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After build, huge lag when looking in a direction.

This happens randomly.. maybe 5 or 10% of the time... but when i complete a build and look in a certain direction it will drop to like 1 fps or less and have massive draw calls... Usually rebuilding tends to fix this, but its a real pain when u spend 8 hours doing a build only for this to happen. Any idea what causes this? I have experienced this in every version of unreal engine 4... including 4.11 Since it just hit me again.

Product Version: UE 4.11
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asked Apr 25 '16 at 03:25 PM in Bug Reports

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avatar image Steve Hardister ♦♦ STAFF Apr 25 '16 at 05:32 PM

Hi kurylo3d,

Does this happen in multiple projects or just one that you have updated through various versions of the Engine? Can you reproduce this in one of the blank template projects? If not, would you be willing to send us a link to your project in a private message to me on our Forum? Also, please post a copy of your dxdiag.


Steve H.

avatar image kurylo3d Apr 25 '16 at 05:55 PM

Hi Steve,

The project is huge like 80 gb and the problem as i said is not easy to duplicate. Its not an every time sort of thing.. I only have had this happen with my main project.. many times in teh course of development over the last year. Its the only thing i use unreal engine for. As i said.. it almost feels completely random... where every now and then the level is unable to perform well and another rebuild fixes it. Alls i can tell you is i use level streaming for different buildings in the scene.... All automatically loaded from the start. And the lag will simply happen if u turn a certain direction toward somewhere in the world.. its as though the worlds mesh draw calls go up to like 40,000 for no apparent reason when its normally less tehn 1000 for all draw calls.

avatar image TorQueMoD Apr 25 '16 at 09:14 PM

When you say turn a certain direction, do you mean the lag spike happens when you face the same area in the world every time, or do you mean it happens randomly? There's probably a thousand reasons why you might be hitting a lag spike... unoptimized geometry, a lot of lights, FX etc. But if its not lagging in those areas after a second build then its a lot harder to pinpoint what the cause of the issue is. Do you experience the same lag spikes if you launch a stand alone game rather than PIE?

avatar image kurylo3d Apr 26 '16 at 12:09 PM

You misunderstand. When the build goes "bad" ... looking in that direction is constnat 40,000 draw calls... Not a lag spike.. just straight up 1 fps or less lol..When the build goes "good" It works fine at around 800 draw calls and closer to 95 fps.. I cant explain that. Nothing in the scene changes.. i just did light build again last night and the build went good and it works fine. The part that is random is wether building lighting will be bad... or good... No lag if it builds good.

But yea everythign is optimized. Its just a strange random occurence from a lighting build. This is kinda why i mark this is a bug personally. I have always excperiened it with every version of unreal engine 4.

avatar image Steve Hardister ♦♦ STAFF Apr 25 '16 at 07:22 PM

Here are a few links concerning draw calls and performance. Please review these links and see if they do not provide pertinent information to your issue:

If you do not find any of these links helpful, please describe how or why your project is different from these examples.

avatar image kurylo3d Apr 25 '16 at 09:09 PM

None of these have anything to do with my problem. As i said... my draw calls (when it builds correctly) are below 1000. This is a bug im experiencing where sometimes if i build it.. i just get a bad "build". In this bad build, if u turn ur camera in a certain direction... it will just skyrocket to like 40,000 draw calls... some rediculous number.. even if your staring at a solid brick wall with nothing around. Building it a 2nd time without any changes at all typically makes it work fine.. but the fact that i have to build the same level multiple times some of the time.. whenever i encounter this ... tis just a HUGE waste of time.

avatar image Silentvision25 Apr 13 '18 at 11:45 AM

did u ever figure out this isse i have the same damn problem..its like ue4 cant handle its own point and area lights ..im so pissed and cant find clear solutions without people over complicating everything....i have made dope as detailed maps with point light and after spending hours on light rebuild and increasing the light mass from 64 on my static meshes to lets say 124 or 512 it takes 5 years to rebuild and then once its done its a little better but i lag in certain direction please help me im about to shoot my brains out!!!

avatar image kurylo3d Apr 13 '18 at 02:29 PM

how many draw calls do u see? If it goes up to a rediculous number that makes no sense then its my bug issue and i would just rebuild it a 2nd time and i would get lucky.. sometimes problems are a fluke occurence..

