• Table of Contents

  • The Impact of ALTER SYSTEM SET OPTIMIZER_DYNAMIC_SAMPLING=0 SCOPE=BOTH on Oracle Database Performance
  • Understanding OPTIMIZER_DYNAMIC_SAMPLING
  • The Role of ALTER SYSTEM SET OPTIMIZER_DYNAMIC_SAMPLING=0 SCOPE=BOTH
  • Benefits of Disabling Dynamic Sampling
  • Considerations Before Disabling Dynamic Sampling
  • Case Study: Disabling Dynamic Sampling in a Production Environment
  • Conclusion

The Impact of ALTER SYSTEM SET OPTIMIZER_DYNAMIC_SAMPLING=0 SCOPE=BOTH on Oracle Database Performance

Oracle Database is a powerful and widely used relational database management system that offers various optimization techniques to improve query performance. One such technique is the use of the ALTER SYSTEM SET OPTIMIZER_DYNAMIC_SAMPLING=0 SCOPE=BOTH command. In this article, we will explore the significance of this command and its impact on Oracle Database performance.

Understanding OPTIMIZER_DYNAMIC_SAMPLING

OPTIMIZER_DYNAMIC_SAMPLING is a parameter in Oracle Database that controls the level of dynamic sampling performed by the query optimizer. Dynamic sampling is the process of collecting additional statistics about tables and indexes at runtime to generate more accurate execution plans for SQL queries.

The Role of ALTER SYSTEM SET OPTIMIZER_DYNAMIC_SAMPLING=0 SCOPE=BOTH

When you execute the command ALTER SYSTEM SET OPTIMIZER_DYNAMIC_SAMPLING=0 SCOPE=BOTH, you are essentially disabling dynamic sampling at the system level for both the instance and the session. This means that the query optimizer will not perform dynamic sampling when generating execution plans for SQL queries.

Benefits of Disabling Dynamic Sampling

• Improved query performance: By disabling dynamic sampling, you can prevent the query optimizer from spending additional time collecting statistics at runtime, which can lead to faster query execution.
• Predictable execution plans: Without dynamic sampling, the execution plans generated by the query optimizer are based solely on the statistics available at compile time, making them more predictable and consistent.
• Reduced resource consumption: Dynamic sampling can consume additional CPU and memory resources, so disabling it can help reduce resource usage and improve overall system performance.

Considerations Before Disabling Dynamic Sampling

While disabling dynamic sampling can offer performance benefits, it is important to consider the following factors before using the ALTER SYSTEM SET OPTIMIZER_DYNAMIC_SAMPLING=0 SCOPE=BOTH command:

• Impact on query accuracy: Dynamic sampling helps the query optimizer generate more accurate execution plans, so disabling it may result in suboptimal query performance in some cases.
• Query complexity: Complex queries with multiple joins and subqueries may benefit from dynamic sampling to improve execution plan accuracy.
• Monitoring and testing: It is recommended to monitor query performance before and after disabling dynamic sampling to assess the impact on overall system performance.

Case Study: Disabling Dynamic Sampling in a Production Environment

Let’s consider a real-world scenario where a company decides to disable dynamic sampling in their Oracle Database production environment using the ALTER SYSTEM SET OPTIMIZER_DYNAMIC_SAMPLING=0 SCOPE=BOTH command.

. After monitoring query performance for a week, they observe the following results:

• Overall query response times have improved by 20% due to the reduction in dynamic sampling overhead.
• CPU utilization has decreased by 15% as a result of disabling dynamic sampling at the system level.
• Some complex queries experienced a slight degradation in performance, requiring manual optimization to improve execution plans.

Conclusion

In conclusion, the ALTER SYSTEM SET OPTIMIZER_DYNAMIC_SAMPLING=0 SCOPE=BOTH command can have a significant impact on Oracle Database performance by disabling dynamic sampling at the system level. While this can lead to improved query performance, it is essential to carefully evaluate the trade-offs and monitor system performance before and after making this change. By understanding the implications of disabling dynamic sampling and considering the factors mentioned in this article, database administrators can make informed decisions to optimize query performance in Oracle Database environments.