What is a deadlock ? Explain .
Two processes wating 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 this processes being killed externally.
What is a Schema ?
The set of objects owned by user account is called the schema.
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.
What is Parallel Server ?
Multiple instances accessing the same database (Only In Multi-CPU environments)
What are the basic element 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 MONito)
PMON (Process MONitor)
LGWR (LoG Write)
DBWR (Data Base Write)
ARCH (ARCHiver)
CKPT (Check Point)
RECO
Dispatcher
User Process with associated PGS
What is clusters ?
Group of tables physically stored together because they share common columns and are often used together is called Cluster.
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 comman (Ver 7.0)
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 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.
What is the use of ANALYZE command ?
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.
What is default tablespace ?
The Tablespace to contain schema objects created without specifying a tablespace name.
What are the system resources that can be controlled through Profile ?
The number of concurrent sessions the user can establish the CPU processing time available to the user's 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 user's session the amout of logical I/O available to a single call to ORACLE made by a SQL statement the allowed amount of idle time for the user's session the allowed amount of connect time for the user's session.
What is Tablespace Quota ?
The collective amount of disk space available to the objects in a schema on a particular tablespace.
What are the different Levels of Auditing ?
Statement Auditing, Privilege Auditing and Object Auditing.
What is Statement Auditing ?
Statement auditing is the auditing of the powerful system privileges without regard to specifically named objects.
What are the database administrators utilities available ?
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.
How can you enable automatic archiving ?
Shut the database
Backup the database
Modify/Include LOG_ARCHIVE_START_TRUE in init.ora file.
Start up the database.
What are roles? How can we implement roles ?
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.
What are Roles ?
Roles are named groups of related privileges that are granted to users or other roles.
What are the use of Roles ?
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 group's 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 user's 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.
What is Privilege Auditing ?
Privilege auditing is the auditing of the use of powerful system privileges without regard to specifically named objects.
What is Object Auditing ?
Object auditing is the auditing of accesses to specific schema objects without regard to user.
What is Auditing ?
Monitoring of user access to aid in the investigation of database use.
Oracle Interview Questions And Answers [3]
What is an Oracle sequence?
A sequence generates a serial list of unique numbers for numerical columns of a database's tables.
What is a synonym?
A synonym is an alias for a table, view, sequence or program unit.
What are the types of synonyms?
There are two types of synonyms private and public.
What is a private synonym?
Only its owner can access a private synonym.
What is a public synonym?
Any database user can access a public synonym.
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.
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.
How are the index updates?
Indexes are automatically maintained and used by Oracle. Changes to table data are automatically incorporated into all relevant indexes.
What is a Tablespace?
A database is divided into Logical Storage Unit called tablespace. A tablespace is used to grouped related logical structures together
What is Rollback Segment ?
A Database contains one or more Rollback Segments to temporarily store "undo" information.
What are the Characteristics of Data Files ?
A data file can be associated with only one database. Once created a data file can't change size. One or more data files form a logical unit of database storage called a tablespace.
How to define Data Block size ?
A data block size is specified for each ORACLE database when the database is created. A database users and allocated free database space in ORACLE data blocks. Block size is specified in INIT.ORA file and can’t be changed latter.
What does a Control file Contain ?
A Control file records the physical structure of the database. It contains the following information.
Database Name
Names and locations of a database's files and redolog files.
Time stamp of database creation.
What is difference between UNIQUE constraint and PRIMARY KEY constraint ?
A column defined as UNIQUE can contain Nulls while a column defined as PRIMARY KEY can't contain Nulls.
What is Index Cluster ?
A Cluster with an index on the Cluster Key
When does a Transaction end ?
When it is committed or Rollbacked.
What is the effect of setting the value "ALL_ROWS" for OPTIMIZER_GOAL parameter of the ALTER SESSION command ? What are the factors that affect OPTIMIZER in choosing an Optimization approach ?
Answer The OPTIMIZER_MODE initialization parameter Statistics in the Data Dictionary the OPTIMIZER_GOAL parameter of the ALTER SESSION command hints in the statement.
What is the effect of setting the value "CHOOSE" for OPTIMIZER_GOAL, parameter of the ALTER SESSION Command ?
The Optimizer chooses Cost_based approach and optimizes with the goal of best throughput if statistics for atleast one of the tables accessed by the SQL statement exist in the data dictionary. Otherwise the OPTIMIZER chooses RULE_based approach.
