?

13. How to find out number of arguments passed to a shell script?
Ans:
$#

14. What is the default value of umask?
Ans:
022

15. How to add user in Solaris/Linux?
Ans:
useradd command

Advertisements

Oracle RMAN Interview Questions/FAQs

1. Difference between catalog and nocatalog?

2. Difference between using recovery catalog and control file?
When new incarnation happens, the old backup information in control file will be lost. It will be preserved in recovery catalog.
In recovery catalog, we can store scripts.
Recovery catalog is central and can have information of many databases.

3. Can we use same target database as catalog?
No. The recovery catalog should not reside in the target database (database to be backed up), because the database can’t be recovered in the mounted state.

4. How do u know how much RMAN task has been completed?
By querying v$rman_status or v$session_longops

5. From where list & report commands will get input?

6. Command to delete archive logs older than 7days?
RMAN> delete archivelog all completed before sysdate-7;

7. How many days backup, by default RMAN stores?

8. What is the use of crosscheck command in RMAN?
Crosscheck will be useful to check whether the catalog information is intact with OS level information.

9. What are the differences between crosscheck and validate commands?

10. Which is one is good, differential (incremental) backup or cumulative (incremental) backup?
A differential backup, which backs up all blocks changed after the most recent incremental backup at level 1 or 0
A cumulative backup, which backs up all blocks changed after the most recent incremental backup at level 0

11. What is Level 0, Level 1 backup?
A level 0 incremental backup, which is the base for subsequent incremental backups, copies all blocks containing data, backing the datafile up into a backup set just as a full backup would. A level 1 incremental backup can be either of the following types:
A differential backup, which backs up all blocks changed after the most recent incremental backup at level 1 or 0
A cumulative backup, which backs up all blocks changed after the most recent incremental backup at level 0

12. Can we perform level 1 backup without level 0 backup?
If no level 0 backup is available, then the behavior depends upon the compatibility mode setting. If compatibility < 10.0.0, RMAN generates a level 0 backup of the file contents at the time of the backup. If compatibility is >= 10.0.0, RMAN copies all blocks changed since the file was created, and stores the results as a level 1 backup. In other words, the SCN at the time the incremental backup is taken is the file creation SCN.

13. Will RMAN put the database/tablespace/datafile in backup mode?
Nope.

14. What is snapshot control file?

15. What is the difference between backup set and backup piece?
Backup set is logical and backup piece is physical.

16. RMAN command to backup for creating standby database?
RMAN> duplicate target database to standby database ….

17. How to do cloning by using RMAN?
RMAN> duplicate target database …

18. You loss one datafile and DB is running in ARCHIVELOG mode. You have full database backup of 1 week/day old and don’t have backup of this (newly created) datafile. How do you restore/recover file?
create the datafile and recover that datafile.
SQL> alter database create datafile ‘…path..’ size n;
RMAN> recover datafile file_id;

19. What is obsolete backup & expired backup?
A status of “expired” means that the backup piece or backup set is not found in the backup destination.
A status of “obsolete” means the backup piece is still available, but it is no longer needed. The backup piece is no longer needed since RMAN has been configured to no longer need this piece after so many days have elapsed, or so many backups have been performed.

20. What is the difference between hot backup & RMAN backup?
For hot backup, we have to put database in begin backup mode, then take backup.
RMAN won’t put database in backup mode.

21. How to put manual/user-managed backup in RMAN (recovery catalog)?
By using catalog command.
RMAN> CATALOG START WITH ‘/tmp/backup.ctl’;

22. What are new features in Oracle 11g RMAN?

23. What is the difference between auxiliary channel and maintenance channel?

Oracle DBA Interview Questions/FAQs

1. What is an instance?
SGA + background processes.

2. What is SGA?
System/Shared Global Area.

3. What is PGA (or) what is pga_aggregate_target?
Programmable Global Area.

4. What are new memory parameters in Oracle 10g?
SGA_TARGET PGA_TARGET

5. What are new memory parameters in Oracle 11g?
MEMORY_TARGET

6. What are the mandatory background processes?
DBWR LGWR SMON PMON CKPT RECO.

7. What are the optional background processes?
ARCH, MMAN, MMNL, MMON, CTWR, ASMB, RBAL, ARBx etc.

8. What are the new background processes in Oracle 10g?
MMAN MMON MMNL CTWR ASMB RBAL ARBx

9. What are the new features in Oracle 9i?
http://satya-dba.blogspot.com/2009/01/whats-new-in-9i.html

10. What are the new features in Oracle 10g?
http://satya-dba.blogspot.com/2009/01/whats-new-in-10g.html

11. What are the new features in Oracle 11g?
http://satya-dba.blogspot.com/2009/01/whats-new-in-11g.html

12. What are the new features in Oracle 11g R2?
http://satya-dba.blogspot.com/2009/09/whats-new-in-11g-release-2.html

13. What are the new features in Oracle 12c?
http://satya-dba.blogspot.com/2012/10/new-features-in-oracle-database-12c.html

14. What process will get data from datafiles to DB cache?
Server process

15. What background process will writes data to datafiles?
DBWR

16. What background process will write undo data?
DBWR

17. What are physical components of Oracle database?
Oracle database is comprised of three types of files. One or more datafiles, two or more redo log files, and one or more control files. Password file and parameter file also come under physical components.

18. What are logical components of Oracle database?
Blocks, Extents, Segments, Tablespaces.

19. What is segment space management?
LMTS and DMTS.

20. What is extent management?
Auto and Manual.

21. What are the differences between LMTS and DMTS?
Tablespaces that record extent allocation in the dictionary are called dictionary managed tablespaces, and tablespaces that record extent allocation in the tablespace header are called locally managed tablespaces.

21. What is a datafile?
Every Oracle database has one or more physical datafiles. Datafiles contain all the database data. The data of logical database structures such as tables and indexes is physically stored in the datafiles allocated for a database.

22. What are the contents of control file?
Database name, SCN, LSN, datafile locations, redolog locations, archive mode, DB Creation Time, RMAN Backup & Recovery Details, Flashback mode.

23. What is the use of redo log files?

24. What are the uses of undo tablespace or redo segments?

25. How undo tablespace can guarantee retain of required undo data?
Alter tablespace undo_ts retention guarantee;

26. What is ORA-01555 – snapshot too old error and how do you avoid it?

27. What is the use/size of temporary tablespace?

28. What is the use of password file?

29. How to create password file?
$ orapwd file=orapwSID password=sys_password force=y nosysdba=y

30. How many types of indexes are there?
Clustered and Non-Clustered

1.B-Tree index
2.Bitmap index
3.Unique index
4.Function based index

Implicit index and explicit index.
Explicit indexes are again of many types like simple index, unique index, Bitmap index, Functional index, Organisational index, cluster index.

31. What is bitmap index & when it’ll be used?
Bitmap indexes are preferred in Data warehousing environment.
Preferred when cardinality is low.

32. What is B-tree index & when it’ll be used?
B-tree indexes are preferred in OLTP environment.
Preferred when cardinality is high.

33. How you will find out fragmentation of index?
AUTO_SPACE_ADVISOR_JOB will run in daily maintenance window and report fragmented indexes/Tables.

analyze index validate structure;
This populates the table ‘index_stats’. It should be noted that this table contains only one row and therefore only one index can be analysed at a time.

An index should be considered for rebuilding under any of the following conditions:
* The percentage of deleted rows exceeds 30% of the total, i.e. if del_lf_rows / lf_rows > 0.3.
* If the ‘HEIGHT’ is greater than 4.
* If the number of rows in the index (‘LF_ROWS’) is significantly smaller than ‘LF_BLKS’ this can indicate a large number of deletes, indicating that the index should be rebuilt.

34. What is the difference between delete and truncate?
Truncate will release the space. Delete won’t.
Delete can be used to delete some records. Truncate can’t.
Delete can be rollbacked.
Delete will generate undo (Delete command will log the data changes in the log file where as the truncate will simply remove the data without it. Hence data removed by Delete command can be rolled back but not the data removed by TRUNCATE).
Truncate is a DDL statement whereas DELETE is a DML statement.
Truncate is faster than delete.

35. What’s the difference between a primary key and a unique key?
Both primary key and unique enforce uniqueness of the column on which they are defined. But by default primary key creates a clustered index on the column, where unique key creates a nonclustered index by default. Primary key doesn’t allow NULLs, but unique key allows one NULL only.

36. What is the difference between schema and user?
Schema is collection of user’s objects.

37. What is the difference between SYSDBA, SYSOPER and SYSASM?
SYSOPER can’t create and drop database.
SYSOPER can’t do incomplete recovery.
SYSOPER can’t change character set.
SYSOPER can’t CREATE DISKGROUP, ADD/DROP/RESIZE DISK

SYSASM can do anything SYSDBA can do.

38. What is the difference between SYS and SYSTEM?
SYSTEM can’t shutdown the database.
SYSTEM can’t create another SYSTEM, but SYS can create another SYS or SYSTEM.

39. How to improve sqlldr (SQL*Loader) performance?

40. What is the difference between view and materialized view?
View is logical, will store only the query, and will always gets latest data.
Mview is physical, will store the data, and may not get latest data.

41. What are materialized view refresh types and which is default?
Complete, fast, force(default)

42. How fast refresh happens?

43. How to find out when was a materialized view refreshed?
Query dba_mviews or dba_mview_analysis or dba_mview_refresh_times
SQL> select MVIEW_NAME, to_char(LAST_REFRESH_DATE,’YYYY-MM-DD HH24:MI:SS’) from dba_mviews;
(or)
SQL> select NAME, to_char(LAST_REFRESH,’YYYY-MM-DD HH24:MI:SS’) from dba_mview_refresh_times;
(or)
SQL> select MVIEW_NAME, to_char(LAST_REFRESH_DATE,’YYYY-MM-DD HH24:MI:SS’) from dba_mview_analysis;

44. What is materialized view log (type)?

45. What is atomic refresh in mviews?
From Oracle 10g, complete refresh of single materialized view can do delete instead of truncate. To force the refresh to do truncate instead of delete, parameter ATOMIC_REFRESH must be set to false.

ATOMIC_REFRESH = FALSE, mview will be truncated and whole data will be inserted. The refresh will go faster, and no undo will be generated.
ATOMIC_REFRESH = TRUE (default), mview will be deleted and whole data will be inserted. Undo will be generated. We will have access at all times even while it is being refreshed.

SQL> EXEC DBMS_MVIEW.REFRESH(‘mv_emp’, ‘C’, atomic_refresh=FALSE);

46. How to find out whether database/tablespace/datafile is in backup mode or not?
Query V$BACKUP view.

47. What is row chaining?
If the row is too large to fit into an empty data block in this case the oracle stores the data for the row in a chain of one or more data blocks. Can occur when the row is inserted.

48. What is row migration?
An update statement increases the amount of data in a row so that the row no longer fits in its data blocks. Now the oracle tries to find another free block with enough space to hold the entire row if such a block is available oracle moves entire row to new block.

49. What are different types of partitions?
With Oracle8, Range partitioning (on single column) was introduced.
With Oracle8i, Hash and Composite(Range-Hash) partitioning was introduced.
With Oracle9i, List partitioning and Composite(Range-List) partitioning was introduced.
With Oracle 11g, Interval partitioning, REFerence partitioning, Virtual column based partitioning, System partitioning and Composite partitioning [Range-Range, List-List, List-Range, List-Hash, Interval-Range, Interval-List, Interval-Interval] was introduced.

50. What is local partitioned index and global partitioned index?
A local index is an index on a partitioned table which is partitioned in the exact same manner as the underlying partitioned table. Each partition of a local index corresponds to one and only one partition of the underlying table.
A global partitioned index is an index on a partitioned or non partitioned tables which are partitioned using a different partitioning key from the table and can have different number of partitions. Global partitioned indexes can only be partitioned using range partitioning.

51. How you will recover if you lost one/all control file(s)?

52. Why more archivelogs are generated, when database is begin backup mode?
During begin backup mode datafile headers get freezed and as result row information cannot be retrieved as a result the entire block is copied to redo logs as a result more redo generated and more log switch and in turn more archive logs. Normally only deltas (change vectors) are logged to the redo logs. When in backup mode, Oracle will write complete changed blocks to the redo log files.

Mainly to overcome fractured blocks. Most of the cases Oracle block size is equal to or a multiple of the operating system block size.

e.g. Consider Oracle blocksize is 2k and OSBlocksize is 4k. so each OS Block is comprised of 2 Oracle Blocks. Now you are doing an update when your db is in backup mode. An Oracle Block is updating and at the same time backup is happening on the OS block which is having this particular DB block. Backup will not be consistent since the one part of the block is being updated and at the same time it is copied to the backup location. In this case we will have a fractured block, so as to avoid this Oracle will copy the whole OS block to redo logfile which can be used for recovery. Because of this redo generation is more.

53. What UNIX parameters you will set while Oracle installation?
shmmax, shmmni, shmall, sem,

54. What is the use of inittrans and maxtrans in table definition?

55. What are differences between dbms_job and dbms_schedular?
Through dbms_schedular we can schedule OS level jobs also.

56. What are differences between dbms_schedular and cron jobs?
Through dbms_schedular we can schedule database jobs, through cron we can’t set.

57. Difference between CPU & PSU patches?
CPU – Critical Patch Update – includes only Security related patches.
PSU – Patch Set Update – includes CPU + other patches deemed important enough to be released prior to a minor (or major) version release.

58. What you will do if (local) inventory corrupted [or] opatch lsinventory is giving error?

59. What are the entries/location of oraInst.loc?
/etc/oraInst.loc is pointer to central/local Oracle Inventory.

60. What is the difference between central/global inventory and local inventory?

61. What is the use of root.sh & oraInstRoot.sh?
Ans:
Changes ownership & permissions of oraInventory
Creating oratab file in the /etc directory
In RAC, starts the clusterware stack

62. What is transportable tablespace (and across platforms)?

63. How can you transport tablespaces across platforms with different endian formats?
Ans:
RMAN

64. What is xtss (cross platform transportable tablespace)?

65. What is the difference between restore point & guaranteed restore point?

66. What is the difference between 10g/11g OEM Grid control and 12c Cloud control?

67. What are the components of Grid control?
Ans:
OMS (Oracle Management Server)
OMR (Oracle Management Repository)
OEM Agent

68. What are the new features of 12c Cloud control?

69. How to find if your Oracle database is 32 bit or 64 bit?
Ans:
execute the command “file $ORACLE_HOME/bin/oracle”, you should see output like /u01/db/bin/oracle: ELF 64-bit MSB executable SPARCV9 Version 1

means you are on 64 bit oracle.

