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Oracle Interview Questions and Answers



What third party tools can be used with Oracle EBU/ RMAN? (for DBA)
The following Media Management Software Vendors have integrated their media management software packages with Oracle Recovery Manager and Oracle7 Enterprise Backup Utility. The Media Management Vendors will provide first line technical support for the integrated backup/recover solutions.
Veritas NetBackup
EMC Data Manager (EDM)
HP OMNIBack II
IBM's Tivoli Storage Manager - formerly ADSM
Legato Networker
ManageIT Backup and Recovery
Sterling Software's SAMS:Alexandria - formerly from Spectralogic
Sun Solstice Backup

Why and when should one tune? (for DBA)
One of the biggest responsibilities of a DBA is to ensure that the Oracle database is tuned properly. The Oracle RDBMS is highly tunable and allows the database to be monitored and adjusted to increase its performance. One should do performance tuning for the following reasons:
The speed of computing might be wasting valuable human time (users waiting for response); Enable your system to keep-up with the speed business is conducted; and Optimize hardware usage to save money (companies are spending millions on hardware). Although this FAQ is not overly concerned with hardware issues, one needs to remember than you cannot tune a Buick into a Ferrari.

How can a break order be created on a column in an existing group? What are the various sub events a mouse double click event involves?
By dragging the column outside the group.

What is the use of place holder column? What are the various sub events a mouse double click event involves?
A placeholder column is used to hold calculated values at a specified place rather than allowing is to appear in the actual row where it has to appear.

What is the use of hidden column? What are the various sub events a mouse double click event involves?
A hidden column is used to when a column has to embed into boilerplate text.

What database aspects should be monitored? (for DBA)
One should implement a monitoring system to constantly monitor the following aspects of a database. Writing custom scripts, implementing Oracle's Enterprise Manager, or buying a third-party monitoring product can achieve this. If an alarm is triggered, the system should automatically notify the DBA (e-mail, page, etc.) to take appropriate action.
Infrastructure availability:
. Is the database up and responding to requests
. Are the listeners up and responding to requests
. Are the Oracle Names and LDAP Servers up and responding to requests
. Are the Web Listeners up and responding to requests

Things that can cause service outages:
. Is the archive log destination filling up?
. Objects getting close to their max extents
. User and process limits reached

Things that can cause bad performance:
See question "What tuning indicators can one use?".

Where should the tuning effort be directed? (for DBA)
Consider the following areas for tuning. The order in which steps are listed needs to be maintained to prevent tuning side effects. For example, it is no good increasing the buffer cache if you can reduce I/O by rewriting a SQL statement. Database Design (if it's not too late):
Poor system performance usually results from a poor database design. One should generally normalize to the 3NF. Selective denormalization can provide valuable performance improvements. When designing, always keep the "data access path" in mind. Also look at proper data partitioning, data replication, aggregation tables for decision support systems, etc.
Application Tuning:
Experience showed that approximately 80% of all Oracle system performance problems are resolved by coding optimal SQL. Also consider proper scheduling of batch tasks after peak working hours.
Memory Tuning:
Properly size your database buffers (shared pool, buffer cache, log buffer, etc) by looking at your buffer hit ratios. Pin large objects into memory to prevent frequent reloads.
Disk I/O Tuning:
Database files needs to be properly sized and placed to provide maximum disk subsystem throughput. Also look for frequent disk sorts, full table scans, missing indexes, row chaining, data fragmentation, etc
Eliminate Database Contention:
Study database locks, latches and wait events carefully and eliminate where possible. Tune the Operating System:
Monitor and tune operating system CPU, I/O and memory utilization. For more information, read the related Oracle FAQ dealing with your specific operating system.

What are the various sub events a mouse double click event involves? What are the various sub events a mouse double click event involves?
Double clicking the mouse consists of the mouse down, mouse up, mouse click, mouse down & mouse up events.

What are the default parameter that appear at run time in the parameter screen? What are the various sub events a mouse double click event involves?
Destype and Desname.

What are the built-ins used for Creating and deleting groups?
CREATE-GROUP (function)
CREATE_GROUP_FROM_QUERY(function)
DELETE_GROUP(procedure)

What are different types of canvas views?
Content canvas views
Stacked canvas views
Horizontal toolbar
vertical toolbar.

What are the different types of Delete details we can establish in Master-Details?
Cascade
Isolate
Non-isolate

What is relation between the window and canvas views?
Canvas views are the back ground objects on which you place the interface items (Text items), check boxes, radio groups etc.,) and boilerplate objects (boxes, lines, images etc.,) that operators interact with us they run your form . Each canvas views displayed in a window.

What is a User_exit?
Calls the user exit named in the user_exit_string. Invokes a 3Gl program by name which has been properly linked into your current oracle forms executable.

How is it possible to select generate a select set for the query in the query property sheet?
By using the tables/columns button and then specifying the table and the column names.

