My server has worked well since 2011, however, nowadays, since updating to 1.8 (actually some subversion of 1.8, not actually 1.8, but I went directly from .2, 3 or something to .8) it lags very much. This is an average message in my server log
[SERVER thread/WARN]: Can't keep up! Did the system time change, or is the server overloaded? Running x behind, skipping x tick(s)
The ticks can go up to 2000+ and 70000ms.
Now, you might think I have 60 plugins with 100 players but I'm running vanilla with max 3 players. I have allocated 2GBs of RAM.
Some of the problems I'm having is that everything is slow, I can travel and the terrain generates 1 minute later (unless I'm kicked with the reason "Timed Out"), or I might hit a monster and suddenly, 30 seconds later I am dead and the mob has walked 30 blocks away.