It is important that you choose the correct number of engines for Adaptive Server:
You cannot configure more engines than CPUs. If a CPU goes offline, you may need to decrease the number of engines by using sp_engine (in process mode) or alter thread pool (in threaded mode).
Adaptive Server may use additional operating system threads to handle I/O operations in threaded mode. In high I/O situations, you must ensure that Adaptive Server has sufficient CPU for these threads to run. For example, an Adaptive Server performing high I/O on an 8 CPU system may achieve maximum performance with 8 engines in process mode, but only require 7 engines in threaded mode. You may experience severe performance degradation if I/O threads compete with engine threads for CPU time.
Have only as many engines as you have usable CPUs. If there is a lot of processing by the client or other non-Adaptive Server processes, one engine per CPU may be excessive. The operating system may take up part of one of the CPUs.
Have enough engines. Start with a few engines and add engines when the existing CPUs are almost fully used. If there are too few engines, the capacity of the existing engines is exceeded and may result in bottlenecks.
Sybase recommends that you have only as many engines as your site requires. More engines do not necessarily translate into better performance. Generally, Adaptive Server perform better with 4 engines that are 80% busy instead of performing with 8 engines that are 40% busy.
