thank you for reply.

i think it was not happened "stop-the-world" issue, because my setting used concurrent garbage collection(and G1GC is same behavior).
when eclipse start up, it is confortable performance in a few minutes or less than one hour(in the sense of me).
after i uses for several tens of minutes, it slowdown in all actions(click something, save file, change perspective, show (context)menu, etc.., i kept waiting about 10 seconds..) every time.

now i take a vacation this week, so i can't try memory profiling, comparing STS 2.9.2(indigo) and STS 3.0.0(juno) each other(and same settings).
after the vacation, i try that and report.

thanks,