ORACLE

                                                                                        **ORACLE 10g DB

Que:- What is the characteristic of RDBMS?

Ans:-

Characteristics of RDBMS Model: -

• It is based on set theory.
• A query is a data retrieval utility allows data manipulation and tables.
• Each table is independent entity and there is no relationship between tables.
• User interface is non procedure DML, since what needs to be done is specified.
• Eliminates parent chain relationship and represents data in database as simple row, column tables of data values.
• Rows of the database tables are called tuple and columns are called attributes.

Que:- Why ORACLE is RDBMS?

Ans:-

ORACLE is RDBMS because there are certain rules to make up a relational data base management system, oracle follows it and so it’s an RDBMS.

Que:- What is characteristic of SQL?

Ans:-

SQL enables end user and system persons to deal with a number of database management systems where it is available.Applications written in SQL can be easily ported across systems. Such porting could be required when the underlying DBMS needs to Upgraded because of change in transaction volumes or when a system developed in one environment is to be used on another.SQL as a language is independent of the way it is implanted internally. A query returns the same result regardless of whether optimizing Has been done with indexes or not. This is because SQL specifies what is required and not how it is to be done. The language while being simple and easy to learn can cope with complex situations. The results to be expected are well defined in SQL. 

Que:- What is DATA, DB, DBMS and RDBMS?

Ans:-

DATA: - The term data means groups of information that represent the qualitative or quantitative attributes of a variable or set of variables.

DB: - Databases consist of software-based "containers" that are structured to collect and store information so users can retrieve, add, update or remove such information in an automatic fashion. Database programs are designed for users so that they can add or delete any information needed. The structure of a database is tabular, consisting of rows and columns of information.

RDBMS: - A relational database management system (RDBMS) is a database management system(DBMS) that is based on the relational model as introduced by E. F. Codd.

Que:- Find out the .env file for SQL to execute for Scott and new Scott?

Ans:-

That is glogin in oracle database.

Que:-How will you see date along with time?

Ans:-

we  use a timestamp datatype  or

Select localtimestamp from dual;

select to_char(sysdate,'YYYY-MM-DD HH:MI:SS') from dual;

Que:- Find out way so that if a new user is created when create session is automatically assign?

Ans:-

Que:- What is an Oracle Instance?

Ans:- 

The oracle background process along with SGA is called ORACLE instance.

Background Processes: Background process maintains relation between Oracle memory area and the physical structure. Oracle memory area is also called as the System global area (SGA).The physical structure consist of (data file, log file and the control file).

The Oracle Process can be divided into 2 processes:

1) User Process.

2) Oracle Process.

Oracle process can be further divided into 2 sub processes:

1) Server Process.       2) Background Process.

1) Server process: They perform the work for user processes. In a dedicated server process one server process is allocated for each user process. In Multi threaded server configuration few shared server process take care of all user processes.

2) Background Processes: Background process maintains relation between Oracle memory area and the physical structure.

Oracle memory area is also called as the System global area (SGA).The physical structure consist of (data file, log file and the control file).There are many background processes as described below:

1) System Monitor (SMON): This process performs system or crash recovery when a failed instance is starts again. In the parallel server option the SMON process of one instance can perform recovery for other instance that has failed. It basically cleans up the temporary segments that are no longer needed and also recovers the dead transactions skipped during the crash and instance recovery because of file read or offline error. SMON also deletes the free extents within the database to make the free space continuous and easy to allocate.

2) Process Monitor (PMON): This process performs the process recovery when a user process fails. It is responsible to make the resources free which the failed process was holding. When the process is killed or it fails PMON releases the lock from the resources it was holding and makes the them free for the users.

3) Queue Monitor (QMN): It is used to monitor the messages queues for the Advanced Queuing. It is an optional background process.

4) Database Writer (DBWn): This process writes the modified blocks to the buffer cache using the (Least Used Algorithm).It writes in batches instead of writing for every command. There are DBW0, DBW1--DBW9 to boost the system performance. DB_WRITER_PROCESSES parameter specifies the number of DBWn processes.

5) Log Writer (LGWR): This process writes the redo log entries to the redo buffer to the online redo log files. These online redo log files are written in the sequential manner unlike the data files which are written in the random manner.

6) Checkpoint Process: At some point of time the DBWn writes all the blocks in the cache to the data file. At this point the log files and the control files are updated to reflect the recent change. This event is called as the checkpoint and the process which takes care of this is called as the checkpoint process. A checkpoint also occurs for the online redo log files and can be set through LOG_CHECKPOINT_INTERVALS for more frequent checkpoints to save the amount of time needed forrecovery.

7) Archiver Process (ARCn): This process is active only when the database is running in the Archive log mode and automatic archiving mode is enabled. As the LGWR writes, and the log file is filled and if the database is running in the Archive log mode then the previous log file is written to the Archive destination which is specified in the parameter file.

8 ) Recover Process (RECO): This process is only created in the distributed database option to resolve the failed transaction due to system or network failure. To create this process we can use the DISTRIBURED_TRANSACTIONS parameter.

9) Lock Process (LCKn): This process is used only is the oracle parallel server process is used. This process is used for inter instance locking. It is an optional process.

10) Job Queue Process (SNPn): This processes are used to automatically refresh the table snapshots in distributed configuration. These processes also execute the job requests submitted by the DBMS_JOB package. SYSTEM GLOBAL AREA (SGA): It is a memory area allocated by the oracle.All the memory structures that resides in the SGA are shared by the concurrent users connected to that instance. Hence SGA is often called as the shared global area.

Que:- What information is stored in Control File?

Ans:- 

Every Oracle database has a control file. A control file is a small binary file that records the physical structure of the database The control files include information about the physical structure of the database, such asdatabase name, names and locations of datafiles and redo log files and time stamp of database creation, tablespace information, datafile offline ranges, log history, archived log information,backup set and backup piece information, backup datafile and redo log information, datafile copy information, the current log sequence number and checkpoint information. The database name is taken from either the name specified by the DB_NAME initialization parameter or the name used in the CREATE DATABASE statement. Each time that a datafile or a redo log file is added to, renamed in, or dropped from DB, a tablespace is created or dropped from DB, the control file is updated to reflect this physical structure change. Therefore, if you make a change to the physical structure of your database (using ALTER DATABASE statements), then you should immediately make a backup of your control file.

