Interview Questions & Answers

Controlfile is Missing

Database failed and you have restored it with the previous days backup and after
restoring you noticed that control file is missing what do you do.


1. If one or more not all control file/s got deleted/corrupted you can replace it by the
    good one from another location. It is only hit and trial basis.


2. If you have backup of the control file you can restore it from the backup.

3. If none of these then create new control file.

What are the views available to see the information about export.

DBA_DATAPUMP_JOBS:

This view will show the active Data Pump jobs, their state, degree of parallelism, and the
number of sessions attached.



DBA_DATAPUMP_SESSIONS:
This view gives the SADDR that assist in determining why a Data Pump session may be
having problems. Join to the V$SESSION view for further information.


V$SESSION_LONGOPS:
This view helps determine how well a Data Pump export is doing. Basically gives you a
progress indicator through the MESSAGE column.

How do you see how many instances are running?

For single instance Oracle Database Server, you can find the number of instances running
using below commands.

In Linux, Unix the command:
$ ps -ef | grep pmon 


In Windows:
services.msc

How to recover if we delete a data file at OS level no backup for that?

Bring the database to the mount state 

SQL>alter database create datafile ;

SQL>recover datafile ;

SQL>alter database open;

DBA Interview Questions

1) Primary database scn is 22 and standby SCN is 24 how you will resolve this issue.

 2) Archive log got deleted before shipped to standby location how you will resolve this
issue.

 3) 3 users running same select but one of them response time is 1hr and for other few
minutes how u will diagnose this.

 4) What is advantage of ASM over os storage and raw storage.

 5) What is remastering in RAC

 6) How you can see database version at OS level.

 7) A job is running since long it was working fine earlier how you will check that How you
will suggest joins to developer

 9) 3 databases sizes 10gb, 100gb, 1TB how which database will take more time.

 10) You lost control file database is using RMAN backup with nocatalog. If you loose whole
db as well same time how you recover database.

 11) what is sync, and async in standby how it works.

 12) Shut immediate is taking too much time how you diagnose what is the issue.

 13) How you take backup of OCR.

 14) What will happen if voting disk is down.

 15) What will happen if virtual IP is down in RAC.

 VIP – Virtual IP address in RAC VIP is mainly used for fast connection in failover. Until 9i
RAC faileover we used physical IP address of another server. When the connection request
come from a client to server, then failure of first server listener then RAC redirect the
connection request to second available server using physical IP address. Hence it is physical
IP address rediretion to second physical IP address is possible only after we get timeout
error from First Physical IP address. So connection should wait a while for getting TCP
connection timeout. From RAC 10g we can use the VIP to save connection timeout wait,
Because ONS (Oracle Notification Service) maintains communication between each nodes
and listeners. Once ONS found any listener down or node down, it will notify another nodes
and listeners. While new connection is trying to establish connection to failure node or
listener, virtual IP of failure node automatically divert to surviving node. This Process will
not wait for TCP/IP timeout event. So new connection will be faster even one listener/node
failed.

RMAN Interview Questions

RMAN Interview Questions

1) If one archive deleted before applying on standby and you do not have backup how u
resolve this issue?. Database size is in TB so recreating Standby is not good idea.

2) If block change tacking is enabled on production database will it be enabled on cloned
database automatically?

3) You have assigned 3-4 channels in RMAN backup how you will identify whether all are
utilized or not?

4) How you do performance tuning for RMANbackups?

5) Can we register manual cold backup in RMAN?

6) Can we recreate oracle inventory if we do not have any backup?

7) What is difference between image copy & normal backup in terms of performance?

8) 10K blocks in your database got corrupted how you will resolve this?

9) What is the benefit of Recovery Catalog and would you create one?

10) Can you register multiple target databases in a single RMAN Catalog?

11) When you try to register a target database in RMAN catalog then you get error that
     Database is already registered? What could be the reason of it and how would you
overcome from this situation?

12) How would you take archivelog log backups?

13) What is the benefits of taking RMAN backups over other backup strategies?

Monday, September 19, 2011

Oracle Jobs Interview Questions and Answers

What is Log Switch? - The point at which ORACLE ends writing to one online redo log file 

                                and begins writing to another is called a log switch.

