Help, can't keep up!

I keep getting "Can't keep up" messages in the server console. While this happens, redstone stops working (usually until a restart) and all entities start moving very quickly, which is very bad on a survival server, especially since I got hard difficulty.

The server has 1GB of RAM (2GB swap) and I got 1/2 of a CPU core, it's Xen. While trying to fix it, I made Bukkit run with 386MB of RAM and moved the map to a Ramdisk, but it didn't help at all. This is a private server (4 people online at the same time at most, and they won't go more than 100 blocks away from each other) with 5 slots. The thing is, the server (with the exact same configuration) worked perfectly with only 256MB of RAM allocated to Java on OpenVZ, so I honestly got no idea about why it won't work. I had to move to Xen, as my old VPS provider is closing down, and I'll only have the VPS for one more month.

If needed, I'll move to a bigger VPS (accepting suggestions on providers, but must be actual VPS, I also need to run a web server), but I sincerely hope that it's not needed.

Does anyone know why this can happen, and can help me fix it?

 

Uhm, try to get around 4GB of ram

 

Minecraft has no problems with Xen, we use a xen hvm with 5G RAM and 4 Cores. Till now we had no problems (20 Players at once) - only during Backups, but that seems to be normal.

 

I think you if you have 1 gb and its only 4 slots with nothing else on it why not run with 512MB or more? Maybe I missed what the op is saying.

 

There is a webserver (hundreds of visitors everyday), so increasing the RAM is not an option. However, I'll try Amazon EC2, maybe it will work better.