Random extremely slow Light Cache calculation

[king_max]

I'm not sure if anybody else is having this issue, but after V-ray NEXT upgrade I'm having extreme slowdowns in the LC precomputation, and it's totally random.
I can launch a test render and it's done in a few seconds, then relaunch the same render at it takes 5 minutes.

[vlado]

Does this happen on a specific scene, or on any scene? Can you get me a log file out of such a slow render compared to a fast render to vlado@chaosgroup.com ?

Best regards,
Vlado

[king_max]

It's happening on a new scene I'm working on which is pretty heavy, but yesterday I've noticed it on an old scene too. You want me to send you the Vraylog.txt file? There are no errors in the log file as far as I can see.

[Margarita.Stoeva]

Hello!

I had the chance to look into your scene and tried to reproduce the slow down using the provided files and additional description but I couldn't. LC was always calculated consistently within seconds.

What I did was a couple of consecutive renders with the scene whithout changing anything, then rotate the dome light and render, repeat, then change its VRayHDRI file and render agan few times.
Is there something I might be missing in the routine? (The only plugin I miss is the splineland.dlm.)
* Which material did you edit when you experienced the slow down? Was the Material editor opened at render time? Slate or Compact editor mode?
* Which camera is the "grass view" that also reproduces it? (I couldn't reproduce it using Cam_Baby_Pool.)
* Can you provide the other hdr file that you used in the dome light which caused the slow down on change?
* Do you use IPR or just single production renders when the slow down occurs?

Since we can't reproduce it here so far some additional information may be helpful in finding the potential issue.
* Does it still happen if you disable "Adaptive dome (WIP)" option in the Sky Dome HDR light parameters?
* Does it still happen if you change the lights calculation type in the Global Switches (Uniform probabilistic or Adaptive lights instead of Full lights evaluation)?
* Does it still happen if you set Override mtl in the Render Settings to shade the complete scene with a default VRayMtl?

I appreciate all the details you share in order to clear the subject.
Thank you!

Best regards,
Margarita

[kosso_olli]

I have a scene here where the LC never finishes calculation, too. I is using an OpenVDB in the scene that is causing the issue.

[Margarita.Stoeva]

Please send it to margarita.stoeva@chaosgroup.com and I'll look into it. Thank you!

[kosso_olli]

I just tested in Next, I don't get the Light Cache problem there.

[Margarita.Stoeva]

Great to hear that!

[king_max]

Hello!

I had the chance to look into your scene and tried to reproduce the slow down using the provided files and additional description but I couldn't. LC was always calculated consistently within seconds.

What I did was a couple of consecutive renders with the scene whithout changing anything, then rotate the dome light and render, repeat, then change its VRayHDRI file and render agan few times.
Is there something I might be missing in the routine? (The only plugin I miss is the splineland.dlm.)
* Which material did you edit when you experienced the slow down? Was the Material editor opened at render time? Slate or Compact editor mode?
* Which camera is the "grass view" that also reproduces it? (I couldn't reproduce it using Cam_Baby_Pool.)
* Can you provide the other hdr file that you used in the dome light which caused the slow down on change?
* Do you use IPR or just single production renders when the slow down occurs?

Since we can't reproduce it here so far some additional information may be helpful in finding the potential issue.
* Does it still happen if you disable "Adaptive dome (WIP)" option in the Sky Dome HDR light parameters?
* Does it still happen if you change the lights calculation type in the Global Switches (Uniform probabilistic or Adaptive lights instead of Full lights evaluation)?
* Does it still happen if you set Override mtl in the Render Settings to shade the complete scene with a default VRayMtl?

I appreciate all the details you share in order to clear the subject.
Thank you!

Best regards,
Margarita

Hi. I did exactly what you did. There are several cameras in the scene, and the problem occurs on each of them randomly. The splineland.dlm isn't required to render since all the visible geometry is collapsed.
I've tried to disable "Adaptive dome" and it didn't solve the problem.
I didn't try the lights calculation types nor the complete ovveride material.
Will get back to you with the results.
Could it be a workstation hardware issue?

[king_max]

I'm till having the issue and it's extremely frustrating. All the CPU cores are at 100%, but nothing happens for a minute or so. RAM usage is fixed, the computer is responsive, but the LC is stuck!
I'm working on a brand new scene which is extremely simple and as soon as I added some proxy trees, the problem started to happen. It's not an adaptive dome light issue, nor adaptive lights issue.
I can confirm the problem persists with an override material applied to all geometry.
One other problem I've noticed from time to time is that 50% of the buckets gets stuck too in the middle of the rendering, and then resume after a while as if nothing happened.
I'll post a video of the issues so you can get a clear idea of what I'm talking about.

