Setting the Degree of Parallelism - Oracle Help Center
In a system that makes aggressive use of parallel execution by using a high DOP, the adaptive algorithm adjusts the DOP down when only a few operations are running in parallel. While the algorithm still ensures optimal resource utilization, users may experience inconsistent response times.
Configuring and Controlling Auto DOP - Oracle
The DOP computed by the optimizer with Auto DOP can be quite high depending on the resource requirements of the statement. You can limit the DOP using the initialization parameter parallel_degree_limit or Database Resource Manager (DBRM). PARALLEL_DEGREE_LIMIT This parameter limits the DOP that can be computed by the optimizer.
Configuring and Controlling Auto DOP
The DOP computed by the optimizer with Auto DOP can be quite high depending on the resource requirements of the statement. You can limit the DOP using the initialization parameter parallel_degree_limit or Database Resource Manager (DBRM). PARALLEL_DEGREE_LIMIT This parameter limits the DOP that can be computed by the optimizer.
How Parallel Execution Works - Oracle
When the connection is between processes in different instances, the messages are sent using external high-speed network protocols over the interconnect. In Figure 8-3, the DOP equals the number of parallel execution servers, which in this case is n. Figure 8-3 does not show the parallel execution coordinator. Each parallel execution server
Oracle Database Understanding Parallel Execution - Part 2
But this means that you need to configure your database objects or use statement hints to use a sensible DOP instead of going with the default. Other options include introducing an artificial DOP limit via the Resource Manager and/or relying on the new Auto DOP feature (available since version 11.2).
- How to configure and control auto DOP?
- Now, let's look at how you can configure and control Auto DOP. There are two ways to enable/disable Auto DOP, you can enable/disable it for the whole system or for a session using the initialization parameter parallel_degree_policy, or you can enable/disable it for specific SQL statements using hints.
- What is auto DOP vs manual DOP?
- As opposed to manual DOP it does not require table/index decorations or hints. Here is the basic decision flow for a SQL statement with Auto DOP. The optimizer first generates a serial plan for the SQL statement and estimates the execution time. If the estimated execution time is less than the specified threshold the statement runs serially.
- What is auto DOP in SQL?
- Introduced in 11.2 Auto DOP enables the optimizer to calculate the DOP for a statement based on resource requirements and HW characteristics. As opposed to manual DOP it does not require table/index decorations or hints. Here is the basic decision flow for a SQL statement with Auto DOP.
- What happens if I enable auto DOP?
- With Auto DOP since the optimizer is deciding when to use parallel execution and the DOP to use, depending on how you configure Auto DOP, the number of parallel statements and their DOPs may change when you enable it. Some serial statements may start running in parallel, some parallel statements may start running serially.
- How do I limit the DOP computed by the optimizer with auto DOP?
- The DOP computed by the optimizer with Auto DOP can be quite high depending on the resource requirements of the statement. You can limit the DOP using the initialization parameter parallel_degree_limit or Database Resource Manager (DBRM). This parameter limits the DOP that can be computed by the optimizer.
- Does DBRM initialization parameter affect auto DOP?
- This parameter has no effect on statements not using Auto DOP. So, for any SQL statement that the optimizer decides to run in parallel with Auto DOP, it takes into account the initialization parameters, DBRM settings, system and object statistics, and HW characteristics to compute the DOP.
