How to specify threads in Parallel CPLEX

Answer

Yes, there are limits. If you are licensed for running parallel optimizers, you can specify a global thread limit (CPX_PARAM_THREADS). If successful, CPLEX will use the specified number of threads for the appropriate optimizer.

For users of CPLEX 12.1 and earlier, you cannot set a value greater than the number of parallel threads allowed in your license. Versions 12.2 and later have no license based restrictions on the number of parallel threads.

For versions 12.4 and earlier, you cannot set a value that is larger than the number of cores on your machine.

In either of these cases, CPLEX will report an error (Error 1015: Parameter value too big.) and will leave the setting unchanged.

CPLEX 12.5 permits setting an arbitrary number of threads. However, this was done primarily to aid in application development and troubleshooting, Setting a thread value larger than the number of cores incurs additional overhead that reduces the chances of improved performance.