Spigot 1.12 - If NPC cannot reach target, it overloads server CPU performance and cost lags

[GreenFlagCZ]

Sever: Spigot 1.12 Build 201707090430
Plugin version: Sentinel 1.3.1

Hello, there is an issue. If NPC has not a clear path and cannot reach target (for example mob is on the tree), the CPU of the server start overloading (in my case up to 70% from normal condition) and its only ONE NPC. I dont know, what happens, if this issue will start with other NPCs on my server. It can cost big server lags.

example:
server start overloading: NPC [Straz] targeted the witch, but hasn't clear path and cant reach the witch, because mob staying on the stone wall
http://riftsite.cz/wp-content/uploads/2017/07/2-NPC-cannot-reach-target.jpg

server stop overloading: NPC [Straz] can again reach target, because has clear path to the witch ( I push the witch from wall)
http://riftsite.cz/wp-content/uploads/2017/07/3-NPC-reach-target-after-mob-is-in-path-range.jpg

Thank you for solving this
Best regards
Green

[mcmonkey4eva]

Can you get a more careful analysis of this? There's a plugin somewhere that shows method-by-method weights of CPU stressors, which will help identify what went wrong here.

Quite possibly just a too big pathfinding range.

[GreenFlagCZ]

I ll try to analyse. I tryed reduce pathfinding and range/chaserange from default 25 to 10, but it's not a solution, it's only reduce the chance if that happend.

[GreenFlagCZ]

....
....
I create a 4 block tower near to him
Spawn monster on tower.

Also I find, if NPC is naturaly blocked, like he is in cage but see target, CPU will no overloads,
but if he hasnt any block and monster is on top of tower, it will overloads

NPC stats above like I described...
in cage:
http://riftsite.cz/wp-content/uploads/2017/08/1.jpg

NPC released
http://riftsite.cz/wp-content/uploads/2017/08/3.jpg
http://riftsite.cz/wp-content/uploads/2017/08/4.jpg

[GreenFlagCZ]

net.Citizensnpcs.api.astar.pathfinder.CachingChunkBlockSource.getBlockTypeIdAt(CachingChunkBlockSour ce.java:41) at net.Citizensnpcs.api.astar.pathfinder.BlockSource.getMaterialAt(BlockSource.java:11) at net.Citizensnpcs.api.astar.pathfinder.BlockSource.getMaterialAt(BlockSource.java:15) at net.Citizensnpcs.npc.ai.CitizensNavigator$DoorExaminer.isPassable(CitizensNavigator.java:394) at net.Citizensnpcs.api.astar.pathfinder.VectorNode.isPassable(VectorNode.java:153) at net.Citizensnpcs.api.astar.pathfinder.VectorNode.getNeighbours(VectorNode.java:104) at net.Citizensnpcs.api.astar.AStarMachine.run(AStarMachine.java:85) at net.Citizensnpcs.api.astar.AStarMachine.runFully(AStarMachine.java:120) at net.Citizensnpcs.npc.ai.AStarNavigationStrategy.update(AStarNavigationStrategy.java:83) at net.Citizensnpcs.npc.ai.MCTargetStrategy$AStarTargeter.setPath(MCTargetStrategy.java:152) at net.Citizensnpcs.npc.ai.MCTargetStrategy.update(MCTargetStrategy.java:119) at net.Citizensnpcs.npc.ai.CitizensNavigator.run(CitizensNavigator.java:164) at net.Citizensnpcs.npc.CitizensNPC.update(CitizensNPC.java:274) at net.Citizensnpcs.nms.v1_12_R1.entity.EntityHumanNPC.B_(EntityHumanNPC.java:158) at net.minecraft.server.v1_12_R1.World.entityJoinedWorld(World.java:1640) at net.Citizensnpcs.nms.v1_12_R1.util.NMSImpl.tick(NMSImpl.java:1018) at net.Citizensnpcs.util.NMS.tick(NMS.java:289) at net.Citizensnpcs.util.PlayerUpdateTask.run(PlayerUpdateTask.java:36) at org.bukkit.craftbukkit.v1_12_R1.scheduler.CraftTask.run(CraftTask.java:71) at org.bukkit.craftbukkit.v1_12_R1.scheduler.CraftScheduler.mainThreadHeartbeat(CraftScheduler.java :353) at net.minecraft.server.v1_12_R1.MinecraftServer.D(MinecraftServer.java:738) at net.minecraft.server.v1_12_R1.DedicatedServer.D(DedicatedServer.java:405) at net.minecraft.server.v1_12_R1.MinecraftServer.C(MinecraftServer.java:678) at net.minecraft.server.v1_12_R1.MinecraftServer.run(MinecraftServer.java:576) at java.lang.Thread.run(Thread.java:745)

CPU overloads to 95%.
Used Last Jenkins update &131 (22.8.2017 15:06:30)

NPC info:

• Meleeattack
• max chase range 25
• max range 25
• targetforget 100 (doesnt matter what I choose here)
• target monsters

[mcmonkey4eva]

Try build DEV-133+ off http://ci.citizensnpcs.co/job/Sentinel/
and lemme know if it still occurs.
(I pushed a relevant change that might help)

[GreenFlagCZ]

I tryied this last version, still have problems :(

[mcmonkey4eva]

Might have to elevate this to Citizens then, as this issue is related to pathfinding buggery.

For a quick fix, lower all ranges, especially /npc pathrange.

I did what I could on my end (in the commit in DEV-133) to prevent re-triggering the pathfinder when there's no point to it... but if it's retriggering itself, that's a Citizens fault probably.

[mcmonkey4eva]

I'm thinking about a potential semi-solution for this:

Catch the case if pathfinding fails, and intentionally delay any further pathfinding attempts for a while.
This runs the risk that players can easily troll the AI by blocking the path momentarily (placing a block, or jumping to a higher spot) to disable the pathfinding, then fight it, then jump back before it reengages pathfinding.

Also I think I haven't mentioned here already:
If you set use-new-finder to false in the Citizens config it's likely to run much more efficiently in this case (though at cost of some pathfinding accuracy).

Also see for relevance, Citizens issue CitizensDev/Citizens2#1561

If you'd like me to add an option for the idea I mentioned above or similar, let me know. Until then, treating this issue as out-of-scope for a Sentinel fix (instead, it should be fixed in Citizens).