Que:- When you start an Oracle DB which file is accessed first?

Ans:-

When you issue the startup command, the first thing the database will do is enter the nomount stage. During the nomount stage, Oracle first opens and reads the initialization parameter file (init.ora) to see how the database is configured. For example, the sizes of all of the memory areas in Oracle are defined within the parameter file. After the parameter file is accessed, the memory areas associated with the database instance are allocated. Also, during the nomount stage, the Oracle background processes are started. Together, we call these processes and the associated allocated memory the Oracle instance. Once the instance has started successfully, the database is considered to be in the nomount stage. If you issue the startup command, then Oracle will automatically move onto the next stage of the startup, the mount stage.

Que:- What is the Job of  SMON, PMON processes?

Ans:-

System Monitor (SMON): This process performs system or crash recovery when a failed instance is starts again. In the parallel server option the SMON process of one instance can perform recovery for other instance that has failed. It basically cleans up the temporary segments that are no longer needed and also recovers the dead transactions skipped during the crash and instance recovery because of file read or offline error. SMON also deletes the free extents within the database to make the free space continuous and easy to allocate.

Process Monitor (PMON): This process performs the process recovery when a user process fails. It is responsible to make the resources free which the failed process was holding. When the process is killed or it fails PMON releases the lock from the resources it was holding and makes the them free for the users.

Que:- What is Instance Recovery?

Ans:-

Oracle performs instance recovery when the database is restarted due to instance failure or shutdown the database with ABORT option(shutdown abort) or startup the database with FORCE option(startup force). Instance recovery is taken care by SMON oracle background process automatically. Instance recovery consists of two steps. One is Roll forward, next is Roll backward.

Roll forward:

Changes being made to the database are recorded in the database buffer cache and buffer cache will be written into data files. At the same time, the changes are recorded in redo log buffer and redo log buffer will be written to redo log file. Oracle writes the data from database buffer cache to data file only when there is enough data in data buffer cache. It is not necessary that, every commit, oracle writes the data buffer cache into data file. When instance fails before committed data are written into data files, Oracle uses the data recorded in the online redo log files to recover the lost data when the associated database is re-started. This process is called Roll forward or cache recovery.

Roll backward:

When we make any changes in the database, the old image will be written into undo segment. Later undo segment will be used to rollback the data when we rollback the transaction. DBWR writes the buffer cache content into data file under different circumstances. It might be possible to write the uncommitted data from database buffer cache into data file. When instance fails and associated database is restarted, it rollback the uncommitted transaction in data file by using undo segment to maintain the read consistency. This is called roll forward or transaction recovery.

Que:- What is written in Redo Log Files?

Ans:-

Log Writer (LGWR): This process writes the redo log entries to the redo buffer to the online redo log files. These online redo log files are written in the sequential manner unlike the data files which are written in the random manner.

Que:- what do you mean by framwork.Give five example?

Ans:-

A framework is a collection of classes and applications, libraries of SDKs and APIs to help the different components all work together.AND a fram work is a basic conceptual structure used to solve or address complex issues,usually a set of tools, materials or components. Especially in a software context the word is used as a name for different kind of toolsets, component bases, then became a kind of buzzword or fashionable keyword.

EXAMPLE:-

1.Compilers for different programming languages and target machines.

2.Financial modeling applications.

3.Earth system modeling applications.

4.Decision support systems.

5.Web applications.

6.Middleware.

Que:- Explain why and how ORACLE 10g has grid facility and what is the benifit of gride?

Ans:-

Grid computing enables groups of networked computers to be pooled and provisioned on demand to meet the changing needs of business.Instead of dedicated servers and storage for each application, grid computing enables multiple applications to share computing infrastructure, resulting in much greater flexibility, cost, power efficiency, performance, scalability and availability, all at the same time. Scale out computing capacity on demand in smaller units, instead of buying oversized systems for peak periods or uncertain growth.Remove unneeded or failed machines without interruptions in service, saving cost and ensuring business continuity. Manage all your     systems end-to-end with integrated and automated administration and monitoring.Oracle offers the most complete and field-proven portfolio of industry leading grid computing solutions, from the Web tier all the way down to middleware, database, servers and storage.

Benifits of Gride

Better look of information

Faster response to changing business priorities

Reduced IT coast

Que:- what is N-tyre architecture?

Ans:-

Usually N-Tier Architecture begins as a 3-Tier model and is expanded. It provides finer granularity. Granularity is the ability of a system, in this case, an application, to be broken down into smaller components or granules. The finer the granularity, the greater the flexibility of a system. It can also be referred to as a systems’s modularity. Therefore, it refers to the pulling apart of an application into separate layers or finer grains. One of the best examples of N-Tier Architecture in web applications is the popular shopping-cart web application. The client tier interacts with the user through GUIs (Graphic User Interfaces) and with the application and the application server. In web applications, this client tier is a web browser. In addition to initiating the request, the web browser also receives and displays code in dynamic HTML (Hypertext Markup Language), the primary language of the World Wide Web. In a shopping cart web application, the presentation tier displays information related to such services as browsing merchandise, purchasing, and shopping cart contents. It communicates with other tiers by outputting results to the browser client tier and all other tiers in the network. This layer calls custom tags throughout the network and to other networks. It also calls database stored procedures and web services, all in the goal of providing a more sophisticated response. This layer glues the whole application together and allows different nodes to communicate with each other and be displayed to the user through the browser. It is located in the application server.

Que:- what is the benifit of sqlplus /nolog?

Ans:-

The benifit of this sentex we enter in a ORACLE secure and nobudy can't see my passwd in

the command of ps -aef|grep sqlplus.

Que:-send an email from an SQL prompt?

Ans:-

Que:- what do you mean performance testing OR load testing OR stress testing OR regression testing?

Ans:-

PERFORMANCE:- Software performance testing is used to determine the speed or effectiveness of a computer, network, software program or device. This process can involve quantitative tests done in a lab, such as measuring the response time or the number of MIPS (millions of instructions per second) at which a system functions.

LOAD:- Load testing is the process of putting demand on a system or device and measuring its response. The term load testing is used in different ways in the professional software  testing community. Load testing generally refers to the practice of modeling the expected usage of a software program by simulating multiple users accessing the program concurrently.

STRESS:- Stress testing is a form of testing that is used to determine the stability of a given system or entity. It involves testing beyond normal operational capacity, often to a  breaking point, in order to observe the results.

