Solved: 15 second lag cycles on FTB Ultimate

[DrLucky]

Hi folks,

Just registered to post a solution to an extremely annoying lag problem I've been experiencing on FTB Ultimate 1.0.1, and which almost certainly applies to other modpacks. I wasn't able to track this down via Google or site searches, so I'm hoping this helps other server hosts:

The problem:

Periodic lag spikes (every 15 seconds or so, typically). Accompanied by elevated tick times, but not data I/O (ie: not chunk updates). The Server GUI load graph doesn't show anything at all. Makes the server unplayable.

The solution:

The lag was caused by a pair of Buildcraft pumps which were pumping lava from a lava ocean in a MystCraft world. They had reached bottom (although due to the lava flow, this wasn't visually apparent). Since they pump from a 64-block wide circle, they were clearly doing a lot of checking of *something*. The problem might be specific to lava, or to pumping from areas with a lot of flow, or to the particulars of my pipe system; I'm not sure. But if you experience similar symptoms, check your pumps!

The evidence:

I had tried various approaches to localizing the problem. Ultimately I downloaded the latest Java JDK from Oracle, and used the provided jvisualvm to profile the server while it was running. Two methods in buildcraft relating to pumps were in the top 9 most time-consuming methods, which led me to destroy the pumps. Destroying the pumps solved the problem immediately.
As an aside, jvisualvm was super useful for this, and I recommend it heartily.

DrLucky

 

[egor66]

TY for taking the time to reg & post, I for one have suspected this for a long time, I stopped using lava a couple servers/months ago, I beleave its the huge area that has to update each tic.

 

[DoctorOr]

The lag was caused by a pair of Buildcraft pumps which were pumping lava from a lava ocean in a MystCraft world.

Yeah this isn't really a normal situation (A lava ocean world is guaranteed instability, for one) unless you're editing config files to make it easy.

If you use a GregTech pump instead, it will remove the flowing lava.

 

[DrLucky]

Hmm. I only have my own experience - I tend to run a series of friendly whitelisted servers, and lava energy is one of the stepping stones we've been using of late when thorium nukes no longer suffice, but iridium supplies are still too low to accomplish grand feats of GregTech.

I'm running with unmodified config files, except to change the limits on chunkloaders. I have also manually updated Twilight forest (1.15.4) and Applied Energistics (v9g I think). I've been chasing this problem for a few weeks, so I haven't moved to FTB Ultimate 1.0.2 yet, but I will make the jump shortly.

I believe I incorporated instability (charged) into the flat lava ocean world when I created it; I've never investigated it for decay or the like, but it has existed for several weeks of runtime now without event.

I haven't used GregTech pumps, but thanks for the tip. My design patterns come from Tekkit days where I had fewer options. Suffice to say I'll be casting more of a gimlet eye at the BC ones

(edit)
At any rate, I expect a similar situation could occur with extensive lava harvesting of the nether in the absence of MystCraft, and might also apply in situations where a water body is drained, perhaps accidentally while making oil wells or the like.

 

[RedBoss]

Wow, I'd lost two pumps and just today decided to track them down,I lost them along with my waypoints when voxel took over from rei's. The funny thing is I'd completely forgotten about them and I was really just looking for stray chunk loaders. Two oil pumps were still in world and I broke them. I've noticed no lag at all tonight. must be the exact same issue. Cool

 

[Bigglesworth]

Ouch, Yeah those guys do a shit ton of checks on a lot of blocks. R U LAVA? NO? K R U LAVA? NO? K























HOW ABOUT NOW? K