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.

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