Oracle Interview Questions and Answers
What command would you use to create a backup control
Alter database backup control file to trace.
Give the stages of instance startup to a usable state
where normal users may access it.
STARTUP NOMOUNT - Instance startup
STARTUP MOUNT - The database is mounted
STARTUP OPEN - The database is opened
What column differentiates the V$ views to the GV$ views
The INST_ID column which indicates the instance in a RAC
environment the information came from.
How would you go about generating an EXPLAIN plan?
Create a plan table with utlxplan.sql.
Use the explain plan set statement_id = 'tst1' into
plan_table for a SQL statement
Look at the explain plan with utlxplp.sql or utlxpls.sql
How would you go about increasing the buffer cache hit
Use the buffer cache advisory over a given workload and
then query the v$db_cache_advice table. If a change was
necessary then I would use the alter system set
Explain an ORA-01555
You get this error when you get a snapshot too old
within rollback. It can usually be solved by increasing
the undo retention or increasing the size of rollbacks.
You should also look at the logic involved in the
application getting the error message.
Explain the difference between $ORACLE_HOME and $ORACLE_BASE.
ORACLE_BASE is the root directory for oracle.
ORACLE_HOME located beneath ORACLE_BASE is where the
oracle products reside.
How would you determine the time zone under which a
database was operating?
select DBTIMEZONE from dual;
Explain the use of setting GLOBAL_NAMES equal to TRUE.
Setting GLOBAL_NAMES dictates how you might connect to a
database. This variable is either TRUE or FALSE and if
it is set to TRUE it enforces database links to have the
same name as the remote database to which they are
What command would you use to encrypt a PL/SQL
Explain the difference between a FUNCTION, PROCEDURE and
A function and procedure are the same in that they are
intended to be a collection of PL/SQL code that carries
a single task. While a procedure does not have to return
any values to the calling application, a function will
return a single value. A package on the other hand is a
collection of functions and procedures that are grouped
together based on their commonality to a business
function or application.
Explain the use of table functions.
Table functions are designed to return a set of rows
through PL/SQL logic but are intended to be used as a
normal table or view in a SQL statement. They are also
used to pipeline information in an ETL process.
Name three advisory statistics you can collect.
Buffer Cache Advice, Segment Level Statistics, & Timed
Where in the Oracle directory tree structure are audit
In unix $ORACLE_HOME/rdbms/audit, in Windows the event
Explain materialized views and how they are used.
Materialized views are objects that are reduced sets of
information that have been summarized, grouped, or
aggregated from base tables. They are typically used in
data warehouse or decision support systems.
When a user process fails, what background process
cleans up after it?
What background process refreshes materialized views?
The Job Queue Processes.
How would you determine what sessions are connected and
what resources they are waiting for?
Use of V$SESSION and V$SESSION_WAIT
Describe what redo logs are.
Redo logs are logical and physical structures that are
designed to hold all the changes made to a database and
are intended to aid in the recovery of a database.
How would you force a log switch?
ALTER SYSTEM SWITCH LOGFILE;
Give two methods you could use to determine what DDL
changes have been made.
You could use Logminer or Streams
What does coalescing a tablespace do?
Coalescing is only valid for dictionary-managed
tablespaces and de-fragments space by combining
neighboring free extents into large single extents.
What is the difference between a TEMPORARY tablespace
and a PERMANENT tablespace?
A temporary tablespace is used for temporary objects
such as sort structures while permanent tablespaces are
used to store those objects meant to be used as the true
objects of the database.
Name a tablespace automatically created when you create
The SYSTEM tablespace.
When creating a user, what permissions must you grant to
allow them to connect to the database?
Grant the CONNECT to the user.
How do you add a data file to a tablespace
ALTER TABLESPACE <tablespace_name> ADD DATAFILE <datafile_name>
How do you resize a data file?
ALTER DATABASE DATAFILE <datafile_name> RESIZE <new_size>;
What view would you use to look at the size of a data
What view would you use to determine free space in a
How would you determine who has added a row to a table?
Turn on fine grain auditing for the table.
How can you rebuild an index?
ALTER INDEX <index_name> REBUILD;
Explain what partitioning is and what its benefit is.
Partitioning is a method of taking large tables and
indexes and splitting them into smaller, more manageable
You have just compiled a PL/SQL package but got errors,
how would you view the errors?
How can you gather statistics on a table?
The ANALYZE command.
How can you enable a trace for a session?
Use the DBMS_SESSION.SET_SQL_TRACE or
Use ALTER SESSION SET SQL_TRACE = TRUE;
What is the difference between the SQL*Loader and IMPORT
These two Oracle utilities are used for loading data
into the database. The difference is that the import
utility relies on the data being produced by another
Oracle utility EXPORT while the SQL*Loader utility
allows data to be loaded that has been produced by other
utilities from different data sources just so long as it
conforms to ASCII formatted or delimited files.
Name two files used for network connection to a
TNSNAMES.ORA and SQLNET.ORA
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