How does one create a new database? (for DBA)
One can create and modify Oracle databases using the Oracle "dbca" (Database Configuration Assistant) utility. The dbca utility is located in the $ORACLE_HOME/bin directory. The Oracle Universal Installer (oui) normally starts it after installing the database server software.
One can also create databases manually using scripts. This option, however, is falling out of fashion, as it is quite involved and error prone. Look at this example for creating and Oracle 9i database:
CONNECT SYS AS SYSDBA
ALTER SYSTEM SET DB_CREATE_FILE_DEST='/u01/oradata/';
ALTER SYSTEM SET DB_CREATE_ONLINE_LOG_DEST_1='/u02/oradata/';
ALTER SYSTEM SET DB_CREATE_ONLINE_LOG_DEST_2='/u03/oradata/';
CREATE DATABASE;
What database block size should I use? (for DBA)
Oracle recommends that your database block size match, or be multiples of your operating system block size. One can use smaller block sizes, but the performance cost is significant. Your choice should depend on the type of application you are running. If you have many small transactions as with OLTP, use a smaller block size. With fewer but larger transactions, as with a DSS application, use a larger block size. If you are using a volume manager, consider your "operating system block size" to be 8K. This is because volume manager products use 8K blocks (and this is not configurable).
What are the different approaches used by Optimizer in choosing an execution plan ?
Rule-based and Cost-based.
What does ROLLBACK do ?
ROLLBACK retracts any of the changes resulting from the SQL statements in the transaction.
How does one coalesce free space ? (for DBA)
SMON coalesces free space (extents) into larger, contiguous extents every 2 hours and even then, only for a short period of time.
SMON will not coalesce free space if a tablespace's default storage parameter "pctincrease" is set to 0. With Oracle 7.3 one can manually coalesce a tablespace using the ALTER TABLESPACE ... COALESCE; command, until then use:
SQL> alter session set events 'immediate trace name coalesce level n';
Where 'n' is the tablespace number you get from SELECT TS#, NAME FROM SYS.TS$;
You can get status information about this process by selecting from the SYS.DBA_FREE_SPACE_COALESCED dictionary view.
How does one prevent tablespace fragmentation? (for DBA)
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. E.g.. 100K, 100K, 200K, 400K, etc.
Use the same extent size for all the segments in a given tablespace. Locally Managed tablespaces (available from 8i onwards) with uniform extent sizes virtually eliminates any tablespace fragmentation. Note that the number of extents per segment does not cause any performance issue anymore, unless they run into thousands and thousands where additional I/O may be required to fetch the additional blocks where extent maps of the segment are stored.
Where can one find the high water mark for a table? (for DBA)
There is no single system table, which contains the high water mark (HWM) for a table. A table's 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.
What is COST-based approach to optimization ?
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.
What does COMMIT do ?
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.
How are extents allocated to a segment? (for DBA)
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 doesn't 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 doesn't always round extents to a multiple of 5 blocks.
The exception to this rule is locally managed tablespaces. If a tablespace is created with local extent management and the extent size is 64K, then Oracle allocates 64K or 8 blocks assuming 8K-block size. Oracle doesn't round it up to the multiple of 5 when a tablespace is locally managed.
Can one rename a database user (schema)? (for DBA)
No, this is listed as Enhancement Request 158508. Workaround:
Do a user-level export of user A
create new user B
Import system/manager fromuser=A touser=B
Drop user A
A sequence generates a serial list of unique numbers for numerical columns of a database's tables.
What is a synonym?
A synonym is an alias for a table, view, sequence or program unit.
What are the types of synonyms?
There are two types of synonyms private and public.
What is a private synonym?
Only its owner can access a private synonym.
What is a public synonym?
Any database user can access a public synonym.
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.
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.
How are the index updates?
Indexes are automatically maintained and used by Oracle. Changes to table data are automatically incorporated into all relevant indexes.
What is a Tablespace?
A database is divided into Logical Storage Unit called tablespace. A tablespace is used to grouped related logical structures together
What is Rollback Segment ?
A Database contains one or more Rollback Segments to temporarily store "undo" information.
What are the Characteristics of Data Files ?
A data file can be associated with only one database. Once created a data file can't change size. One or more data files form a logical unit of database storage called a tablespace.
How to define Data Block size ?
A data block size is specified for each ORACLE database when the database is created. A database users and allocated free database space in ORACLE data blocks. Block size is specified in INIT.ORA file and can’t be changed latter.
What does a Control file Contain ?
A Control file records the physical structure of the database. It contains the following information.
Database Name
Names and locations of a database's files and redolog files.
Time stamp of database creation.