If your oracle is 32 bit you should see output like below
oracle: ELF 32-bit MSB executable SPARC Version 1

70. How to find opatch Version ?
Ans:
opatch is utility to apply database patch, In order to find opatch version execute”$ORACLE_HOME/OPatch/opatch version”

Oracle Data Guard Interview Questions/FAQs

1. How to setup Data Guard?

2. What are different types of modes in Data Guard and which is default?
Maximum performance:
This is the default protection mode. It provides the highest level of data protection that is possible without affecting the performance of a primary database. This is accomplished by allowing transactions to commit as soon as all redo data generated by those transactions has been written to the online log.

Maximum protection:
This protection mode ensures that no data loss will occur if the primary database fails. To provide this level of protection, the redo data needed to recover a transaction must be written to both the online redo log and to at least one standby database before the transaction commits. To ensure that data loss cannot occur, the primary database will shut down, rather than continue processing transactions.

Maximum availability:
This protection mode provides the highest level of data protection that is possible without compromising the availability of a primary database. Transactions do not commit until all redo data needed to recover those transactions has been written to the online redo log and to at least one standby database.

3. How many standby databases we can create (in 10g/11g)?
Till Oracle 10g, 9 standby databases are supported.
From Oracle 11g R2, we can create 30 standby databases.

4. What are the parameters we’ve to set in primary/standby for Data Guard?

5. What is the use of fal_server & fal_client, is it mandatory to set these?

6. What are differences between physical, logical, snapshot standby and ADG (or) what are different types of standby databases?
Physical standby – in mount state, MRP will apply archives
ADG – in READ ONLY state, MRP will apply archives
Logical standby – in READ ONLY state, LSP will run
Snapshot standby databases – Physical standby database can be converted to snapshot standby database, which will be in READ WRITE mode, can do any kind of testing, then we can convert back snapshot standby database to physical standby database and start MRP which will apply all pending archives.

7. How to find out backlog of standby?
select round((sysdate – a.NEXT_TIME)*24*60) as “Backlog”,m.SEQUENCE#-1 “Seq Applied”,m.process, m.status
from v$archived_log a, (select process,SEQUENCE#, status from v$managed_standby where process like ‘%MRP%’)m where a.SEQUENCE#=(m.SEQUENCE#-1);

8. If you didn’t have access to the standby database and you wanted to find out what error has occurred in a data guard configuration, what view would you check in the primary database to check the error message?
You can check the v$dataguard_status view.
select message from v$dataguard_status;

9. How can u recover standby which far behind from primary (or) without archive logs how can we make standby sync?
By using RMAN incremental backup.

10. What is snapshot standby (or) How can we give a physical standby to user in READ WRITE mode and let him do updates and revert back to standby?
Till Oralce 10g, create guaranteed restore point, open in read write, let him do updates, flashback to restore point, start MRP.
From Oracle 11g, convert physical standby to snapshot standby, let him do updates, convert to physical standby, start MRP.

11. What are new features in 11g Data Guard?

12. What are the uses of standby redo log files?

13. What is dg_config?

14. What is RTA (real time apply) mode MRP?

15. What is the difference between normal MRP (managed apply) and RTA MRP (real time apply)?

16. What are various parameters in log_archive_dest and it’s use?

17. What is the difference between SYNC/ASYNC, LGWR/ARCH, and AFFIRM/NOAFFIRM?

18. What is Data Guard broker (or) what is the use of dgmgrl?

19. What is StaticConnectIdentifier property used for?

20. What is failover/switchover (or) what is the difference between failover & switchover?

21. What are the background processes involved in Data Guard?
MRP, LSP,

Oracle ASM Interview Questions/FAQs

1. What is the use of ASM (or) Why ASM preferred over filesystem?
ASM provides striping and mirroring.

2. What are the init parameters related to ASM?
INSTANCE_TYPE = ASM
ASM_POWER_LIMIT = 11
ASM_DISKSTRING = ‘/dev/rdsk/*s2’, ‘/dev/rdsk/c1*’
ASM_DISKGROUPS = DG_DATA, DG_FRA

3. What is rebalancing (or) what is the use of ASM_POWER_LIMIT?
ASM_POWER_LIMIT is dynamic parameter, which will be useful for rebalancing the data across disks.
Value can be 1(lowest) to 11 (highest).

4. What are different types of redundancies in ASM & explain?
External redundancy,
Normal redundancy,
High redundancy.

5. How to copy file to/from ASM from/to filesystem?
By using ASMCMD cp command

6. How to find out the databases, which are using the ASM instance?
ASMCMD> lsct
SQL> select DB_NAME from V$ASM_CLIENT;

7. What are different types of stripings in ASM & their differences?
Fine-grained striping
Coarse-grained striping
lsdg
select NAME,ALLOCATION_UNIT_SIZE from v$asm_diskgroup;

8. What is allocation unit and what is default value of au_size and how to change?
Every ASM disk is divided into allocation units (AU). An AU is the fundamental unit of allocation within a disk group. A file extent consists of one or more AU. An ASM file consists of one or more file extents.
CREATE DISKGROUP disk_group_2 EXTERNAL REDUNDANCY DISK ‘/dev/sde1’ ATRRIBUTE ‘au_size’ = ’32M’;

9. What are the background processes in ASM?

10. What process does the rebalancing?
RBAL, ARBn

11. How to add/remove disk to/from diskgroup?

Oracle DBA interview questions

Interview FAQ2

1. Explain the difference between a hot backup and a cold backup and the benefits

associated with each.

A hot backup is basically taking a backup of the database while it is still up and running

and it must be in archive log mode. A cold backup is taking a backup of the database

while it is shut down and does not require being in archive log mode. The benefit of

taking a hot backup is that the database is still available for use while the backup is

occurring and you can recover the database to any ball in time. The benefit of taking a

cold backup is that it is typically easier to administer the backup and recovery process.

In addition, since you are taking cold backups the database does not require being in

archive log mode and thus there will be a slight performance gain as the database is not

cutting archive logs to disk.

2. You have just had to restore from backup and do not have any control files. How

would you go about bringing up this database?

I would create a text based backup control file, stipulating where on disk all the data

files where and then issue the recover command with the using backup control file

clause.

3. How do you switch from an init.ora file to a spfile?

Issue the create spfile from pfile command.

4. Explain the difference between a data block, an extent and a segment.

A data block is the smallest unit of logical storage for a database object. As objects

grow they take chunks of additional storage that are composed of contiguous data

blocks. These groupings of contiguous data blocks are called extents. All the extents

that an object takes when grouped together are considered the segment of the database

object.

5. Give two examples of how you might determine the structure of the table DEPT.

Use the describe command or use the dbms_metadata.get_ddl package.

6. Where would you look for errors from the database engine?

In the alert log.

7. Compare and contrast TRUNCATE and DELETE for a table.

Both the truncate and delete command have the desired outcome of getting rid of all the

rows in a table. The difference between the two is that the truncate command is a DDL

operation and just moves the high water mark and produces a now rollback. The delete

command, on the other hand, is a DML operation, which will produce a rollback and

thus take longer to complete.

8. Give the reasoning behind using an index.

Faster access to data blocks in a table.

9. Give the two types of tables involved in producing a star schema and the type of

data they hold.

Fact tables and dimension tables. A fact table contains measurements while dimension

tables will contain data that will help describe the fact tables.

10. What type of index should you use on a fact table?

A Bitmap index.

11. Give two examples of referential integrity constraints.

A primary key and a foreign key.

12. A table is classified as a parent table and you want to drop and re-create it. How

would you do this without affecting the children tables?

Disable the foreign key constraint to the parent, drop the table, re-create the table,

enable the foreign key constraint.

13. Explain the difference between ARCHIVELOG mode and NOARCHIVELOG mode and the benefits and disadvantages to each.

ARCHIVELOG mode is a mode that you can put the database in for creating a backup

of all transactions that have occurred in the database so that you can recover to any ball

in time. NOARCHIVELOG mode is basically the absence of ARCHIVELOG mode and

has the disadvantage of not being able to recover to any ball in time.

NOARCHIVELOG mode does have the advantage of not having to write transactions

to an archive log and thus increases the performance of the database slightly.

14. What command would you use to create a backup control file?

Alter database backup control file to trace.

15. Give the stages of instance startup to a usable state where normal users may access it.

STARTUP NOMOUNT – Instance startup

STARTUP MOUNT – The database is mounted

STARTUP OPEN – The database is opened

16. What column differentiates the V$ views to the GV$ views and how?

The INST_ID column which indicates the instance in a RAC environment the

information came from.

17. How would you go about generating an EXPLAIN plan?

Create a plan table with utlxplan.sql.

Use the explain plan set statement_id = ‘tst1′ into plan_table for a SQL statement

Look at the explain plan with utlxplp.sql or utlxpls.sql

18. How would you go about increasing the buffer cache hit ratio?

Use the buffer cache advisory over a given workload and then query the

v$db_cache_advice table. If a change was necessary then I would use the alter system

set db_cache_size command.

19. Explain an ORA-01555

You get this error when you get a snapshot too old within rollback. It can usually be

solved by increasing the undo retention or increasing the size of rollbacks. You should

also look at the logic involved in the application getting the error message.

20. Explain the difference between $ORACLE_HOME and $ORACLE_BASE.

ORACLE_BASE is the root directory for oracle. ORACLE_HOME located beneath

ORACLE_BASE is where the oracle products reside.

1. Describe the difference between a procedure, function and anonymous pl/sql

block.

Candidate should mention use of DECLARE statement, a function must return a value

while a procedure doesn?t have to.

2. What is a mutating table error and how can you get around it?

This happens with triggers. It occurs because the trigger is trying to update a row it is

currently using. The usual fix involves either use of views or temporary tables so the

database is selecting from one while updating the other.

3. Describe the use of %ROWTYPE and %TYPE in PL/SQL

Expected answer: %ROWTYPE allows you to associate a variable with an entire table

row. The %TYPE associates a variable with a single column type.

4. 4What packages (if any) has Oracle provided for use by developers?

Expected answer: Oracle provides the DBMS_ series of packages. There are many

which developers should be aware of such as DBMS_SQL, DBMS_PIPE,

DBMS_TRANSACTION, DBMS_LOCK, DBMS_ALERT, DBMS_OUTPUT,

DBMS_JOB, DBMS_UTILITY, DBMS_DDL, UTL_FILE. If they can mention a few

of these and describe how they used them, even better. If they include the SQL routines

provided by Oracle, great, but not really what was asked.

5. Describe the use of PL/SQL tables

Expected answer: PL/SQL tables are scalar arrays that can be referenced by a binary

integer. They can be used to hold values for use in later queries or calculations. In

Oracle 8 they will be able to be of the %ROWTYPE designation, or RECORD.

6. When is a declare statement needed ?

The DECLARE statement is used in PL/SQL anonymous blocks such as with stand

alone, non-stored PL/SQL procedures. It must come first in a PL/SQL stand alone file if

it is used.

7. In what order should a open/fetch/loop set of commands in a PL/SQL block be

implemented if you use the %NOTFOUND cursor variable in the exit when statement? Why?

Expected answer: OPEN then FETCH then LOOP followed by the exit when. If not

specified in this order will result in the final return being done twice because of the way

the %NOTFOUND is handled by PL/SQL.

8. What are SQLCODE and SQLERRM and why are they important for PL/SQL

developers?

Expected answer: SQLCODE returns the value of the error number for the last error

encountered. The SQLERRM returns the actual error message for the last error

encountered. They can be used in exception handling to report, or, store in an error log

table, the error that occurred in the code. These are especially useful for the WHEN

OTHERS exception.

9. How can you find within a PL/SQL block, if a cursor is open?

Expected answer: Use the %ISOPEN cursor status variable.

10. How can you generate debugging output from PL/SQL?

Expected answer: Use the DBMS_OUTPUT package. Another possible method is to

just use the SHOW ERROR command, but this only shows errors. The

DBMS_OUTPUT package can be used to show intermediate results from loops and the

status of variables as the procedure is executed. The new package UTL_FILE can also

be used.

11. What are the types of triggers?

Expected Answer: There are 12 types of triggers in PL/SQL that consist of

combinations of the BEFORE, AFTER, ROW, TABLE, INSERT, UPDATE, DELETE

and ALL key words:

BEFORE ALL ROW INSERT

AFTER ALL ROW INSERT

BEFORE INSERT

AFTER INSERT etc.

1. Give one method for transferring a table from one schema to another:

There are several possible methods, export-import, CREATE TABLE… AS SELECT, or

COPY.

2. What is the purpose of the IMPORT option IGNORE? What is it?s default setting

The IMPORT IGNORE option tells import to ignore “already exists” errors. If it is not

specified the tables that already exist will be skipped. If it is specified, the error is

ignored and the tables data will be inserted. The default value is N.

3. You have a rollback segment in a version 7.2 database that has expanded beyond

optimal, how can it be restored to optimal

Use the ALTER TABLESPACE ….. SHRINK command.

4. If the DEFAULT and TEMPORARY tablespace clauses are left out of a CREATE USER command what happens? Is this bad or good? Why

The user is assigned the SYSTEM tablespace as a default and temporary tablespace.

This is bad because it causes user objects and temporary segments to be placed into the

SYSTEM tablespace resulting in fragmentation and improper table placement (only

data dictionary objects and the system rollback segment should be in SYSTEM).

