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Oracle Interview Questions and Answers - 22 Nov 2008

Posted on :26-02-2016
Oracle Interview Questions and Answers - 22 Nov 2008:-

Q1. What is user Account in Oracle database?

ANS:
An 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.


Q2. What is a SNAPSHOT?

ANS:
Snapshots are read-only copies of a master table located on a remote node which is periodically refreshed to reflect changes made to the master table.


Q3. What are the benefits of distributed options in databases?

ANS:
Database on other servers can be updated and those transactions can be grouped together with others in a logical unit.
Database uses a two phase commit.


Q4. Differentiate simple and complex snapshots?

ANS:
- A simple snapshot is based on a query that does not contains GROUP BY clauses, CONNECT BY clauses, JOINs, sub-query or snapshot of operations.
- A complex snapshots contain atleast any one of the above.


Q5. 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.


Q6. 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.


Q7. What are clusters?

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


Q8. What are visual attributes?

ANS:
Visual attributes are the font, color, pattern proprieties that you set for form and menu objects that appear in your application interface.


Q9. Explain about horizontal, Vertical tool bar canvas views?

ANS:
Tool bar canvas views are used to create tool bars for individual windows. Horizontal tool bars are display at the top of a window, just under its menu bar. Vertical Tool bars are displayed along the left side of a window.


Q10. What is the use of image_zoom built-in?

ANS:
To manipulate images in image items.


Q11. What is pop list?

ANS:
The pop list style list item appears initially as a single field (similar to a text item field). When the operator selects the list icon, a list of available choices appears.


Q12. What are the different file extensions that are created by oracle reports?

ANS:
Rep file and Rdf file.


Q13. What are the different types of Record Groups?

ANS:
Query Record Groups
Non Query Record Groups
State Record Group


Q14. 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.


Q15. 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.)


Q16. What is Full Backup?

ANS:
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.


Q17. What is an Oracle sequence?

ANS:
A sequence generates a serial list of unique numbers for numerical columns of a databases tables


Q18. 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.


Q19. What does ROLLBACK do?

ANS:
ROLLBACK retracts any of the changes resulting from the SQL statements in the transaction.


Q20. Define Transaction.

ANS:
A Transaction is a logical unit of work that comprises one or more SQL statements executed by a single user.


Q21. What is a deadlock? Explain

ANS:
Two processes wanting to update the rows of a table which are locked by the other process then deadlock arises. In a database environment this will often happen because of not issuing 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 these processes being killed externally.


Q22. What is Privilege Auditing?

ANS:
Privilege auditing is the auditing of the use of powerful system privileges without regard to specifically named objects.


Q23. What is a profile?

ANS:
Each database user is assigned a Profile that specifies limitations on various system resources available to the user.


Q24. What are the dictionary tables used to monitor a database spaces?

ANS:
DBA_FREE_SPACE
DBA_SEGMENTS
DBA_DATA_FILES


Q25. What is dynamic data replication?

ANS:
Updating or Inserting records in remote database through database triggers. It may fail if remote database is having any problem.


Q26. What is snapshot log?

ANS:
It is a table that maintains a record of modifications to the master table in a snapshot. It is stored in the same database as master table and is only available for simple snapshots. It should be created before creating snapshots.


Q27. What is Distributed database?

ANS:
A distributed database is a network of databases managed by multiple database servers that appears to a user as single logical database. The data of all databases in the distributed database can be simultaneously accessed and modified.


Q28. 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.


Q29. How do you display console on a window?

ANS:
The console includes the status line and message line, and is displayed at the bottom of the window to which it is assigned. To specify that the console should be displayed, set the console window form property to the name of any window in the form. To include the console, set console window to Null.


Q30. What are the types of calculated columns available?

ANS:
Summary, Formula, Placeholder column


Q31. Which parameter can be used to set read level consistency across multiple queries?

ANS: Read only


Q32. What is the basic data structure that is required for creating an LOV?

ANS: Record Group.


Q33. What is the Maximum allowed length of Record group Column?

ANS: Record group column names cannot exceed 30 characters.


Q34. What is strip sources generate options?

ANS:
Removes the source code from the library file and generates a library files that contains only pcode. The resulting file can be used for final deployment, but can not be subsequently edited in the designer.ex. f45gen module=old_lib.pll userid=scott/tiger strip_source YES output_file


Q35. Does Oracle write to data files in begin/hot backup mode? 

