Posted by: Monish | October 10, 2008

Lock/Unlock Oracle Users

Normal 0

false false false MicrosoftInternetExplorer4

In spite of deleting an oracle user, we can LOCK it. In that way the user won’t be accessible. In future if we want we can UNLOCK it.

create a user named JACK which is LOCKED:

SQL> create user jack identified by jack account lock;

User created.

Now grant him the CONNECT & RESOURCE privilege:

SQL> grant connect, resource to jack;

Grant succeeded.

Now, try to connect the user:

SQL> conn jack/jack;
ERROR:
ORA-28000: the account is locked

Warning: You are no longer connected to ORACLE.

Now, connect to the SYS accout:

SQL> conn sys as sysdba
Enter password:
Connected.
SQL>

Now, see the account status:

SQL> select USERNAME,ACCOUNT_STATUS,LOCK_DATE from dba_users where USERNAME='JACK';
USERNAME                       ACCOUNT_STATUS                   LOCK_DATE
------------------------------ -------------------------------- ---------
JACK                           LOCKED                           10-OCT-08

To, unlock the Jack:

SQL> alter user jack account unlock;

User altered.

SQL>
SQL> conn jack/jack;
Connected.

==================

Otherwise we can do one thing, we can revoke its CONNECT privilege. In that way the user can’t connect to the db.

SQL> revoke connect from jack;

Revoke succeeded.

SQL> conn jack/jack;
ERROR:
ORA-01045: user JACK lacks CREATE SESSION privilege; logon denied


Warning: You are no longer connected to ORACLE.

SQL> conn sys as sysdba
Enter password:
Connected.
SQL>
SQL> grant connect to jack;

Grant succeeded.

SQL>
SQL> conn jack/jack;
Connected.

>>>Please leave your comment on the post.

=========

Readers are leaders. You can only master the craft if you constantly study and keep up the hands-on practice. Following are some of the great books for your reference.

Please use the below links to grab your copy. Thank you! 🙂

Expert Oracle Database Architecture (by Thomas Kyte and Darl Kuhn) –> https://amzn.to/2EZ8eUE

Expert Oracle Database Architecture: Oracle Database 9i, 10g, and 11g Programming Techniques and Solutions –> https://amzn.to/2F17qPh

Oracle Database 12c DBA Handbook (Oracle Press) –> https://amzn.to/2F0tJoh
RMAN Recipes for Oracle Database 12c-A Problem-Solution Approach –> https://amzn.to/2EYY3ja
Oracle Database 12c Performance Tuning Recipes –> https://amzn.to/2F01uGj

Oracle RMAN 11g Backup and Recovery (Oracle Press) –> https://amzn.to/2NQ3OT9

OCA/OCP Oracle Database 12c All-in-One Exam Guide (Exams 1Z0-061, 1Z0-062, & 1Z0-063) –> https://amzn.to/2F0jTD0

OCA/OCP Oracle Database 11g All-in-One Exam Guide with CD-ROM –> https://amzn.to/2SPPJWJ

Expert Oracle RAC Performance Diagnostics and Tuning –> https://amzn.to/2NTXxWr

Pro Oracle Database 11g Administration (Expert’s Voice in Oracle) –> https://amzn.to/2NRj0iD

Posted by: Monish | October 5, 2008

Oracle 10g new Features

I’m adding this post for my own reference. It contains the top 20 oracle 10g features. I have got this information from Oracle.com

Flashback Versions Query
Rollback Monitoring
Tablespace Management
Oracle Data Pump
Flashback Table
Automatic Workload Repository
SQL*Plus Rel 10.1
Automatic Storage Management
RMAN
Auditing Wait Interface
Materialized Views
Enterprise Manager 10g
Virtual Private Database
Automatic Segment Management
Transportable Tablespaces
Automatic Shared Memory Management
ADDM and SQL Tuning Advisor
Scheduler

For the details on the above features click here.

