ASA Database Administration Guide
Running the Database Server
Some common options
Controlling threading from the command line
On Windows NT/2000/XP, tasks are lightweight threads called fibers. When Adaptive Server Anywhere receives a request, a fiber picks up the request and runs until the request is complete. If the database server receives another request while the first request is running, the second request is assigned to a different fiber. If a fiber blocks while processing a request, it yields control to another fiber until it can proceed: it does not pick up another request.
Threads host fibers, and the fibers are scheduled co-operatively. A fiber must explicitly yield control to another fiber when it is waiting to process a request, for example, while waiting for an I/O operation to complete. If a fiber blocks and does not yield control, it blocks the thread that is hosting it and prevents other fibers from running on that thread. If more than one thread is hosting fibers, only the thread that is hosting the waiting fiber is blocked: other threads are still free to run fibers.
You can set the number of threads used to run fibers with the -gx option. Unless you are using Java or Remote Data Access, you should need only one thread per CPU.
When you use Java or Remote Data Access and the fiber running Java or Remote Data Access blocks, that fiber may not yield control to another fiber, which in turn blocks the thread. For this reason, the number of operating system threads assigned to the database server defaults to one more thread than the number of CPUs on the machine. This ensures that there is at least one thread available to host fibers if the thread being used by Java or Remote Data Access is blocked. Specifying a higher number of threads than the default by using the -gx option has a minimal impact on performance.