ANS:
Oracle will stop updating file headers, but will continue to write data to the database files even if a table space is in backup mode. 
In backup mode, Oracle will write out complete changed blocks to the redo log files. Normally only deltas (changes) are logged to the redo logs. This is done to enable reconstruction of a block if only half of it was backed up (split blocks). Because of this, one should notice increased log activity and archiving during on-line backups.


Q36. What is schema?

ANS: A schema is collection of database objects of a user.


Q37. What is Partial Backup?

ANS:
A Partial Backup is any operating system backup short of a full backup, taken while the database is open or shut down


Q38. 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.


Q39. What are Schema Objects?

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


Q40. What is Mirrored on-line Redo Log?

ANS:
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.


Q41. 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


Q42. What are the components of logical database structure of Oracle database?

ANS:
There are tablespaces and databases schema objects


Q43. 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.


Q44. What is a Redo Log?

ANS:
The set of Redo Log files YSDATE,UID,USER or USERENV SQL functions, or the pseudo columns LEVEL or ROWNUM.


Q45. What are the Referential actions supported by FOREIGN KEY integrity constraint?

ANS:
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.


Q46. What is 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.


Q47. What is an Index Segment?

ANS:
Each Index has an Index segment that stores all of its data.


Q48. 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


Q49. What are the different type of Segments?

ANS:
Data Segment, Index Segment, Rollback Segment and Temporary Segment


Q50. 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


Q51. What is an Integrity Constrains?

ANS:
An integrity constraint is a declarative way to define a business rule for a column of a table.


Q52. What is an 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.


Q53. 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.


Q54. What is a 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.)


Q55. 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.


Q56. What is a synonym?

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


Q57. What are the types of synonyms?

ANS:
There are two types of synonyms private and public.


Q58. What is a private synonym?

ANS:
Only its owner can access a private synonym.


Q59. What is a public synonym?

ANS:
Any database user can access a public synonym.


Q60. 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.


Q61. 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


Q62. What is a Tablespace?

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


Q63. What is Rollback Segment?

ANS:
A Database contains one or more Rollback Segments to temporarily store undo information.


Q64. What are the Characteristics of Data Files?

ANS:
A data file can be associated with only one database. Once created a data file cannot change size. One or more data files form a logical unit of database storage called a tablespace.


Q65. 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 datablocks. Block size is specified in INIT.ORA file and cant be changed latter.


Q66. What does a Control file Contain?

ANS:
A Control file records the physical structure of the database. It contains the following information.
Database Name
Names and locations of a databases files and redolog files.
Time stamp of database creation


Q67. What is the difference between UNIQUE constraint and PRIMARY KEY constraint?

ANS:A column defined as UNIQUE can contain Nulls while a column defined as PRIMARY KEY cant contain Nulls.


Q68. What is Index Cluster?

ANS:
A Cluster with an index on the Cluster Key


Q69. When does a Transaction end?

ANS:
When it is committed or Rollbacked.


Q70. 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?

ANS:
The OPTIMIZER_MODE initialization parameter Statistics in the Data Dictionary the OPTIMIZER_GOAL parameter of the ALTER SESSION command hints in the statement.


Q71. What is the effect of setting the value CHOOSE for OPTIMIZER_GOAL, parameter of the ALTER SESSION Command?

ANS:
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.


Q72. What are the different approaches used by Optimizer in choosing an execution plan?

ANS:
Rule-based and Cost-based.


Q73. What is COST-based approach to optimization?

ANS:
Considering available access paths and determining the most efficient execution plan based on statistics in the data dictionary for the tables accessed by the statement and their associated clusters and indexes.


Q74. Can one rename a database user (schema)?
 
ANS:
No, this is listed as Enhancement Request 158508. Workaround:
Do a user-level export of user A
create new user B
Import system/manager from user=A to user=B
Drop user A


Q75. What is Read-Only Transaction?

ANS:
A Read-Only transaction ensures that the results of each query executed in the transaction are consistent with respect to the same point in time.


Q76. What is a cluster Key?

ANS:
The related columns of the tables in a cluster 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.


Q77. What are clusters?

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


Q78. 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 common (Ver 7.0)


Q79. 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 process can be shared by all users. The memory structure that are used to store most queried data from database. This helps up to improve database performance by decreasing the amount of I/O performed against data file.


Q80. What is the use of ANALYZE command?