Posted by: Monish | October 3, 2008

Oracle OCA/OCP Study Materials

Oracle Database 10g: Administration I

This post is for those who want to sit for the 10g OCA exam. To know the details like exam fees, topics, no of questions etc. click here. For 1z0-042 exam dumps click here. Please don’t misuse them. Those dumps are provided for educational purpose only. Thanx…………….

Hi Friends,

I have removed the dumps from the post. It’s not wise to blindly follow them and Oracle consider them as cheating.

Though for study and mock test purpose you can use the below links. Hope they will be helpful.

 Book 1

Book 2

For Mock Test

Posted by: Monish | October 3, 2008

Oracle Interview Questions

Oracle Concepts and Architecture Database Structures

1. What are the components of physical database structure of Oracle database?

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

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

There are tablespaces and database’s schema objects.

3. What is a tablespace?

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

4. What is SYSTEM tablespace and when is it created?

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.

5. 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.

6. What is schema?

A schema is collection of database objects of a user.

7. What are Schema Objects?

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.

8. Can objects of the same schema reside in different tablespaces?

Yes.

9. Can a tablespace hold objects from different schemes?

Yes.

10. What is Oracle 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.

11. What is an Oracle 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.)

12. Do a view contain data?

Views do not contain or store data.

13. Can a view based on another view?

Yes.

14. What are the advantages of views?

– 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.

15. What is an Oracle sequence?

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

16. What is a synonym?

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

17. What are the types of synonyms?

There are two types of synonyms private and public.

18. What is a private synonym?

Only its owner can access a private synonym.

19. What is a public synonym?

Any database user can access a public synonym.

20. What are synonyms used for?

– 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.

21. What is an Oracle 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.

22. How are the indexes update?

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

23. What are clusters?

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

24. What is cluster key?

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

25. What is index cluster?

A cluster with an index on the cluster key.

26. 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.

27. When can hash cluster used?

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.

28. What is database link?

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

29. What are the types of database links?

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

30. What is private database link?

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.

31. What is public database link?

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.

32. What is network database link?

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.

33. What is data block?

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.

34. 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 data blocks. Block size is specified in init.ora file and cannot be changed latter.

35. What is row chaining?

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.

36. 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.

37. What is a segment?

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

38. What are the different types of segments?

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

39. What is a data segment?

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.

40. What is an index segment?

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

41. What is rollback segment?

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

42. What are the uses of rollback segment?

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

43. What is a temporary segment?

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.

44. What is a datafile?

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.

45. 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.

46. What is a redo log?

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

47. What is the function of redo log?

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

48. What is the use of redo log information?

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.

49. What does a control file contains?

– Database name

– Names and locations of a database’s files and redolog files.

– Time stamp of database creation.

50. 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.

Database Administration

51. What is a database instance? Explain.

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.

52. What is Parallel Server?

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

53. What is a schema?

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

54. What is an index? How it is implemented in Oracle database?

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.

55. What are clusters?

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

56. What is a cluster key?

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.

57. What are the basic elements of base configuration of an Oracle database?

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 MONitor)

PMON (Process MONitor)

LGWR R (LoG Write)

DBWR (Data Base Writer)

ARCH (ARCHiver)

CKPT (Check Point)

RECO

Dispatcher

User Process with associated PGS.

58. What is a deadlock? Explain.

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

59. What is SGA?

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.

60. What is a shared pool?

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.

61. What is mean by Program Global Area (PGA)?

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

62. What is a data segment?

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

63. What are the factors causing the reparsing of SQL statements in SGA?

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.

Database Logical & Physical Architecture

64. What is Database Buffers?

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.

65. What is dictionary cache?

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

66. What is meant by recursive hints?

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.

67. What is redo log buffer?

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.

68. How will you swap objects into a different table space for an existing database?

– 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.

69. List the Optional Flexible Architecture (OFA) of Oracle database? How can we

organize the tablespaces in Oracle database to have maximum performance?

SYSTEM – Data dictionary tables.

DATA – Standard operational tables.

DATA2- Static tables used for standard operations

INDEXES – Indexes for Standard operational tables.

INDEXES1 – Indexes of static tables used for standard operations.

TOOLS – Tools table.

