Problem Can't keep up!

[RelieveTheMind]

I'm getting a message in my console of my server that says "[Server] WARNING Can't keep up! Did the system time change, or is the server overloaded?" about every 2 seconds or sometimes minutes but anyway it is lagging the server a lot in different intervals. It's basically a complete lag cycle. I have a 3 GB server and all I would need is a 2 GB to run a FTB server, I have about 13 people on usually and I get this error message. My cpu is always 100% and will occasionally go to about 92%. If anyone could tell me what the issue is and how to fix it that would be much appreciated.

23.02 19:16:56 [Server] INFO at java.lang.Thread.run(Unknown Source)
23.02 19:16:56 [Server] INFO at aiw.run(SourceFile:22)
23.02 19:16:56 [Server] INFO at aiw.b(SourceFile:29)
23.02 19:16:56 [Server] INFO at aam.c(AnvilChunkLoader.java:184)
23.02 19:16:56 [Server] INFO at aam.a(AnvilChunkLoader.java:198)
23.02 19:16:56 [Server] INFO at ca.a(CompressedStreamTools.java:140)
23.02 19:16:56 [Server] INFO at cd.a(SourceFile:114)
23.02 19:16:56 [Server] INFO at bq.a(SourceFile:24)
23.02 19:16:56 [Server] INFO at java.util.HashMap$ValueIterator.next(Unknown Source)
23.02 19:16:56 [Server] INFO at java.util.HashMap$HashIterator.nextEntry(Unknown Source)
23.02 19:16:56 [Server] INFO java.util.ConcurrentModificationException

 

[Francis Baster]

I believe that the can't keep up message simply means that the server is processing less than 20 ticks per second; in layman's terms your server is lagging. This is very common for modded servers and can be caused by almost anything. Here are the two most common causes of lag I've encountered on my MindCrack server, and how I've dealt with them.

The first thing you should do to check the cause of the lag is whitelist the server so that you are the only player online. If the server is still lagging, it is likely that chunkloaders, probably quarries, are heavily loading your server. The ChickenChunks mod provides a handy command, /chunkloaders which displays chunkloader statistics and shows the location of nearby chunkloaders. Remember, lots of different items can chunkload including quarries, MFFS blocks, and portals. If the number of forced chunks is too high, you may want to consider banning certain items using Forge Essentials or the Recipe Remover mod.

If your lag seems to come and go periodically, it is highly likely that a certain player has a large number of item entities, or possibly mob entities near their base. When they move towards their base, the item entities are loaded and the lag begins. If this is your problem, OP yourself, and activate NEI's magnet mode, and teleport to the location of the items. They will be sucked into your inventory, where you can use NEI's delete button to remove them. Alternatively, Forge Essentials has the /remove command which removes all item entities within a certain radius of your player.

Hope this helps,
Francis