REGRESSION:- Any time you modify an implementation within a program, you should also do regression testing. You can do so by rerunning existing tests against the modified code to determine whether the changes break anything that worked prior to the change and by writing new tests where necessary. Adequate coverage without wasting time should be a primary consideration when conducting regression tests.

Que:- How to Take a backup with RMAN, datagard tool?

Ans:-

RMAN

Configure for multiple archiver processes

SELECT value FROM gv$parameter WHERE name = 'log_archive_max_processes';

ALTER SYSTEM SET log_archive_max_processes=3;

SELECT log_mode FROM v$database;

SHUTDOWN;

STARTUP MOUNT EXCLUSIVE;

ALTER DATABASE ARCHIVELOG;

ALTER DATABASE OPEN;

SELECT log_mode FROM v$database;

SHUTDOWN;

After configure this you have to logout from database and start RMAN

rman TARGET /

STARTUP MOUNT;

REPORT SCHEMA;

BACKUP DATABASE;

LIST BACKUP;

LIST COPY;

VALIDATE BACKUPSET 3;

SHUTDOWN immediate;

Restore and recovere database files;

And restart RMAN with TARGET

rman TARGET /

restore database;

recover database;

alter database

show all

Que:- what is the situation error when we use startup force?

Ans:-

In unusual circumstances, you might experience problems when attempting to start a database instance. You should not force a database to start unless you are faced with the following: You cannot shut down the current instance with the SHUTDOWN NORMAL, SHUTDOWN IMMEDIATE, or SHUTDOWN TRANSACTIONAL commands. If one of these situations arises, you can usually solve the problem by starting a new instance (and optionally mounting and opening the database) using the STARTUP command with the FORCE option:

STARTUP FORCE

If an instance is running, STARTUP FORCE shuts it down with mode ABORT before restarting it. 

Que:- find out ORACLE internal error?

Ans:-

This is a catchall internal error message for Oracle program exceptions. It indicates that a process has met a low-level, unexpected condition. Various causes of this message include:

• time-outs
• file corruption
• failed data checks in memory
• hardware, memory, or I/O errors
• incorrectly restored files

Que:- what is diff between undo and temp tablespace?

Ans:-

Temporary tablespaces:

Temporary tablespaces are logical units within an Oracle database that are used for sort operations. When you join two large tables, or when you are sorting a table by using the ORDER by clause, Oracle uses the temporary tablespace if in memory sort (area specified by SORT_AREA_SIZE or within the PGA) is not possible due to insufficient memory allocation.It is important to note that TEMPORARY TABLESPACES have volatile or non-persistent data. You don’t need to include temporary tablespaces in your backup policy and can just create them after you have performed a recovery.

Undo tablespaces:

Undo tablespaces contain before image of data, that can be used to rollback a particular transaction. Broadly, undo tablespaces are used for Roll back transactions when a ROLLBACK statement is issued Recover the database Provide read consistency Analyze data as of an earlier point in time by using Flashback Query Recover from logical corruptions using Flashback features.

Que:- what is recursive SQL?

Ans:-

When you issue a SQL statement, the database must determine many things before it can even start executing that SQL statement. If you query a table, do you have permissions to access that table? Does that table even exist? Which tablespace holds that table?  Oracle needs answers to these questions and more. One of the things that Oracle is really good at is processing SQL statements. So if Oracle needs to find out if a table exists,  Oracle will issue a SQL statement against the Data Dictionary to answer that question. This is similar to you querying DBA_TABLES to determine if the table exists. All of the SQL that Oracle issues behind the scenes on your behalf is called "recursive SQL." Some of the recursive SQL statements will require other questions to be asked, which spawns a new level of recursive SQL.

If Oracle finds a problem with your SQL statement, like the table does not exist, then Oracle will raise an error (ORA-00942). If Oracle does not find any problem, then your SQL statement will be executed. Executing your SQL statement may require additional recursive SQL statements. 

Que:- what is Bitmap Index in oracle?

Ans:-

A bitmap index is a type of index that uses a string of bits to quickly locate rows in a table. Bitmap indexes are normally used to index low cardinality columns in a warehouse environment.

CREATE BITMAP INDEX emp_bitmap_idx ON big_emp(sex);

OR

CREATE BITMAP INDEX emp_dept_loc ON emp(dept.loc)

FROM emp, dept

WHERE emp.deptno = dept.deptno

TABLESPACE index_ts1;

Que:- Install ORACLE with Hindi character set?

Ans:-

IN8ISCII Multiple-Script Indian Standard 8-bit Latin/Indian

Que:- Create table with LOB datatype insert and select sum LOB data?

Ans:-

DONE in the '/export/home/oracle/image' directory.

Que:- What is BEQ protocol in unix?

Ans:-

The BEQ Protocol Adapter, is both a communications mechanism and a process spawning mechanism. If a service name is not specified, either directly by the user on the command line or the login screen, or indirectly through an environment variable such as TWO_TASK, then the BEQ Protocol Adapter will be used. In which case, a dedicated server will always be used, and the multi-threaded server will never be used. This dedicated server is started automatically by the BEQ Protocol Adapter, which waits for the server process to start and attach to an existing SGA. If the startup of the server process is successful, the BEQ Protocol Adapter then provides inter-process communication via UNIX pipes.

An important feature of the BEQ Protocol Adapter is that no network Listener is required for its operation, since the adapter is linked into the client tools and directly starts its own server process with no outside interaction. However, the BEQ Protocol Adapter can only be used when the client program and the Oracle8 server reside on the same machine. The BEQ Protocol Adapter is always installed, and always linked in to all client tools and to the Oracle8 server.

Que:- What should be the TEN quality of network?

Ans:-

1.SECURITY                    2.Transparency

3.DATA INTEGRITY       4.ENCAPSULATION,DECAPSULATION

5.SPEED                           6.ACCESSABILITY (anywhere)

7.CONNECTIVITY         8.AWARENESS (prevent other)

9.NETWORK MAP         10.SHARING NETWORK

Que:- What are dead locks in oracle?

Ans:-

A deadlock occurs when two or more threads of control are blocked, each waiting on a resource held by the other thread. When this happens, there is no possibility of the threads ever making forward progress unless some outside agent takes action to break the deadlock. 