5. What are some of the Oracle provided packages that DBAs should be aware of

Oracle provides a number of packages in the form of the DBMS_ packages owned by

the SYS user. The packages used by DBAs may include: DBMS_SHARED_POOL,

DBMS_UTILITY, DBMS_SQL, DBMS_DDL, DBMS_SESSION, DBMS_OUTPUT

and DBMS_SNAPSHOT. They may also try to answer with the UTL*.SQL or

CAT*.SQL series of SQL procedures. These can be viewed as extra credit but aren?t

part of the answer.

6. What happens if the constraint name is left out of a constraint clause

The Oracle system will use the default name of SYS_Cxxxx where xxxx is a system

generated number. This is bad since it makes tracking which table the constraint

belongs to or what the constraint does harder.

7. What happens if a tablespace clause is left off of a primary key constraint clause

This results in the index that is automatically generated being placed in then users

default tablespace. Since this will usually be the same tablespace as the table is being

created in, this can cause serious performance problems.

8. What is the proper method for disabling and re-enabling a primary key constraint

You use the ALTER TABLE command for both. However, for the enable clause you

must specify the USING INDEX and TABLESPACE clause for primary keys.

9. What happens if a primary key constraint is disabled and then enabled without fully specifying the index clause

The index is created in the user?s default tablespace and all sizing information is lost.

Oracle doesn?t store this information as a part of the constraint definition, but only as

part of the index definition, when the constraint was disabled the index was dropped

and the information is gone.

10. (On UNIX) When should more than one DB writer process be used? How many should be used

If the UNIX system being used is capable of asynchronous IO then only one is required,

if the system is not capable of asynchronous IO then up to twice the number of disks

used by Oracle number of DB writers should be specified by use of the db_writers

initialization parameter.

11. You are using hot backup without being in archivelog mode, can you recover in the event of a failure? Why or why not

You can?t use hot backup without being in archivelog mode. So no, you couldn?t

recover.

12. What causes the “snapshot too old” error? How can this be prevented or mitigated

This is caused by large or long running transactions that have either wrapped onto their

own rollback space or have had another transaction write on part of their rollback space.

This can be prevented or mitigated by breaking the transaction into a set of smaller

transactions or increasing the size of the rollback segments and their extents.

13. How can you tell if a database object is invalid

By checking the status column of the DBA_, ALL_ or USER_OBJECTS views,

depending upon whether you own or only have permission on the view or are using a

DBA account.

13. A user is getting an ORA-00942 error yet you know you have granted them

permission on the table, what else should you check

You need to check that the user has specified the full name of the object (select empid

from scott.emp; instead of select empid from emp;) or has a synonym that balls to the

object (create synonym emp for scott.emp;)

14. A developer is trying to create a view and the database won?t let him. He has the

“DEVELOPER” role which has the “CREATE VIEW” system privilege and SELECT grants on the tables he is using, what is the problem

You need to verify the developer has direct grants on all tables used in the view. You

can?t create a stored object with grants given through views.

15. If you have an example table, what is the best way to get sizing data for the

production table implementation

The best way is to analyze the table and then use the data provided in the

DBA_TABLES view to get the average row length and other pertinent data for the

calculation. The quick and dirty way is to look at the number of blocks the table is

actually using and ratio the number of rows in the table to its number of blocks against

the number of expected rows.

16. How can you find out how many users are currently logged into the database? How

can you find their operating system id

There are several ways. One is to look at the v$session or v$process views. Another

way is to check the current_logins parameter in the v$sysstat view. Another if you are

on UNIX is to do a “ps -ef|grep oracle|wc -l? command, but this only works against a

single instance installation.

17. A user selects from a sequence and gets back two values, his select is:

SELECT pk_seq.nextval FROM dual;What is the problem

Somehow two values have been inserted into the dual table. This table is a single row,

single column table that should only have one value in it.

18. How can you determine if an index needs to be dropped and rebuilt

Run the ANALYZE INDEX command on the index to validate its structure and then

calculate the ratio of LF_BLK_LEN/LF_BLK_LEN+BR_BLK_LEN and if it isn?t near

1.0 (i.e. greater than 0.7 or so) then the index should be rebuilt. Or if the ratio

BR_BLK_LEN/ LF_BLK_LEN+BR_BLK_LEN is nearing 0.3

1. How can variables be passed to a SQL routine

By use of the & symbol. For passing in variables the numbers 1-8 can be used (&1,

&2,…,&8) to pass the values after the command into the SQLPLUS session. To be

prompted for a specific variable, place the ampersanded variable in the code itself:

“select * from dba_tables where owner=&owner_name;” . Use of double ampersands

tells SQLPLUS to resubstitute the value for each subsequent use of the variable, a

single ampersand will cause a reprompt for the value unless an ACCEPT statement is

used to get the value from the user.

2. You want to include a carriage return/linefeed in your output from a SQL script, how

can you do this

The best method is to use the CHR() function (CHR(10) is a return/linefeed) and the

concatenation function “||”. Another method, although it is hard to document and isn?t

always portable is to use the return/linefeed as a part of a quoted string.

3. How can you call a PL/SQL procedure from SQL

By use of the EXECUTE (short form EXEC) command.

4. How do you execute a host operating system command from within SQL

By use of the exclamation ball “!” (in UNIX and some other OS) or the HOST (HO)

command.

5. You want to use SQL to build SQL, what is this called and give an example

This is called dynamic SQL. An example would be:

set lines 90 pages 0 termout off feedback off verify off

spool drop_all.sql

select ?drop user ?||username||? cascade;? from dba_users

where username not in (“SYS?,?SYSTEM?);

spool off

Essentially you are looking to see that they know to include a command (in this case

DROP USER…CASCADE;) and that you need to concatenate using the ?||? the values

selected from the database.

6. What SQLPlus command is used to format output from a select

This is best done with the COLUMN command.

7. You want to group the following set of select returns, what can you group on

Max(sum_of_cost), min(sum_of_cost), count(item_no), item_no

The only column that can be grouped on is the “item_no” column, the rest have

aggregate functions associated with them.

8. What special Oracle feature allows you to specify how the cost based system treats

a SQL statement

The COST based system allows the use of HINTs to control the optimizer path

selection. If they can give some example hints such as FIRST ROWS, ALL ROWS,

USING INDEX, STAR, even better.

9. You want to determine the location of identical rows in a table before attempting to

place a unique index on the table, how can this be done

Oracle tables always have one guaranteed unique column, the rowid column. If you use

a min/max function against your rowid and then select against the proposed primary

key you can squeeze out the rowids of the duplicate rows pretty quick. For example:

select rowid from emp e

where e.rowid > (select min(x.rowid)

from emp x

where x.emp_no = e.emp_no);

In the situation where multiple columns make up the proposed key, they must all be

used in the where clause.

10. What is a Cartesian product

A Cartesian product is the result of an unrestricted join of two or more tables. The result

set of a three table Cartesian product will have x * y * z number of rows where x, y, z

correspond to the number of rows in each table involved in the join.

11. You are joining a local and a remote table, the network manager complains about

the traffic involved, how can you reduce the network traffic

Push the processing of the remote data to the remote instance by using a view to preselect

the information for the join. This will result in only the data required for the join

being sent across.

11. What is the default ordering of an ORDER BY clause in a SELECT statement

Ascending

12. What is tkprof and how is it used

The tkprof tool is a tuning tool used to determine cpu and execution times for SQL

statements. You use it by first setting timed_statistics to true in the initialization file and

then turning on tracing for either the entire database via the sql_trace parameter or for

the session using the ALTER SESSION command. Once the trace file is generated you

run the tkprof tool against the trace file and then look at the output from the tkprof tool.

This can also be used to generate explain plan output.

13. What is explain plan and how is it used

The EXPLAIN PLAN command is a tool to tune SQL statements. To use it you must

have an explain_table generated in the user you are running the explain plan for. This is

created using the utlxplan.sql script. Once the explain plan table exists you run the

explain plan command giving as its argument the SQL statement to be explained. The

explain_plan table is then queried to see the execution plan of the statement. Explain

plans can also be run using tkprof.

14. How do you set the number of lines on a page of output? The width

The SET command in SQLPLUS is used to control the number of lines generated per

page and the width of those lines, for example SET PAGESIZE 60 LINESIZE 80 will

generate reports that are 60 lines long with a line width of 80 characters. The

PAGESIZE and LINESIZE options can be shortened to PAGES and LINES.

15. How do you prevent output from coming to the screen

The SET option TERMOUT controls output to the screen. Setting TERMOUT OFF

turns off screen output. This option can be shortened to TERM.

16. How do you prevent Oracle from giving you informational messages during and after

a SQL statement execution

The SET options FEEDBACK and VERIFY can be set to OFF.

17. How do you generate file output from SQL

By use of the SPOOL command

1. A tablespace has a table with 30 extents in it. Is this bad? Why or why not.

Multiple extents in and of themselves aren?t bad. However if you also have chained

rows this can hurt performance.

2. How do you set up tablespaces during an Oracle installation?

You should always attempt to use the Oracle Flexible Architecture standard or another

partitioning scheme to ensure proper separation of SYSTEM, ROLLBACK, REDO

LOG, DATA, TEMPORARY and INDEX segments.

3. You see multiple fragments in the SYSTEM tablespace, what should you check first?

Ensure that users don?t have the SYSTEM tablespace as their TEMPORARY or

DEFAULT tablespace assignment by checking the DBA_USERS view.

4. What are some indications that you need to increase the SHARED_POOL_SIZE

parameter?

Poor data dictionary or library cache hit ratios, getting error ORA-04031. Another

indication is steadily decreasing performance with all other tuning parameters the same.

5. What is the general guideline for sizing db_block_size and db_multi_block_read for an

application that does many full table scans?

Oracle almost always reads in 64k chunks. The two should have a product equal to 64

or a multiple of 64.

6. What is the fastest query method for a table

Fetch by rowed

7. Explain the use of TKPROF? What initialization parameter should be turned on to get

full TKPROF output?

The tkprof tool is a tuning tool used to determine cpu and execution times for SQL

statements. You use it by first setting timed_statistics to true in the initialization file and

then turning on tracing for either the entire database via the sql_trace parameter or for

the session using the ALTER SESSION command. Once the trace file is generated you

run the tkprof tool against the trace file and then look at the output from the tkprof tool.

This can also be used to generate explain plan output.

8. When looking at v$sysstat you see that sorts (disk) is high. Is this bad or good? If

bad -How do you correct it?

If you get excessive disk sorts this is bad. This indicates you need to tune the sort area

parameters in the initialization files. The major sort are parameter is the

SORT_AREA_SIZe parameter.

9. When should you increase copy latches? What parameters control copy latches

When you get excessive contention for the copy latches as shown by the “redo copy”

latch hit ratio. You can increase copy latches via the initialization parameter

LOG_SIMULTANEOUS_COPIES to twice the number of CPUs on your system.

10. Where can you get a list of all initialization parameters for your instance? How about

an indication if they are default settings or have been changed

You can look in the init.ora file for an indication of manually set parameters. For all

parameters, their value and whether or not the current value is the default value, look in

the v$parameter view.

11. Describe hit ratio as it pertains to the database buffers. What is the difference

between instantaneous and cumulative hit ratio and which should be used for tuning

The hit ratio is a measure of how many times the database was able to read a value from

the buffers verses how many times it had to re-read a data value from the disks. A value

greater than 80-90% is good, less could indicate problems. If you simply take the ratio

of existing parameters this will be a cumulative value since the database started. If you

do a comparison between pairs of readings based on some arbitrary time span, this is

the instantaneous ratio for that time span. Generally speaking an instantaneous reading

gives more valuable data since it will tell you what your instance is doing for the time it

was generated over.

12. Discuss row chaining, how does it happen? How can you reduce it? How do you

correct it

Row chaining occurs when a VARCHAR2 value is updated and the length of the new

value is longer than the old value and won?t fit in the remaining block space. This

results in the row chaining to another block. It can be reduced by setting the storage

parameters on the table to appropriate values. It can be corrected by export and import

of the effected table.

13. When looking at the estat events report you see that you are getting busy buffer

waits. Is this bad? How can you find what is causing it

Buffer busy waits could indicate contention in redo, rollback or data blocks. You need

to check the v$waitstat view to see what areas are causing the problem. The value of the

“count” column tells where the problem is, the “class” column tells you with what.

UNDO is rollback segments, DATA is data base buffers.

14. If you see contention for library caches how can you fix it

Increase the size of the shared pool.

15. If you see statistics that deal with “undo” what are they really talking about

Rollback segments and associated structures.

16. If a tablespace has a default pctincrease of zero what will this cause (in relationship

to the smon process)

The SMON process won?t automatically coalesce its free space fragments.

17. If a tablespace shows excessive fragmentation what are some methods to

defragment the tablespace? (7.1,7.2 and 7.3 only)

In Oracle 7.0 to 7.2 The use of the ‘alter session set events ‘immediate trace name

coalesce level ts#’;? command is the easiest way to defragment contiguous free space

fragmentation. The ts# parameter corresponds to the ts# value found in the ts$ SYS

table. In version 7.3 the ?alter tablespace coalesce;? is best. If the free space isn?t

contiguous then export, drop and import of the tablespace contents may be the only way

to reclaim non-contiguous free space.

18. How can you tell if a tablespace has excessive fragmentation

If a select against the dba_free_space table shows that the count of a tablespaces extents

is greater than the count of its data files, then it is fragmented.

19. You see the following on a status report:

redo log space requests 23

redo log space wait time 0

Is this something to worry about? What if redo log space wait time is high? How

can you fix this

Since the wait time is zero, no. If the wait time was high it might indicate a need for

more or larger redo logs.

20. What can cause a high value for recursive calls? How can this be fixed

A high value for recursive calls is cause by improper cursor usage, excessive dynamic

space management actions, and or excessive statement re-parses. You need to determine

the cause and correct it By either relinking applications to hold cursors, use proper

space management techniques (proper storage and sizing) or ensure repeat queries are

placed in packages for proper reuse.

21. If you see a pin hit ratio of less than 0.8 in the estat library cache report is this a

problem? If so, how do you fix it

This indicate that the shared pool may be too small. Increase the shared pool size.

