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Configure the max degree of parallelism Server Configuration Option

This topic describes how to configure the max degree of parallelism server configuration option in SQL Server 2014 by using SQL Server Management Studio or Transact-SQL. When an instance of SQL Server runs on a computer that has more than one microprocessor or CPU, it detects the best degree of parallelism, that is, the number of processors employed to run a single statement, for each parallel plan execution. You can use the max degree of parallelism option to limit the number of processors to use in parallel plan execution. SQL Server considers parallel execution plans for queries, index data definition language (DDL) operations, and static and keyset-driven cursor population.

In This Topic

Limitations and Restrictions

  • If the affinity mask option is not set to the default, it may restrict the number of processors available to SQL Server on symmetric multiprocessing (SMP) systems.

Recommendations

  • This option is an advanced option and should be changed only by an experienced database administrator or certified SQL Server technician.

  • To enable the server to determine the maximum degree of parallelism, set this option to 0, the default value. Setting maximum degree of parallelism to 0 allows SQL Server to use all the available processors up to 64 processors. To suppress parallel plan generation, set max degree of parallelism to 1. Set the value to a number from 1 to 32,767 to specify the maximum number of processor cores that can be used by a single query execution. If a value greater than the number of available processors is specified, the actual number of available processors is used. If the computer has only one processor, the max degree of parallelism value is ignored.

  • You can override the max degree of parallelism value in queries by specifying the MAXDOP query hint in the query statement. For more information, see Query Hints (Transact-SQL).

  • Index operations that create or rebuild an index, or that drop a clustered index, can be resource intensive. You can override the max degree of parallelism value for index operations by specifying the MAXDOP index option in the index statement. The MAXDOP value is applied to the statement at execution time and is not stored in the index metadata. For more information, see Configure Parallel Index Operations.

  • In addition to queries and index operations, this option also controls the parallelism of DBCC CHECKTABLE, DBCC CHECKDB, and DBCC CHECKFILEGROUP. You can disable parallel execution plans for these statements by using trace flag 2528. For more information, see Trace Flags (Transact-SQL).

Security

Permissions

Execute permissions on sp_configure with no parameters or with only the first parameter are granted to all users by default. To execute sp_configure with both parameters to change a configuration option or to run the RECONFIGURE statement, a user must be granted the ALTER SETTINGS server-level permission. The ALTER SETTINGS permission is implicitly held by the sysadmin and serveradmin fixed server roles.

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To configure the max degree of parallelism option

  1. In Object Explorer, right-click a server and select Properties.

  2. Click the Advanced node.

  3. In the Max Degree of Parallelism box, select the maximum number of processors to use in parallel plan execution.

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To configure the max degree of parallelism option

  1. Connect to the Database Engine.

  2. From the Standard bar, click New Query.

  3. Copy and paste the following example into the query window and click Execute. This example shows how to use sp_configure to configure the max degree of parallelism option to 8.

USE AdventureWorks2012 ;
GO 
EXEC sp_configure 'show advanced options', 1;
GO
RECONFIGURE WITH OVERRIDE;
GO
EXEC sp_configure 'max degree of parallelism', 8;
GO
RECONFIGURE WITH OVERRIDE;
GO

For more information, see Server Configuration Options (SQL Server).

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The setting takes effect immediately without restarting the server.

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