If its just a performance issue ... ue4 seems to not do well with having too many objects in teh scene even if they are culled. I dont know why. Ive had areas of my level with 100 draw calls that fall to 30 fps on a gtx 980.. it makes no senese but the fps improves when i use sublevels to hide areas...You can try using multiple sublevels and hiding them for more performance but then that typically creates a lag spike everytime u hide/ unhide...

HLOD might be a solution to help mitigate as well.. Merging things by distance.. But problem with HLOD is its pretty much broken. Not all models merge.. sometimes it gives 0 poly merges as a bug... so thats useless to us.. (I hear they are working on something to replace HLOD)

something that can help some performance in some levels is r.HZBOcclusion 1 or 2.. It decides how to cull things differently.

My main hope is something that replaces HLOD so less objects in the scene because it switches them out with merged meshes by distance... even lower poly ones..

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1 answer: sort voted first

Thanks for clarifying... In order for us to identify this as a bug, I will need the information that I requested before:

  1. Is this the same project that you have updated over multiple versions of the Engine?

  2. If so, did you open a copy of the project in the newer version of the Engine or did you overwrite the original each time?

  3. Please post a copy of your Dxdiag, so that we can run tests on a comparable machine.

Also, do you have Swarm Agent active when you do a light build? If not, double click the icon to activate window, then build lighting. If an error is occuring you will see what's going on in the build logs:


Save log and post here (do not send a screen shot).


Lastly, you can try adjusting settings in Swarm Agent to see if this resolves the issue. Increase cache size and decrease number of jobs kept:


If adjusting Swarm Settings does not resolve the issue, please send all requested information including the light build log from Swarm Agent.

swarmlog.png (194.3 kB)
swarmlog2.png (156.2 kB)
swarmsettings3.png (79.1 kB)
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answered Apr 26 '16 at 02:10 PM

avatar image kurylo3d Apr 26 '16 at 02:25 PM

I'll try to keep that in mind next time i get that bug. It doesnt happen that often. And I am not sure the next time I will need to build. I will let you know when i do.

To answer your questions.. This project has gone from numerous versions. I usually open a copy and then rename the directory back to the original name.

I usually keep a copy of previous versions on hand.

I am not home right now, but my comp is running a gtx980 with a 4ghz i7 .. I am not home right now to get the dx diag. Aside from that the other comp on swarm is a laptop that also has a gtx 980m with i7... And my third comp is a gtx 780 with another i7 but only like 6 gb of ram on that one with very little hard drive space left.. But this bug tends to happen without that third comp either way... Though that third comp may be the cause of another issue.. when its on swarm my build gets stuck at 99.88% some of the time with that comp in on the build. I seem tobe a magnet for weird bugs. Makes it difficult to get anything done.

avatar image Steve Hardister ♦♦ STAFF Apr 26 '16 at 03:06 PM

Thanks for the info. We use info from the dxdiag to check for any known hardware conflicts with drivers, etc. GTX980 running the latest drivers has no reported known issues and your processor should be fine as well. We'd still like to have the dxdiag, if possible.

We have seen a number of bugs happening when converting a project from 4.10 to 4.11 and have been working to "iron these out" so that may be why you feel like a magnet for weird bugs. Next time you build and run into a problem, please provide the Swarm logs and we will see if we can identify the root cause.

One last question: If you have your original 4.10 version of the project, do you still experience this issue while working in that version?

avatar image kurylo3d Apr 26 '16 at 03:25 PM

This issue happened all the way back to 4.6... I have experienced it at least once in every iteration of the engine, but again.. difficult to replicate when i want it to happen for testing purposes... I do a lot of builds... I think 4.6 may have been when i first went to unreal. Point being every version i have used when i started developing my level had this.. Part of me once to say something to do with when first started messing with level streaming (even though every level is active at the same time).. But i could be totally wrong.

avatar image Steve Hardister ♦♦ STAFF Apr 28 '16 at 03:08 PM

Hey kurylo3d,

I'm marking this "Resolved" for now as I cannot offer much support in the way of reporting this as a bug until you can post the Swarm Logs from when the Light Build stalls and/or fails. When you are able to, post these logs and this post will be reopened.

In the meantime, be sure you are practicing the best modeling techniques to ensure optimal light building which include but are not limited to:

  • Breaking up geometry to prevent lightmaps becoming crowded into a single UV, which then requires higher lightmap resolutions which, in turn, taxes Swarm agent when distributed across multiple computers

  • Breaking up assets into "chunks" and using modular design to allow occlusion culling, which greatly optimizes light building.

-Steve H.

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