An
SMP (symmetric multi-processor) can have multiple CPUs that might have one or more cores
to perform tasks at a given time. These tasks are either software processes or threads
that the operating system schedules. MAXWHTHREADS= controls the number of threads
that a single process can create when performing a task in parallel.
SPD Server WHERE clause evaluation, parallel group by, parallel join, and parallel sorts will use multiple
threads for performance. An appropriate
thread count is based on your system architecture, the number of expected concurrent users
of the system, and the types of queries they are submitting.
You might need to experiment
with different MAXWHTHREADS= values until you find an appropriate
setting. Setting MAXWHTHREADS= too low can minimize parallelism.
Setting MAXWHTHREADS= too high can overcommit CPU resources. For information
to help you determine an appropriate setting for your site, see
SAS Technical Papers — SAS Scalable Performance Data
Server.
Note: The value specified for MAXWHTHREADS=
sets the upper limit for the value that users can specify in the SPDSTCNT
macro variable and THREADNUM= table option.