22. If you see the value for reloads is high in the estat library cache report is this a

matter for concern

Yes, you should strive for zero reloads if possible. If you see excessive reloads then

increase the size of the shared pool.

23. You look at the dba_rollback_segs view and see that there is a large number of

shrinks and they are of relatively small size, is this a problem? How can it be fixed if it is

a problem

A large number of small shrinks indicates a need to increase the size of the rollback

segment extents. Ideally you should have no shrinks or a small number of large shrinks.

To fix this just increase the size of the extents and adjust optimal accordingly.

24. You look at the dba_rollback_segs view and see that you have a large number of

wraps is this a problem

A large number of wraps indicates that your extent size for your rollback segments are

probably too small. Increase the size of your extents to reduce the number of wraps.

You can look at the average transaction size in the same view to get the information on

transaction size.

25. In a system with an average of 40 concurrent users you get the following from a

query on rollback extents:

ROLLBACK CUR EXTENTS

——————— ————————–

R01 11

R02 8

R03 12

R04 9

SYSTEM 4

26. You have room for each to grow by 20 more extents each. Is there a problem? Should

you take any action

No there is not a problem. You have 40 extents showing and an average of 40

concurrent users. Since there is plenty of room to grow no action is needed.

27. You see multiple extents in the temporary tablespace. Is this a problem

As long as they are all the same size this isn?t a problem. In fact, it can even improve

performance since Oracle won?t have to create a new extent when a user needs one.

28. Define OFA.

OFA stands for Optimal Flexible Architecture. It is a method of placing directories and

files in an Oracle system so that you get the maximum flexibility for future tuning and

file placement.

29. How do you set up your tablespace on installation

The answer here should show an understanding of separation of redo and rollback, data

and indexes and isolation os SYSTEM tables from other tables. An example would be

to specify that at least 7 disks should be used for an Oracle installation so that you can

place SYSTEM tablespace on one, redo logs on two (mirrored redo logs) the

TEMPORARY tablespace on another, ROLLBACK tablespace on another and still

have two for DATA and INDEXES. They should indicate how they will handle archive

logs and exports as well. As long as they have a logical plan for combining or further

separation more or less disks can be specified.

30. What should be done prior to installing Oracle (for the OS and the disks)

adjust kernel parameters or OS tuning parameters in accordance with installation guide.

Be sure enough contiguous disk space is available.

31. You have installed Oracle and you are now setting up the actual instance. You have

been waiting an hour for the initialization script to finish, what should you check first to

determine if there is a problem

Check to make sure that the archiver isn?t stuck. If archive logging is turned on during

install a large number of logs will be created. This can fill up your archive log

destination causing Oracle to stop to wait for more space.

32. When configuring SQLNET on the server what files must be set up

INITIALIZATION file, TNSNAMES.ORA file, SQLNET.ORA file

33. When configuring SQLNET on the client what files need to be set up

SQLNET.ORA, TNSNAMES.ORA

34. What must be installed with ODBC on the client in order for it to work with Oracle

SQLNET and PROTOCOL (for example: TCPIP adapter) layers of the transport

programs.

35. You have just started a new instance with a large SGA on a busy existing server.

Performance is terrible, what should you check for

The first thing to check with a large SGA is that it isn?t being swapped out.

36. What OS user should be used for the first part of an Oracle installation (on UNIX)

You must use root first.

37. When should the default values for Oracle initialization parameters be used as is

Never

38. How many control files should you have? Where should they be located

At least 2 on separate disk spindles. Be sure they say on separate disks, not just file

systems.

39. How many redo logs should you have and how should they be configured for

maximum recoverability

You should have at least three groups of two redo logs with the two logs each on a

separate disk spindle (mirrored by Oracle). The redo logs should not be on raw devices

on UNIX if it can be avoided.

40. You have a simple application with no “hot” tables (i.e. uniform IO and access

requirements). How many disks should you have assuming standard layout for SYSTEM,

USER, TEMP and ROLLBACK tablespaces

At least 7, see disk configuration answer above.

41. Describe third normal form

Something like: In third normal form all attributes in an entity are related to the primary

key and only to the primary key

42. Is the following statement true or false:

“All relational databases must be in third normal form”

False. While 3NF is good for logical design most databases, if they have more than just

a few tables, will not perform well using full 3NF. Usually some entities will be

denormalized in the logical to physical transfer process.

43. What is an ERD

An ERD is an Entity-Relationship-Diagram. It is used to show the entities and

relationships for a database logical model.

44. Why are recursive relationships bad? How do you resolve them

A recursive relationship (one where a table relates to itself) is bad when it is a hard

relationship (i.e. neither side is a “may” both are “must”) as this can result in it not

being possible to put in a top or perhaps a bottom of the table (for example in the

EMPLOYEE table you couldn?t put in the PRESIDENT of the company because he has

no boss, or the junior janitor because he has no subordinates). These type of

relationships are usually resolved by adding a small intersection entity.

45. What does a hard one-to-one relationship mean (one where the relationship on both

ends is “must”)

Expected answer: This means the two entities should probably be made into one entity.

46. How should a many-to-many relationship be handled

By adding an intersection entity table

47. What is an artificial (derived) primary key? When should an artificial (or derived)

primary key be used

A derived key comes from a sequence. Usually it is used when a concatenated key

becomes too cumbersome to use as a foreign key.

48. When should you consider denormalization

Whenever performance analysis indicates it would be beneficial to do so without

compromising data integrity.

49. How can you determine if an Oracle instance is up from the operating system level

There are several base Oracle processes that will be running on multi-user operating

systems, these will be smon, pmon, dbwr and lgwr. Any answer that has them using

their operating system process showing feature to check for these is acceptable. For

example, on UNIX a ps -ef|grep dbwr will show what instances are up.

50. Users from the PC clients are getting messages indicating :

ORA-06114: (Cnct err, can’t get err txt. See Servr Msgs & Codes Manual)

What could the problem be

The instance name is probably incorrect in their connection string.

51. Users from the PC clients are getting the following error stack:

ERROR: ORA-01034: ORACLE not available

ORA-07318: smsget: open error when opening sgadef.dbf file.

HP-UX Error: 2: No such file or directory

What is the probable cause

The Oracle instance is shutdown that they are trying to access, restart the instance.

52. How can you determine if the SQLNET process is running for SQLNET V1? How about

V2

For SQLNET V1 check for the existence of the orasrv process. You can use the

command “tcpctl status” to get a full status of the V1 TCPIP server, other protocols

have similar command formats. For SQLNET V2 check for the presence of the

LISTENER process(s) or you can issue the command “lsnrctl status”.

53. What file will give you Oracle instance status information? Where is it located

The alert.ora log. It is located in the directory specified by the background_dump_dest

parameter in the v$parameter table.

54. Users aren?t being allowed on the system. The following message is received:

ORA-00257 archiver is stuck. Connect internal only, until freed

What is the problem

The archive destination is probably full, backup the archive logs and remove them and

the archiver will re-start.

55. Where would you look to find out if a redo log was corrupted assuming you are using

Oracle mirrored redo logs

There is no message that comes to the SQLDBA or SRVMGR programs during startup

in this situation, you must check the alert.log file for this information.

56. You attempt to add a datafile and get:

ORA-01118: cannot add anymore datafiles: limit of 40 exceeded

What is the problem and how can you fix it

When the database was created the db_files parameter in the initialization file was set to

40. You can shutdown and reset this to a higher value, up to the value of

MAX_DATAFILES as specified at database creation. If the MAX_DATAFILES is set

to low, you will have to rebuild the control file to increase it before proceeding.

57. You look at your fragmentation report and see that smon hasn?t coalesced any of

you tablespaces, even though you know several have large chunks of contiguous free

extents. What is the problem

Check the dba_tablespaces view for the value of pct_increase for the tablespaces. If

pct_increase is zero, smon will not coalesce their free space.

58. Your users get the following error:

ORA-00055 maximum number of DML locks exceeded

What is the problem and how do you fix it

The number of DML Locks is set by the initialization parameter DML_LOCKS. If this

value is set to low (which it is by default) you will get this error. Increase the value of

DML_LOCKS. If you are sure that this is just a temporary problem, you can have them

wait and then try again later and the error should clear.

59. You get a call from you backup DBA while you are on vacation. He has corrupted all

of the control files while playing with the ALTER DATABASE BACKUP CONTROLFILE

command. What do you do

As long as all datafiles are safe and he was successful with the BACKUP controlfile

command you can do the following:

CONNECT INTERNAL

STARTUP MOUNT

(Take any read-only tablespaces offline before next step ALTER DATABASE

DATAFILE …. OFFLINE;)

RECOVER DATABASE USING BACKUP CONTROLFILE

ALTER DATABASE OPEN RESETLOGS;

(bring read-only tablespaces back online)

Shutdown and backup the system, then restart

If they have a recent output file from the ALTER DATABASE BACKUP CONTROL

FILE TO TRACE; command, they can use that to recover as well.

If no backup of the control file is available then the following will be required:

CONNECT INTERNAL

STARTUP NOMOUNT

CREATE CONTROL FILE …..;

However, they will need to know all of the datafiles, logfiles, and settings for

MAXLOGFILES, MAXLOGMEMBERS, MAXLOGHISTORY, MAXDATAFILES

for the database to use the command.

Oracle DBA Interview questions

Differentiate between TRUNCATE and DELETE.

The Delete command will log the data changes in the log file where as the truncate will

simply remove the data without it. Hence Data removed by Delete command can be

rolled back but not the data removed by TRUNCATE. Truncate is a DDL statement

whereas DELETE is a DML statement.

What is the maximum buffer size that can be specified using the

DBMS_OUTPUT.ENABLE function?

1000000

Can you use a commit statement within a database trigger?

Yes, if you are using autonomous transactions in the Database triggers.

What is an UTL_FILE? What are different procedures and functions associated

with it?

The UTL_FILE package lets your PL/SQL programs read and write operating system

(OS) text files. It provides a restricted version of standard OS stream file input/output

(I/O).

Subprogram -Description

FOPEN function-Opens a file for input or output with the default line size.

IS_OPEN function -Determines if a file handle refers to an open file.

FCLOSE procedure -Closes a file.

FCLOSE_ALL procedure -Closes all open file handles.

GET_LINE procedure -Reads a line of text from an open file.

PUT procedure-Writes a line to a file. This does not append a line terminator.

NEW_LINE procedure-Writes one or more OS-specific line terminators to a file.

PUT_LINE procedure -Writes a line to a file. This appends an OS-specific line

terminator.

PUTF procedure -A PUT procedure with formatting.

FFLUSH procedure-Physically writes all pending output to a file.

FOPEN function -Opens a file with the maximum line size specified.

Difference between database triggers and form triggers?

Database triggers are fired whenever any database action like INSERT, UPATE,

DELETE, LOGON LOGOFF etc occurs. Form triggers on the other hand are fired in

response to any event that takes place while working with the forms, say like navigating

from one field to another or one block to another and so on.

What is OCI. What are its uses?

OCI is Oracle Call Interface. When applications developers demand the most powerful

interface to the Oracle Database Server, they call upon the Oracle Call Interface (OCI).

OCI provides the most comprehensive access to all of the Oracle Database functionality.

The newest performance, scalability, and security features appear first in the OCI API. If

you write applications for the Oracle Database, you likely already depend on OCI. Some

types of applications that depend upon OCI are:

· PL/SQL applications executing SQL

· C++ applications using OCCI

· Java applications using the OCI-based JDBC driver

· C applications using the ODBC driver

· VB applications using the OLEDB driver

· Pro*C applications

· Distributed SQL

What are ORACLE PRECOMPILERS?

A precompiler is a tool that allows programmers to embed SQL statements in high-level

source programs like C, C++, COBOL, etc. The precompiler accepts the source program

as input, translates the embedded SQL statements into standard Oracle runtime library

calls, and generates a modified source program that one can compile, link, and execute in

the usual way. Examples are the Pro*C Precompiler for C, Pro*Cobol for Cobol, SQLJ

for Java etc.

What is syntax for dropping a procedure and a function? Are these operations

possible?

Drop Procedure/Function ; yes, if they are standalone procedures or functions. If they are

a part of a package then one have to remove it from the package definition and body and

recompile the package.

How to check if Apps 11i System is Autoconfig enabled ?

Under $AD_TOP/bin check for file adcfginfo.sh and if this exists use adcfginfo.sh

contextfile=<CONTEXT> show=enabled

If this file is not there , look for any configuration file under APPL_TOP if system is

Autoconfig enabled then you will see entry like

How to check if Oracle Apps 11i System is Rapid Clone enabled ?

For syetem to be Rapid Clone enabled , it should be Autoconfig enabled (Check above

How to confirm if Apps 11i is Autoconfig enabled). You should have Rapid Clone

Patches applied , Rapid Clone is part of Rapid Install Product whose Family Pack Name

is ADX. By default all Apps 11i Instances 11.5.9 and above are Autoconfig and Rapid

Clone enabled.

Whats is difference between two env files in <CONTEXT>.env and

APPS<CONTEXT>.env under $APPL_TOP ?

APPS<CONTEXT>.env is main environment file which inturn calls other environment

files like <CONTEXT>.env under $APPL_TOP, <CONTEXT>.env under 806

ORACLE_HOME and custom.env for any Customized environment files.

Whats main concurrent Manager types.

# ICM – Internal Concurrent Manager which manages concurrent Managers

# Standard Managers – Which Manage processesing of requests.

# CRM – Conflict Resolution Managers , resolve conflicts in case of incompatibility.

Whats US directory in $AD_TOP or under various product TOP’s .

US directory is defauly language directory in Oracle Applications. If you have multiple

languages Installed in your Applications then you will see other languages directories

besides US, that directory will contain reports, fmx and other code in that respective

directory like FR for France, AR for arabic, simplifies chinese or spanish.

Where is Concurrent Manager log file location.

By default standard location is $APPLCSF/$APPLLOG , in some cases it can go to

$FND_TOP/log as well.

Where would i find .rf9 file, and what execatly it dose ?