ANS:
To perform one of these function on an index,table, or cluster:
- To collect statistics about object used by the optimizer and store them in the data dictionary.
- To delete statistics about the object used by object from the data dictionary.
- To validate the structure of the object.
- To identify migrated and chained rows of the table or cluster.


Q81. What is default tablespace?

ANS:
The Tablespace to contain schema objects created without specifying a tablespace name.


Q82. What are the system resources that can be controlled through Profile?

ANS:
The number of concurrent sessions the user can establish the CPU processing time available to the users session the CPU processing time available to a single call to ORACLE made by a SQL statement the amount of logical I/O available to the users session the amount of logical I/O available to a single call to ORACLE made by a SQL statement the allowed amount of idle time for the users session the allowed amount of connect time for the users session.


Q83. What is Tablespace Quota?

ANS:
The collective amount of disk space available to the objects in a schema on a particular tablespace.


Q84. What are the different Levels of Auditing?

ANS:
Statement Auditing, Privilege Auditing and Object Auditing.


Q85. What is Statement Auditing? 

ANS:
Statement auditing is the auditing of the powerful system privileges without regard to specifically named objects.


Q86. What are the database administrators utilities available?

ANS:
SQL * DBA - This allows DBA to monitor and control an ORACLE database. SQL * Loader - It loads data from standard operating system files (Flat files) into ORACLE database tables. Export (EXP) and Import (imp) utilities allow you to move existing data in ORACLE format to and from ORACLE database.


Q87. How can you enable automatic archiving?

ANS:
Shut the database
Backup the database
Modify/Include LOG_ARCHIVE_START_TRUE in init.ora file.
Start up the database.


Q88. What are roles? How can we implement roles?

ANS:
Roles are the easiest way to grant and manage common privileges needed by different groups of database users. Creating roles and assigning provides to roles. Assign each role to group of users. This will simplify the job of assigning privileges to individual users.


Q89. What are Roles?

ANS:
Roles are named groups of related privileges that are granted to users or other roles.


Q90. What is Object Auditing?

ANS:
Object auditing is the auditing of accesses to specific schema objects without regard to user.


Q91. What is Auditing?

ANS:
Monitoring of user access to aid in the investigation of database use.


Q92. How does one get the view definition of fixed views/tables?

ANS:
Query v$fixed_view_definition. Example: SELECT * FROM v$fixed_view_definition WHERE view_name=V$SESSION;


Q93. When will the data in the snapshot log be used?

ANS:
We must be able to create a after row trigger on table (i.e., it should be not be already available) After giving table privileges. We cannot specify snapshot log name because oracle uses the name of the master table in the name of the database objects that support its snapshot log. The master table name should be less than or equal to 23 characters. (The table name created will be MLOGS_tablename, and trigger name will be TLOGS name).


Q94. What is Two-Phase Commit?

ANS:
Two-phase commit is mechanism that guarantees a distributed transaction either commits on all involved nodes or rolls back on all involved nodes to maintain data consistency across the global distributed database. It has two phase, a Prepare Phase and a Commit Phase.


Q95. How can you Enforce Referential Integrity in snapshots?

ANS:
Time the references to occur when master tables are not in use. Perform the reference the manually immediately locking the master tables. We can join tables in snapshots by creating a complex snapshots that will based on the master tables.


Q96 . What is a SQL * NET?

ANS:
SQL *NET is ORACLEs mechanism for interfacing with the communication protocols used by the networks that facilitate distributed processing and distributed databases. It is used in Clint-Server and Server-Server communications.


Q97. What is the mechanism provided by ORACLE for table replication?

ANS:
Snapshots and SNAPSHOT LOGs


Q98. What are the various types of snapshots?

ANS:
Simple and Complex.


Q99. Describe two phases of Two-phase commit?

ANS:
Prepare phase - The global coordinator (initiating node) ask a participants to prepare (to promise to commit or rollback the transaction, even if there is a failure) Commit - Phase - If all participants respond to the coordinator that they are prepared, the coordinator asks all nodes to commit the transaction, if all participants cannot prepare, the coordinator asks all nodes to roll back the transaction.


Q100. What are the options available to refresh snapshots?

ANS:
COMPLETE - Tables are completely regenerated using the snapshots query and the master tables every time the snapshot referenced.
FAST - If simple snapshot used then a snapshot log can be used to send the changes to the snapshot tables.
FORCE - Default value. If possible it performs a FAST refresh; Otherwise it will perform a complete refresh.


Q101. What is a SNAPSHOT LOG?