• What is On-line Redo Log? - The On-line Redo Log is a set of tow or more on-line redo                                                                                              files that record all committed changes made to the database. Whenever a trans-                                                                          -action is committed, the corresponding redo entries temporarily stores in redo                                                                               log buffers of the SGA are written to an on-line redo log file by the background                                                                               process LGWR. The on-line redo log files are used in cyclical fashion.
• Which parameter specified in the DEFAULT STORAGE clause of CREATE                                                                                 TABLESPACE cannot be altered after creating the tablespace? - All the default storage                                                                        parameters defined for the tablespace can be changed using the ALTER TABLESPACE                                                                            command. When objects are created their INITIAL and MINEXTENS values cannot be                                                                                 changed.
• What are the steps involved in Database Startup? - Start an instance, Mount the Database                                                                                and Open the Database.
• What are the steps involved in Instance Recovery? - Rolling forward to recover data that                                                                                 has not been recorded in data files, yet has been recorded in the on-line redo log, including                                                                                  the contents of rollback segments. Rolling back transactions that have been explicitly rolled                                                                                  back or have not been committed as indicated by the rollback segments regenerated in step                                                                                    a. Releasing any resources (locks) held by transactions in process at the time of the failure.                                                                         Resolving any pending distributed transactions undergoing a two-phase commit at the time                                                                                    of the instance failure.
• Can Full Consistent Backup be performed when the database is open? - No.
• What are the different modes of mounting a Database with the Parallel Server?                                                                                                - Exclusive Mode If the first instance that mounts a database does so in exclusive mode,                                                                                              only that Instance can mount the database. Parallel Mode If the first instance that mounts                                                                                          a database is started in parallel mode, other instances that are started in parallel mode can                                                                                         also mount the database.
• What are the advantages of operating a database in ARCHIVELOG mode over                                                                                                  operating it in NO ARCHIVELOG mode? - Complete database recovery from disk                                                                                    failure is possible only in ARCHIVELOG mode. Online database backup is possible only                                                                                      in ARCHIVELOG mode.
• What are the steps involved in Database Shutdown? - Close the Database, Dismount the                                                                                      Database and Shutdown the Instance.
• What is Archived Redo Log? - Archived Redo Log consists of Redo Log files that have                                                                                        archived before being reused.
• What is Restricted Mode of Instance Startup? - An instance can be started in                                                                                                           (or later altered to be in) restricted mode so that when the database is open connections                                                                                             are limited only to those whose user accounts have been granted the RESTRICTED                                                                                                 SESSION system privilege.
• What is Partial Backup? - A Partial Backup is any operating system backup short of a                                                                                               full backup, taken while the database is open or shut down.
• What is Mirrored on-line Redo Log? - A mirrored on-line redo log consists of copies of                                                                                          on-line redo log files physically located on separate disks, changes made to one member                                                                                          of the group are made to all members.
• What is Full Backup? - A full backup is an operating system backup of all data files, on-                                                                                           line redo log files and control file that constitute ORACLE database and the parameter.
• Can a View based on another View? - Yes.
• Can a Tablespace hold objects from different Schemes? - Yes.
• Can objects of the same Schema reside in different tablespaces? - Yes.
• What is the use of Control File? - When an instance of an ORACLE database is started,                                                                                            its control file is used to identify the database and redo log files that must be opened for                                                                                            database operation to proceed. It is also used in database recovery.
• Do View contain Data? - Views do not contain or store data.
• What are the Referential actions supported by FOREIGN KEY integrity constraint?                                                                                             - UPDATE and DELETE Restrict - A referential integrity rule that disallows the update                                                                                            or deletion of referenced data. DELETE Cascade - When a referenced row is deleted all                                                                                            associated dependent rows are deleted.
• What are the type of Synonyms? - There are two types of Synonyms Private and Public
• What is a Redo Log? - The set of Redo Log files YSDATE,UID,USER or USERENV SQL                                                                                        functions, or the pseudo columns LEVEL or ROWNUM.
• What is an Index Segment? - Each Index has an Index segment that stores all of its data.
• Explain the relationship among Database, Tablespace and Data file.? - Each databases                                                                                            logically divided into one or more tablespaces one or more data files are explicitly                                                                                                   created for each tablespace
• What are the different type of Segments? - Data Segment, Index Segment, Rollback                                                                                                   Segment and Temporary Segment.
• What are Clusters? - Clusters are groups of one or more tables physically stores together                                                                                             to share common columns and are often used together.