TOOLS1 – Indexes for tools table.

RBS – Standard Operations Rollback Segments,

RBS1,RBS2 – Additional/Special Rollback segments.

TEMP – Temporary purpose tablespace

TEMP_USER – Temporary tablespace for users.

USERS – User tablespace.

70. How will you force database to use particular rollback segment?

SET TRANSACTION USE ROLLBACK SEGMENT rbs_name.

71. What is meant by free extent?

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.

72. Which parameter in Storage clause will reduce number of rows per block?

PCTFREE parameter. Row size also reduces no of rows per block.

73. What is the significance of having storage clause?

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.

74. How does Space allocation table place within a block?

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)

75. What is the role of PCTFREE parameter is storage clause?

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

76. What is the OPTIMAL parameter?

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

77. What is the functionality of SYSTEM table space?

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

78. How will you create multiple rollback segments in a database?

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

– Create a second rollback segment name R0 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 R0 and activate the newly created rollback segments.

79. How the space utilization takes place within rollback segments?

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)

80. Why query fails sometimes?

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.

81. How will you monitor the space allocation?

By querying DBA_SEGMENT table/view.

82. How will you monitor rollback segment status?

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.

83. 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.

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.

84. How can we plan storage for very large tables?

Limit the number of extents in the table.

Separate table from its indexes.

Allocate sufficient temporary storage.

85. How will you estimate the space required by a non-clustered tables?

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 10 % additional space to calculate the initial extent size for a working table.

86. It is possible to use raw devices as data files and what are the advantages over

file system files?

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.

87. What is a Control file?

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.

88. How to implement the multiple control files for an existing database?

Shutdown the database.

Copy one of the existing controlfile to new location.

Edit Config ora file by adding new control filename. Restart the database.

89. What is redo log file mirroring? How can be achieved?

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.

90. What is advantage of having disk shadowing / mirroring?

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.

91. What is use of rollback segments in Oracle database?

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

92. What is a rollback segment entry?

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.

93. What is hit ratio?

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.

94. When will be a segment released?

When Segment is dropped.

When Shrink (RBS only).

When truncated (TRUNCATE used with drop storage option).

95. What are disadvantages of having raw devices?

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.

96. List the factors that can affect the accuracy of the estimations?

– 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.

Database Security & Administration

97. What is user Account in Oracle database?

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.

98. How will you enforce security using stored procedures?

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.

99. What are the dictionary tables used to monitor a database space?

DBA_FREE_SPACE

DBA_SEGMENTS

DBA_DATA_FILES.

SQL*Plus Statements

100. What are the types of SQL statement?

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.

101. What is a transaction?

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

102. What is difference between TRUNCATE & DELETE?

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.

103. What is a join? Explain the different types of joins?

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.

104. What is the sub-query?

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

105. What is correlated sub-query?

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

106. Explain CONNECT BY PRIOR?

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

107. Difference between SUBSTR and INSTR?

INSTR (String1, String2 (n, (m)),

INSTR returns the position of the mth 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 nth position of string1.

108. Explain UNION, MINUS, UNION ALL and INTERSECT?

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.

109. What is ROWID?

ROWID is a pseudo column attached to each row of a table. It is 18 characters long, blockno, rownumber are the components of ROWID.

110. What is the fastest way of accessing a row in a table?

Using ROWID. CONSTRAINTS.

111. What is an integrity constraint?

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

112. What is referential integrity constraint?

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.

113. What is the usage of SAVEPOINTS?

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.

114. What is ON DELETE CASCADE?

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.

115. What are the data types allowed in a table?

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

116. What is difference between CHAR and VARCHAR2? What is the maximum SIZE allowed for each type?

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.

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

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

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

– 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.

119. Where the integrity constraints are stored in data dictionary?

The integrity constraints are stored in USER_CONSTRAINTS.

120. How will you activate/deactivate integrity constraints?

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

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

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

122. What is a database link?

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

123. 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?

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

124. What is CYCLE/NO CYCLE in a Sequence?

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.