ANS:
A snapshot log is a table in the master database that is associated with the master table. ORACLE uses a snapshot log to track the rows that have been updated in the master table. Snapshot logs are used in updating the snapshots based on the master table.


Q102. How can we reduce the network traffic?

ANS:
- Replication of data in distributed environment.
- Using snapshots to replicate data.
- Using remote procedure calls.


Q103. What are the Built-ins used for sending parameters to forms?

ANS:
You can pass parameter values to a form when an application executes the call_form, New_form, Open_form or Run_product.


Q104. Can you have more than one content canvas view attached with a window?

ANS:
Yes. Each window you create must have atleast one content canvas view assigned to it. You can also create a window that has manipulated content canvas view. At run time only one of the content canvas views assign to a window is displayed at a time.


Q105. Is the After report trigger fired if the report execution fails?

ANS: Yes.


Q106. Does a Before form trigger fire when the parameter form is suppressed?

ANS:Yes.


Q107. What is meant by Program Global Area (PGA)?

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


Q108. 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 1 then increase the SHARED_POOL_SIZE.


Q109. How will you enforce security using stored procedures?

ANS:
Dont 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.


Q110. Can a property clause itself  be based on a property clause?

ANS: Yes


Q111. If a parameter is used in a query without being previously defined, what difference exist between report 2.0 and 2.5 when the query is applied?

ANS:
While both reports 2.0 and 2.5 create the parameter, report 2.5 gives a message that a bind parameter has been created.


Q112. What are the SQL clauses supported in the link property sheet?

ANS:
Where start with having.


Q113. What is trigger associated with the timer?

ANS:
When-timer-expired.


Q114. What are the trigger associated with image items?

ANS:
When-image-activated fires when the operators double clicks on an image item when-image-pressed fires when an operator clicks or double clicks on an image item


Q115. What are the different windows events activated at runtimes?

ANS:
When_window_activated
When_window_closed
When_window_deactivated
When_window_resized
Within this triggers, you can examine the built in system variable system. event_window to determine the name of the window for which the trigger fired.


Q116. When do you use data parameter type?

ANS:
When the value of a data parameter being passed to a called product is always the name of the record group defined in the current form. Data parameters are used to pass data to produts invoked with the run_product built-in subprogram.


Q117. What is difference between open_form and call_form?

ANS:
when one form invokes another form by executing open_form the first form remains displayed, and operators can navigate between the forms as desired. when one form invokes another form by executing call_form, the called form is modal with respect to the calling form. That is, any windows that belong to the calling form are disabled, and operators cannot navigate to them until they first exit the called form.


Q118. What is new_form built-in?

ANS:
When one form invokes another form by executing new_form oracle form exits the first form and releases its memory before loading the new form calling new form completely replace the first with the second. If there are changes pending in the first form, the operator will be prompted to save them before the new form is loaded.


Q119. What is the LOV of Validation Property of an item? What is the use of it?

ANS:
When LOV for Validation is set to True, Oracle Forms compares the current value of the text item to the values in the first column displayed in the LOV. Whenever the validation event occurs. If the value in the text item matches one of the values in the first column of the LOV, validation succeeds, the LOV is not displayed, and processing continues normally. If the value in the text item does not match one of the values in the first column of the LOV, Oracle Forms displays the LOV and uses the text item value as the search criteria to automatically reduce the list.


Q120. What is the diff. when Flex mode is mode on and when it is off?

ANS:
When flex mode is on, reports automatically resizes the parent when the child is resized.


Q121. What is the diff. when confine mode is on and when it is off?

ANS:
When confine mode is on, an object cannot be moved outside its parent in the layout


Q122. Which of the two views should objects according to possession?

ANS:
view by structure.


Q123. What are the two types of views available in the object navigator(specific to report 2.5)?

ANS:
View by structure and view by type.


Q124. What are the vbx controls?

ANS:
Vbx control provide a simple method of building and enhancing user interfaces. The controls can use to obtain user inputs and display program outputs.vbx control where originally develop as extensions for the ms visual basic environments and include such items as sliders, rides and knobs.


Q125. What is the use of transactional triggers?

ANS:
Using transactional triggers we can control or modify the default functionality of the oracle forms.


Q126. How do you create a new session while open a new form?

ANS:
Using open_form built-in setting the session option Ex. Open_form(Stocks, active,session). When invoke the multiple forms with open form and call_form in the same application, state whether the following are true/False


Q127. What are the ways to monitor the performance of the report?

