Processing thread count for 8-core server

In reference to the information here:  https://www.objectdb.com/java/jpa/setting/database#The_processing_element_

We are working with an 8-core processor.  The recommended thread count is "more than the number of cores but not too many."  What would be an appropriate number of threads for the processing thread pool in order to get good performance for our 8-core server?

It could be in the range of 15-30 threads, but choosing the best value will require some tuning tests on your side, since it depends on the specific application.