• What is an Integrity Constrains? - An integrity constraint is a declarative way to define                                                                                             a business rule for a column of a table.
• What is an Index? - An Index is an optional structure associated with a table to have direct                                                                                           access to rows, which can be created to increase the performance of data retrieval. Index                                                                                           can be created on one or more columns of a table.
• What is an Extent? - An Extent is a specific number of contiguous data blocks, obtained                                                                                                in a single allocation, and used to store a specific type of information.
• What is a View? - A view is a virtual table. Every view has a Query attached to it.                                                                                                          (The Query is a SELECT statement that identifies the columns and rows of the table(s)                                                                                              the view uses.)
• What is Table? - A table is the basic unit of data storage in an ORACLE database.                                                                                                            The tables of a database hold all of the user accessible data. Table data is stored in                                                                                                     rows and columns.
• What is a Synonym? - A synonym is an alias for a table, view, sequence or program unit.
• What is a Sequence? - A sequence generates a serial list of unique numbers for numerical                                                                                                 columns of a database’s tables.
• What is a Segment? - A segment is a set of extents allocated for a certain logical structure.
• What is schema? - A schema is collection of database objects of a User.
• Describe Referential Integrity? - A rule defined on a column (or set of columns) in one                                                                                                    table that allows the insert or update of a row only if the value for the column or set                                                                                                  of columns (the dependent value) matches a value in a column of a related table                                                                                                         (the referenced value). It also specifies the type of data manipulation allowed on                                                                                                       referenced data and the action to be performed on dependent data as a result of any                                                                                                  action on referenced data.
• What is Hash Cluster? - A row is stored in a hash cluster based on the result of applying a                                                                                         hash function to the row’s cluster key value. All rows with the same hash key value are                                                                                              stores together on disk.
• What is a Private Synonyms? - A Private Synonyms can be accessed only by the owner.
• What is Database Link? - A database link is a named object that describes a “path” from                                                                                             one database to another.
• What is a Tablespace? - A database is divided into Logical Storage Unit called tablespaces.                                                                                                A tablespace is used to grouped related logical structures together
• What is Rollback Segment? - A Database contains one or more Rollback Segments to                                                                                                                                     temporarily store “undo” information.
• What are the Characteristics of Data Files? - A data file can be associated with only                                                                                               one database. Once created a data file can’t change size. One or more data files form a                                                                                              logical unit of database storage called a tablespace.
• How to define Data Block size? - A data block size is specified for each ORACLE                                                                                        database when the database is created. A database users and allocated free database space                                                                                         in ORACLE datablocks. Block size is specified in INIT.ORA file and can’t be changed                                                                                              latter.
• What does a Control file Contain? - A Control file records the physical structure of the                                                                                           database. It contains the following information. Database Name Names and locations of                                                                                            a database’s files and redolog files. Time stamp of database creation.
• What is difference between UNIQUE constraint and PRIMARY KEY constraint?                                                                                                  - A column defined as UNIQUE can contain Nulls while a column defined as                                                                                                           PRIMARY KEY can’t contain Nulls. 47.What is Index Cluster? - A Cluster with an                                                                                                  index on the Cluster Key 48.When does a Transaction end? - When it is committed or                                                                                             Rollbacked.
• What is the effect of setting the value “ALL_ROWS” for OPTIMIZER_GOAL                                                                                   parameter of the ALTER SESSION command? - What are the factors that affect                                                                                                      OPTIMIZER in choosing an Optimization approach? - Answer The OPTIMIZER_MODE                                                                                         initialization parameter Statistics in the Data Dictionary the OPTIMIZER_GOAL                                                                                                     parameter of the ALTER SESSION command hints in the statement.
• What is the effect of setting the value “CHOOSE” for OPTIMIZER_GOAL,                                                                                           parameter of the ALTER SESSION Command? - The Optimizer chooses Cost_based                                                                                           approach and optimizes with the goal of best throughput if statistics for atleast one of the                                                                                             tables accessed by the SQL statement exist in the data dictionary. Otherwise the                                                                                                    OPTIMIZER chooses RULE_based approach.
• What is the function of Optimizer? - The goal of the optimizer is to choose the most                                                                                                efficient way to execute a SQL statement.
• What is Execution Plan? - The combinations of the steps the optimizer chooses to                                                                                              execute a statement is called an execution plan.
• What are the different approaches used by Optimizer in choosing an execution plan?                                                                                           - Rule-based and Cost-based.