ANS:
Use reports profile executable statement. Use SQL trace facility.


Q128. If two groups are not linked in the data model editor, What is the hierarchy between them?

ANS:
Two group that is above are the left most rank higher than the group that is to right or below it.


Q129. An open form can not be execute the call_form procedure if you chain of called forms has been initiated by another open form?

ANS: True


Q130. What is the purpose of the product order option in the column property sheet?

ANS:
To specify the order of individual group evaluation in a cross products.


Q131. How do you reference a parameter indirectly?

ANS:
To indirectly reference a parameter use the NAME IN, COPY built-ins to indirectly set and reference the parameters value Example name_in (capital parameter my param), Copy (SURESH,Parameter my_param)


Q132. What is a timer?

ANS:
Timer is an internal time clock that you can programmatically create to perform an action each time the times.


Q133. What are the two phases of block coordination?

ANS:
There are two phases of block coordination: the clear phase and the population phase. During, the clear phase, Oracle Forms navigates internally to the detail block and flushes the obsolete detail records. During the population phase, Oracle Forms issues a SELECT statement to repopulate the detail block with detail records associated with the new master record. These operations are accomplished through the execution of triggers.


Q134. What are Most Common types of Complex master-detail relationships?

ANS:
There are three most common types of complex master-detail relationships:
master with dependent details
master with independent details
detail with two masters


Q135. What is a text list?

ANS:
The text list style list item appears as a rectangular box which displays the fixed number of values. When the text list contains values that can not be displayed, a vertical scroll bar appears, allowing the operator to view and select undisplayed values.


Q136. What is term?

ANS:
The term is terminal definition file that describes the terminal form which you are using r20run.


Q137. What is use of term?

ANS:
The term file which key is correspond to which oracle report functions.


Q138. What is the maximum number of chars the parameter can store?

ANS:
The maximum no of chars the parameter can store is only valid for char parameters, which can be upto 64K. No parameters default to 23Bytes and Date parameter default to 7Bytes.


Q139. What are the default extensions of the files created by library module?

ANS:
The default file extensions indicate the library module type and storage format .pll - pl/sql library module binary


Q140. What are the Coordination Properties in a Master-Detail relationship?

ANS:
The coordination properties are
Deferred
Auto-Query
These Properties determine when the population phase of block coordination should occur.


Q141. What are the different Parameter types?

ANS:
Text Parameters, Data Parameters


Q142. State any three mouse events system variables?

ANS:
System.mouse_button_pressed, System.mouse_button_shift


Q143. Explain about stacked canvas views?

ANS:
Stacked canvas view is displayed in a window on top of, or stacked on the content canvas view assigned to that same window. Stacked canvas views obscure some part of the underlying content canvas view, and or often shown and hidden programmatically.


Q144. What is the difference between SHOW_EDITOR and EDIT_TEXTITEM?

ANS:
Show editor is the generic built-in which accepts any editor name and takes some input string and returns modified output string. Whereas the edit_textitem built-in needs the input focus to be in the text item before the built-in is executed.


Q145. What are the built-ins that are used to Attach an LOV programmatically to an item?

ANS:
set_item_property
get_item_property
(by setting the LOV_NAME property)


Q146. How does one backup archived log files?

ANS:
One can backup archived log files using RMAN or any operating system backup utility. Remember to delete files after backing them up to prevent the archive log directory from filling up. If the archive log directory becomes full, your database will hang! Look at this simple RMAN backup script:
RMAN> run {
2> allocate channel dev1 type disk;
3> backup
4> format /app/oracle/arch_backup/log_t%t_s%s_p%p
5> (archivelog all delete input);
6> release channel dev1;
7> }


Q147. How does one put a database into ARCHIVELOG mode?

ANS:
The main reason for running in archive log mode is that one can provide 24-hour availability and guarantee complete data recoverability. It is also necessary to enable ARCHIVELOG mode before one can start to use on-line database backups. To enable ARCHIVELOG mode, simply change your database startup command script, and bounce the database:
SQLPLUS> connect sys as sysdba
SQLPLUS> startup mount exclusive;
SQLPLUS> alter database archivelog;
SQLPLUS> archive log start;
SQLPLUS> alter database open;
NOTE1: Remember to take a baseline database backup right after enabling archivelog mode. Without it one would not be able to recover. Also, implement an archivelog backup to prevent the archive log directory from filling-up.
NOTE2: ARCHIVELOG mode was introduced with Oracle V6, and is essential for database point-in-time recovery. Archiving can be used in combination with on-line and off-line database backups.
NOTE3: You may want to set the following INIT.ORA parameters when enabling ARCHIVELOG mode: log_archive_start=TRUE, log_archive_dest=... and log_archive_format=...
NOTE4: You can change the archive log destination of a database on-line with the ARCHIVE LOG START TO directory; statement. This statement is often used to switch archiving between a set of directories.
NOTE5: When running Oracle Real Application Server (RAC), you need to shut down all nodes before changing the database to ARCHIVELOG mode.