125. What are the advantages of VIEW?

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

– To hide complexity of a query.

– To hide complexity of calculations.

126. Can a view be updated/inserted/deleted? If Yes – under what conditions?

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.

127. If a view on a single base table is manipulated will the changes be reflected on the base table?

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.

>>>Please leave your comment…………

Posted by: Monish | September 27, 2008

10g Architecture

Oracle 10g architecture

The above image illustrates the architecture of Oracle 10g.

Posted by: Monish | September 27, 2008

Startup & Shutdown

STARTUP

Normal database operation means that an instance is started and the database is mounted and open. This mode allows any valid user to connect to the database and perform typical data access operations.

Start an instance, read the initialization parameters from the default server parameter file location, and then mount and open the database by using the STARTUP command by itself (you can, of course, optionally specify the PFILE clause):

STARTUP NOMOUNT

You can start an instance without mounting a database. Typically, you can do so only during database creation. Use the STARTUP command with the NOMOUNT clause:

STARTUP MOUNT

You can start an instance and mount a database without opening it, allowing you to perform specific maintenance operations. For example, the database must be mounted but not open during the following tasks:

  • Enabling and disabling redo log-archiving options.
  • Performing full database recovery.

Start an instance and mount the database, but leave it closed by using the STARTUP command with the MOUNT clause:

STARTUP FORCE

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.
  • You experience problems when starting an instance.

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 clause:

STARTUP RESTRICT

You can start an instance, and optionally mount and open a database, in restricted mode so that the instance is available only to administrative personnel (not general database users). Use this mode of instance startup when you need to accomplish one of the following tasks:

  • Perform an export or import of database data
  • Perform a data load (with SQL*Loader)
  • Temporarily prevent typical users from using data
  • During certain migration and upgrade operations

Typically, all users with the CREATE SESSION system privilege can connect to an open database. Opening a database in restricted mode allows database access only to users with both the CREATE SESSION and RESTRICTED SESSION system privilege. Only database administrators should have the RESTRICTED SESSION system privilege. Further, when the instance is in restricted mode, a database administrator cannot access the instance remotely through an Oracle Net listener, but can only access the instance locally from the machine that the instance is running on.

Start an instance (and, optionally, mount and open the database) in restricted mode by using the STARTUP command with the RESTRICT clause:

Later, use the ALTER SYSTEM statement to disable the RESTRICTED SESSION feature:

ALTER SYSTEM DISABLE RESTRICTED SESSION;

STARTUP OPEN RECOVER

If you know that media recovery is required, you can start an instance, mount a database to the instance, and have the recovery process automatically start by using the STARTUP command with the RECOVER clause.

=====================================================================

SHUTDOWN NORMAL

To shut down a database in normal situations, use the SHUTDOWN command with the NORMAL clause:

Normal database shutdown proceeds with the following conditions:

  • No new connections are allowed after the statement is issued.
  • Before the database is shut down, the database waits for all currently connected users to disconnect from the database.

The next startup of the database will not require any instance recovery procedures.

SHUTDOWN IMMEDIATE

Use immediate database shutdown only in the following situations:

  • To initiate an automated and unattended backup
  • When a power shutdown is going to occur soon
  • When the database or one of its applications is functioning irregularly and you cannot contact users to ask them to log off or they are unable to log off

To shut down a database immediately, use the SHUTDOWN command with the IMMEDIATE clause:

Immediate database shutdown proceeds with the following conditions:

  • No new connections are allowed, nor are new transactions allowed to be started, after the statement is issued.
  • Any uncommitted transactions are rolled back. (If long uncommitted transactions exist, this method of shutdown might not complete quickly, despite its name.)
  • Oracle Database does not wait for users currently connected to the database to disconnect. The database implicitly rolls back active transactions and disconnects all connected users.

The next startup of the database will not require any instance recovery procedures.