What is difference between UNIQUE constraint and PRIMARY KEY constraint ?
A column defined as UNIQUE can contain Nulls while a column defined as PRIMARY KEY can't contain Nulls.
What is Index Cluster ?
A Cluster with an index on the Cluster Key
When does a Transaction end ?
When it is committed or Rollbacked.
What is the effect of setting the value "ALL_ROWS" for OPTIMIZER_GOAL parameter of the ALTER SESSION command ? What are the factors that affect OPTIMIZER in choosing an Optimization approach ?
Answer The OPTIMIZER_MODE initialization parameter Statistics in the Data Dictionary the OPTIMIZER_GOAL parameter of the ALTER SESSION command hints in the statement.
What is the effect of setting the value "CHOOSE" for OPTIMIZER_GOAL, parameter of the ALTER SESSION Command ?
The Optimizer chooses Cost_based approach and optimizes with the goal of best throughput if statistics for atleast one of the tables accessed by the SQL statement exist in the data dictionary. Otherwise the OPTIMIZER chooses RULE_based approach.
How does one create a new database? (for DBA)
One can create and modify Oracle databases using the Oracle "dbca" (Database Configuration Assistant) utility. The dbca utility is located in the $ORACLE_HOME/bin directory. The Oracle Universal Installer (oui) normally starts it after installing the database server software.
One can also create databases manually using scripts. This option, however, is falling out of fashion, as it is quite involved and error prone. Look at this example for creating and Oracle 9i database:
CONNECT SYS AS SYSDBA
ALTER SYSTEM SET DB_CREATE_FILE_DEST='/u01/oradata/';
ALTER SYSTEM SET DB_CREATE_ONLINE_LOG_DEST_1='/u02/oradata/';
ALTER SYSTEM SET DB_CREATE_ONLINE_LOG_DEST_2='/u03/oradata/';
CREATE DATABASE;
What database block size should I use? (for DBA)
Oracle recommends that your database block size match, or be multiples of your operating system block size. One can use smaller block sizes, but the performance cost is significant. Your choice should depend on the type of application you are running. If you have many small transactions as with OLTP, use a smaller block size. With fewer but larger transactions, as with a DSS application, use a larger block size. If you are using a volume manager, consider your "operating system block size" to be 8K. This is because volume manager products use 8K blocks (and this is not configurable).
What are the different approaches used by Optimizer in choosing an execution plan ?
Rule-based and Cost-based.
What does ROLLBACK do ?
ROLLBACK retracts any of the changes resulting from the SQL statements in the transaction.
How does one coalesce free space ? (for DBA)
SMON coalesces free space (extents) into larger, contiguous extents every 2 hours and even then, only for a short period of time.
SMON will not coalesce free space if a tablespace's default storage parameter "pctincrease" is set to 0. With Oracle 7.3 one can manually coalesce a tablespace using the ALTER TABLESPACE ... COALESCE; command, until then use:
SQL> alter session set events 'immediate trace name coalesce level n';
Where 'n' is the tablespace number you get from SELECT TS#, NAME FROM SYS.TS$;
You can get status information about this process by selecting from the SYS.DBA_FREE_SPACE_COALESCED dictionary view.
How does one prevent tablespace fragmentation? (for DBA)
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. E.g.. 100K, 100K, 200K, 400K, etc.
Use the same extent size for all the segments in a given tablespace. Locally Managed tablespaces (available from 8i onwards) with uniform extent sizes virtually eliminates any tablespace fragmentation. Note that the number of extents per segment does not cause any performance issue anymore, unless they run into thousands and thousands where additional I/O may be required to fetch the additional blocks where extent maps of the segment are stored.
Where can one find the high water mark for a table? (for DBA)
There is no single system table, which contains the high water mark (HWM) for a table. A table's 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.
What is COST-based approach to optimization ?
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.
What does COMMIT do ?
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.
How are extents allocated to a segment? (for DBA)
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 doesn't 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 doesn't always round extents to a multiple of 5 blocks.
The exception to this rule is locally managed tablespaces. If a tablespace is created with local extent management and the extent size is 64K, then Oracle allocates 64K or 8 blocks assuming 8K-block size. Oracle doesn't round it up to the multiple of 5 when a tablespace is locally managed.
Can one rename a database user (schema)? (for DBA)
No, this is listed as Enhancement Request 158508. Workaround:
Do a user-level export of user A
create new user B
Import system/manager fromuser=A touser=B
Drop user A
Oracle Interview Questions And Answers [2]
What is a tablespace?