For example, if Txn A is blocked by Txn B at the same time Txn B is blocked by Txn A then the threads of control containing Txn A and Txn B are deadlocked; neither thread can make any forward progress because neither thread will ever release the lock that is blocking the other thread. When two threads of control deadlock, the only solution is to have a mechanism external to the two threads capable of recognizing the deadlock and notifying at least one thread that it is in a deadlock situation. Once notified, a thread of control must abandon the attempted operation in order to resolve the deadlock. DB's locking subsystem offers a deadlock notification mechanism.

Que:- what is the facility give by oracle to avoid dead lock (automaticity)?

Ans:-

The DBMS_LOCK package makes Oracle lock management services available to PL/SQL developers. User locks created and managed using DBMS_LOCK are functionally identical to native RDBMS locks, even down to the various sharing modes and the deadlock detection.

Locks are typically used to provide serialized access to some resource. Within the database, the most familiar use of locking is to prevent multiple users from updating the same row in a table at the same time. Using DBMS_LOCK, applications can be written that serialize and coordinate access or usage of nondata resources. For instance, user locks can be used to do the following:

Provide exclusive access to an external device or service (e.g a printer).

Coordinate or synchronize parallelized applications.

Disable or enable execution of programs at specific times.

Detect whether a session has ended a transaction using COMMIT or ROLLBACK.

Que:- Connect listener to client with different port number?

Ans:-

We have two utility and one technique to configure listener with diff port:

1.netmgr

2.netca

3.we can copy the same line in the listener.ora file and do some changes like lsnt "NAME","PORT".

After configure it you start,restart the lsnr by name.

Que:- Search about "oracle manager connection" on google?

Ans:-

Oracle Connection Manager is a multipurpose networking solution that offers increased scalability, multiprotocol connectivity and secure network access control. It offers the following features to Oracle network: 

• Connection multiplexing
• Access control
• Source routing
• Multiprotocol Support
• Firewall Proxy Support

Oracle Connection Manager enables large numbers of users to connect to a single server by acting as a connection concentrator to "funnel" multiple client database sessions across a single network connection. This is done through multiplexed network connections, a networking feature included with Oracle Net. Oracle Connection Manager reduces operating system resource requirements by minimizing the number of network connections made to a server. Network bottlenecks are thus avoided and system scalability significantly increases so that thousands of users can now access a single database. 

Que:- What is trigger,procedure,function,cursor in oracle

Ans:-

CURSOR: When a query is executed in oracle, a result set is produced and stored in the memory. Oracle allows the programmer to access this result set in the memory through cursors.

TRIGGER: Trigger is program of PL/SQL that execute automaticaly when you give a specified condition.

PROCEDURE: Procedures are code fragments that don’t normally return a value, but may have some outside effects (like updating tables).

FUNCTION: Functions are special types of procedures that have capability to return a value.

Que:- Take a backup datapump?

Ans:-

Create DIRECTORY "name" '/to/path"

grant read,write on directory "name" to "username"

expdp user/password tables="name","name" directory="name" dumpfile="name.dmp"

Que:- Insert a row via SQL loader?

Ans:-

First you should create a file control file like dada.ctl

LOAD DATA

INFILE chacha.txt

APPEND INTO TABLE "table ka name"

FIELDS TERMINATED BY ',' OPTIONALLY ENCLOSED BY '"'

(id, name)

And you give the text file code like this form 12,"name"

Que:- Create a user with three table and views after that you take backup with expdp utility and import only those views starting from any "word"?

Ans:-

create DIRECTORY "name" '/to/path"

grant read,write on directory "name" to "username"

create user,tables and views

expdp user/password tables="name","name" directory="name" dumpfile="name.dmp"

logfile="name.log";

after that you delete all tables,view from user

impdp user/password dumpfile="name" directory="name" include=views:\"LIKE \'name%\'\";   

Que:- Find out and try to understand the source code where bugzilla has created oracle schema?

Ans:-:-

In browser when we click on "create new account" and give e-mail and userid/passwd information:find out what happened to that information for which consequently to get an e-mail also find out which language has been used to process open a new account information.

Que:- which one utility is best for take the backup from Oracle DB?

Ans:-

This is our own decision that which one is the best for backup exp, expdp, DBCA, RMAN, dba_rollback_segs;

Que:- Why is a UNION ALL faster than a UNION?

Ans:-

The union operation, you will recall, brings two sets of data together. It will *NOT* however produce duplicate or redundant rows. To perform this feat of magic, a SORT operation is done on both tables. This is obviously computationally intensive, and uses significant memory as well. A UNION ALL conversely just dumps collection of both sets together in random order, not worrying about duplicates.

Que:- What are some advantages to using Oracle's CREATE DATABASE statement to create a new database manually?

Ans:-

You can script the process to include it in a set of install scripts you deliver with a product.

You can put your create database script in CVS for version control, so as you make changes or adjustments to it, you can track them like you do changes to software code.

You can log the output and review it for errors.

You learn more about the process of database creation, such as what options are available and why.

Que:- What are three rules of thumb to create good passwords? How would a DBA enforce those rules in Oracle? What business challenges might you encounter?

Ans:-

Typical password cracking software uses a dictionary in the local language, as well as a list of proper names, and combinations thereof to attempt to guess unknown passwords. Since computers can churn through 10's of thousands of attempts quickly, this can be a very affective way to break into a database. A good password therefore should not be a dictionary word, it should not be a proper name, birthday, or other obvious guessable information. It should also be of sufficient length, such as eight to ten characters, including upper and lowercase, special characters, and even alternate characters if possible.
Oracle has a facility called password security profiles. When installed they can enforce complexity, and length rules as well as other password related security measures. In the security arena, passwords can be made better, and it is a fairly solvable problem. However, what about in the real-world? Often the biggest challenge is in implementing a set of rules like this in the enterprise. There will likely be a lot of resistance to this, as it creates additional hassles for users of the system who may not be used to thinking about security seriously. Educating business folks about the real risks, by coming up with real stories of vulnerabilities and break-ins you've encountered on the job, or those discussed on the internet goes a long way towards emphasizing what is at stake.

Que:- Describe the Oracle Wait Interface, how it works, and what it provides. What are some limitations? What do the db_file_sequential_read and db_file_scattered_read events indicate?

