Question 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 are more redo log files, and one or more control files.
Question 2 :
What are the components of logical database structure of Oracle database?
There are tablespaces and database's schema objects.
Question 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.
Question 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.
Question 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.
Question 6 :
What is schema?
A schema is collection of database objects of a user.
Question 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.
Question 8 :
Can objects of the same schema reside in different tablespaces?
Question 9 :
Can a tablespace hold objects from different schemes?
Question 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.
Question 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.)
Question 12 :
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.
Question 13 :
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.
Question 14 :
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.
Question 15 :
Can a View based on another View ?
Question 16 :
Can a Tablespace hold objects from different Schemes ?
Question 17 :
Can objects of the same Schema reside in different tablespace ?
Question 18 :
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.
Question 19 :
Do View contain Data ?
Views do not contain or store data.
Question 20 :
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.
Question 21 :
What are the type of Synonyms?
There are two types of Synonyms Private and Public.
Question 22 :
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.
Question 23 :
What is an Index Segment ?
Each Index has an Index segment that stores all of its data.
Question 24 :
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
Question 25 :
What are the different type of Segments ?
Data Segment, Index Segment, Rollback Segment and Temporary Segment.
Question 26 :
What are Clusters ?
Clusters are groups of one or more tables physically stores together to share common columns and are often used together.
Question 27 :
What is an Integrity Constrains ?
An integrity constraint is a declarative way to define a business rule for a column of a table.
Question 28 :
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.
Question 29 :
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.
Question 30 :
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.)
Question 31 :
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.
Question 32 :
Can a view based on another view?
Question 33 :
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.
Question 34 :
What is an Oracle sequence?
A sequence generates a serial list of unique numbers for numerical columns of a database's tables.
Question 35 :
What is a synonym?
A synonym is an alias for a table, view, sequence or program unit.
Question 36 :
What are the types of synonyms?
There are two types of synonyms private and public.
Question 37 :
What is a private synonym?
Only its owner can access a private synonym.
Question 38 :
What is a public synonym?
Any database user can access a public synonym.
Question 39 :
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.
Question 40 :
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.
Question 41 :
How are the index updates?
Indexes are automatically maintained and used by Oracle. Changes to table data are automatically incorporated into all relevant indexes.
Question 42 :
What is a Tablespace?
A database is divided into Logical Storage Unit called tablespace. A tablespace is used to grouped related logical structures together
Question 43 :
What is Rollback Segment ?
A Database contains one or more Rollback Segments to temporarily store "undo" information.
Question 44 :
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.
Question 45 :
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.
Question 46 :
What does a Control file Contain ?
A Control file records the physical structure of the database. It contains the following information.
Names and locations of a database's files and redolog files.
Time stamp of database creation.
Question 47 :
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.
Question 48 :
What is Index Cluster ?
A Cluster with an index on the Cluster Key
Question 49 :
When does a Transaction end ?
When it is committed or Rollbacked.
Question 50 :
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 ?
The OPTIMIZER_MODE initialization parameter Statistics in the Data Dictionary the OPTIMIZER_GOAL parameter of the ALTER SESSION command hints in the statement.
Question 51 :
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.
Question 52 :
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;
Question 53 :
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).
Question 54 :
What are the different approaches used by Optimizer in choosing an execution plan ?
Rule-based and Cost-based.
Question 55 :
What does ROLLBACK do ?
ROLLBACK retracts any of the changes resulting from the SQL statements in the transaction.
Question 56 :
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.
Question 57 :
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.
Question 58 :
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.
Question 59 :
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.
Question 60 :
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.
Question 61 :
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.
Question 62 :
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
Question 63 :
Define Transaction ?
A Transaction is a logical unit of work that comprises one or more SQL statements executed by a single user.
Question 64 :
What is Read-Only Transaction ?
A Read-Only transaction ensures that the results of each query executed in the transaction are consistant with respect to the same point in time.
Question 65 :
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.
Question 66 :
What is a Schema ?
The set of objects owned by user account is called the schema.
Question 67 :
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.
Question 68 :
What is Parallel Server ?
Multiple instances accessing the same database (Only In Multi-CPU environments)
Question 69 :
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
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)
CKPT (Check Point)
User Process with associated PGS
Question 70 :
What is clusters ?
Group of tables physically stored together because they share common columns and are often used together is called Cluster.
Question 71 :
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)
Question 72 :
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.
Question 73 :
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.
Question 74 :
What is default tablespace ?
The Tablespace to contain schema objects created without specifying a tablespace name.
Question 75 :
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.
Question 76 :
What is Tablespace Quota ?
The collective amount of disk space available to the objects in a schema on a particular tablespace.
Question 77 :
What are the different Levels of Auditing ?
Statement Auditing, Privilege Auditing and Object Auditing.
Question 78 :
What is Statement Auditing ?
Statement auditing is the auditing of the powerful system privileges without regard to specifically named objects.
Question 79 :
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.
Question 80 :
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.
Question 81 :
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.
Question 82 :
What are Roles ?
Roles are named groups of related privileges that are granted to users or other roles.
Question 83 :
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.
Question 84 :
What is Privilege Auditing ?
Privilege auditing is the auditing of the use of powerful system privileges without regard to specifically named objects.
Question 85 :
What is Object Auditing ?
Object auditing is the auditing of accesses to specific schema objects without regard to user.
Question 86 :
What is Auditing ?
Monitoring of user access to aid in the investigation of database use.
