How to Fix Lag on a Server?

You may want to try NoLagg and its Examine function while breaking some blocks. It should give a clue of what's causing the problem.

It is most likely your location to the server that is causing your lag issues as it takes a while to send the block updates to the server and recieve the packet that the block has broken to the client.

Try adding more RAM, that helped me on my server.

Is the lag only in one area? Is the lag effecting everyone, or just you?

If the lag is only in one area, check around for too many entities being created. I've had people create massive chicken farms on my server that have over a 1000 chickens and it lags the server extremely bad.

If the lag is effecting everyone then I'm not sure what to tell you. If you're hosting it from your computer then you probably need better internet/better computer.

Call Fix-It-Felix, he likes "fixing" things #Wreck-It-Ralph

Many things could be causing your lag issues. Before you trouble shoot, you have to find out if the lag is due to your internet connection, or your server's hardware. After you figure that out, you can proceed from there. If it is your internet speed, you obviously would have to fix that. If it is your server, it is most likely a poorly coded plugin that is causing it. I would recommend you disable each plugin 1 by 1 until you find out what is causing it. Your host could also be the problem, try getting a new host if you can't find out the problem.

what is your upload speed?

Dont break blocks.

you hit it with a brick