I have a hosted server over Linux with anywhere from 1-3 players at any given time. Most of the map runs fine. When any player enters specific chunks, that player will experience extreme lag. Back away from the lag zone into a non-affected chunk, and performance resumes to normal. This is 100% repeatable and affects all players running on different PCs. The chunks are 100% consistent. The issue seems to be data corruption. I've been trying to map which ones are affected but it's too big an area. Server does not report errors. Client reports a stream of:
[Client thread/INFO]: Warning: Clientside chunk ticking took 1616 ms

I've attached a crash dump from when I am just about to enter a lag chunk, and another from right after it's entered. The only obvious difference I see is that memory surges from 45MB to 134MB.

On request I can make a server snapshot available and will provide developers access to the server. This is 100% reproducible.

At some point we created a farm with about 200 animals and that caused the first lag. We killed all animals but the lag persisted and expanded several chunks away from the original chunk.

The affected chunks are almost entirely undeveloped and we can delete/regenerate them if required - but I'd think you would want to know what causes this. There is no redstone and the entity counts are normal.

EDIT: The original report and debug attachments were for v1.7.5. I've just updated to CraftBukkit 1.7.9 and updated clients to 1.7.9 and the exact same issue persists. Again, I believe this is a data issue, not software, but I think it would be good to find out what the exact issue is for anyone who may encounter this in the future.

I'll provide other info on request. Thanks.