A database is divided into Logical Storage Unit called tablespaces. A tablespace is used to grouped related logical structures together.
What is 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.
Explain the relationship among database, tablespace and data file ?
Each databases logically divided into one or more tablespaces one or more data files are explicitly created for each tablespace.
What is schema?
A schema is collection of database objects of a user.
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.
Can objects of the same schema reside in different tablespaces?
Yes.
Can a tablespace hold objects from different schemes?
Yes.
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.
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.)
What is Partial Backup ?
A Partial Backup is any operating system backup short of a full backup, taken while the database is open or shut down.
What is Mirrored on-line Redo Log ?
A mirrored on-line redo log consists of copies of on-line redo log files physically located on separate disks, changes made to one member of the group are made to all members
What is Full Backup ?
A full backup is an operating system backup of all data files, on-line redo log files and control file that constitute ORACLE database and the parameter.
Can a View based on another View ?
Yes.
Can a Tablespace hold objects from different Schemes ?
Yes.
Can objects of the same Schema reside in different tablespace ?
Yes.
What is the use of Control File ?
When an instance of an ORACLE database is started, its control file is used to identify the database and redo log files that must be opened for database operation to proceed. It is also used in database recovery.
Do View contain Data ?
Views do not contain or store data.
What are the Referential actions supported by FOREIGN KEY integrity constraint ?
UPDATE and DELETE Restrict - A referential integrity rule that disallows the update or deletion of referenced data. DELETE Cascade - When a referenced row is deleted all associated dependent rows are deleted.
What are the type of Synonyms?
There are two types of Synonyms Private and Public.
What is a Redo Log ?
The set of Redo Log files YSDATE,UID,USER or USERENV SQL functions, or the pseudo columns LEVEL or ROWNUM.
What is an Index Segment ?
Each Index has an Index segment that stores all of its data.
Explain the relationship among Database, Tablespace and Data file?
Each databases logically divided into one or more tablespaces one or more data files are explicitly created for each tablespace
What are the different type of Segments ?
Data Segment, Index Segment, Rollback Segment and Temporary Segment.
What are Clusters ?
Clusters are groups of one or more tables physically stores together to share common columns and are often used together.
What is an Integrity Constrains ?
An integrity constraint is a declarative way to define a business rule for a column of a table.
What is an Index ?
An Index is an optional structure associated with a table to have direct access to rows, which can be created to increase the performance of data retrieval. Index can be created on one or more columns of a table.
What is an Extent ?
An Extent is a specific number of contiguous data blocks, obtained in a single allocation, and used to store a specific type of information.
What is a View ?
A view is a virtual table. Every view has a Query attached to it. (The Query is a SELECT statement that identifies the columns and rows of the table(s) the view uses.)
What is Table ?
A table is the basic unit of data storage in an ORACLE database. The tables of a database hold all of the user accessible data. Table data is stored in rows and columns.
A database is divided into Logical Storage Unit called tablespaces. A tablespace is used to grouped related logical structures together.
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.
Explain the relationship among database, tablespace and data file ?
Each databases logically divided into one or more tablespaces one or more data files are explicitly created for each tablespace.
What is schema?
A schema is collection of database objects of a user.
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.
Can objects of the same schema reside in different tablespaces?
Yes.
Can a tablespace hold objects from different schemes?
Yes.
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.
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.)
What is Partial Backup ?
A Partial Backup is any operating system backup short of a full backup, taken while the database is open or shut down.
What is Mirrored on-line Redo Log ?
A mirrored on-line redo log consists of copies of on-line redo log files physically located on separate disks, changes made to one member of the group are made to all members
What is Full Backup ?
A full backup is an operating system backup of all data files, on-line redo log files and control file that constitute ORACLE database and the parameter.
Can a View based on another View ?
Yes.
Can a Tablespace hold objects from different Schemes ?
Yes.
Can objects of the same Schema reside in different tablespace ?
Yes.
What is the use of Control File ?
When an instance of an ORACLE database is started, its control file is used to identify the database and redo log files that must be opened for database operation to proceed. It is also used in database recovery.
Do View contain Data ?
Views do not contain or store data.
What are the Referential actions supported by FOREIGN KEY integrity constraint ?
UPDATE and DELETE Restrict - A referential integrity rule that disallows the update or deletion of referenced data. DELETE Cascade - When a referenced row is deleted all associated dependent rows are deleted.
What are the type of Synonyms?
There are two types of Synonyms Private and Public.
What is a Redo Log ?