Ans:-

The Oracle Wait Interface refers to Oracle's data dictionary for managing wait events. Selecting from tables such as v$system_event and v$session_event give you event totals through the life of the database (or session). The former are totals for the whole system, and latter on a per session basis. The event db_file_sequential_read refers to single block reads, and table accesses by rowid. db_file_scattered_read conversely refers to full table scans. It is so named because the blocks are read, and scattered into the buffer cache.

Que:- How do you return the top-N results of a query in Oracle? Why doesn't the obvious method work?

Ans:-

Most people think of using the ROWNUM pseudocolumn with ORDER BY. Unfortunately the ROWNUM is determined *before* the ORDER BY so you don't get the results you want. The answer is to use a subquery to do the ORDER BY first. For example to return the top-5 employees by salary:
SELECT * FROM (SELECT * FROM employees ORDER BY salary) WHERE ROWNUM < 5;

Que:- Can Oracle's Data Guard be used on Standard Edition, and if so how? How can you test that the standby database is in sync?

Ans:-

Oracle's Data Guard technology is a layer of software and automation built on top of the standby database facility. In Oracle Standard Edition it is possible to be a standby database, and update it *manually*. Roughly, put your production database in archivelog mode. Create a hotbackup of the database and move it to the standby machine. Then create a standby controlfile on the production machine, and ship that file, along with all the archived redolog files to the standby server. Once you have all these files assembled, place them in their proper locations, recover the standby database, and you're ready to roll. From this point on, you must manually ship, and manually apply those archived redologs to stay in sync with production. To test your standby database, make a change to a table on the production server, and commit the change. Then manually switch a logfile so those changes are archived. Manually ship the newest archived redolog file, and manually apply it on the standby database. Then open your standby database in read-only mode, and select from your changed table to verify those changes are available. Once you're done, shutdown your standby and startup again in standby mode.

Que:- What is a database link? What is the difference between a public and a private database link? What is a fixed user database link?

Ans:-

Database link allows you to make a connection with a remote database, Oracle or not, and query tables from it, even incorporating those accesses with joins to local tables. Private database link only works for, and is accessible to the user/schema that owns it. A global one can be accessed by any user in the database. Fixed user link specifies that you will connect to the remote db as one and only one user that is defined in the link. Alternatively, a current user database link will connect as the current user you are logged in as.

50 DBA Professional focused Interview Questions-Answers:(By James F. Koopmann )

Que:- Explain the difference between a hot backup and a cold backup and the benefits associated with each.

Ans:-

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 point 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.

Que:-  You have just had to restore from backup and do not have any control files. How would you go about bringing up this database?

Ans:-

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.

Que:- How do you switch from an init.ora file to a spfile?

Ans:-

Issue the create spfile from pfile command.

Que:- Explain the difference between a data block, an extent and a segment.

Ans:-

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.

Que:- Give two examples of how you might determine the structure of the table DEPT.

Ans:-

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

Que:- Where would you look for errors from the database engine?

Ans:-

In the alert log.

Que:- Compare and contrast TRUNCATE and DELETE for a table.

Ans:-

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.

Que:- Give the reasoning behind using an index.

Ans:-

Faster access to data blocks in a table.

Que:- Give the two types of tables involved in producing a star schema and the type of data they hold.

Ans:-

Fact tables and dimension tables. A fact table contains measurements while dimension tables will contain data that will help describe the fact tables.

Que:- What type of index should you use on a fact table?

Ans:-

A Bitmap index.

Que:- Give two examples of referential integrity constraints.

Ans:-

A primary key and a foreign key.

Que:- 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?

Ans:-

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

Que:- Explain the difference between ARCHIVELOG mode and NOARCHIVELOG mode and the benefits and disadvantages to each.

Ans:-

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 point in time. NOARCHIVELOG mode is basically the absence of ARCHIVELOG mode and has the disadvantage of not being able to recover to any point 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.

Que:- What command would you use to create a backup control file?

Ans:-

Alter database backup control file to trace.

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

Ans:-

STARTUP NOMOUNT - Instance startup

STARTUP MOUNT - The database is mounted

STARTUP OPEN - The database is opened

Que:- What column differentiates the V$ views to the GV$ views and how?

Ans:-

The INST_ID column which indicates the instance in a RAC environment the information came from.

Que:- How would you go about generating an EXPLAIN plan?

Ans:-

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

Que:- How would you go about increasing the buffer cache hit ratio?

Ans:-

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.

Que:- Explain an ORA-01555.

Ans:-

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.

Que:- Explain the difference between $ORACLE_HOME and $ORACLE_BASE.

Ans:-

ORACLE_BASE is the root directory for oracle. ORACLE_HOME located beneath ORACLE_BASE is where the oracle products reside.

Que:- How would you determine the time zone under which a database was operating?

Ans:-

select DBTIMEZONE from dual;

Que:- Explain the use of setting GLOBAL_NAMES equal to TRUE.

Ans:-

Setting GLOBAL_NAMES dictates how you might connect to a database. This variable is either TRUE or FALSE and if it is set to TRUE it enforces database links to have the same name as the remote database to which they are linking.

Que:- What command would you use to encrypt a PL/SQL application?

Ans:-

WRAP

Que:- Explain the difference between a FUNCTION, PROCEDURE and PACKAGE.

Ans:-

A function and procedure are the same in that they are intended to be a collection of PL/SQL code that carries a single task. While a procedure does not have to return any values to the calling application, a function will return a single value. A package on the other hand is a collection of functions and procedures that are grouped together based on their commonality to a business function or application.

Que:- Explain the use of table functions.

Ans:-

Table functions are designed to return a set of rows through PL/SQL logic but are intended to be used as a normal table or view in a SQL statement. They are also used to pipeline information in an ETL process.

Que:- Name three advisory statistics you can collect.

Ans:-

Buffer Cache Advice, Segment Level Statistics, & Timed Statistics

Que:- Where in the Oracle directory tree structure are audit traces placed?

Ans:-

In unix $ORACLE_HOME/rdbms/audit, in Windows the event viewer

Que:- Explain materialized views and how they are used.

Ans:-

Materialized views are objects that are reduced sets of information that have been summarized, grouped, or aggregated from base tables. They are typically used in data warehouse or decision support systems.

Que:- When a user process fails, what background process cleans up after it?

Ans:-

PMON

Que:- What background process refreshes materialized views?

Ans:-

The Job Queue Processes.

