MAXDOP (Maximum Degree of Parallelism) is a configuration option in SQL Server that controls the number of processors that can be used in parallel execution of a query. Here are some best practices for using MAXDOP in SQL Server:
Set MAXDOP based on the number of processors: The default value for MAXDOP is 0, which means that SQL Server can use all available processors. However, it is best to set MAXDOP based on the number of processors on the server. For example, if you have a quad-core processor, you should set MAXDOP to 4.
Monitor performance and adjust MAXDOP accordingly: Monitor the performance of your SQL Server and adjust MAXDOP as needed. If you are experiencing performance issues, you may need to reduce the value of MAXDOP.
Test different values of MAXDOP: Test different values of MAXDOP to determine the optimal value for your server and workload.
Be careful with large tables: When querying large tables, it’s best to limit MAXDOP to 1 because large tables can cause a lot of contention on the parallel threads
Use MAXDOP in conjunction with other options: Use MAXDOP in conjunction with other options such as cost threshold for parallelism and optimize for ad hoc workloads to improve performance.
Limit MAXDOP to the number of physical cores: limit MAXDOP to the number of physical cores, not logical cores.
Here’s an example of how to set MAXDOP to 4:
EXEC sp_configure 'show advanced options', 1;
GO
RECONFIGURE;
GO
EXEC sp_configure 'max degree of parallelism', 4;
GO
RECONFIGURE;
GO
It’s worth noting that the best value for MAXDOP will depend on your specific environment and workload, and you will need to test different values to find the optimal setting for your SQL Server.