Question 87 :
How does one see the uptime for a database? (for DBA )
Look at the following SQL query:
SELECT to_char (startup_time,'DD-MON-YYYY HH24: MI: SS') "DB Startup Time"
Marco Bergman provided the following alternative solution:
SELECT to_char (logon_time,'Dy dd Mon HH24: MI: SS') "DB Startup Time" FROM sys.v_$session WHERE Sid=1 /* this is pmon */
Users still running on Oracle 7 can try one of the following queries:
Column STARTED format a18 head 'STARTUP TIME' Select C.INSTANCE, to_date (JUL.VALUE, 'J') || to_char (floor (SEC.VALUE/3600), '09') || ':' -- || Substr (to_char (mod (SEC.VALUE/60, 60), '09'), 2, 2) || Substr (to_char (floor (mod (SEC.VALUE/60, 60)), '09'), 2, 2) || '.' || Substr (to_char (mod (SEC.VALUE, 60), '09'), 2, 2) STARTED from SYS.V_$INSTANCE JUL, SYS.V_$INSTANCE SEC, SYS.V_$THREAD C Where JUL.KEY like '%JULIAN%' and SEC.KEY like '%SECOND%'; Select to_date (JUL.VALUE, 'J') || to_char (to_date (SEC.VALUE, 'SSSSS'), ' HH24:MI:SS') STARTED from SYS.V_$INSTANCE JUL, SYS.V_$INSTANCE SEC where JUL.KEY like '%JULIAN%' and SEC.KEY like '%SECOND%'; select to_char (to_date (JUL.VALUE, 'J') + (SEC.VALUE/86400), -Return a DATE 'DD-MON-YY HH24:MI:SS') STARTED from V$INSTANCE JUL, V$INSTANCE SEC where JUL.KEY like '%JULIAN%' and SEC.KEY like '%SECOND%';
Question 88 :
Where are my TEMPFILES, I don't see them in V$DATAFILE or DBA_DATA_FILE? (for DBA )
Tempfiles, unlike normal datafiles, are not listed in v$datafile or dba_data_files. Instead query v$tempfile or dba_temp_files:
SELECT * FROM v$tempfile; SELECT * FROM dba_temp_files;
Question 89 :
How do I find used/free space in a TEMPORARY tablespace? (for DBA )
Unlike normal tablespaces, true temporary tablespace information is not listed in DBA_FREE_SPACE. Instead use the V$TEMP_SPACE_HEADER view:
SELECT tablespace_name, SUM (bytes used), SUM (bytes free) FROM V$temp_space_header GROUP BY tablespace_name;
Question 90 :
How can one see who is using a temporary segment? (for DBA )
For every user using temporary space, there is an entry in SYS.V$_LOCK with type 'TS'.
All temporary segments are named 'ffff.bbbb' where 'ffff' is the file it is in and 'bbbb' is first block of the segment. If your temporary tablespace is set to TEMPORARY, all sorts are done in one large temporary segment. For usage stats, see SYS.V_$SORT_SEGMENT
From Oracle 8.0, one can just query SYS.v$sort_usage. Look at these examples:
select s.username, u."USER", u.tablespace, u.contents, u.extents, u.blocks from sys.v_$session s, sys.v_$sort_usage u where s.addr = u.session_addr / select s.osuser, s.process, s.username, s.serial#, Sum (u.blocks)*vp.value/1024 sort_size from sys.v_$session s, sys.v_$sort_usage u, sys.v_$parameter VP where s.saddr = u.session_addr and vp.name = 'db_block_size' and s.osuser like '&1' group by s.osuser, s.process, s.username, s.serial#, vp.value /
Question 91 :
What is a profile ?
Each database user is assigned a Profile that specifies limitations on various system resources available to the user.
Question 92 :
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.
Question 93 :
How does one get the view definition of fixed views/tables?
Query v$fixed_view_definition. Example: SELECT * FROM v$fixed_view_definition WHERE view_name='V$SESSION';
Question 94 :
What are the dictionary tables used to monitor a database spaces ?
Question 95 :
How can we specify the Archived log file name format and destination?
By setting the following values in init.ora file. LOG_ARCHIVE_FORMAT = arch %S/s/T/tarc (%S - Log sequence number and is zero left paded, %s - Log sequence number not padded. %T - Thread number lef-zero-paded and %t - Thread number not padded). The file name created is arch 0001 are if %S is used. LOG_ARCHIVE_DEST = path.
Question 96 :
What is user Account in Oracle database?
An user account is not a physical structure in Database but it is having important relationship to the objects in the database and will be having certain privileges.
Question 97 :
When will the data in the snapshot log be used?
We must be able to create a after row trigger on table (i.e., it should be not be already available) After giving table privileges. We cannot specify snapshot log name because oracle uses the name of the master table in the name of the database objects that support its snapshot log. The master table name should be less than or equal to 23 characters. (The table name created will be MLOGS_tablename, and trigger name will be TLOGS name).
Question 98 :
What dynamic data replication?
Updating or Inserting records in remote database through database triggers. It may fail if remote database is having any problem.
Question 99 :
What is Two-Phase Commit ?
Two-phase commit is mechanism that guarantees a distributed transaction either commits on all involved nodes or rolls back on all involved nodes to maintain data consistency across the global distributed database. It has two phase, a Prepare Phase and a Commit Phase.
Question 100 :
How can you Enforce Referential Integrity in snapshots ?
Time the references to occur when master tables are not in use. Peform the reference the manually immdiately locking the master tables. We can join tables in snopshots by creating a complex snapshots that will based on the master tables.
Question 101 :
What is a SQL * NET?
SQL *NET is ORACLE's mechanism for interfacing with the communication protocols used by the networks that facilitate distributed processing and distributed databases. It is used in Clint-Server and Server-Server communications.