You may have seen this:
GWT Compilation Performance
. Can/should the Vaadin plugin allow the equivalent tweaking for workers ?
The Vaadin Eclipse plugin uses the number of available processor cores as the number of local worker threads by default. The number can be adjusted in the project properties. The memory size given to the GWT compiler should be reasonable for most developer machines and widgetsets (max 512 MB, permanent generation max 512 MB), striking a balance between performance and avoiding swapping.
The Maven archetypes we are delivering also set a reasonable memory size, but by default let the gwt-maven-plugin determine the optimal number of worker threads. I think it, too, decides the number of threads based on the number of available cores, but I am not certain about this. The number can be adjusted with a parameter in the POM.