lightweight pooling Server Configuration Option

Applies to: SQL Server (all supported versions)

Use the lightweight pooling option to provide a means of reducing the system overhead associated with the excessive context switching sometimes seen in symmetric multiprocessing (SMP) environments. When excessive context switching is present, lightweight pooling can provide better throughput by performing the context switching inline, thus helping to reduce user/kernel ring transitions.

Fiber mode is intended for certain situations in which the context switching of the UMS workers are the critical bottleneck in performance. Because this is rare, fiber mode rarely enhances performance or scalability on the typical system. Improved context switching in Microsoft Windows Server 2003 has also reduced the need for fiber mode. We do not recommend that you use fiber mode scheduling for routine operation. This is because it can decrease performance by inhibiting the regular benefits of context switching, and because some components of SQL Server that use Thread Local Storage (TLS) or thread-owned objects, such as mutexes (a type of Win32 kernel object), cannot function correctly in fiber mode.

Setting lightweight pooling to 1 causes SQL Server to switch to fiber mode scheduling. The default value for this option is 0.

The lightweight pooling option is an advanced option. If you are using the sp_configure system stored procedure to change the setting, you can change lightweight pooling only when show advanced options is set to 1. The setting takes effect after the server is restarted.


Lightweight pooling is not supported for Microsoft Windows 2000 and Microsoft Windows XP. Windows Server 2003 provides full support for lightweight pooling.


Common language runtime (CLR) execution is not supported under lightweight pooling. Disable one of two options: "clr enabled" or "lightweight pooling". Features that rely upon CLR and that do not work properly in fiber mode include the hierarchy data type, replication, and Policy-Based Management.

See Also

clr enabled Server Configuration Option
Server Configuration Options (SQL Server)
sp_configure (Transact-SQL)
clr enabled Server Configuration Option