Worker Threads

Microsoft SQL Server maintains a pool of Windows operating-system threads to service batches of SQL Server commands submitted to the database server. The total of these threads (called worker threads) available to service all incoming command batches is dictated by the setting for the sp_configure option max worker threads. If the number of connections actively submitting batches is greater than the number specified for max worker threads, the worker threads are shared among connections actively submitting batches. The default setting of 255 works well for many installations.

Worker threads write out most of the dirty 8-KB pages from the SQL Server buffer cache. I/O operations are scheduled by worker threads asynchronously for maximum performance.

For more information, see SQL Server Books Online.