Que:- How would you determine what sessions are connected and what resources they are waiting for?

Ans:-

Use of V$SESSION and V$SESSION_WAIT

Que:- Describe what redo logs are.

Ans:-

Redo logs are logical and physical structures that are designed to hold all the changes made to a database and are intended to aid in the recovery of a database.

Que:- How would you force a log switch?

Ans:-

ALTER SYSTEM SWITCH LOGFILE;

Que:- Give two methods you could use to determine what DDL changes have been made.

Ans:-

You could use Logminer or Streams

Que:- What does coalescing a tablespace do?

Ans:-

Coalescing is only valid for dictionary-managed tablespaces and de-fragments space by combining neighboring free extents into large single extents.

Que:- What is the difference between a TEMPORARY tablespace and a PERMANENT tablespace?

Ans:-

A temporary tablespace is used for temporary objects such as sort structures while permanent tablespaces are used to store those objects meant to be used as the true objects of the database.

Que:- Name a tablespace automatically created when you create a database.

Ans:-

The SYSTEM tablespace.

Que:- When creating a user, what permissions must you grant to allow them to connect to the database?

Ans:-

Grant the CONNECT to the user.

Que:- How do you add a data file to a tablespace?

Ans:-

ALTER TABLESPACE ADD DATAFILE SIZE

Que:- How do you resize a data file?

Ans:-

ALTER DATABASE DATAFILE RESIZE ;

Que:- What view would you use to look at the size of a data file_

Ans:-

DBA_DATA_FILES

Que:- What view would you use to determine free space in a tablespace?

Ans:-

DBA_FREE_SPACE

Que:- How would you determine who has added a row to a table?

Ans:-

Turn on fine grain auditing for the table.

Que:- How can you rebuild an index?

Ans:-

ALTER INDEX REBUILD;

Que:- Explain what partitioning is and what its benefit is.

Ans:-

Partitioning is a method of taking large tables and indexes and splitting them into smaller, more manageable pieces.

Que:- You have just compiled a PL/SQL package but got errors, how would you view the errors?

Ans:-

SHOW ERRORS

Que:- How can you gather statistics on a table?

Ans:-

The ANALYZE command.

Que:- How can you enable a trace for a session?

Ans:-

Use the DBMS_SESSION.SET_SQL_TRACE or

Use ALTER SESSION SET SQL_TRACE = TRUE;

Que:- What is the difference between the SQL*Loader and IMPORT utilities?

Ans:-

These two Oracle utilities are used for loading data into the database. The difference is that the import utility relies on the data being produced by another Oracle utility EXPORT while the SQL*Loader utility allows data to be loaded that has been produced by other utilities from different data sources just so long as it conforms to ASCII formatted or delimited files.

Que:- Name two files used for network connection to a database.

Ans:-

TNSNAMES.ORA and SQLNET.ORA

Que:- Give two UNIX kernel parameters that effect an Oracle install

Ans:-

SHMMAX & SHMMNI

Que:- Briefly, how do you install Oracle software on UNIX.Basically, set up disks, kernel parameters, and run orainst.

Ans:-

Que:- What are the components of physical database structure of Oracle database?

Ans:-

Oracle database is comprised of three types of files. One or more datafiles, two are more redo log files, and one or more control files.

Que:- What are the components of logical database structure of Oracle database?

Ans:-

There are tablespaces and database's schema objects.

Que:- What is a tablespace?

Ans:-

A database is divided into Logical Storage Unit called tablespaces. A tablespace is used to grouped related logical structures together.

Que:- What is SYSTEM tablespace and when is it created?

Ans:-

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.

Que:- Explain the relationship among database, tablespace and data file.

Ans:-

Each databases logically divided into one or more tablespaces one or more data files are explicitly created for each tablespace.

Que:- What is schema?

Ans:-

A schema is collection of database objects of a user.

Que:- What are Schema Objects?

Ans:-

Schema objects are the logical structures that directly refer to the database's data. Schema objects include tables, views, sequences, synonyms, indexes, clusters, database triggers, procedures, functions packages and database links.

Que:- Can objects of the same schema reside in different tablespaces?

Ans:-

Yes.

Que:- Can a tablespace hold objects from different schemes?

Ans:-

Yes.

Que:- What is Oracle table?

Ans:-

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.

Que:- What is an Oracle view?

Ans:-

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.)

Que:- Do a view contain data?

Ans:-

Views do not contain or store data.

Que:- Can a view based on another view?

Ans:-

Yes.

Que:- What are the advantages of views?

Ans:-

- 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.

Que:- What is an Oracle sequence?

Ans:-

A sequence generates a serial list of unique numbers for numerical columns of a database's tables.

Que:- What is a synonym?

Ans:-

A synonym is an alias for a table, view, sequence or program unit.

Que:- What are the types of synonyms?

Ans:-

There are two types of synonyms private and public.

Que:- What is a private synonym?

Ans:-

Only its owner can access a private synonym.

Que:- What is a public synonym?

Ans:-

Any database user can access a public synonym.

Que:- What are synonyms used for?

Ans:-

- 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.

Que:- What is an Oracle index?

Ans:-

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.

Que:- How are the index updates?

Ans:-

Indexes are automatically maintained and used by Oracle. Changes to table data are automatically incorporated into all relevant indexes.

Que:- What are clusters?

Ans:-

Clusters are groups of one or more tables physically stores together to share common columns and are often used together.

Que:- What is cluster key?

Ans:-

The related columns of the tables in a cluster are called the cluster key.

Que:- What is index cluster?

Ans:-

A cluster with an index on the cluster key.

Que:- What is hash cluster?

Ans:-

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.

Que:- When can hash cluster used?

Ans:-

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.

Que:- What is database link?

Ans:-

A database link is a named object that describes a "path" from one database to another.

Que:- What are the types of database links?

Ans:-

Private database link, public database link & network database link.

Que:- What is private database link?

Ans:-

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.

Que:- What is public database link?

Ans:-

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.

Que:- What is network database link?

Ans:-

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.

Que:- What is data block?

Ans:-

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.

Que:- How to define data block size?

Ans:-

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.

Que:- What is row chaining?

Ans:-

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.

Que:- What is an extent?

Ans:-

An extent is a specific number of contiguous data blocks, obtained in a single allocation and used to store a specific type of information.

Que:- What is a segment?

Ans:-

A segment is a set of extents allocated for a certain logical structure.