SHUTDOWN TRANSACTIONAL

When you want to perform a planned shutdown of an instance while allowing active transactions to complete first, use the SHUTDOWN command with the TRANSACTIONAL clause:

Transactional database shutdown proceeds with the following conditions:

  • No new connections or new transactions allowed starting after the statement is issued.
  • After all transactions have completed, any client still connected to the instance is disconnected.
  • At this point, the instance shuts down just as it would when a SHUTDOWN IMMEDIATE statement is submitted.

The next startup of the database will not require any instance recovery procedures.

A transactional shutdown prevents clients from losing work, and at the same time, does not require all users to log off.

SHUTDOWN ABORT

You can shut down a database instantaneously by aborting the database instance. If possible, perform this type of shutdown only in the following situations:

The database or one of its applications is functioning irregularly and none of the other types of shutdown works.

  • You need to shut down the database instantaneously (for example, if you know a power shutdown is going to occur in one minute).
  • You experience problems when starting a database instance.

When you must do a database shutdown by aborting transactions and user connections, issue the SHUTDOWN command with the ABORT clause:

An aborted database shutdown proceeds with the following conditions:

  • After issuing the statement, no new connection or transaction are allowed.
  • Current client SQL statements being processed by Oracle Database are immediately terminated.
  • Uncommitted transactions are not roll back.
  • Oracle Database does not wait for users currently connected to the database to disconnect. The database implicitly disconnects all connected users.

The next startup of the database will require instance recovery procedures.

>>> Please leave your comment on the above post..

Posted by: Monish | September 12, 2008

Dedicated and Shared Server Processes

About Dedicated and Shared Server Processes

Oracle Database creates server processes to handle the requests of user processes connected to an instance. A server process can be either of the following:

· A dedicated server process, which services only one user process

· A shared server process, which can service multiple user processes

Your database is always enabled to allow dedicated server processes, but you must specifically configure and enable shared server by setting one or more initialization parameters.

Dedicated Server Processes

Figure 4-1, “Oracle Database Dedicated Server Processes” illustrates how dedicated server processes work. In this diagram two user processes are connected to the database through dedicated server processes.

In general, it is better to be connected through a dispatcher and use a shared server process. This is illustrated in Figure 4-2, “Oracle Database Shared Server Processes”. A shared server process can be more efficient because it keeps the number of processes required for the running instance low.

In the following situations, however, users and administrators should explicitly connect to an instance using a dedicated server process:

· To submit a batch job (for example, when a job can allow little or no idle time for the server process)

· To use Recovery Manager (RMAN) to back up, restore, or recover a database

To request a dedicated server connection when Oracle Database is configured for shared server, users must connect using a net service name that is configured to use a dedicated server. Specifically, the net service name value should include the SERVER=DEDICATED clause in the connect descriptor.

Figure 4-1 Oracle Database Dedicated Server Processes

Shared Server Processes

Consider an order entry system with dedicated server processes. A customer phones the order desk and places an order, and the clerk taking the call enters the order into the database. For most of the transaction, the clerk is on the telephone talking to the customer. A server process is not needed during this time, so the server process dedicated to the clerk’s user process remains idle. The system is slower for other clerks entering orders, because the idle server process is holding system resources.

Shared server architecture eliminates the need for a dedicated server process for each connection (see Figure 4-2).

In a shared server configuration, client user processes connect to a dispatcher. The dispatcher can support multiple client connections concurrently. Each client connection is bound to a virtual circuit, which is a piece of shared memory used by the dispatcher for client database connection requests and replies. The dispatcher places a virtual circuit on a common queue when a request arrives.

An idle shared server process picks up the virtual circuit from the common queue, services the request, and relinquishes the virtual circuit before attempting to retrieve another virtual circuit from the common queue. This approach enables a small pool of server processes to serve a large number of clients. A significant advantage of shared server architecture over the dedicated server model is the reduction of system resources, enabling the support of an increased number of users.

For even better resource management, shared server can be configured for connection pooling. Connection pooling lets a dispatcher support more users by enabling the database server to time-out protocol connections and to use those connections to service an active session. Further, shared server can be configured for session multiplexing, which combines multiple sessions for transmission over a single network connection in order to conserve the operating system’s resources.

