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Oracle DBA Interview Questions

Most asked Oracle DBA Interview Questions.

60 Technical Questions
42 Backup & Recovery Questions

Unix For Oracle DBA 20 Questions

Oracle DBA Topics

Overview of Oracle Grid Architecture

Difference between cluster and grid

Responsibilities of DBA's

Creating Oracle Database

Creating Database using SQL

Creating DB in 12c using DBCA

Creating DB in 12c using SQL commands

Managing Oracle 12c Container Databases

Creating Users in Oracle 12c

Managing Pluggable Databases in Oracle 12c

Creating Pluggable Database

Cloning Pluggable Database

Unplug and Plug databases in CDB's

Managing Tablespaces and Datafiles

Extending tablespaces

Decreasing size of a tablespace

Coalescing Tablespaces

Taking tablespaces Offline or Online

Making a Tablespace Read only

Renaming Tablespaces

Dropping Tablespaces

Viewing Info about Tablespaces

Renaming Datafiles

Relocating Datafiles

Relocating Datafiles in Multiple Tablespaces

Temporary Tablespace

Changing the size

Tablespace Groups

Creating a Temp. Tablespace Group

Assigning a Tablespace Group

Diagnosing and Repairing LMT

Scenario 1: Fixing Bitmap

Scenario 2: Dropping a Corrupted Segment

Scenario 3: Fixing Bitmap when Overlapped

Scenario 4: Correcting Corruption of Blocks

Scenario 5: Migrating from a Dictionary-Managed to LMT

Transporting Tablespaces

Procedure for transporting tablespaces

Transporting Tablespace Example


Adding New Redo Logfile Group

Adding Members to group

Dropping Members from group

Dropping Logfile Group

Resizing Logfiles

Renaming or Relocating Logfiles


Viewing Info About Logfiles

Managing Control Files

Multiplexing Control File

Changing the Name of a Database

Creating A New Control File

Cloning an Oracle Database


Switching to Automatic Management

Calculate Undo Retention

Altering UNDO Tablespace

Dropping an Undo Tablespace

Switching Undo Tablespaces

Viewing Information

SQL Loader


From Fixed Length file

From MySQL to Oracle

Using WHEN condition

Conventional and Direct Path Load

Direct Path

Restrictions on Using Direct Path Loads

Export and Import

Invoking Export and Import

Parameters of Export tool

Exporting Full Database

Exporting Schemas

Exporting Tables

Exporting Consistent Image of tables

Using Import Utility

Example Importing Tables

Import from One User to another User

Using Pattern Matching

Migrating a Database across platforms


Data Pump Export

Exporting a Full Database

Exporting a Schema

Exporting Individual Tables

Filtering Objects during Export

Filter Rows during Export

Suspending and Resuming Export

Data Pump Import Utility

Importing Full Dump File

Importing Objects between Schemas

Loading Objects between Tablespaces

Generating SQL File of DDL commands

Import objects of a Schema

Importing Only Particular Tables

Interactive Mode

Flash Back Features

Flashback Query

Flashback Version Query

Flashback Table to Past States

Purging Objects from Recycle Bin

Flashback Objects With Same Name

Flashback instead of PIT Recovery

Enabling Flash Back Database

Sizing flash recovery area

How far we can flashback database

Example:Flashing Back Database

Flashback Data Archive (FDA)
(Oracle Total Recall)


Creating FDA tablespace

Creating FDA

Querying historical data

Log Miner

LogMiner Configuration

LogMiner Dictionary Options

Using the Online Catalog

Extracting Dictionary to Log Files

Extracting Dictionary to File

Redo Log File Options

Example: Finding All Modifications

Mining Logfiles in a Time Range


Opening DB in Archivelog Mode

Reverting back to NoArchiveLog mode

Taking Offline (COLD) Backups

Taking Online (HOT) Backups

Recovering from the Loss of a Datafile

When in Noarchivelog Mode

When in Archivelog Mode

Recovering from loss of Control File

Recovery Manager ( RMAN )

Offline Backups using RMAN

Recover DB when in NOARCHIVELOG

Online Backups using RMAN

Backup tablespaces or datafiles

Image Backups in RMAN

Incremental Backup using RMAN

Updating backup copy for fast recovery

View info about RMAN backups

Configuring Retention policy

Configure Options in RMAN

Maintaining RMAN Repository

Recover datafiles (Archivelog mode)

Recover datafiles by renaming

Performing Disaster Recovery










Repairing Tablespaces in Oracle

Diagnosing and Repairing Locally Managed Tablespace Problems

To diagnose and repair corruptions in Locally Managed Tablespaces Oracle has supplied a package called DBMS_SPACE_ADMIN. This package has many procedures described below:




Verifies the consistency of the extent map of the segment.