How can values be passed bet. precompiler exits & Oracle call interface?
By using the statement EXECIAFGET & EXECIAFPUT.

How can a square be drawn in the layout editor of the report writer?
By using the rectangle tool while pressing the (Constraint) key.

How can a text file be attached to a report while creating in the report writer?
By using the link file property in the layout boiler plate property sheet.

How can I message to passed to the user from reports?
By using SRW.MESSAGE function.

Does one need to drop/ truncate objects before importing? (for DBA)
Before one import rows into already populated tables, one needs to truncate or drop these tables to get rid of the old data. If not, the new data will be appended to the existing tables. One must always DROP existing Sequences before re-importing. If the sequences are not dropped, they will generate numbers inconsistent with the rest of the database. Note: It is also advisable to drop indexes before importing to speed up the import process. Indexes can easily be recreated after the data was successfully imported.

How can a button be used in a report to give a drill down facility?
By setting the action associated with button to Execute pl/sql option and using the SRW.Run_report function.

Can one import/export between different versions of Oracle? (for DBA)
Different versions of the import utility is upwards compatible. This means that one can take an export file created from an old export version, and import it using a later version of the import utility. This is quite an effective way of upgrading a database from one release of Oracle to the next.
Oracle also ships some previous catexpX.sql scripts that can be executed as user SYS enabling older imp/exp versions to work (for backwards compatibility). For example, one can run $ORACLE_HOME/rdbms/admin/catexp7.sql on an Oracle 8 database to allow the Oracle 7.3 exp/imp utilities to run against an Oracle 8 database.

What are different types of images?
Boiler plate imagesImage Items

Can one export to multiple files?/ Can one beat the Unix 2 Gig limit? (for DBA)
From Oracle8i, the export utility supports multiple output files. This feature enables large exports to be divided into files whose sizes will not exceed any operating system limits (FILESIZE= parameter). When importing from multi-file export you must provide the same filenames in the same sequence in the FILE= parameter. Look at this example:
exp SCOTT/TIGER FILE=D:\F1.dmp,E:\F2.dmp FILESIZE=10m LOG=scott.log
Use the following technique if you use an Oracle version prior to 8i:
Create a compressed export on the fly. Depending on the type of data, you probably can export up to 10 gigabytes to a single file. This example uses gzip. It offers the best compression I know of, but you can also substitute it with zip, compress or whatever.
# create a named pipe
mknod exp.pipe p
# read the pipe - output to zip file in the background
gzip < exp.pipe > scott.exp.gz &
# feed the pipe
exp userid=scott/tiger file=exp.pipe ...

What is bind reference and how can it be created?
Bind reference are used to replace the single value in sql, pl/sql statements a bind reference can be created using a (:) before a column or a parameter name.

How can one improve Import/ Export performance? (for DBA)
EXPORT:

. Set the BUFFER parameter to a high value (e.g. 2M)
. Set the RECORDLENGTH parameter to a high value (e.g. 64K)
. Stop unnecessary applications to free-up resources for your job.
. If you run multiple export sessions, ensure they write to different physical disks.
. DO NOT export to an NFS mounted filesystem. It will take forever.
IMPORT:

. Create an indexfile so that you can create indexes AFTER you have imported data. Do this by setting INDEXFILE to a filename and then import. No data will be imported but a file containing index definitions will be created. You must edit this file afterwards and supply the passwords for the schemas on all CONNECT statements.
. Place the file to be imported on a separate physical disk from the oracle data files
. Increase DB_CACHE_SIZE (DB_BLOCK_BUFFERS prior to 9i) considerably in the init$SID.ora file
. Set the LOG_BUFFER to a big value and restart oracle.
. Stop redo log archiving if it is running (ALTER DATABASE NOARCHIVELOG;)
. Create a BIG tablespace with a BIG rollback segment inside. Set all other rollback segments offline (except the SYSTEM rollback segment of course). The rollback segment must be as big as your biggest table (I think?)
. Use COMMIT=N in the import parameter file if you can afford it
. Use ANALYZE=N in the import parameter file to avoid time consuming ANALYZE statements
. Remember to run the indexfile previously created

Give the sequence of execution of the various report triggers?
Before form , After form , Before report, Between page, After report.

What are the common Import/ Export problems? (for DBA )
ORA-00001: Unique constraint (...) violated - You are importing duplicate rows. Use IGNORE=NO to skip tables that already exist (imp will give an error if the object is re-created).
ORA-01555: Snapshot too old - Ask your users to STOP working while you are exporting or use parameter CONSISTENT=NO
ORA-01562: Failed to extend rollback segment - Create bigger rollback segments or set parameter COMMIT=Y while importing
IMP-00015: Statement failed ... object already exists... - Use the IGNORE=Y import parameter to ignore these errors, but be careful as you might end up with duplicate rows.

Why is it preferable to create a fewer no. of queries in the data model?
Because for each query, report has to open a separate cursor and has to rebind, execute and fetch data.

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