Oracle Materialized Views (MV) are a powerful feature that can greatly enhance the performance of your database by pre-computing and storing the results of a query. However, as the data in the underlying tables changes, the MV needs to be refreshed to reflect the latest data. This process can sometimes take a significant amount of time and impact the overall performance of your database. In this article, we will discuss some strategies for optimizing the refresh time of Oracle Materialized Views.
1. Understand the Different Types of Materialized Views
The first step in optimizing the refresh time of Oracle Materialized Views is to understand the different types of MVs and their refresh methods. There are three types of MVs: Complete, Fast, and Force. A Complete MV is refreshed by re-running the query that defines the MV, while a Fast MV uses incremental refresh techniques to update the data. A Force MV is refreshed on-demand, meaning it is only refreshed when explicitly requested.
2. Use the Appropriate Refresh Method for Your MVs
Choosing the right refresh method for your MVs is crucial for optimizing the refresh time. Complete MVs are suitable for small MVs with infrequent data changes, as they require a full refresh each time. Fast MVs are better suited for larger MVs with frequent data changes, as they only update the changed data. Force MVs should be used for MVs that need to be refreshed on-demand, and the refresh time is not critical.
3. Properly Index the Materialized View
Proper indexing of the MV can significantly improve the refresh time. Make sure to include all the necessary indexes on the underlying tables used in the MV's query. Also, consider creating an index on the MV itself, especially if it is a Fast or Force MV. This will help in speeding up the refresh process.
4. Use Parallelism
Parallelism is a feature that allows the MV refresh to be split into multiple processes, running in parallel. This can greatly reduce the refresh time, especially for large MVs. You can specify the degree of parallelism for each MV, depending on its size and the available system resources.
5. Schedule Refreshes During Off-Peak Hours
Another way to optimize the refresh time is to schedule it during off-peak hours when the system is not heavily used. This will reduce the impact on the database performance and allow the refresh to complete faster. You can use the DBMS_SCHEDULER package to schedule the refreshes at specific times.
6. Use Materialized View Logs
Materialized View Logs (MVLs) are used to track the changes made to the underlying tables and are essential for incremental refresh of Fast MVs. Make sure to create and maintain MVLs for all the MVs that require fast refresh. Also, consider using compressed MVLs, as they can significantly reduce the storage required for tracking the changes.
7. Consider Using Query Rewrite
Query Rewrite is a feature that allows the database to automatically use an MV instead of the underlying tables when executing a query. This can greatly improve the performance of queries that use the MV. However, enabling this feature may increase the refresh time of the MV, as the rewrite process needs to be executed each time the MV is refreshed.
In conclusion, optimizing the refresh time of Oracle Materialized Views is crucial for maintaining the performance of your database. By understanding the different types of MVs and their refresh methods, properly indexing the MV, using parallelism