These files are used during restart of patch in case of patch failure because of some

reason.

Where is appsweb.cfg or appsweb_$CONTEXT.cfg stored and why its used ?

This file is defined by environment variable FORMS60_WEB_CONFIG_FILE This is

usually in directory $OA_HTML/bin on forms tier.

This file is used by any forms client session. When a user try to access forms , f60webmx

picks up this file and based on this configuration file creates a forms session to

user/client.

What is Multi Node System ?

Multi Node System in Oracle Applications 11i means you have Applications 11i

Component on more than one system. Typical example is Database, Concurrent Manager

on one machine and forms, Web Server on second machine is example of Two Node

System.

Can a function take OUT parameters. If not why?

yes, IN, OUT or IN OUT.

Can the default values be assigned to actual parameters?

Yes. In such case you don’t need to specify any value and the actual parameter will take

the default value provided in the function definition.

What is difference between a formal and an actual parameter?

The formal parameters are the names that are declared in the parameter list of the header

of a module. The actual parameters are the values or expressions placed in the parameter

list of the actual call to the module.

What are different modes of parameters used in functions and procedures?

There are three different modes of parameters: IN, OUT, and IN OUT.

IN – The IN parameter allows you to pass values in to the module, but will not pass

anything out of the module and back to the calling PL/SQL block. In other words, for the

purposes of the program, its IN parameters function like constants. Just like constants, the

value of the formal IN parameter cannot be changed within the program. You cannot

assign values to the IN parameter or in any other way modify its value.

IN is the default mode for parameters. IN parameters can be given default values in the

program header.

OUT – An OUT parameter is the opposite of the IN parameter. Use the OUT parameter to

pass a value back from the program to the calling PL/SQL block. An OUT parameter is

like the return value for a function, but it appears in the parameter list and you can, of

course, have as many OUT parameters as you like.

Inside the program, an OUT parameter acts like a variable that has not been initialised. In

fact, the OUT parameter has no value at all until the program terminates successfully

(without raising an exception, that is). During the execution of the program, any

assignments to an OUT parameter are actually made to an internal copy of the OUT

parameter. When the program terminates successfully and returns control to the calling

block, the value in that local copy is then transferred to the actual OUT parameter. That

value is then available in the calling PL/SQL block.

IN OUT – With an IN OUT parameter, you can pass values into the program and return a

value back to the calling program (either the original, unchanged value or a new value set

within the program). The IN OUT parameter shares two restrictions with the OUT

parameter:

An IN OUT parameter cannot have a default value.

An IN OUT actual parameter or argument must be a variable. It cannot be a constant,

literal, or expression, since these formats do not provide a receptacle in which PL/SQL

can place the outgoing value.

Difference between procedure and function.

A function always returns a value, while a procedure does not. When you call a function

you must always assign its value to a variable.

Can cursor variables be stored in PL/SQL tables. If yes how. If not why?

Yes. Create a cursor type – REF CURSOR and declare a cursor variable of that type.

DECLARE

/* Create the cursor type. */

TYPE company_curtype IS REF CURSOR RETURN company%ROWTYPE;

/* Declare a cursor variable of that type. */

company_curvar company_curtype;

/* Declare a record with same structure as cursor variable. */

company_rec company%ROWTYPE;

BEGIN

/* Open the cursor variable, associating with it a SQL statement. */

OPEN company_curvar FOR SELECT * FROM company;

/* Fetch from the cursor variable. */

FETCH company_curvar INTO company_rec;

/* Close the cursor object associated with variable. */

CLOSE company_curvar;

END;

Can you clone from multi node system to single node system and vice versa ?

Yes , this is now supported via Rapid Clone, Check if your system has all prereq. patches

for Rapid Clone and you are on latest rapid clone patch.

Does rapid clone takes care of Updating Global oraInventory or you have to register

manually in Global OraInventory after clone ?

Rapid Clone will automatically Update Global oraInventory during configuration phase.

You don’t have to do any thing manually for Global oraInventory.

What is .dbc file , where its stored , whats use of .dbc file ?

dbc as name says is database connect descriptor file which stores database connection

information used by application tier to connect to database. This file is in directory

$FND_TOP/secure also called as FND_SECURE

Whats things you do to reduce patch timing ?

You can take advantage of following –

# Merging patches via admrgpch

# Use various adpatch options like nocompiledb or nocompilejsp

# Use defaults file

# Staged APPL_TOP during upgrades

# Increase batch size (Might result into negative )

How you put Applications 11i in Maintenance mode ?

Use adadmin to change Maintenance mode is Oracle Apps. With AD.I you need to enable

maintenance mode in order to apply apps patch via adpatch utility. If you don’t want to

put apps in maintenance mode you can use adpatch options=hotpatch feature.

Can you apply patch without putting Applications 11i in Maintenance mode ?

Yes, use options=hotpatch as mentioned above with adpatch.

What are various options available with adpatch ?

Various options available with adpatch depending on your AD version are autoconfig,

check_exclusive, checkfile, compiledb, compilejsp, copyportion, databaseprtion,

generateportion, hotpatch, integrity, maintainmrc, parallel, prereq, validate

ADIDENT UTILITY is used for what ?

ADIDENT UTILITY in oracle apps is used to find version of any file . AD Identification.

for ex. “adident Header <filename>

How do you pass cursor variables in PL/SQL?

Pass a cursor variable as an argument to a procedure or function. You can, in essence,

share the results of a cursor by passing the reference to that result set.

How do you open and close a cursor variable. Why it is required?

Using OPEN cursor_name and CLOSE cursor_name commands. The cursor must be

opened before using it in order to fetch the result set of the query it is associated with.

The cursor needs to be closed so as to release resources earlier than end of transaction, or

to free up the cursor variable to be opened again.

What should be the return type for a cursor variable. Can we use a scalar data type

as return type?

The return type of a cursor variable can be %ROWTYPE or record_name%TYPE or a

record type or a ref cursor type. A scalar data type like number or varchar can’t be used

but a record type may evaluate to a scalar value.

What is use of a cursor variable? How it is defined?

Cursor variable is used to mark a work area where Oracle stores a multi-row query output

for processing. It is like a pointer in C or Pascal. Because it is a TYPE, it is defined as

TYPE REF CURSOR RETURN ;

What WHERE CURRENT OF clause does in a cursor?

The Where Current Of statement allows you to update or delete the record that was last

fetched by the cursor.

Difference between NO DATA FOUND and %NOTFOUND

NO DATA FOUND is an exception which is raised when either an implicit query returns

no data, or you attempt to reference a row in the PL/SQL table which is not yet defined.

SQL%NOTFOUND, is a BOOLEAN attribute indicating whether the recent SQL

statement does not match to any row.

What is a cursor for loop?

A cursor FOR loop is a loop that is associated with (actually defined by) an explicit

cursor or a SELECT statement incorporated directly within the loop boundary. Use the

cursor FOR loop whenever (and only if) you need to fetch and process each and every

record from a cursor, which is a high percentage of the time with cursors.

What is iAS Patch ?

iAS Patch are patches released to fix bugs associated with IAS_ORACLE_HOME (Web

Server Component) Usually these are shiiped as Shell scripts and you apply iAS patches

by executing Shell script. Note that by default ORACLE_HOME is pointing to 8.0.6

ORACLE_HOME and if you are applying iAS patch export ORACLE_HOME to iAS .

You can do same by executing environment file under $IAS_ORACLE_HOME

If we run autoconfig which files will get effected ?

In order to check list of files changes during Autoconfig , you can run adchkcfg utility

which will generate HTML report. This report will list all files and profile options going

to change when you run AutoConfig.

What is difference between .xml file and AutoConfig ?

Autoconfig is Utility to configure your Oracle Application environment. .xml file is

repository of all configuration from which AutoConfig picks configuration and polulates

related files

.

What is .lgi files ?

lgi files are created with patching along with .log files . .lgi files are informative log files

containing information related to patch. You can check .lgi files to see what activities

patch has done. Usually informative logs.

How will you skip worker during patch ?

If in your adctrl there are six option shown then seventh is hidden option.(If there are

seven options visible then 8th option is to Skip worker depending on ad version).

Which two tables created at start of Apps Patch and drops at end of Patch ?

FND_INSTALLED_PROCESS and AD_DEFFERED_JOBS are the tables that get

updated while applying a patch mainly d or unified driver.

How to compile an Oracle Reports file ?

Utility adrepgen is used to compile Reports. Synatx is given below adrepgen

userid=apps\<psswd> source = $PRODUCT_TOP\srw\filename.rdf

dest=$PRODUCT_TOP\srw\filename.rdf stype=rdffile dtype=rdffile logfile=x.log

overwrite=yes batch=yes dunit=character

What is difference between AD_BUGS and AD_APPLID_PATCHES ?

AD_BUGS holds information about the various Oracle Applications bugs whose fixes

have been applied (ie. patched) in the Oracle Applications installation.

AD_APPLIED_PATCHES holds information about the “distinct” Oracle Applications

patches that have been applied. If 2 patches happen to have the same name but are

different in content (eg. “merged” patches), then they are considered distinct and this

table will therefore hold 2 records.

What is ADSPLICE UTILITY ?

ADSPLICE UTILITY in oracle apps is utility to add a new product.

How can you licence a product after installation ?

You can use ad utility adlicmgr to licence product in Oracle Apps.

What is MRC ? What you do as Apps DBA for MRC ?

MRC also called as Multiple Reporting Currency in oracle Apps. Default you have

currency in US Dollars but if your organization operating books are in other currency

then you as apps dba need to enable MRC in Apps. How to enable MRC coming soon..

What is access_log in apache , what entries are recored in access_log ? Where is

default location of thsi file ?

access_log in Oracle Application Server records all users accessing oracle applications

11i. This file location is defined in httpd.conf with default location at

$IAS_ORACLE_HOME/Apache/Apache/logs. Entries in this file is defined by directive

LogFormat in httpd.conf Typical entry in access_log is

198.0.0.1 – – [10/Sep/2006:18:37:17 +0100] “POST /OA_HTML/OA.jsp?…. HTTP/1.1″

200 28035

where 200 is HTTP status code and last digits 28035 is bytes dowloaded as this page(Size

of page)

Where is Jserv configuration files stored ?

Jserv configuration files are stored in $IAS_ORACLE_HOME/Apache/Jserv/etc

Where is applications start/stop scripts stored ?

applications start/stop scripts are in directory

$COMMON_TOP/admin/scripts/$CONTEXT_NAME

What are main configuration files in Web Server (Apache) ?

Main configuration files in Oracle Apps Web Server are

# httpd.conf, apps.conf, oracle_apache.conf, httpd_pls.conf

# jserv.conf, ssp_init.txt, jserv.properties, zone.properties

# plsql.conf, wdbsvr.app, plsql.conf

Can C driver in apps patch create Invalid Object in database ?

No , C driver only copies files in File System. Database Object might be invalidated

during D driver when these objects are created/dropped/modified.

What is dev60cgi and f60cgi ?

CGI stands for Common Gateway Interface and these are Script Alias in Oracle Apps

used to access forms server . Usually Form Server access directly via

http://hostname:port/dev60cgi/f60cgi

Why does a worker fails in Oracle Apps Patch and few scenarios in which it failed

for you ?

Apps Patch worker can fail in case it doesn’t find expected data, object, files or any thing

which driver is trying to update/edit/modify. Possible symptoms may be underlying

tables/objects are invalid, a prereq patch is missing , login information is incorrect,

inconsistency in seeded data…

What is difference between mod_osso and mod_ose in Oracle HTTP Server ?

mod_osso is Oracle Single Sign-On Module where as mod_ose is module for Oracle

Servlet Engine.

mod_osso is module in Oracle’s HTTP Server serves as Conduit between Oracle Apache

Server and Singl Sign-On Server where as mod_ose is also another module in Oracle’s

HTTP Server serves as conduit between Oracle Apache and Oracle Servlet Engine.

What is difference between COMPILE_ALL=SPECIAL and COMPILE=ALL while

compiling Forms ?

Both the options will compile all the PL/SQL in the resultant .FMX, .PLX, or .MMX file

but COMPILE_ALL=YES also changes the cached version in the source .FMB, .PLL, or

.MMB file. This confuses version control and build tools (CVS, Subversion, make,

scons); they believe you’ve made significant changes to the source.

COMPILE_ALL=SPECIAL does not do this.

What is GSM in Oracle application E-Business Suite ?

GSM stands for Generic Service Management Framework. Oracle E-Business Suite

consist of various compoennts like Forms, Reports, Web Server, Workflow, Concurrent

Manager ..

Earlier each service used to start at their own but managing these services (given that)

they can be on various machines distributed across network. So Generic Service

Management is extension of Concurrent Processing which manages all your services ,

provide fault tolerance (If some service is down ICM through FNDSM and other

processes will try to start it even on remote server) With GSM all services are centrally

managed via this Framework.

What is FNDSM ?

FNDSM is executable and core component in GSM ( Generic Service Management

Framework discussed above). You start FNDSM services via APPS listener on all Nodes

in Application Tier in E-Business Suite.

What are cursor attributes?

Cursor attributes are used to get the information about the current status of your cursor.

Both explicit and implicit cursors have four attributes, as shown:

Name Description

%FOUND Returns TRUE if record was fetched successfully, FALSE otherwise.

%NOTFOUND Returns TRUE if record was not fetched successfully, FALSE otherwise.

%ROWCOUNT Returns number of records fetched from cursor at that point in time.

%ISOPEN Returns TRUE if cursor is open, FALSE otherwise.

Difference between an implicit and an explicit cursor.

The implicit cursor is used by Oracle server to test and parse the SQL statements and the

explicit cursors are declared by the programmers.

What is a cursor?

A cursor is a mechanism by which you can assign a name to a “select statement” and

manipulate the information within that SQL statement.

What is the purpose of a cluster?