Que:- What are the different types of segments?

Ans:-

Data segment, index segment, rollback segment and temporary segment.

Que:- What is a data segment?

Ans:-

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.

Que:- What is an index segment?

Ans:-

Each index has an index segment that stores all of its data.

Que:- What is rollback segment?

Ans:-

A database contains one or more rollback segments to temporarily store "undo" information.

Que:- What are the uses of rollback segment?

Ans:-

To generate read-consistent database information during database recovery and to rollback uncommitted transactions by the users.

Que:- What is a temporary segment?

Ans:-

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.

Que:- What is a datafile?

Ans:-

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.

Que:- What are the characteristics of data files?

Ans:-

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.

Que:- What is a redo log?

Ans:-

The set of redo log files for a database is collectively known as the database redo log.

Que:- What is the function of redo log?

Ans:-

The primary function of the redo log is to record all changes made to data.

Que:- What is the use of redo log information?

Ans:-

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.

Que:- What does a control file contains?

Ans:-

- Database name

- Names and locations of a database's files and redolog files.

- Time stamp of database creation.

Que:- What is the use of control file?

Ans:-

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

Que:- What is a database instance? Explain.

Ans:-

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.

Que:- What is Parallel Server?

Ans:-

Multiple instances accessing the same database (only in multi-CPU environments)

Que:- What is a schema?

Ans:-

The set of objects owned by user account is called the schema.

Que:- What is an index? How it is implemented in Oracle database?

Ans:-

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

Que:- What are clusters?

Ans:-

Group of tables physically stored together because they share common columns and are often used together is called cluster.

Que:- What is a cluster key?

Ans:-

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.

Que:- What are the basic element of base configuration of an Oracle database?

Ans:-

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

Que:- What is a deadlock? Explain.

Ans:-

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

Que:- What is SGA?

Ans:-

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.

Que:- What is a shared pool?

Ans:-

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.

Que:- What is mean by Program Global Area (PGA)?

Ans:-

It is area in memory that is used by a single Oracle user process.

Que:- What is a data segment?

Ans:-

Data segment are the physical areas within a database block in which the data associated with tables and clusters are stored.

Que:- What are the factors causing the reparsing of SQL statements in SGA?

Ans:-

Due to insufficient shared pool size. Monitor the ratio of the reloads takes place while executing SQL statements. If the ratio is greater than

Que:- Then increase the SHARED_POOL_SIZE.
Ans:-

Database Logical & Physical Architecture

Que:- What is Database Buffers?

Ans:-

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.

Que:- What is dictionary cache?

Ans:-

Dictionary cache is information about the database objects stored in a data dictionary table.

Que:- What is meant by recursive hints?

Ans:-

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.

Que:- What is redo log buffer?

Ans:-

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.

Que:- How will you swap objects into a different table space for an existing database?

Ans:-

- 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.

Que:- List the Optional Flexible Architecture (OFA) of Oracle database? How can we organize the tablespaces in Oracle database to have maximum performance?

Ans:-

SYSTEM - Data dictionary tables.

DATA - Standard operational tables.

DATAQue:- Static tables used for standard operations

INDEXES - Indexes for Standard operational tables.

INDEXESQue:-- Indexes of static tables used for standard operations.

TOOLS - Tools table.

TOOLSQue:-- Indexes for tools table.

RBS - Standard Operations Rollback Segments,

RBSQue:-RBSQue:-- Additional/Special Rollback segments.

TEMP - Temporary purpose tablespace

TEMP_USER - Temporary tablespace for users.

USERS - User tablespace.

Que:- How will you force database to use particular rollback segment?

Ans:-

SET TRANSACTION USE ROLLBACK SEGMENT rbs_name.

Que:- What is meant by free extent?

Ans:-

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.

Que:- Which parameter in Storage clause will reduce number of rows per block?

Ans:-

PCTFREE parameter

Row size also reduces no of rows per block.

Que:- What is the significance of having storage clause?

Ans:-

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.,

Que:- How does Space allocation table place within a block?

Ans:-

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)

Que:- What is the role of PCTFREE parameter is storage clause?

Ans:-

This is used to reserve certain amount of space in a block for expansion of rows.

Que:- What is the OPTIMAL parameter?

Ans:-

It is used to set the optimal length of a rollback segment.

Que:- What is the functionality of SYSTEM table space?

Ans:-

To manage the database level transactions such as modifications of the data dictionary table that record information about the free space usage.

Que:- How will you create multiple rollback segments in a database?

Ans:-

- Create a database, which implicitly creates a SYSTEM rollback segment in a SYSTEM tablespace.

- Create a second rollback segment name RQue:-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 RQue:-and activate the newly created rollback segments.

Que:- How the space utilization takes place within rollback segments?

Ans:-

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)

Que:- Why query fails sometimes?

Ans:-

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.

Que:- How will you monitor the space allocation?

Ans:-

By querying DBA_SEGMENT table/view

Que:- How will you monitor rollback segment status?

Ans:-

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.

Que:- 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.

Ans:-

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.

Que:- How can we plan storage for very large tables?

Ans:-

Limit the number of extents in the table

Separate table from its indexes.

Allocate sufficient temporary storage.

Que:- How will you estimate the space required by a non-clustered tables?

Ans:-

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

Que:- % additional space to calculate the initial extent size for a working table.

Ans:-

Que:- It is possible to use raw devices as data files and what are the advantages over file system files?

Ans:-

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.

Que:- What is a Control file?

Ans:-

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.

Que:- How to implement the multiple control files for an existing database?

Ans:-

Shutdown the database

Copy one of the existing controlfile to new location

Edit Config ora file by adding new control filename

Restart the database.

Que:- What is redo log file mirroring? How can be achieved?

Ans:-

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.

Que:- What is advantage of having disk shadowing / mirroring?

Ans:-

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.

Que:- What is use of rollback segments in Oracle database?

Ans:-

They allow the database to maintain read consistency between multiple transactions.

Que:- What is a rollback segment entry?

Ans:-

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.

Que:- What is hit ratio?

Ans:-

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.

Que:- When will be a segment released?

Ans:-

When Segment is dropped.

When Shrink (RBS only)

When truncated (TRUNCATE used with drop storage option)

Que:- What are disadvantages of having raw devices?

Ans:-

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.

Que:- List the factors that can affect the accuracy of the estimations?

