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cost threshold for parallelism Option

SQL Server 2000

Use the cost threshold for parallelism option to specify the threshold where Microsoft® SQL Server™ creates and executes parallel plans. SQL Server creates and executes a parallel plan for a query only when the estimated cost to execute a serial plan for the same query is higher than the value set in cost threshold for parallelism. The cost refers to an estimated elapsed time in seconds required to execute the serial plan on a specific hardware configuration. Only set cost threshold for parallelism on symmetric multiprocessors (SMP).

Longer queries usually benefit from parallel plans; the performance advantage negates the additional time required to initialize, synchronize, and terminate the plan. The cost threshold for parallelism option is actively used when a mix of short and longer queries is executed. The short queries execute serial plans while the longer queries use parallel plans. The value of cost threshold for parallelism determines which queries are considered short, thus executing only serial plans.

In certain cases, a parallel plan may be chosen even though the query's cost plan is less than the current cost threshold for parallelism value. This is because the decision to use a parallel or serial plan, with respect to cost threshold for parallelism, is based on a cost estimate provided before the full optimization is complete.

The cost threshold for parallelism option can be set to any value from 0 through 32767. The default value is 5.

If your computer has only one processor, if only a single CPU is available to SQL Server because of the affinity mask configuration value, or if the max degree of parallelism option is set to 1, SQL Server ignores cost threshold for parallelism.

cost threshold for parallelism is an advanced option. If you are using the sp_configure system stored procedure to change the setting, you can change cost threshold for parallelism only when show advanced options is set to 1. The setting takes effect immediately (without a server stop and restart).

To configure the cost threshold for parallelism

Enterprise Manager

Transact-SQL

SQL-DMO

See Also

affinity mask Option

max degree of parallelism Option

Parallel Query Processing

RECONFIGURE

Setting Configuration Options

sp_configure

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