Q148. How does one backup a database using RMAN?

ANS:
The biggest advantage of RMAN is that it only backup used space in the database. Rman does not put tablespaces in backup mode, saving on redo generation overhead. RMAN will re-read database blocks until it gets a consistent image of it. Look at this simple backup example.
rman target sys/*** nocatalog
run {
allocate channel t1 type disk;
backup
format /app/oracle/db_backup/%d_t%t_s%s_p%p
( database );
release channel t1;
}
Example RMAN restore:
rman target sys/*** nocatalog
run {
allocate channel t1 type disk;
# set until time Aug 07 2000 :51;
restore tablespace users;
recover tablespace users;
release channel t1;
}

The examples above are extremely simplistic and only useful for illustrating basic concepts. By default Oracle uses the database control files to store information about backups. Normally one would rather setup a RMAN catalog database to store RMAN metadata in. Read the Oracle Backup and Recovery Guide before implementing any RMAN backups.
Note: RMAN cannot write image copies directly to tape. One needs to use a third-party media manager that integrates with RMAN to backup directly to tape. Alternatively one can backup to disk and then manually copy the backups to tape.


Q149. Can a Tablespace hold objects from different Schemes?

ANS:Yes


Q150. Can objects of the same Schema reside in different tablespaces?

ANS: Yes


Q151. Can a Tablespace hold objects from different Schemes?

ANS: Yes


Q152. Can objects of the same Schema reside in different tablespaces?

ANS: Yes


Q153. Do View contain Data?

ANS:
Views do not contain or store data


Q154. Can a view based on another view?

ANS: Yes


Q155. How does one create a new database? 

ANS:
One can create and modify Oracle databases using the Oracle dbca (Database Configuration Assistant) utility. The dbca utility is located in the $ORACLE_HOME/bin directory. The Oracle Universal Installer (oui) normally starts it after installing the database server software.
One can also create databases manually using scripts. This option, however, is falling out of fashion, as it is quite involved and error prone. Look at this example for creating and Oracle 9i database:
CONNECT SYS AS SYSDBA
ALTER SYSTEM SET DB_CREATE_FILE_DEST=/u01/oradata/;
ALTER SYSTEM SET DB_CREATE_ONLINE_LOG_DEST_1=/u02/oradata/;
ALTER SYSTEM SET DB_CREATE_ONLINE_LOG_DEST_2=/u03/oradata/;
CREATE DATABASE;


Q156. What database block size should I use?

ANS:
Oracle recommends that your database block size match, or be multiples of your operating system block size. One can use smaller block sizes, but the performance cost is significant. Your choice should depend on the type of application you are running. If you have many small transactions as with OLTP, use a smaller block size. With fewer but larger transactions, as with a DSS application, use a larger block size. If you are using a volume manager, consider your operating system block size to be 8K. This is because volume manager products use 8K blocks.


Q157. How does one coalesce free space?

ANS:
SMON coalesces free space (extents) into larger, contiguous extents every 2 hours and even then, only for a short period of time.
SMON will not coalesce free space if a tablespaces default storage parameter pctincrease is set to 0. With Oracle 7.3 one can manually coalesce a tablespace using the ALTER TABLESPACE ... COALESCE; command, until then use:
SQL> alter session set events immediate trace name coalesce level n;
Where n is the tablespace number you get from SELECT TS#, NAME FROM SYS.TS$;
You can get status information about this process by selecting from the SYS.DBA_FREE_SPACE_COALESCED dictionary view.


Q158. Where can one find the high water mark for a table? 