The set of Redo Log files YSDATE,UID,USER or USERENV SQL functions, or the pseudo columns LEVEL or ROWNUM.
What is an Index Segment ?
Each Index has an Index segment that stores all of its data.
Explain the relationship among Database, Tablespace and Data file?
Each databases logically divided into one or more tablespaces one or more data files are explicitly created for each tablespace
What are the different type of Segments ?
Data Segment, Index Segment, Rollback Segment and Temporary Segment.
What are Clusters ?
Clusters are groups of one or more tables physically stores together to share common columns and are often used together.
What is an Integrity Constrains ?
An integrity constraint is a declarative way to define a business rule for a column of a table.
What is an Index ?
An Index is an optional structure associated with a table to have direct access to rows, which can be created to increase the performance of data retrieval. Index can be created on one or more columns of a table.
What is an Extent ?
An Extent is a specific number of contiguous data blocks, obtained in a single allocation, and used to store a specific type of information.
What is a View ?
A view is a virtual table. Every view has a Query attached to it. (The Query is a SELECT statement that identifies the columns and rows of the table(s) the view uses.)
What is Table ?
A table is the basic unit of data storage in an ORACLE database. The tables of a database hold all of the user accessible data. Table data is stored in rows and columns.
Oracle Interview Questions And Answers
What is Auditing ?
The database has the ability to audit all actions that take place within it.
a) Login attempts, b) Object Accesss, c) Database Action Result of Greatest(1,NULL) or Least(1,NULL) NULL
While designing in client/server what are the 2 imp. things to be considered ?
Network Overhead (traffic), Speed and Load of client server
When to create indexes ?
To be created when table is queried for less than 2% or 4% to 25% of the table rows.
How can you avoid indexes ?
TO make index access path unavailable - Use FULL hint to optimizer for full table scan - Use INDEX or AND-EQUAL hint to optimizer to use one index or set to indexes instead of another. - Use an expression in the Where Clause of the SQL.
What is the result of the following SQL :
Select 1 from dual
UNION
Select 'A' from dual;
Error
Can database trigger written on synonym of a table and if it can be then what would be the effect if original table is accessed.
Yes, database trigger would fire.
Can you alter synonym of view or view ?
No
Can you create index on view ?
No
What is the difference between a view and a synonym ?
Synonym is just a second name of table used for multiple link of database. View can be created with many tables, and with virtual columns and with conditions. But synonym can be on view.
What is the difference between alias and synonym ?
Alias is temporary and used with one query. Synonym is permanent and not used as alias.
What is the effect of synonym and table name used in same Select statement ?
Valid
What's the length of SQL integer ?
32 bit length
What is the difference between foreign key and reference key ?
Foreign key is the key i.e. attribute which refers to another table primary key. Reference key is the primary key of table referred by another table.
Can dual table be deleted, dropped or altered or updated or inserted ?
Yes
If content of dual is updated to some value computation takes place or not ?
Yes
If any other table same as dual is created would it act similar to dual?
Yes
For which relational operators in where clause, index is not used ?
<> , like '% ...' is NOT functions, field +constant, field || ''
Assume that there are multiple databases running on one machine. How can you switch from one to another ?
Changing the ORACLE_SID
What are the advantages of Oracle ?
Portability : Oracle is ported to more platforms than any of its competitors, running on more than 100 hardware platforms and 20 networking protocols.
Market Presence : Oracle is by far the largest RDBMS vendor and spends more on R & D than most of its competitors earn in total revenue. This market clout means that you are unlikely to be left in the lurch by Oracle and there are always lots of third party interfaces available.
Backup and Recovery : Oracle provides industrial strength support for on-line backup and recovery and good software fault tolerence to disk failure. You can also do point-in-time recovery.
Performance : Speed of a 'tuned' Oracle Database and application is quite good, even with large databases. Oracle can manage > 100GB databases.
Multiple database support : Oracle has a superior ability to manage multiple databases within the same transaction using a two-phase commit protocol.
What is a forward declaration ? What is its use ?
PL/SQL requires that you declare an identifier before using it. Therefore, you must declare a subprogram before calling it. This declaration at the start of a subprogram is called forward declaration. A forward declaration consists of a subprogram specification terminated by a semicolon.
What are actual and formal parameters ?
Actual Parameters : Subprograms pass information using parameters. The variables or expressions referenced in the parameter list of a subprogram call are actual parameters. For example, the following procedure call lists two actual parameters named emp_num and amount:
Eg. raise_salary(emp_num, amount);
Formal Parameters : The variables declared in a subprogram specification and referenced in the subprogram body are formal parameters. For example, the following procedure declares two formal parameters named emp_id and increase: Eg. PROCEDURE raise_salary (emp_id INTEGER, increase REAL) IS current_salary REAL;
What are the types of Notation ?
