Sometimes Eclipse hangs/lags for a very long time - typically because you have minimized it - and/or not used it for a long time. I just stumbled upon this fix:http://suif.stanford.edu/pub/keepresident/
Windows only, but afaik, it is only windows that suffer from it:
The performance of Eclipse (and other large Java applications) has long suffered due to the Windows virtual memory manager. Windows has a tendency to preemptively swap Java processes out of physical memory, even when there is still plenty of physical memory available. This interacts very poorly with Java processes, which do not have good locality and touch a lot of memory. The problem is exacerbated when Java performs garbage collection, which causes the Java process to touch lots of memory that has been paged out to disk. Ever had Eclipse randomly hang for 15-20 seconds? This is most likely the culprit.