A cluster provides an optional method of storing table data. A cluster is comprised of a

group of tables that share the same data blocks, which are grouped together because they

share common columns and are often used together. For example, the EMP and DEPT

table share the DEPTNO column. When you cluster the EMP and DEPT, Oracle

physically stores all rows for each department from both the EMP and DEPT tables in the

same data blocks. You should not use clusters for tables that are frequently accessed

individually.

How do you find the number of rows in a Table ?

select count(*) from table, or from NUM_ROWS column of user_tables if the table

statistics has been collected.

Display the number value in Words?

What is a pseudo column. Give some examples?

Information such as row numbers and row descriptions are automatically stored by

Oracle and is directly accessible, ie. not through tables. This information is contained

within pseudo columns. These pseudo columns can be retrieved in queries. These pseudo

columns can be included in queries which select data from tables.

Available Pseudo Columns

· ROWNUM – row number. Order number in which a row value is retrieved.

· ROWID – physical row (memory or disk address) location, ie. unique row identification.

· SYSDATE – system or today’s date.

· UID – user identification number indicating the current user.

· USER – name of currently logged in user.

Whats is location of access_log file ?

access_log file by default is located in $IAS_ORACLE_HOME/ Apache/Apache/logs.

Location of this file is defined in httpd.conf by patameter CustomLog or TransferLog

What is your Oracle Apps 11i Webserver Version and how to find it ?

From 11.5.8 to 11.5.10 Webserver version is iAS 1.0.2.2.2, In order to find version under

$IAS_ORACLE_HOME/Apache/Apache/bin execute ./httpd -version

./httpd -version

Server version: Oracle HTTP Server Powered by Apache/1.3.19

Server built: Dec 6 2005 14:59:13 (iAS 1.0.2.2.2 rollup 5)

What is Location of Jserv configuration files ?

Jserv configuration files are located in $IAS_ORACLE_HOME /Apache/Jserv/etc .

What is plssql/database cache ?

In order to improve performance mod_pls (Apache component) caches some database

content to file. This database/plssql cache is usually of type session and plsql cache

# session cache is used to store session information.

# plsql cache is used to store plsql cache i.e. used by mod_pls

Where is DATABASE/PLSSQL cache stored ?

PLSSQL and session cache are stored under $IAS_ORACLE_HOME/

Apache/modplsql/cache directory.

What is *.DBC file and whats is location of DBC file ?

DBC as name stands for is database connect descriptor file used to connect to database.

This file by default located in $FND_TOP/secure directory also called as

$FND_SECURE directory.

What is content of DBC file and why its important ?

DBC file is quite important as whenever Java or any other program like forms want to

connect to database it uses DBC file. Typical entry in DBC file is

GUEST_USER_PWD

APPS_JDBC_URL

DB_HOST

What are few profile options which you update after cloning ?

Rapid clone updates profile options specific to site level . If you have any profile option

set at other levels like server, responsibility, user….level then reset them.

How to retrieve SYSADMIN password ?

If forgot password link is enabled and SYSADMIN account is configured with mail id

user forget password link else you can reset sSYSADMIN password via FNDCPASS.

Whats is TWO_TASK in Oracle Database ?

TWO_TASK mocks your tns alias which you are going to use to connect to database.

Lets assume you have database client with tns alias defined as PROD to connect to

Database PROD on machine teachmeoracle.com listening on port 1521. Then usual way

to connect is sqlplus username/passwd@PROD ; now if you don’t want to use @PROD

then you set TWO_TASK=PROD and then can simply use sqlplus username/passwd then

sql will check that it has to connect to tnsalias define by value PROD i.e. TWO_TASK

What is GWYUID ?

GWYUID , stands for Gateway User ID and password. Usually like APPLSYSPUB/PUB

Where GWYUID defined and what is its used in Oracle Applications ?

GWYUID is defined in dbc i.e. Database Connect Descriptor file . It is used to connect to

database by think clients.

If APPS_MRC schema is not used in 11.5.10 and higher then How MRC is

working ?

For products like Payable, Recievables which uses MRC and if MRC is enabled then

each transaction table in base schema related to currency now has an assoicated MRC

Subtables.

When you apply C driver patch does it require database to be Up and Why ?

Yes , database and db listener should be Up when you apply any driver patch in apps.

even if driver is not updating any database object connection is required to validate

appsand other schema and to upload patch history information in database tables.

How you will avoid your query from using indexes?

By changing the order of the columns that are used in the index, in the Where condition,

or by concatenating the columns with some constant values.

What is a OUTER JOIN?

An OUTER JOIN returns all rows that satisfy the join condition and also returns some or

all of those rows from one table for which no rows from the other satisfy the join

condition.

Which is more faster – IN or EXISTS?

Well, the two are processed very differently.

Select * from T1 where x in ( select y from T2 )

is typically processed as:

select *

from t1, ( select distinct y from t2 ) t2

where t1.x = t2.y;

The sub query is evaluated, distinct’ed, indexed (or hashed or sorted) and then joined to

the original table — typically. As opposed to select * from t1 where exists ( select null

from t2 where y = x )

That is processed more like:

for x in ( select * from t1 )

loop

if ( exists ( select null from t2 where y = x.x )

then

OUTPUT THE RECORD

end if

end loop

It always results in a full scan of T1 whereas the first query can make use of an index on

T1(x). So, when is where exists appropriate and in appropriate? Lets say the result of the

sub query ( select y from T2 ) is “huge” and takes a long time. But the table T1 is

relatively small and executing ( select null from t2 where y = x.x ) is very fast (nice index

on t2(y)). Then the exists will be faster as the time to full scan T1 and do the index probe

into T2 could be less then the time to simply full scan T2 to build the sub query we need

to distinct on.

Lets say the result of the sub query is small — then IN is typically more appropriate. If

both the sub query and the outer table are huge — either might work as well as the other

—     depends on the indexes and other factors.

When do you use WHERE clause and when do you use HAVING clause?

The WHERE condition lets you restrict the rows selected to those that satisfy one or more

conditions. Use the HAVING clause to restrict the groups of returned rows to those

groups for which the specified condition is TRUE.

There is a % sign in one field of a column. What will be the query to find it?

SELECT column_name FROM table_name WHERE column_name LIKE ‘%\%%’

ESCAPE ‘\’;

Where will you find forms configuration details apart from xml file ?

Forms configuration at time of startup is in script adfrmctl.sh and

appsweb_$CONTEXT_NAME.cfg (defined by environment variable

FORMS60_WEB_CONFIG_FILE) for forms client connection used each time a user

initiates forms connection.

What is forms server executable Name ?

f60srvm

What are different modes of forms in which you can start Forms Server and which

one is default ?

You can start forms server in SOCKET or SERVLET by defualt Forms are configured to

start in socket mode.

How you will start Discoverer in Oracle Apps 11i ?

In order to start dicoverer you can use script addisctl.sh under

$OAD_TOP/admin/scripts/$CONTEXT_NAME or startall.sh under

$ORACLE_HOME/discwb4/util (under Middle/Application Tier)

How many ORACLE HOME are Oracle Apps and whats significance of each ?

There are three $ORACLE_HOME in Oracle Apps, Two for Application Tier (Middle

Tier) and One in Database Tier.

# ORACLE_HOME 1 : On Application Tier used to store 8.0.6 techstack software. This

is used by forms, reports and discoverer. ORACLE_HOME should point to this

ORACLE_HOME which applying Apps Patch.

# ORACLE_HOME 2: On Application Tier used by iAS (Web Server) techstack

software. This is used by Web Listener and contains Apache.

# ORACLE_HOME 3: On Database Tier used by Database Software usually 8i,9i or 10g

database.

Where is HTML Cache stored in Oracle Apps Server ?

Oracle HTML Cache is available at $COMMON_TOP/_pages for some previous

versions you might find it in $OA_HTML/_pages

Where is plssql cache stored in Oracle Apps ?

Usually two type of cache session and plssql stored under

$IAS_ORACLE_HOME/Apache/modplsql/cache

What happens if you don’t give cache size while defining Concurrent Manager ?

Lets first understand what is cache size in Concurrent Manager. When Manager picks

request from FND CONCURRENT REQUESTS Queues, it will pick up number of

requests defined by cache size in one shot and will work on them before going to sleep. If

you don’t define cache size while defining CM then it will take default value 1, i.e.

picking up one request per cycle.

There are lot of DBC file under $FND_SECURE, How its determined that which

dbc file to use from $FND_SECURE ?

This value is determined from profile option “Applications Database ID”

What is RRA/FNDFS ?

Report Review Agent(RRA) also referred by executable FNDFS is default text viewer in

Oracle Applications 11i for viewing output files and log files. As most of apps dba’s are

not clear about Report Server and RRA, I’ll discuss one on my blog and update link here .

What is PCP is Oracle Applications 11i ?

PCP is acronym for Parallel Concurrurent processing. Usually you have one Concurrent

Manager executing your requests but if you can configure Concurrent Manager running

on two machines (Yes you need to do some additional steps in order to configure Parallel

Concurrent Processing) . So for some of your requests primary CM Node is on machine1

and secondary CM node on machine2 and for some requests primary CM is on machine2

and secondary CM on machine1.

Why I need two Concurrent Processing Nodes or in what scenarios PCP is Used ?

Well If you are running GL Month end reports or taxation reports annually these reposrts

might take couple of days. Some of these requests are very resource intensive so you can

have one node running long running , resource intensive requests while other processing

your day to day short running requets.

Another scenario is when your requests are very critical and you want high resilience for

your Concurrent Processing Node , you can configure PCP. So if node1 goes down you

still have CM node available processing your requests.

Output and Logfiles for requests executed on source Instance not working on cloned

Instance

Here is exact problem description – You cloned an Oracle Apps Instance from

PRODBOX to another box with Instance name say CLONEBOX on 1st of August. You

can any CM logs/output files after 1st of August only becuase these all are generated on

CLONEBOX itself, But unable to view the logs/output files which are prior to 1st

August. What will you do and where to check ?

Log , Output file path and location is stored in table

FND_CONCURRENT_REQUESTS. Check select logfile_name, logfile_node_name,

outfile_name, outfile_node_name from fnd_concurrent_requests where

request_id=&requestid ; where requestid is id of request for which you are not able to see

log or out files. You should see output like /u01/PRODBOX/log/l123456.req,

host1,/u01/PRODBOX/out/o123456.out, host1

Update it according to your cloned Instance Variables.

How to confirm if Report Server is Up and Running ?

Report Server is started by executable rwmts60 on concurrent manager Node and this file

is under $ORACLE_HOME/bin .execute command on your server like

ps -ef | grep rwmts60

You should get output like

applmgr ……. rwmts60

What is difference between ICM, Standard Managers and CRM in Concurrent

Manager ?

# ICM stand for Internal Concurrent Manager, which controls other managers. If it finds

other managers down , it checks and try to restart them. You can say it as administrator to

other concurrent managers. It has other tasks as well.

# Standard Manager These are normal managers which control/action on the requests nd

does batch or single request processing. # CRM acronym for Conflict Resolution

Manager is used to resolve conflicts between managers nd request. If a request is

submitted whose execution is clashing or it is defined not to run while a particular type of

request is running then such requests are actioned/assigned to CRM for Incompatibilities

and Conflict resolution.

What is difference between SUBSTR and INSTR?

INSTR function search string for sub-string and returns an integer indicating the position

of the character in string that is the first character of this occurrence. SUBSTR function

return a portion of string, beginning at character position, substring_length characters

long. SUBSTR calculates lengths using characters as defined by the input character set.

Which data type is used for storing graphics and images?

Raw, Long Raw, and BLOB.

What is difference between SQL and SQL*PLUS?

SQL is the query language to manipulate the data from the database. SQL*PLUS is the

tool that lets to use SQL to fetch and display the data.

What is difference between UNIQUE and PRIMARY KEY constraints?

An UNIQUE key can have NULL whereas PRIMARY key is always not NOT NULL.

Both bears unique values.

What is difference between Rename and Alias?

Rename is actually changing the name of an object whereas Alias is giving another name

(additional name) to an existing object.

Rename is a permanent name given to a table or column whereas Alias is a temporary

name given to a table or column which do not exist once the SQL statement is executed.

What are various joins used while writing SUBQUERIES?

=, , IN, NOT IN, IN ANY, IN ALL, EXISTS, NOT EXISTS.

What is use of Apps listener ?

Apps Listener usually running on All Oracle Applications 11i Nodes with listener alias as

APPS_$SID is mainly used for listening requests for services like FNDFS and FNDSM.

How to start Apps listener ?

In Oracle 11i, you have script adalnctl.sh which will start your apps listener. You can also

start it by command lsnrctl start APPS_$SID (Replace sid by your Instance SID Name)

How to confirm if Apps Listener is Up and Running ?

execute below command

lsnrctl status APPS_$SID (replcae SID with your Instance Name)

so If your SID is VISION then use lsnrctl status APPS_VISION out put should be like

Services Summary…

FNDFS has 1 service handler(s)

FNDSM has 1 service handler(s)

What is Web Listener ?

Web Listener is Web Server listener which is listening for web Services(HTTP) request.

This listener is started by adapcctl.sh and defined by directive (Listen, Port) in httpd.conf

for Web Server. When you initially type request like

http://becomeappsdba.blogspot.com:80 to access application here port number 80 is Web

Listener port.

How will you find Invalid Objects in database ?

using query SQLPLUS> select count(*) from dba_objects where status like ‘INVALID’;

How to compile Invalid Objects in database ?

You can use adadmin utility to compile or you can use utlrp.sql script shipped with

Oracle Database to compile Invalid Database Objects.

How to compile JSP in Oracle Apps ?

You can use ojspCompile.pl perl script shipped with Oracle apps to compile JSP files.

This script is under $JTF_TOP/admin/scripts. Sample compilation method is

perl ojspCompile.pl –compile –quiet

What is difference between ADPATCH and OPATCH ?

# ADPATCH is utility to apply oracle apps Patches whereas

# OPATCH is utility to apply database patches

Can you use both ADPATCH and OPATCH in Apps ?

Yes you have to use both in apps , for apps patches you will use ADPATCH UTILITY

and for applying database patch in apps you will use opatch UTILITY.

