Engine groups do not exist in threaded mode. When you switch from threaded to process mode, execution classes are assigned to the default engine groups. For example, if you switch from threaded to process mode and then add the Eng_Group execution class and associate it with engine number 3, the default execution classes EC1 and EC2 are associated with the ANYENGINE engine group, and EC3, with the highest engine number, is associated with the LASTONLINE engine group:
sp_showexeclass
classname priority engine_group engines ------------------------------ ---------- ------------------------------ ------------------------------ EC1 HIGH ANYENGINE ALL EC2 MEDIUM ANYENGINE ALL EC3 LOW LASTONLINE 0 Eng_Group LOW new_engine_group 3
When you switch to threaded mode, execution classes lose their engine group affinity and are assigned to syb_default_pool. In threaded mode, the example above becomes:
sp_showexeclass
classname priority threadpool ------------------------------ ---------- ------------------------------ EC1 HIGH syb_default_pool EC2 MEDIUM syb_default_pool EC3 LOW syb_default_pool Eng_Group LOW new_engine_group