ANS:
There is no single system table, which contains the high water mark (HWM) for a table. A tables HWM can be calculated using the results from the following SQL statements:
SELECT BLOCKS
FROM DBA_SEGMENTS
WHERE OWNER=UPPER(owner) AND SEGMENT_NAME = UPPER(table);
ANALYZE TABLE owner.table ESTIMATE STATISTICS;
SELECT EMPTY_BLOCKS
FROM DBA_TABLES
WHERE OWNER=UPPER(owner) AND SEGMENT_NAME = UPPER(table);
Thus, the tables HWM = (query result 1) - (query result 2) - 1
NOTE: You can also use the DBMS_SPACE package and calculate the HWM = TOTAL_BLOCKS - UNUSED_BLOCKS - 1.


Q159. How does one prevent table space fragmentation?

ANS:
Always set PCTINCREASE to 0 or 100.
Bizarre values for PCTINCREASE will contribute to fragmentation. For example if you set PCTINCREASE to 1 you will see that your extents are going to have weird and wacky sizes: 100K, 100K, 101K, 102K, etc. Such extents of bizarre size are rarely re-used in their entirety. PCTINCREASE of 0 or 100 gives you nice round extent sizes that can easily be reused. Eg. 100K, 100K, 200K, 400K, etc.


Q160. What does COMMIT do?

ANS:
COMMIT makes permanent the changes resulting from all SQL statements in the transaction. The changes made by the SQL statements of a transaction become visible to other user sessions transactions that start only after transaction is committed.


Q161. How are extents allocated to a segment? 

ANS:
Oracle8 and above rounds off extents to a multiple of 5 blocks when more than 5 blocks are requested. If one requests 16K or 2 blocks (assuming a 8K block size), Oracle does not round it up to 5 blocks, but it allocates 2 blocks or 16K as requested. If one asks for 8 blocks, Oracle will round it up to 10 blocks.
Space allocation also depends upon the size of contiguous free space available. If one asks for 8 blocks and Oracle finds a contiguous free space that is exactly 8 blocks, it would give it you. If it were 9 blocks, Oracle would also give it to you. Clearly Oracle does not always round extents to a multiple of 5 blocks.
The exception to this rule is locally managed table spaces. If a table space is created with local extent management and the extent size is 64K, then Oracle allocates 64K or 8 blocks assuming 8K-block size. Oracle does not round it up to the multiple of 5 when a table space is locally managed.


Q162. What is a Schema?

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


Q163. What is Parallel Server?

ANS:
Multiple instances accessing the same database (Only In Multi-CPU environments)


Q164. What are the uses of Roles?

ANS:
REDUCED GRANTING OF PRIVILEGES - Rather than explicitly granting the same set of privileges to many users a database administrator can grant the privileges for a group of related users granted to a role and then grant only the role to each member of the group.
DYNAMIC PRIVILEGE MANAGEMENT - When the privileges of a group must change, only the privileges of the role need to be modified. The security domains of all users granted the groups role automatically reflect the changes made to the role.
SELECTIVE AVAILABILITY OF PRIVILEGES - The roles granted to a user can be selectively enable (available for use) or disabled (not available for use). This allows specific control of a users privileges in any given situation.
APPLICATION AWARENESS - A database application can be designed to automatically enable and disable selective roles when a user attempts to use the application.


Q165. How does one see the uptime for a database?

ANS: 
Look at the following SQL query:

SELECT to_char (startup_time,DD-MON-YYYY HH24: MI: SS) DB Startup Time
FROM sys.v_$instance;
Marco Bergman provided the following alternative solution:
SELECT to_char (logon_time,Dy dd Mon HH24: MI: SS) DB Startup Time
FROM sys.v_$session
WHERE Sid=1 /* this is pmon */
/
Users still running on Oracle 7 can try one of the following queries:
Column STARTED format a18 head STARTUP TIME
Select C.INSTANCE,
to_date (JUL.VALUE, J)
|| to_char (floor (SEC.VALUE/3600), 09)
|| :
-- || Substr (to_char (mod (SEC.VALUE/60, 60), 09), 2, 2)
|| Substr (to_char (floor (mod (SEC.VALUE/60, 60)), 09), 2, 2)
|| .
|| Substr (to_char (mod (SEC.VALUE, 60), 09), 2, 2) STARTED
from SYS.V_$INSTANCE JUL,
SYS.V_$INSTANCE SEC,
SYS.V_$THREAD C
Where JUL.KEY like %JULIAN%
and SEC.KEY like %SECOND%;
Select to_date (JUL.VALUE, J)
|| to_char (to_date (SEC.VALUE, SSSSS),  HH24:MI:SS) STARTED
from SYS.V_$INSTANCE JUL,
SYS.V_$INSTANCE SEC
where JUL.KEY like %JULIAN%
and SEC.KEY like %SECOND%;
select to_char (to_date (JUL.VALUE, J) + (SEC.VALUE/86400), -Return a DATE
DD-MON-YY HH24:MI:SS) STARTED
from V$INSTANCE JUL,
V$INSTANCE SEC
where JUL.KEY like %JULIAN%
and SEC.KEY like %SECOND%;


Q166. How will you enforce security using stored procedures?

