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.
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Client and server upgraded. Description updated.
I just moved the world to my PC and get the exact same results in the exact same chunks when running unmodified vanilla 1.7.9.
I just used MCEdit to delete a selection of contiguous chunks. On opening the game the chunks regenerate but the exact same chunks are still affected. I can attach a zip of the world for diagnostic if requested. Or - what else can I do to get a detail log of activity, memory consumption, entities, etc? I have saves of the world pre- and post- the MCEdit.
I just found the issue is due to a mob farm we have nearby to the lagging chunks. If I turn off the redstone timer (hoppers feeding into one another pushing redstone to activate a circuit), lagging elsewhere goes away. We only lag when the timer is running and we have moved away from it. If the client Render Distance is 6 chunks, the player lags when moving 6 chunks away from that timer. If the Render Distance is 16 chunks, the player lags 16 chunks away from the timer and not any closer! I'm guessing some code attempts to take chunks out of memory for a player when that player is out of range, but it's having a problem doing so. Does that help?
Modified description and other headers. This is not a SMP issue, nor is it related to mods or data corruption. This seems to be a chunk memory release issue in the current version, perhaps related to locks.
This appears to be the same issue reported in MC-44801.
Also seems to be documented in this forum post:
http://forums.teamextrememc.com/index.php?/topic/22158-about-chunk-ticking-client-lag/
In that posting the hopper timer is specifically referenced as a cause of this symptom in 1.7. Falling water is also cited as another trigger, as are dispensers with buckets - I have all of these.
Google "minecraft chunk ticking" for many other reports of similar symptoms.
This ticket is invalid, as it pertains to a modified server.