Position, Named, Mixed and Restrictions.
What all important parameters of the init.ora are supposed to be increased if you want to increase the SGA size ?
In our case, db_block_buffers was changed from 60 to 1000 (std values are 60, 550 & 3500) shared_pool_size was changed from 3.5MB to 9MB (std values are 3.5, 5 & 9MB) open_cursors was changed from 200 to 300 (std values are 200 & 300) db_block_size was changed from 2048 (2K) to 4096 (4K) {at the time of database creation}.
The initial SGA was around 4MB when the server RAM was 32MB and The new SGA was around 13MB when the server RAM was increased to 128MB.
If I have an execute privilege on a procedure in another users schema, can I execute his procedure even though I do not have privileges on the tables within the procedure ?
Yes
What are various types of joins ?
Equijoins, Non-equijoins, self join, outer join
What is a package cursor ?
A package cursor is a cursor which you declare in the package specification without an SQL statement. The SQL statement for the cursor is attached dynamically at runtime from calling procedures.
If you insert a row in a table, then create another table and then say Rollback. In this case will the row be inserted ?
Yes. Because Create table is a DDL which commits automatically as soon as it is executed. The DDL commits the transaction even if the create statement fails internally (eg table already exists error) and not syntactically.
What are the various types of queries ??
Normal Queries
Sub Queries
Co-related queries
Nested queries
Compound queries
What is a transaction ?
A transaction is a set of SQL statements between any two COMMIT and ROLLBACK statements.
What is implicit cursor and how is it used by Oracle ?
An implicit cursor is a cursor which is internally created by Oracle. It is created by Oracle for each individual SQL.
Which of the following is not a schema object : Indexes, tables, public synonyms, triggers and packages ?
Public synonyms
What is PL/SQL?
PL/SQL is Oracle's Procedural Language extension to SQL. The language includes object oriented programming techniques such as encapsulation, function overloading, information hiding (all but inheritance), and so, brings state-of-the-art programming to the Oracle database server and a variety of Oracle tools.
Is there a PL/SQL Engine in SQL*Plus?
No. Unlike Oracle Forms, SQL*Plus does not have a PL/SQL engine. Thus, all your PL/SQL are send directly to the database engine for execution. This makes it much more efficient as SQL statements are not stripped off and send to the database individually.
Is there a limit on the size of a PL/SQL block?
Currently, the maximum parsed/compiled size of a PL/SQL block is 64K and the maximum code size is 100K. You can run the following select statement to query the size of an existing package or procedure.
SQL> select * from dba_object_size where name = 'procedure_name'
Can one read/write files from PL/SQL?
Included in Oracle 7.3 is a UTL_FILE package that can read and write files. The directory you intend writing to has to be in your INIT.ORA file (see UTL_FILE_DIR=... parameter). Before Oracle 7.3 the only means of writing a file was to use DBMS_OUTPUT with the SQL*Plus SPOOL command.
DECLARE
fileHandler UTL_FILE.FILE_TYPE;
BEGIN
fileHandler := UTL_FILE.FOPEN('/home/oracle/tmp', 'myoutput','W');
UTL_FILE.PUTF(fileHandler, 'Value of func1 is %sn', func1(1));
UTL_FILE.FCLOSE(fileHandler);
END;
How can I protect my PL/SQL source code?
PL/SQL V2.2, available with Oracle7.2, implements a binary wrapper for PL/SQL programs to protect the source code. This is done via a standalone utility that transforms the PL/SQL source code into portable binary object code (somewhat larger than the original). This way you can distribute software without having to worry about exposing your proprietary algorithms and methods. SQL*Plus and SQL*DBA will still understand and know how to execute such scripts. Just be careful, there is no "decode" command available.
The syntax is:
wrap iname=myscript.sql oname=xxxx.yyy
Can one use dynamic SQL within PL/SQL? OR Can you use a DDL in a procedure ? How ?
From PL/SQL V2.1 one can use the DBMS_SQL package to execute dynamic SQL statements.