Oracle DBA interview questions

Oracle Concepts and Architecture Database Structures

1. What are the components of physical database structure of Oracle database?

Physical Structure

The physical layer of the database consists of three types of files:

  1. One or more Datafiles
  2. Two or more redo log files
  3. One or more control files

Datafiles (.dbf files):

Datafiles store the information contained in the database. One can have as few as one data file or as many as hundreds of datafiles. The information for a single table can span many datafiles or many tables can share a set of datafiles. Spreading tablespaces over many datafiles can have a significant positive effect on performance. The number of datafiles that can be configured is limited by the Oracle parameter MAXDATAFILES.

Redo Log Files (.rdo & .arc):

Oracle maintains logs of all the transaction against the database. These transactions are recorded in files called Online Redo Log Files (Redo Logs). The main purpose of the Redo log files is to hold information as recovery in the event of a system failure. Redo log stores a log of all changes made to the database. The redo log files must perform well and be protected against hardware failures (through software or hardware fault tolerance). If redo log information is lost, one cannot recover the system.

When a transaction occurs in the database, it is entered in the redo log buffers, while the data blocks affected by the transactions are not immediately written to disk. In anOracle database there are at least three or more Redo Log files.

Oracle writes to redo log file in a cyclical order i.e. after the first log file is filled, it writes to the second log file, until that one is filled. When all the Redo Log files have been filled, it returns to the first log file and begin overwrite its content with new transaction data. Note, if the database is running in the ARCHIVELOG Mode, the database will make a copy of the online redo log files before overwriting them.

Control Files (.ctl):

Control files record control information about all of the files within the database. These files maintain internal consistency and guide recovery operation. Control files contain information used to start an instance, such as the location of datafiles and redo log files; Oracle needs this information to start the database instance. Control files must be protected. Oracle provides a mechanism for storing multiple copies of control files. These multiple copies are stored on separate disks to minimize the potential damage due to disk failure. The names of the database’s control files are specified via the CONTROL_FILES initialization parameter.

2. What are the components of logical database structure of Oracle database?

Oracle is an RDBMS (Relational Database Management System). The Oracle database architecture can be described in terms of logical and physical structures. The advantage of separating the logical and physical structure is that the physical storage structure can be changed without affecting the logical structure.

Logical Structure

The logical structure for Oracle RDBMS consists of the following elements:

  • Tablespace
  • Schema

Tablespace

The Oracle database consists of one or more logical portions called as ‘Tablespaces’. A tablespace is a logical grouping of related data.

A database administrator can use Tablespaces to do the following:

  • Control disk space allocation for database data.
  • Assign specific space quotas for database users.
  • Perform partial database backup or recovery operations.
  • Allocate data storage across devices to improve performance.

Each database has at least one Tablespace called SYSTEM Tablespace. As part of the process of creating the database, Oracle automatically creates the SYSTEM tablespace. Although a small database can fit within the SYSTEM tablespace, it’s recommended that to create a separate tablespace for user data.

Oracle uses the SYSTEM tablespace to store information like the data dictionary. Data dictionary stores the metadata (or the data about data). This includes information like table access permissions, information about keys etc.

Data is stored in the database in form of files called as datafiles. Each Tablespace is a collection of one or more Datafiles. Each data file consists of ‘Data blocks’, ‘extents’ and ‘segments’.

Data Blocks

At the finest level of granularity, an ORACLE database’s data is stored in data blocks (also called logical blocks, ORACLE blocks, or pages). An ORACLE database uses and allocates free database space in ORACLE data blocks.

Extents

The next level of logical database space is called an extent. An extent is a specific number of contiguous data blocks that are allocated for storing a specific type of information.

Segments

The level of logical database storage above an extent is called a segment. A segment is a set of extents that have been allocated for a specific type of data structure, and all are stored in the same tablespace. For example, each table’s data is stored in its own data segment, while each index’s data is stored in its own index segment. ORACLE allocates space for segments in extents. Therefore, when the existing extents of a segment are full, ORACLE allocates another extent for that segment. Because extents are allocated as needed, the extents of a segment may or may not be contiguous on disk, and may or may not span files.

An Oracle database can use four types of segments:

  • Data segment–Stores user data within the database.
  • Index segment–Stores indexes.
  • Rollback segment–Stores rollback information. This information is used when data must be rolled back.
  • Temporary segment–Created when a SQL statement needs a temporary work area; these segments are destroyed when the SQL statement is finished. These segments are used during various database operations, such as sorts.

Schema

The database schema is a collection of logical-structure objects, known as schema objects that define how you see the database’s data. A schema also defines a level of access for the users. All the logical objects in oracle are grouped into a schema.

A scheme is a logical grouping of objects such as:

  • Tables
  • Clusters
  • Indexes
  • Views
  • Stored procedures
  • Triggers
  • Sequences

3. What is a tablespace?

A tablespace is a logical storage unit within an Oracle database. It is logical because a tablespace is not visible in the file system of the machine on which the database resides. A tablespace, in turn, consists of at least one datafile which, in turn, are physically located in the file system of the server. Btw, a datafile belongs to exactly one tablespace.

Each table, index and so on that is stored in an Oracle database belongs to a tablespace. The tablespace builds the bridge between the Oracle database and the filesystem in which the table’s or index’ data is stored.

There are three types of tablespaces in Oracle:

A tablespace is created with the create tablespace sql command.

See adding tablespaces to primary servers if you want to add a tablespace to a primary server in a standby environment.

Dropping a tablespace

Dropping a tablespace is a structural change to the database that requires a backup.

The extent size of the objects in the tablespace are subject to the tablespace’s minimum extent size.

Quotas on tablespaces

Users can have (space) quotas on tablespaces. This is a means to limit how much space a user uses on a tablespace. This quota can be set using alter user quota…

Tablespace groups

This is a feature that is available with Oracle 10g.

Assigning a tablespace to a tablespace group:

alter tablespace ts_user tablespace group ts_grp_user;

Renaming Tablespaces

This is a feature that is available with Oracle 10g and can be useful in transportable tablespace scenarios.

alter tablespace ts_user rename to ts_user_01;

The system and sysaux tablespace cannot be renamed, though. But that will not be much of a problem, will it? However, read only tablespaces can be renamed.

After renaming a tablespace, the controlfiles should immediatly be backed up.

The system tablespace

The system tablespace is always available when a database is open (it cannot be taken offline).

The system tablespace stores the data dictionary (or their base tables, respectively).

The sysaux tablespace

The sysaux tablespace is new with Oracle 10g. It is used to store database components that were stored in the system tablespace in prior releases of the database.
Also, the tablespaces that were needed for RMAN’s recovery catalog, for Ultra Search, for Data Mining, for XDP and for OLAP are going to sysaux with 10g.
Additionally, it is the place where automatic workload repository stores its information.

occupants

An occupant is a set of (application-) tables within the sysaux tablespace. The occupants can be viewed with the v$sysaux_occupants

Transportable tablespaces

See transportable tablespaces

Bigfile tablespaces

This is a feature of Oracle 10g. A bigfile tablespace contains only one datafile (or tempfile) which can be as big as 2^32 (=4GB) blocks.

create bigfile tablespace beeeg_ts data file '/o1/dat/beeeg.dbf' size 2T

Bigfile tablespaces are supported only for locally managed tablespaces with automatic segment-space management (which is the default setting since Oracle 9i). There are two exceptions: locally managed undo and temporary tablespaces can be bigfile tablespaces, even though their segments are manually managed.

The system and sysaux tablespace cannot be created as bigfile tablespace.

Bigfile tablespaces should be used with automatic storage management, or other logical volume managers that support dynamically extensible logical volumes, striping and RAID.

Smallfile tablespaces

A smallfile tablespace is a traditional tablespace that can contain up to 1022 datafiles.

Default tablespaces

An Oracle database can be configured with a default tablespace and a default temporary tablespace. These are used for users who are not configured with default tablespaces or default temporary tablespaces.

Displaying tablespaces

The dba_tablespaces view displays all tablespaces along with the respective relevant information.

Space management

Oracle maintains extents for a tablespace. There are two different methods for Oracle to keep track of free and used (occupied) extents:

It’s not possible to alter the space allocation method of a tablespace after it has been created. (Update 10g R2: it seems that is now possible with dbms_space_admin.)

Dictionary managed tablespaces

Extents are allocated according to the following storage parameters

  • initial
  • next
  • pctincrease

The information about used and free extents is stored in the dictionary.

Locally managed tablespaces

A ‘bitmap’ is stored within the tablespace. Each bit within this bitmap determines if a corresponding extent in the tablespace is free or used.

The extent sizes are either uniform or autoallocate. Hence, the following storage parameters don’t make sense and are not permitted:

  • next
  • pctincrease
  • minextents
  • maxextents
  • default storage

Locally managed tablespaces have two advantages: recursive space management is avoided and adjacent free space is automatically coalesced.

Tablespace count limits

As per 10g, a database cannot have more than 65536 tablespaces. See also datafile count limits.

A bigfile tablespace can address 4294967296 (or 232) db blocks. A smallfile tablespace can address 4194304 (or 222) db blocks.

State of tablespaces

A tablespace is either online (ready to be accessed) or offline (not accessible).

A tablespace becomes offline either

  • when the DBA explicitely makes the tablespace offline, or
  • when an error occures while Oracle accesses a datafile within the tablespace.

Offline tablespaces cannot be transported to other databases.

Read Only Tablespaces

Read only tablespaces have the benefit that they need be backed up only once.

4. What is SYSTEM tablespace and when is it created?

Every Oracle database contains a tablespace named SYSTEM, which is automatically created when the database is created. The SYSTEM tablespace always contains the data dictionary tables for the entire database.

5. Explain the relationship among database, tablespace and data file.?

Each databases logically divided into one or more tablespaces one or more data files are explicitly created for each tablespace.

6. What is schema?

A schema is collection of database objects of a User.

7. What are Schema Objects?

Schema objects are the logical structures that directly refer to the database’s data. Schema bjects include tables, views, sequences, synonyms, indexes, clusters, database triggers, procedures, functions packages and database links.

8. Can objects of the same schema reside in different tablespaces?

Yes

9. Can a tablespace hold objects from different schemes?

Yes

10. What is Oracle table?

A table is the basic unit of data storage in an Oracle database. The tables of a database hold all of the user accessible data. Table data is stored in rows and columns.

11. What is an Oracle view?

A view is a virtual table. Every view has a query attached to it. (The query is a SELECT statement that identifies the columns and rows of the table(s) the view uses.)

A View in Oracle and in other database systems is simply the representation of a SQL statement that is stored in memory so that it can easily be re-used. For example, if we frequently issue the following query

SELECT customerid, customername FROM customers WHERE countryid='US';

To create a view use the CREATE VIEW command as seen in this example

CREATE VIEW view_uscustomers
AS
SELECT customerid, customername FROM customers WHERE countryid='US';

This command creates a new view called view_uscustomers. Note that this command does not result in anything being actually stored in the database at all except for a data dictionary entry that defines this view. This means that every time you query this view, Oracle has to go out and execute the view and query the database data. We can query the view like this:

SELECT * FROM view_uscustomers WHERE customerid BETWEEN 100 AND 200;

And Oracle will transform the query into this:

SELECT * 
FROM (select customerid, customername from customers WHERE countryid='US') 
WHERE customerid BETWEEN 100 AND 200

12. Do a view contain data?

Views do not contain or store data.

13. Can a view based on another view?

Yes

14. What are the advantages of views?

– Provide an additional level of table security, by restricting access to a predetermined set

of rows and columns of a table.

– Hide data complexity.

– Simplify commands for the user.

– Present the data in a different perspective from that of the base table.

– Store complex queries.

15. What is an Oracle sequence?

A sequence generates a serial list of unique numbers for numerical columns of a

database’s tables.

16. What is a synonym?

A synonym is an alias for a table, view, sequence or program unit.

17. What are the types of synonyms?

There are two types of synonyms private and public.

18. What is a private synonym?

Only its owner can access a private synonym.

19. What is a public synonym?

Any database user can access a public synonym.

20. What are 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.

21. What is 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.

22. How are the index updates?

Indexes are automatically maintained and used by Oracle. Changes to table data are

automatically incorporated into all relevant indexes.

23. What are clusters?

Clusters are groups of one or more tables physically stores together to share common

columns and are often used together.

24. What is cluster key?

The related columns of the tables in a cluster are called the cluster key.

25. What is index cluster?

A cluster with an index on the cluster key.

26. What is 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.

27. 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.

28. What is database link?

A database link is a named object that describes a “path” from one database to another.

29. What are the types of database links?

Private database link, public database link & network database link.

30. What is 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 or procedures.

31. What is 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.

32. What is 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.

33. What is 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.

34. 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 latter.

35. What is 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.

36. What is an extent?

An extent is a specific number of contiguous data blocks, obtained in a single allocation

and used to store a specific type of information.

37. What is a segment?

A segment is a set of extents allocated for a certain logical structure.

38. What are the different types of segments?

Data segment, index segment, rollback segment and temporary segment.

39. What is a data segment?

Each non-clustered table has a data segment. All of the table’s data is stored in the extents

of its data segment. Each cluster has a data segment. The data of every table in the cluster

is stored in the cluster’s data segment.

40. What is an index segment?

Each index has an index segment that stores all of its data.

41. What is rollback segment?

A database contains one or more rollback segments to temporarily store “undo”

information.

42. What are the uses of rollback segment?

To generate read-consistent database information during database recovery and to

rollback uncommitted transactions by the users.

43. What is a temporary segment?

Temporary segments are created by Oracle when a SQL statement needs a temporary

work area to complete execution. When the statement finishes execution, the temporary

segment extents are released to the system for future use.

44. What is a datafile?

Every Oracle database has one or more physical data files. A database’s data files contain

all the database data. The data of logical database structures such as tables and indexes is

physically stored in the data files allocated for a database.

45. What are the characteristics of data files?

A data file can be associated with only one database. Once created a data file can’t change

size. One or more data files form a logical unit of database storage called a tablespace.

46. What is a redo log?

The set of redo log files for a database is collectively known as the database redo log.

