Render sequence gets slower and slower!

[yolao]

Hi.

So i have a big interior scene with lots of polys, SSS, a single animated displacement, DOF and MB, with a 0.5 of denoissing, but with out hair and fur in any object.  I let the render working over night and at the next day i discover that the rendering gets slower and slower with each frame. A render frame that normally takes about 6 minutes it takes in that rendering sequence 10 minutes or more, so is a big difference.

I render the scene sequence with Path Tracing and UHD Cache in corona 1.6 Hot Fix 1.

Is this increasing of rendering time normal when rendering a sequence..., or is a corona issue?..

Thanks

[maru]

What kind of render limit are you using? Is it maybe noise limit?
What kind of animation is this? Is there a lot of things changing? For example camera moving from interior to exterior, or a lot of sky visible in one frame, and only objects visible in other frame?

[yolao]

I`m using a pass limit of 8 (i will increase it later for final renders) and is an animation of a character that is in a chair just talking, so there is not much movement.
On the Back Ground i have 8 TVs with an animated sequence on each screen, the animated sequence is applied in to a light material to have the illumination of the screens.

I also have a big box in front of the camera in the whole scene for volume scattering and "Animation (Flicker-Free)" in UHD Cache section check.

There is no camera movement or objects movement apart from the character. Apart from all that, as i said if i render frame 140 in a single render it takes about 6 minutes, but if i then render a sequence from frame 80 for example to frame 140, the frame 140 will take 10 to 12 minutes to render... that is huge difference.

I forgot to mention that i have 16GB of RAM.

[cgifarm]

Hey there..

One resonable explanation is that the computer gets tired over the night and puts some cores to sleep.. :) ..

I would try to render a sample of the animation like this : 0, 50, 100, 150 . To see if there are different render times
during the frame range. Or do single frame renders on different times of the animation, if you get different results from your
full render, then it's odd, but usually there's something with the scene.

Another thing that pops into my mind, is the power setting on your windows machine, make sure that's set on high and there's no sleep on the hard
drives (should not happen as it's working, but you never know what windows is doing). Windows updates also turned off on the rendering machine, downloading software etc..

But I would start with a sample of the frame range first.
Good luck!

[maru]

Is this actual?

If so, my guesses would be:
-overheating and CPU lowering frequency
-running our of RAM

[sk-films]

Same here:

3642 frames to render. Limit: 10 passes.

One by one it takes 2 minutes (+- 10 sec)  to render each frame (random frames).
However rendering animation (with Flicker Free option) gradually went to 4 minutes per frame (at frame 1351 - that's what I render currently)).

So looks like render times increases with each frame.

CPU is max on 40 degrees. And ram used only 24GB from 64 GB.

UPD: I noticed that it might be "scene preparation" is what takes longer (Currently only preparation takes 2 minutes)

UPD 2: On frame 1521 it already takes 4 minutes 53 second (2:37 as Scene and Geometry preparation).

[Ondra]

sounds like RAM fragmentation issue (where frequent memory allocations/deallocations fragment the free memory positions in RAM so subsequent operations take longer because it is more difficult to find empty space in RAM). If you provide us the scene, we can investigate it

[sk-films]

As mentioned, less than half of RAM is used (only 24GB out of 64GB).
But might still be it.

Just an update - I've stooped and started render again and looks like it didn't improve anything at that point. However gradually it went back to 2 minutes.
So it it could be that it did slow down due to some heavy frames.  I'll double check that a bit later (also want to do a render time chart to see how restarts affected it).

Regarding sharing scene - unfortunately can't do that due to NDA.

Will be looking at it and if I'll see some logic in that or how to reproduce it I'll post it here.