Marks the segment corrupt or valid so that appropriate error recovery can be done. Cannot be used for a locally managed SYSTEM tablespace.


Drops a segment currently marked corrupt (without reclaiming space). Cannot be used for a locally managed SYSTEM tablespace.


Dumps the segment header and extent map of a given segment.


Verifies that the bitmaps and extent maps for the segments in the tablespace are in sync.


Rebuilds the appropriate bitmap. Cannot be used for a locally managed SYSTEM tablespace.


Marks the appropriate data block address range (extent) as free or used in bitmap. Cannot be used for a locally managed SYSTEM tablespace.


Rebuilds quotas for given tablespace.


Migrates a locally managed tablespace to dictionary-managed tablespace. Cannot be used to migrate a locally managed SYSTEM tablespace to a dictionary-managed SYSTEM tablespace.


Migrates a tablespace from dictionary-managed format to locally managed format.


Relocates the bitmaps to the destination specified. Cannot be used for a locally managed system tablespace.


Fixes the state of the segments in a tablespace in which migration was aborted.


Be careful using the above procedures if not used properly you will corrupt your database. Contact Oracle Support before using these procedures.

Following are some of the Scenarios where you can use the above procedures

Scenario 1: Fixing Bitmap When Allocated Blocks are Marked Free (No Overlap)

The TABLESPACE_VERIFY procedure discovers that a segment has allocated blocks that are marked free in the bitmap, but no overlap between segments is reported.

In this scenario, perform the following tasks:

  1. Call the SEGMENT_DUMP procedure to dump the ranges that the administrator allocated to the segment.
  2. For each range, call the TABLESPACE_FIX_BITMAPS procedure with the TABLESPACE_EXTENT_MAKE_USED option to mark the space as used.
  3. Call TABLESPACE_REBUILD_QUOTAS to fix up quotas.

Scenario 2: Dropping a Corrupted Segment

You cannot drop a segment because the bitmap has segment blocks marked "free". The system has automatically marked the segment corrupted.

In this scenario, perform the following tasks:

  1. Call the SEGMENT_VERIFY procedure with the SEGMENT_VERIFY_EXTENTS_GLOBAL option. If no overlaps are reported, then proceed with steps 2 through 5.
  2. Call the SEGMENT_DUMP procedure to dump the DBA ranges allocated to the segment.
  3. For each range, call TABLESPACE_FIX_BITMAPS with the TABLESPACE_EXTENT_MAKE_FREE option to mark the space as free.
  4. Call SEGMENT_DROP_CORRUPT to drop the SEG$ entry.
  5. Call TABLESPACE_REBUILD_QUOTAS to fix up quotas.

Scenario 3: Fixing Bitmap Where Overlap is Reported

The TABLESPACE_VERIFY procedure reports some overlapping. Some of the real data must be sacrificed based on previous internal errors.

After choosing the object to be sacrificed, in this case say, table t1, perform the following tasks:

  1. Make a list of all objects that t1 overlaps.
  2. Drop table t1. If necessary, follow up by calling the SEGMENT_DROP_CORRUPT procedure.
  3. Call the SEGMENT_VERIFY procedure on all objects that t1 overlapped. If necessary, call the TABLESPACE_FIX_BITMAPS procedure to mark appropriate bitmap blocks as used.
  4. Rerun the TABLESPACE_VERIFY procedure to verify the problem is resolved.

Scenario 4: Correcting Media Corruption of Bitmap Blocks

A set of bitmap blocks has media corruption.

In this scenario, perform the following tasks:

  1. Call the TABLESPACE_REBUILD_BITMAPS procedure, either on all bitmap blocks, or on a single block if only one is corrupt.
  2. Call the TABLESPACE_REBUILD_QUOTAS procedure to rebuild quotas.
  3. Call the TABLESPACE_VERIFY procedure to verify that the bitmaps are consistent.

Scenario 5: Migrating from a Dictionary-Managed to a Locally Managed Tablespace

To migrate a dictionary-managed tablespace to a locally managed tablespace. You use the TABLESPACE_MIGRATE_TO_LOCAL procedure.

For example if you want to migrate a dictionary managed tablespace ICA2 to Locally managed then give the following command.





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