Eg: CREATE OR REPLACE PROCEDURE DYNSQL
AS
cur integer;
rc integer;
BEGIN
cur := DBMS_SQL.OPEN_CURSOR;
DBMS_SQL.PARSE(cur,'CREATE TABLE X (Y DATE)', DBMS_SQL.NATIVE);
rc := DBMS_SQL.EXECUTE(cur);
DBMS_SQL.CLOSE_CURSOR(cur);
END;
The database has the ability to audit all actions that take place within it.
a) Login attempts, b) Object Accesss, c) Database Action Result of Greatest(1,NULL) or Least(1,NULL) NULL
While designing in client/server what are the 2 imp. things to be considered ?
Network Overhead (traffic), Speed and Load of client server
When to create indexes ?
To be created when table is queried for less than 2% or 4% to 25% of the table rows.
How can you avoid indexes ?
TO make index access path unavailable - Use FULL hint to optimizer for full table scan - Use INDEX or AND-EQUAL hint to optimizer to use one index or set to indexes instead of another. - Use an expression in the Where Clause of the SQL.
What is the result of the following SQL :
Select 1 from dual
UNION
Select 'A' from dual;
Error
Can database trigger written on synonym of a table and if it can be then what would be the effect if original table is accessed.
Yes, database trigger would fire.
Can you alter synonym of view or view ?
No
Can you create index on view ?
No
What is the difference between a view and a synonym ?
Synonym is just a second name of table used for multiple link of database. View can be created with many tables, and with virtual columns and with conditions. But synonym can be on view.
What is the difference between alias and synonym ?
Alias is temporary and used with one query. Synonym is permanent and not used as alias.
What is the effect of synonym and table name used in same Select statement ?
Valid
What's the length of SQL integer ?
32 bit length
What is the difference between foreign key and reference key ?
Foreign key is the key i.e. attribute which refers to another table primary key. Reference key is the primary key of table referred by another table.
Can dual table be deleted, dropped or altered or updated or inserted ?
Yes
If content of dual is updated to some value computation takes place or not ?
Yes
If any other table same as dual is created would it act similar to dual?
Yes
For which relational operators in where clause, index is not used ?
<> , like '% ...' is NOT functions, field +constant, field || ''
Assume that there are multiple databases running on one machine. How can you switch from one to another ?
Changing the ORACLE_SID
What are the advantages of Oracle ?
Portability : Oracle is ported to more platforms than any of its competitors, running on more than 100 hardware platforms and 20 networking protocols.
Market Presence : Oracle is by far the largest RDBMS vendor and spends more on R & D than most of its competitors earn in total revenue. This market clout means that you are unlikely to be left in the lurch by Oracle and there are always lots of third party interfaces available.
Backup and Recovery : Oracle provides industrial strength support for on-line backup and recovery and good software fault tolerence to disk failure. You can also do point-in-time recovery.
Performance : Speed of a 'tuned' Oracle Database and application is quite good, even with large databases. Oracle can manage > 100GB databases.
Multiple database support : Oracle has a superior ability to manage multiple databases within the same transaction using a two-phase commit protocol.
What is a forward declaration ? What is its use ?
PL/SQL requires that you declare an identifier before using it. Therefore, you must declare a subprogram before calling it. This declaration at the start of a subprogram is called forward declaration. A forward declaration consists of a subprogram specification terminated by a semicolon.
What are actual and formal parameters ?
Actual Parameters : Subprograms pass information using parameters. The variables or expressions referenced in the parameter list of a subprogram call are actual parameters. For example, the following procedure call lists two actual parameters named emp_num and amount:
Eg. raise_salary(emp_num, amount);
Formal Parameters : The variables declared in a subprogram specification and referenced in the subprogram body are formal parameters. For example, the following procedure declares two formal parameters named emp_id and increase: Eg. PROCEDURE raise_salary (emp_id INTEGER, increase REAL) IS current_salary REAL;
What are the types of Notation ?
Position, Named, Mixed and Restrictions.
What all important parameters of the init.ora are supposed to be increased if you want to increase the SGA size ?
In our case, db_block_buffers was changed from 60 to 1000 (std values are 60, 550 & 3500) shared_pool_size was changed from 3.5MB to 9MB (std values are 3.5, 5 & 9MB) open_cursors was changed from 200 to 300 (std values are 200 & 300) db_block_size was changed from 2048 (2K) to 4096 (4K) {at the time of database creation}.
The initial SGA was around 4MB when the server RAM was 32MB and The new SGA was around 13MB when the server RAM was increased to 128MB.
If I have an execute privilege on a procedure in another users schema, can I execute his procedure even though I do not have privileges on the tables within the procedure ?
Yes
What are various types of joins ?
Equijoins, Non-equijoins, self join, outer join
What is a package cursor ?
