Index Monitoring in Oracle: What It Is and How to Use It

Index Monitoring in Oracle Database is a powerful tool to help optimize performance and resource usage. Indexes play a crucial role in speeding up data retrieval, but they come with a maintenance cost during INSERT, UPDATE, and DELETE operations, and they take up storage space. It’s important to ensure that indexes are actively being used to justify their overhead.

What Is Index Monitoring?

Index Monitoring allows you to track whether an index is being utilized by queries or Data Manipulation Language (DML) operations. This feature helps you identify which indexes are truly beneficial for performance, and which ones can be safely removed to reduce overhead.

How to Enable Index Monitoring

To enable monitoring for an index, use the following command:

ALTER INDEX index_name MONITORING USAGE;

From that point, Oracle will track any query or operation that uses the index. It’s recommended to leave monitoring on for a reasonable period that reflects normal database activity—typically a few weeks to a few months.

Checking Index Usage

After a period of monitoring, you can check whether the index has been used with this query:

select * from DBA_OBJECT_USAGE
WHERE INDEX_NAME = 'index_name';

If the USED column shows YES, the index has been accessed during the monitoring period. If it shows NO, the index hasn’t been used.

Disabling Index Monitoring

You can stop monitoring an index at any time:

ALTER INDEX index_name NOMONITORING USAGE;

When to Remove an Index

Removing an unused index can have several benefits:

• Reduced overhead: Every index must be updated during DML operations. Unnecessary indexes slow down these operations.
• Storage savings: Indexes consume space, and removing unused ones can free up valuable resources.

However, the decision to remove an index should always be based on actual usage data to avoid impacting query performance.

Real-World Example

In a typical scenario, you might have indexes that were created to support old queries or reporting functions that are no longer relevant. By monitoring their usage, you may find that certain indexes are no longer required, allowing you to remove them and streamline database performance.

Conclusion

Index monitoring in Oracle is a critical practice to ensure efficient database performance. By identifying unused indexes, you can make informed decisions about which ones to keep or remove, optimizing both performance and resource utilization.