I was working on the exact same workstation with V-ray 3 and it didn't have this issue, so I'm king of ruling out a hardware problem.

[king_max]

Hi. I've recorded a short video illustrating the problem on LC calculation. As you can see, the machine is working at 100% but the LC is not computing until I change 3DS MAX process priority to "high" and change it back to "normal". In the video, after changing the priority to high, the recording freezed, so what you don't see in the video is me changing it back to "normal" after which the LC instantly resumed and computed in seconds. The bucket rendering is not affected by this at all.
This is a completely random issue that affects almost all more complex scenes. In fact, the more complex the scene, the more prominent the issue. Especially if using a lot of high poly proxies.

[DanSHP]

Hi. I've recorded a short video illustrating the problem on LC calculation. As you can see, the machine is working at 100% but the LC is not computing until I change 3DS MAX process priority to "high" and change it back to "normal". In the video, after changing the priority to high, the recording freezed, so what you don't see in the video is me changing it back to "normal" after which the LC instantly resumed and computed in seconds. The bucket rendering is not affected by this at all.
This is a completely random issue that affects almost all more complex scenes. In fact, the more complex the scene, the more prominent the issue. Especially if using a lot of high poly proxies.

I've had exactly the same issue. 3.6.

Render starts and progresses a little ( to a smiliar form of progression in the VFB seen on your video), stops for a while not updating the VFB, then suddenly takes off and starts to render the rest. I don't have to wait quite as long as you.

[Margarita.Stoeva]

Hello!

I believe you experience an issue that is already discussed in another thread:
https://forums.chaosgroup.com/forum/...703#post999703
Yavor has already provided some information there on how to handle this for now.

Best regards,
Margarita

[king_max]

Hello!

I believe you experience an issue that is already discussed in another thread:
https://forums.chaosgroup.com/forum/...703#post999703
Yavor has already provided some information there on how to handle this for now.

Best regards,
Margarita

I am aware of the VRAY_NUM_THREADS "trick" and in this case it's not working. This is not the VFB not responding issue people (me included) are having with Max 2018. I've reverted to V-ray 3.6 and tested the same scenes and it's calculating everything as it should. Having to randomly change 3ds Max process priority is NOT A SOLUTION. Many times it doesn't help except totally locking your system when setting the priority above "normal". My computer is perfectly responsive when rendering. The issue seems somehow related to the LC calculation phase, and it's something that was introduced with the NEXT release.
Back this year I was one of the first persons to start the "VFB" not responding thread and Vlado sent me various nightly builds to try and fix the issue. In my case this was happening only on Max 2018 (V-ray 3.6). Today I've tested V-ray NEXT on max 2018 and the LC issue is still present + the not responding VFB.

To clarify things. This is not an issue of locked down system due to high CPU utilization where you cannot access the system while it's rendering, but an issue where V-ray is literally doing "nothing" in the LC calculation phase. It is most probably still related to system threads priority, but now it manifests itself across all 3ds MAX versions. As a result, the LC calculation takes 500% more time than it should, and you can't cancel the render.

https://www.dropbox.com/s/oru1wev0uq...y_3_6.flv?dl=0 - Vray 3.6 same scene - after loading all the textures/proxies it's blazing fast

https://www.dropbox.com/s/v2nfbc70n1...EXT_A.flv?dl=0 - Vray NEXT same scene - the first render was same as 3.6, but as soon as I relaunched the render it gets stuck

https://www.dropbox.com/s/qzdfppo21a...EXT_B.flv?dl=0 - Vray NEXT same scene - other camera view demonstrating what happens when you try to stop/cancel the render

I'm kindly asking someone to take a look into this issue as it's not the same as the other forum threads.
Is there any way I could get a Vray NEXT build where the "low thread priority" is not enabled by default?

[olika]

Hi king_max ,

i'm also encountering exactly the same problem as you have and for my understanding it's also not related to the num_threads thing, there is something different going on here.
Same as you i had no problems last year with vray 3.6 to render scenes like that. But now it`s hardly possible to work with that bug.
I posted it 5 minutes ago here:
https://forums.chaosgroup.com/forum/...rting-a-render

A fast solution to this would be awesome as i'm stucked right in a project with this bug!