Ans:-

- 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.

Que:- What is user Account in Oracle database?

Ans:-

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.

Que:- How will you enforce security using stored procedures?

Ans:-

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.

Que:- What are the dictionary tables used to monitor a database space?

Ans:-

DBA_FREE_SPACE

DBA_SEGMENTS

DBA_DATA_FILES.

SQL*Plus Statements

Que:- What are the types of SQL statement?

Ans:-

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.

Que:- What is a transaction?

Ans:-

Transaction is logical unit between two commits and commit and rollback.

Que:- What is difference between TRUNCATE & DELETE?

Ans:-

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.

Que:- What is a join? Explain the different types of joins?

Ans:-

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.

Que:- What is the sub-query?

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Sub-query is a query whose return values are used in filtering conditions of the main query.

Que:- What is correlated sub-query?

Ans:-

Correlated sub-query is a sub-query, which has reference to the main query.

Que:- Explain CONNECT BY PRIOR?

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Retrieves rows in hierarchical order e.g select empno, ename from emp where.

Que:- Difference between SUBSTR and INSTR?

Ans:-

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.

Que:- Explain UNION, MINUS, UNION ALL and INTERSECT?

Ans:-

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.

Que:- what is ROWID?

Ans:-

ROWID is a pseudo column attached to each row of a table. It is Que:- characters long, blockno, rownumber are the components of ROWID.

Que:- What is the fastest way of accessing a row in a table?

Ans:-

Using ROWID .

Que:- What is an integrity constraint?

Ans:-

Integrity constraint is a rule that restricts values to a column in a table.

Que:- What is referential integrity constraint?

Ans:-

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.

Que:- What is the usage of SAVEPOINTS?

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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.

Que:- What is ON DELETE CASCADE?

Ans:-

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.

Que:- What are the data types allowed in a table?

Ans:-

CHAR, VARCHAR2, NUMBER, DATE, RAW, LONG and LONG RAW.

Que:- What is the maximum SIZE allowed for each type?

Ans:-

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.

Que:- How many LONG columns are allowed in a table? Is it possible to use LONG columns in WHERE clause or ORDER BY?

Ans:-

Only one LONG column is allowed. It is not possible to use LONG column in WHERE or ORDER BY clause.

Que:- What are the pre-requisites to modify datatype of a column and to add a column with NOT NULL constraint?

Ans:-

- 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.

Que:- Where the integrity constraints are stored in data dictionary?

Ans:-

The integrity constraints are stored in USER_CONSTRAINTS.

Que:- How will you activate/deactivate integrity constraints?

Ans:-

The integrity constraints can be enabled or disabled by ALTER TABLE ENABLE CONSTRAINT / DISABLE CONSTRAINT.

Que:- If unique key constraint on DATE column is created, will it validate the rows that are inserted with SYSDATE?

Ans:-

It won't, Because SYSDATE format contains time attached with it.

Que:- What is a database link?

Ans:-

Database link is a named path through which a remote database can be accessed.

Que:- 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?

Ans:-

Sequence name CURRVAL, sequence name NEXTVAL. It is not possible. Only if you access next value in the session, current value can be accessed.

Que:- What is CYCLE/NO CYCLE in a Sequence?

Ans:-

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.

Que:- What are the advantages of VIEW?

Ans:-

- To protect some of the columns of a table from other users.

- To hide complexity of a query.

- To hide complexity of calculations.

Que:- Can a view be updated/inserted/deleted? If Yes - under what conditions?

Ans:-

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.

Que:- If a view on a single base table is manipulated will the changes be reflected on the base table?

Ans:-

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.

Que:- Which default Database roles are created when you create a Database?

Ans:- RESOURCE

Que:- What is a Checkpoint?

Ans:-

Que:- Which Process reads data from Datafiles?

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Que:- Which Process writes data in Datafiles?

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Que:- Can you make a Datafile auto extendible. If yes, how?

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Que:- What is a Shared Pool?

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Que:- What is kept in the Database Buffer Cache?

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Que:- How many maximum Redo Log Files one can have in a Database?

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Que:- What is difference between PFile and SPFile?

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Que:- What is PGA_AGGREGRATE_TARGET parameter?

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Que:- Large Pool is used for what?

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Que:- What is PCT Increase setting?

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Que:- What is PCTFREE and PCTUSED Setting?

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Que:- What is Row Migration and Row Chaining?

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Que:- What is 01555 - Snapshot Too Old error and how do you avoid it?

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Que:- What is a Locally Managed Tablespace?

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Que:- Can you audit SELECT statements?

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Que:- What does DBMS_FGA package do?

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Que:- What is Cost Based Optimization?

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Que:- How often you should collect statistics for a table?

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Que:- How do you collect statistics for a table, schema and Database?

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Que:- Can you make collection of Statistics for tables automatic?

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Que:- On which columns you should create Indexes?

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Que:- What type of Indexes are available in Oracle?

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Que:- What is B-Tree Index?

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Que:- A table is having few rows, should you create indexes on this table?

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Que:- A Column is having many repeated values which type of index you should create on this column, if you have to?

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Que:- When should you rebuilt indexes?

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Que:- Can you built indexes online?

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Que:- Can you see Execution Plan of a statement.

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Que:- A table is created with the following setting storage (initial 200k next 200k minextents 2 maxextents 100 pctincrease 40). What will be size of 4th extent?

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Que:- What is DB Buffer Cache Advisor?

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Que:- What is STATSPACK tool?

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Que:- Can you change SHARED_POOL_SIZE online?

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Que:- Can you Redefine a table Online?

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Que:- Can you assign Priority to users?

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Que:- You want users to change their passwords every 2 months. How do you enforce this?

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Que:- How do you delete duplicate rows in a table?

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Que:- What is Automatic Management of Segment Space setting?

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Que:- What is COMPRESS and CONSISTENT setting in EXPORT utility?

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Que:- What is the difference between Direct Path and Convention Path loading?

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Que:- What is the difference between Range Partitioning and Hash Partitioning?

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Que:- What is difference between Multithreaded/Shared Server and Dedicated Server?

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Que:- Can you import objects from Oracle ver. 7.3 to 9i?

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Que:- How do you move tables from one tablespace to another tablespace?

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Que:- Use of latch in oracle?

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Que:- Explain the purpose of automatic transaction in oracle database?

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