How do I check Data Guard apply lag?

Query V$DATAGUARD_STATS and review the Apply Lag value.

How do I check Data Guard transport lag?

Query V$DATAGUARD_STATS and review the Transport Lag value.

How do I detect archive gaps?

Use SELECT * FROM V$ARCHIVE_GAP.

What is RMAN Backup Validation?

RMAN Backup Validation verifies Oracle backup integrity and recoverability without performing a restore.

What does RESTORE DATABASE VALIDATE do?

It verifies that RMAN backups can be restored successfully without actually restoring files.

How do I detect Oracle block corruption?

Use V$DATABASE_BLOCK_CORRUPTION and RMAN VALIDATE DATABASE CHECK LOGICAL.

What are the most important Oracle DBA interview topics?

Oracle Architecture, RMAN, Backup and Recovery, Data Guard, RAC, Performance Tuning, Security, and Troubleshooting are the most important Oracle DBA interview topics.

Is Oracle DBA still a good career in 2026?

Yes. Oracle DBA remains a strong career path due to the widespread use of Oracle databases in enterprise environments.

What Oracle version should I learn in 2026?

Oracle 19c and Oracle 23ai are the most valuable Oracle database versions to learn in 2026.

What does ORA-01034 ORACLE Not Available mean?

ORA-01034 indicates that the Oracle database instance is unavailable because it is not started, cannot be accessed, or failed during startup.

How do I fix ORA-01034?

Verify ORACLE_HOME and ORACLE_SID, review the Alert Log, check listener status, confirm background processes are running, and start the database using SQL*Plus as SYSDBA.

Why does ORA-27101 appear with ORA-01034?

ORA-27101 usually occurs when Oracle cannot locate the shared memory for the specified database instance because the database is not running or the environment variables are incorrect.

UNDO tablespace increasing/growing and not release space

Applies to:

Oracle Database 10gR2

Description:

Undo tablespace start growing abnormally. UNDO_RETENTION parameter is set to 900 seconds, but undo data did not release the space. After doing some research work, I found the following solution:

Solution:

Set the following hidden parameter in init.ora file and check the free space in undo tablespace after 3-4 Hrs.

_smu_debug_mode=33554432

or

SQL> Alter system set "_smu_debug_mode" = 33554432;

Related Oracle Errors

👉 Check our complete guide: Oracle Error Codes Guide

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About the Author

Rana Abdul Wahid is an experienced Oracle Database Administrator with expertise in Oracle Database Administration, Oracle Data Guard, RMAN Backup & Recovery, Oracle RAC, Oracle E-Business Suite, Performance Tuning, and High Availability Solutions.

Through this blog, he shares practical Oracle DBA solutions, troubleshooting guides, interview preparation resources, and production-tested best practices for database professionals worldwide.