47. What is the function of redo log?

The primary function of the redo log is to record all changes made to data.

48. What is the use of redo log information?

The information in a redo log file is used only to recover the database from a system or

media failure prevents database data from being written to a database’s data files.

49. What does a control file contains?

– Database name

– Names and locations of a database’s files and redolog files.

– Time stamp of database creation.

50. What is the use of control file?

When an instance of an Oracle database is started, its control file is used to identify the

database and redo log files that must be opened for database operation to proceed. It is

also used in database recovery.

Data Base Administration

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 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 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 SQL statements 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.

Database Logical & Physical Architecture

64. What is Database Buffers?

Database buffers are cache in the SGA used to hold the data blocks that are read from the

data segments in the database such as tables, indexes and clusters

DB_BLOCK_BUFFERS parameter in INIT.ORA decides the size.

65. What is dictionary cache?

Dictionary cache is information about the database objects stored in a data dictionary

table.

66. What is meant by recursive hints?

Number of times processes repeatedly query the dictionary table is called recursive hints.

It is due to the data dictionary cache is too small. By increasing the

SHARED_POOL_SIZE parameter we can optimize the size of data dictionary cache.

67. What is redo log buffer?

Changes made to the records are written to the on-line redo log files. So that they can be

used in roll forward operations during database recoveries. Before writing them into the

redo log files, they will first brought to redo log buffers in SGA and LGWR will write

into files frequently. LOG_BUFFER parameter will decide the size.

68. How will you swap objects into a different table space for an existing database?

– Export the user

– Perform import using the command imp system/manager file=export.dmp

indexfile=newrite.sql. This will create all definitions into newfile.sql.

– Drop necessary objects.

– Run the script newfile.sql after altering the tablespaces.

– Import from the backup for the necessary objects.

69. List the Optional Flexible Architecture (OFA) of Oracle database? How can we

organize the tablespaces in Oracle database to have maximum performance?

SYSTEM – Data dictionary tables.

DATA – Standard operational tables.

DATA2- Static tables used for standard operations

INDEXES – Indexes for Standard operational tables.

INDEXES1 – Indexes of static tables used for standard operations.

TOOLS – Tools table.

TOOLS1 – Indexes for tools table.

RBS – Standard Operations Rollback Segments,

RBS1,RBS2 – Additional/Special Rollback segments.

TEMP – Temporary purpose tablespace

TEMP_USER – Temporary tablespace for users.

USERS – User tablespace.

70. How will you force database to use particular rollback segment?

SET TRANSACTION USE ROLLBACK SEGMENT rbs_name.

71. What is meant by free extent?

A free extent is a collection of continuous free blocks in tablespace. When a segment is

dropped its extents are reallocated and are marked as free.

72.Which parameter in Storage clause will reduce number of rows per block?

PCTFREE parameter

Row size also reduces no of rows per block.

73. What is the significance of having storage clause?

We can plan the storage for a table as how much initial extents are required, how much

can be extended next, how much % should leave free for managing row updating, etc.,

74. How does Space allocation table place within a block?

Each block contains entries as follows

Fixed block header

Variable block header

Row Header, row date (multiple rows may exists)

PCTEREE (% of free space for row updating in future)

75. What is the role of PCTFREE parameter is storage clause?

This is used to reserve certain amount of space in a block for expansion of rows.

76. What is the OPTIMAL parameter?

It is used to set the optimal length of a rollback segment.

77. What is the functionality of SYSTEM table space?

To manage the database level transactions such as modifications of the data dictionary

table that record information about the free space usage.

78. How will you create multiple rollback segments in a database?

– Create a database, which implicitly creates a SYSTEM rollback segment in a SYSTEM

tablespace.

– Create a second rollback segment name R0 in the SYSTEM tablespace.

– Make new rollback segment available (after shutdown, modify init.ora file and start

database)

– Create other tablespaces (RBS) for rollback segments.

– Deactivate rollback segment R0 and activate the newly created rollback segments.

79. How the space utilization takes place within rollback segments?

It will try to fit the transaction in a cyclic fashion to all existing extents. Once it found an

extent is in use then it forced to acquire a new extent (number of extents is based on the

optimal size)

80. Why query fails sometimes?

Rollback segment dynamically extent to handle larger transactions entry loads.

A single transaction may wipeout all available free space in the rollback segment

tablespace. This prevents other user using rollback segments.

81. How will you monitor the space allocation?

By querying DBA_SEGMENT table/view

82. How will you monitor rollback segment status?

Querying the DBA_ROLLBACK_SEGS view

IN USE – Rollback Segment is on-line.

AVAILABLE – Rollback Segment available but not on-line.

OFF-LINE – Rollback Segment off-line

INVALID – Rollback Segment Dropped.

NEEDS RECOVERY – Contains data but need recovery or corrupted.

PARTLY AVAILABLE – Contains data from an unresolved transaction involving a

distributed database.

83. List the sequence of events when a large transaction that exceeds beyond its

optimal value when an entry wraps and causes the rollback segment to expand into

another extend.

Transaction Begins.

An entry is made in the RES header for new transactions entry

Transaction acquires blocks in an extent of RBS

The entry attempts to wrap into second extent. None is available, so that the RBS must

extent.

The RBS checks to see if it is part of its OPTIMAL size.

RBS chooses its oldest inactive segment.

Oldest inactive segment is eliminated.

RBS extents

The data dictionary tables for space management are updated.

Transaction Completes.

84. How can we plan storage for very large tables?

Limit the number of extents in the table

Separate table from its indexes.

Allocate sufficient temporary storage.

85. How will you estimate the space required by a non-clustered tables?

Calculate the total header size

Calculate the available data space per data block

Calculate the combined column lengths of the average row

Calculate the total average row size.

Calculate the average number rows that can fit in a block

Calculate the number of blocks and bytes required for the table.

After arriving the calculation, add 10 % additional space to calculate the initial extent

size for a working table.

86. It is possible to use raw devices as data files and what are the advantages over

file system files?

Yes.

The advantages over file system files are that I/O will be improved because Oracle is

bye-passing the kernel which writing into disk. Disk corruption will be very less.

87. What is a Control file?

Database’s overall physical architecture is maintained in a file called control file. It will

be used to maintain internal consistency and guide recovery operations. Multiple copies

of control files are advisable.

88. How to implement the multiple control files for an existing database?

Shutdown the database

Copy one of the existing controlfile to new location

Edit Config ora file by adding new control filename

Restart the database.

89. What is redo log file mirroring? How can be achieved?

Process of having a copy of redo log files is called mirroring.

This can be achieved by creating group of log files together, so that LGWR will

automatically writes them to all the members of the current on-line redo log group. If any

one group fails then database automatically switch over to next group. It degrades

performance.

90. What is advantage of having disk shadowing / mirroring?

Shadow set of disks save as a backup in the event of disk failure. In most operating

systems if any disk failure occurs it automatically switchover to place of failed disk.

Improved performance because most OS support volume shadowing can direct file I/O

request to use the shadow set of files instead of the main set of files. This reduces I/O

load on the main set of disks.

91. What is use of rollback segments in Oracle database?

They allow the database to maintain read consistency between multiple transactions.

92. What is a rollback segment entry?

It is the set of before image data blocks that contain rows that are modified by a

transaction.

Each rollback segment entry must be completed within one rollback segment.

A single rollback segment can have multiple rollback segment entries.

93. What is hit ratio?

It is a measure of well the data cache buffer is handling requests for data.

Hit Ratio = (Logical Reads – Physical Reads – Hits Misses)/ Logical Reads.

94. When will be a segment released?

When Segment is dropped.

When Shrink (RBS only)

When truncated (TRUNCATE used with drop storage option)

95. What are disadvantages of having raw devices?

We should depend on export/import utility for backup/recovery (fully reliable)

The tar command cannot be used for physical file backup, instead we can use dd

command, which is less flexible and has limited recoveries.

96. List the factors that can affect the accuracy of the estimations?

– The space used transaction entries and deleted records, does not become free

immediately after completion due to delayed cleanout.

– Trailing nulls and length bytes are not stored.

– Inserts of, updates to and deletes of rows as well as columns larger than a single data

block, can cause fragmentation a chained row pieces.

Database Security & Administration

97. What is user Account in Oracle database?

A user account is not a physical structure in database but it is having important

relationship to the objects in the database and will be having certain privileges.

98. How will you enforce security using stored procedures?

Don’t grant user access directly to tables within the application.

Instead grant the ability to access the procedures that access the tables.

When procedure executed it will execute the privilege of procedures owner. Users cannot

access tables except via the procedure.

99. What are the dictionary tables used to monitor a database space?

DBA_FREE_SPACE

DBA_SEGMENTS

DBA_DATA_FILES.

SQL*Plus Statements

100. What are the types of SQL statement?

Data Definition Language: CREATE, ALTER, DROP, TRUNCATE, REVOKE, NO

AUDIT & COMMIT.

Data Manipulation Language: INSERT, UPDATE, DELETE, LOCK TABLE, EXPLAIN

PLAN & SELECT.

Transactional Control: COMMIT & ROLLBACK

Session Control: ALTERSESSION & SET ROLE

System Control: ALTER SYSTEM.

101. What is a transaction?

Transaction is logical unit between two commits and commit and rollback.

102. What is difference between TRUNCATE & DELETE?

TRUNCATE commits after deleting entire table i.e., cannot be rolled back.

Database triggers do not fire on TRUNCATE

DELETE allows the filtered deletion. Deleted records can be rolled back or committed.

Database triggers fire on DELETE.

103. What is a join? Explain the different types of joins?

Join is a query, which retrieves related columns or rows from multiple tables.

Self Join – Joining the table with itself.

Equi Join – Joining two tables by equating two common columns.

Non-Equi Join – Joining two tables by equating two common columns.

Outer Join – Joining two tables in such a way that query can also retrieve rows that do not

have corresponding join value in the other table.

104. What is the sub-query?

Sub-query is a query whose return values are used in filtering conditions of the main

query.

105. What is correlated sub-query?

Correlated sub-query is a sub-query, which has reference to the main query.

106. Explain CONNECT BY PRIOR?

Retrieves rows in hierarchical order eg.

select empno, ename from emp where.

107. Difference between SUBSTR and INSTR?

INSTR (String1, String2 (n, (m)),

INSTR returns the position of the m-th occurrence of the string 2 in string1. The search

begins from nth position of string1.

SUBSTR (String1 n, m)

SUBSTR returns a character string of size m in string1, starting from n-th position of

string1.

108. Explain UNION, MINUS, UNION ALL and INTERSECT?

INTERSECT – returns all distinct rows selected by both queries.

MINUS – returns all distinct rows selected by the first query but not by the second.

UNION – returns all distinct rows selected by either query

UNION ALL – returns all rows selected by either query, including all duplicates.

109. What is ROWID?

ROWID is a pseudo column attached to each row of a table. It is 18 characters long,

blockno, rownumber are the components of ROWID.

110. What is the fastest way of accessing a row in a table?

Using ROWID.

CONSTRAINTS

111. What is an integrity constraint?

Integrity constraint is a rule that restricts values to a column in a table.

112. What is referential integrity constraint?

Maintaining data integrity through a set of rules that restrict the values of one or more

columns of the tables based on the values of primary key or unique key of the referenced

table.

113. What is the usage of SAVEPOINTS?

SAVEPOINTS are used to subdivide a transaction into smaller parts. It enables rolling

back part of a transaction. Maximum of five save points are allowed.

114. What is ON DELETE CASCADE?

When ON DELETE CASCADE is specified Oracle maintains referential integrity by

automatically removing dependent foreign key values if a referenced primary or unique

key value is removed.

115. What are the data types allowed in a table?

CHAR, VARCHAR2, NUMBER, DATE, RAW, LONG and LONG RAW.

116. What is difference between CHAR and VARCHAR2? What is the maximum

SIZE allowed for each type?

CHAR pads blank spaces to the maximum length.

VARCHAR2 does not pad blank spaces.

For CHAR the maximum length is 255 and 2000 for VARCHAR2.

117. How many LONG columns are allowed in a table? Is it possible to use LONG

columns in WHERE clause or ORDER BY?

Only one LONG column is allowed. It is not possible to use LONG column in WHERE

or ORDER BY clause.

118. What are the pre-requisites to modify datatype of a column and to add a

column with NOT NULL constraint?

– To modify the datatype of a column the column must be empty.

– To add a column with NOT NULL constrain, the table must be empty.

119. Where the integrity constraints are stored in data dictionary?

The integrity constraints are stored in USER_CONSTRAINTS.

120. How will you activate/deactivate integrity constraints?

The integrity constraints can be enabled or disabled by ALTER TABLE ENABLE

CONSTRAINT / DISABLE CONSTRAINT.

121. If unique key constraint on DATE column is created, will it validate the rows

that are inserted with SYSDATE?

It won’t, Because SYSDATE format contains time attached with it.

122. What is a database link?

Database link is a named path through which a remote database can be accessed.

123. How to access the current value and next value from a sequence? Is it possible

to access the current value in a session before accessing next value?

Sequence name CURRVAL, sequence name NEXTVAL. It is not possible. Only if you

access next value in the session, current value can be accessed.

124. What is CYCLE/NO CYCLE in a Sequence?

CYCLE specifies that the sequence continue to generate values after reaching either

maximum or minimum value. After pan-ascending sequence reaches its maximum value,

it generates its minimum value. After a descending sequence reaches its minimum, it

generates its maximum.

NO CYCLE specifies that the sequence cannot generate more values after reaching its

maximum or minimum value.

125. What are the advantages of VIEW?

– To protect some of the columns of a table from other users.

– To hide complexity of a query.

– To hide complexity of calculations.

126. Can a view be updated/inserted/deleted? If Yes – under what conditions?

A View can be updated/deleted/inserted if it has only one base table if the view is based

on columns from one or more tables then insert, update and delete is not possible.

127. If a view on a single base table is manipulated will the changes be reflected on

the base table?

If changes are made to the tables and these tables are the base tables of a view, then the

changes will be reference on the view.