For servers running multiple engines, task-to-engine affinity improves performance by reducing the number of times the task context has to be switched between engines. The only visible effects of this are during system tuning. When there are fewer tasks running than there are engines, you may see some engines showing high utilization, while others are idle for the entire interval. For example, in earlier versions, while a single task runs a select * query, you would generally see each of 6 engines performing about 16% of the work. In version 11.9.2, sp_sysmon might report:
Engine Busy Utilization
Engine 0 97.2 %
Engine 1 0.0 %
Engine 2 0.0 %
Engine 3 0.0 %
Engine 4 0.0 %
Engine 5 0.0 %
----------- --------------- ----------------
Summary Total 97.2 % Average 16.2 %
For more information, see the Performance and Tuning Guide.