ANS:
Do not 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.


Q167. Where are my TEMPFILES, I do not see them in V$DATAFILE or DBA_DATA_FILE?
 
ANS:
Tempfiles, unlike normal datafiles, are not listed in v$datafile or dba_data_files. Instead query v$tempfile or dba_temp_files:
SELECT * FROM v$tempfile;
SELECT * FROM dba_temp_files;


Q168. How can one see who is using a temporary segment?

ANS:
For every user using temporary space, there is an entry in SYS.V$_LOCK with type TS.
All temporary segments are named ffff.bbbb where ffff is the file it is in and bbbb is first block of the segment. If your temporary tablespace is set to TEMPORARY, all sorts are done in one large temporary segment. For usage stats, see SYS.V_$SORT_SEGMENT
From Oracle 8.0, one can just query SYS.v$sort_usage. Look at these examples:
select s.username, u.USER, u.tablespace, u.contents, u.extents, u.blocks
from sys.v_$session s, sys.v_$sort_usage u
where s.addr = u.session_addr
/
select s.osuser, s.process, s.username, s.serial#,
Sum (u.blocks)*vp.value/1024 sort_size
from sys.v_$session s, sys.v_$sort_usage u, sys.v_$parameter VP
where s.saddr = u.session_addr
and vp.name = db_block_size
and s.osuser like &1
group by s.osuser, s.process, s.username, s.serial#, vp.value


Q169. How do I find used/free space in a TEMPORARY tablespace?
 
ANS:
Unlike normal tablespaces, true temporary tablespace information is not listed in DBA_FREE_SPACE. Instead use the V$TEMP_SPACE_HEADER view:
SELECT tablespace_name, SUM (bytes used), SUM (bytes free)

FROM V$temp_space_header
GROUP BY tablespace_name;


Q170. How can we specify the Archived log file name format and destination?

ANS:
By setting the following values in init.ora file. LOG_ARCHIVE_FORMAT = arch %S/s/T/tarc (%S - Log sequence number and is zero left paded, %s - Log sequence number not padded. %T - Thread number lef-zero-paded and %t - Thread number not padded). The file name created is arch 0001 are if %S is used. LOG_ARCHIVE_DEST = path.


Q171. How does one do off-line database backups? 

ANS:
Shut down the database from sqlplus or server manager. Backup all files to secondary storage (eg. tapes). Ensure that you backup all data files, all control files and all log files. When completed, restart your database.
Do the following queries to get a list of all files that needs to be backed up:
select name from sys.v_$datafile;
select member from sys.v_$logfile;
select name from sys.v_$controlfile;
Sometimes Oracle takes forever to shutdown with the immediate option. As workaround to this problem, shutdown using these commands:
alter system checkpoint;
shutdown abort
startup restrict
shutdown immediate
Note that if you database is in ARCHIVELOG mode, one can still use archived log files to roll forward from an off-line backup. If you cannot take your database down for a cold (off-line) backup at a convenient time, switch your database into ARCHIVELOG mode and perform hot (on-line) backups.


Q172. How does one do on-line database backups? 

ANS:
Each tablespace that needs to be backed-up must be switched into backup mode before copying the files out to secondary storage (tapes). Look at this simple example.
ALTER TABLESPACE xyz BEGIN BACKUP;
! cp xyfFile1 /backupDir/
ALTER TABLESPACE xyz END BACKUP;
It is better to backup tablespace for tablespace than to put all tablespaces in backup mode. Backing them up separately incurs less overhead. When done, remember to backup your control files. Look at this example:
ALTER SYSTEM SWITCH LOGFILE; -- Force log switch to update control file headers
ALTER DATABASE BACKUP CONTROLFILE TO /backupDir/control.dbf;
NOTE: Do not run on-line backups during peak processing periods. Oracle will write complete database blocks instead of the normal deltas to redo log files while in backup mode. This will lead to excessive database archiving and even database freezes.


Q173. What are the basic elements 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.


  
   






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