A package cursor is a cursor which you declare in the package specification without an SQL statement. The SQL statement for the cursor is attached dynamically at runtime from calling procedures.
If you insert a row in a table, then create another table and then say Rollback. In this case will the row be inserted ?
Yes. Because Create table is a DDL which commits automatically as soon as it is executed. The DDL commits the transaction even if the create statement fails internally (eg table already exists error) and not syntactically.
What are the various types of queries ??
Normal Queries
Sub Queries
Co-related queries
Nested queries
Compound queries
What is a transaction ?
A transaction is a set of SQL statements between any two COMMIT and ROLLBACK statements.
What is implicit cursor and how is it used by Oracle ?
An implicit cursor is a cursor which is internally created by Oracle. It is created by Oracle for each individual SQL.
Which of the following is not a schema object : Indexes, tables, public synonyms, triggers and packages ?
Public synonyms
What is PL/SQL?
PL/SQL is Oracle's Procedural Language extension to SQL. The language includes object oriented programming techniques such as encapsulation, function overloading, information hiding (all but inheritance), and so, brings state-of-the-art programming to the Oracle database server and a variety of Oracle tools.
Is there a PL/SQL Engine in SQL*Plus?
No. Unlike Oracle Forms, SQL*Plus does not have a PL/SQL engine. Thus, all your PL/SQL are send directly to the database engine for execution. This makes it much more efficient as SQL statements are not stripped off and send to the database individually.
Is there a limit on the size of a PL/SQL block?
Currently, the maximum parsed/compiled size of a PL/SQL block is 64K and the maximum code size is 100K. You can run the following select statement to query the size of an existing package or procedure.
SQL> select * from dba_object_size where name = 'procedure_name'
Can one read/write files from PL/SQL?
Included in Oracle 7.3 is a UTL_FILE package that can read and write files. The directory you intend writing to has to be in your INIT.ORA file (see UTL_FILE_DIR=... parameter). Before Oracle 7.3 the only means of writing a file was to use DBMS_OUTPUT with the SQL*Plus SPOOL command.
DECLARE
fileHandler UTL_FILE.FILE_TYPE;
BEGIN
fileHandler := UTL_FILE.FOPEN('/home/oracle/tmp', 'myoutput','W');
UTL_FILE.PUTF(fileHandler, 'Value of func1 is %sn', func1(1));
UTL_FILE.FCLOSE(fileHandler);
END;
How can I protect my PL/SQL source code?
PL/SQL V2.2, available with Oracle7.2, implements a binary wrapper for PL/SQL programs to protect the source code. This is done via a standalone utility that transforms the PL/SQL source code into portable binary object code (somewhat larger than the original). This way you can distribute software without having to worry about exposing your proprietary algorithms and methods. SQL*Plus and SQL*DBA will still understand and know how to execute such scripts. Just be careful, there is no "decode" command available.
The syntax is:
wrap iname=myscript.sql oname=xxxx.yyy
Can one use dynamic SQL within PL/SQL? OR Can you use a DDL in a procedure ? How ?
From PL/SQL V2.1 one can use the DBMS_SQL package to execute dynamic SQL statements.
Eg: CREATE OR REPLACE PROCEDURE DYNSQL
AS
cur integer;
rc integer;
BEGIN
cur := DBMS_SQL.OPEN_CURSOR;
DBMS_SQL.PARSE(cur,'CREATE TABLE X (Y DATE)', DBMS_SQL.NATIVE);
rc := DBMS_SQL.EXECUTE(cur);
DBMS_SQL.CLOSE_CURSOR(cur);
END;
Core programming Questions-4
1) Design the implementation and thread models for I/O completion ports. Remember to take into account multi-processor machines.
2) Write a function that takes in a string parameter and checks to see whether or not it is an integer, and if it is then return the integer value.
3) Write a function to print all of the permutations of a string.
4) Implement malloc.
5) Write a function to print the Fibonacci numbers.
6) Write a function to copy two strings, A and B. The last few bytes of string A overlap the first few bytes of string B.
7) How would you write qsort?
8) How would you print out the data in a binary tree, level by level, starting at the top?
2) Write a function that takes in a string parameter and checks to see whether or not it is an integer, and if it is then return the integer value.
3) Write a function to print all of the permutations of a string.
4) Implement malloc.
5) Write a function to print the Fibonacci numbers.
6) Write a function to copy two strings, A and B. The last few bytes of string A overlap the first few bytes of string B.
7) How would you write qsort?
8) How would you print out the data in a binary tree, level by level, starting at the top?
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