Shared server architecture requires Oracle Net Services. User processes targeting the shared server must connect through Oracle Net Services, even if they are on the same machine as the Oracle Database instance.

>>> Please leave your comment on the above post…………

Posted by: Monish | August 21, 2008

Create Database on LINUX

STEPS TO CREATE DATABASE MANUALLY ON LINUX

Step 1:

First create all the necessary directories. Followings are my directories:

testdb1]$ ls

admin backup archive

admin]$ ls

adump bdump cdump udump

Step 2:

Next prepare the database creation script. Following is my script “testdb1.sql

CREATE DATABASE “testdb1”

MAXLOGFILES 5

MAXLOGMEMBERS 5

MAXDATAFILES 100

MAXINSTANCES 1

MAXLOGHISTORY 292

LOGFILE

GROUP 1 ‘/d02/monish/testdb1/redo1.log’ SIZE 10M,

GROUP 2 ‘/d02/monish/testdb1/redo2.log’ SIZE 10M,

GROUP 3 ‘/d02/monish/testdb1/redo3.log’ SIZE 10M

DATAFILE

‘/d02/monish/testdb1/system.dbf’ size 100m,

‘/d02/monish/testdb1/usr04.dbf’ size 10m

sysaux datafile ‘/d02/monish/testdb1/sysaux.dbf’ size 100m

undo tablespace undotbs

datafile ‘/d02/monish/testdb1/undo.dbf’ size 50m

CHARACTER SET US7ASCII

;

Step 3:

Prepare the init file. Like this one [inittestdb1.ora]

*.audit_file_dest=’/d02/monish/testdb1/admin/adump’

*.background_dump_dest=’/d02/monish/testdb1/admin/bdump’

*.compatible=’10.2.0.3.0′

*.control_files=’/d02/monish/testdb1/control01.ctl’,

‘/d02/monish/testdb1/control02.ctl’,’/d02/monish/testdb1/control03.ctl’

*.core_dump_dest=’/d02/monish/testdb1/admin/cdump’

*.db_block_size=8192

*.db_domain=”

*.db_file_multiblock_read_count=16

*.db_name=’testdb1′

*.dispatchers='(PROTOCOL=TCP) (SERVICE=indiaXDB)’

*.job_queue_processes=10

*.log_archive_dest_1=’LOCATION=/d02/monish/testdb1/archive’

*.log_archive_format=’%t_%s_%r.dbf’

*.open_cursors=300

*.pga_aggregate_target=200278016

*.processes=150

*.remote_login_passwordfile=’EXCLUSIVE’

*.sga_target=601882624

*.undo_management=’AUTO’

*.undo_tablespace=’UNDOTBS’

*.user_dump_dest=’/d02/monish/testdb1/admin/udump’

*.db_recovery_file_dest=’/d02/monish/testdb1/backup’

*.db_recovery_file_dest_size=2147483648

Step 4:

Now perform the following steps:

$ export ORACLE_SID=testdb1

$ sqlplus / as sysdba

SQL*Plus: Release 10.2.0.3.0 – Production on Thu May 22 17:35:28 2008

Copyright (c) 1982, 2006, Oracle. All Rights Reserved.

Connected to an idle instance.

SQL> startup pfile=/u01/app/oracle/product/10.2.0/db_1/dbs/inittestdb1.ora nomount

ORACLE instance started.

Total System Global Area 603979776 bytes

Fixed Size 1263176 bytes

Variable Size 167774648 bytes

Database Buffers 427819008 bytes

Redo Buffers 7122944 bytes

SQL> @testdb1.sql

Database created.

Step 5:

So your database is create. Now just run the catalog.sql and catproc.sql scripts.

You will find the in $ cd $ORACLE_HOME/rdbms/admin

SQL> @/u01/app/oracle/product/10.2.0/db_1/rdbms/admin/catalog.sql

SQL> @/u01/app/oracle/product/10.2.0/db_1/rdbms/admin/catproc.sql

SQL> select name from v$database;

NAME

———

TESTDB1

Okay, now your database is ready to use…

« Newer Posts - Older Posts »

Categories