CGTalk - Huge disparity in render time between render view and batch render. What gives?

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Samizdat

05-05-2009, 05:36 PM

Hi there,

I'm working with a project that has something a bit mysterious going on - a huge difference in the amount of time it takes to render a frame in the render view and the batch renderer. It can take between 5-10x longer for batch render to handle a particular frame then it takes to simply render it in Maya's render view window.

The truly strange thing is I'm not sure what the batch renderer is doing in all that extra time. There's a long pause where nothing seems to be happening. The batch renderer isn't taking up much CPU time (less than 5%), or RAM (less than 300MB) - and no messages appear in the script window. It just looks like it's hung.

Once the script window actually becomes active and starts reporting percentage completed of a frame (5% complete, 10% complete, etc) - it seems to finish the frame as quickly as the render view render does.

Then - another long pause.

Has anyone run into this problem? How would I go about troubleshooting? It's a maya software render in a fairly simple scene.

Thanks for your help.

scarface1

05-05-2009, 06:43 PM

i had this problem when i had a scene with fluids,that i rendered the fluid seperately,i also put a script on onother thread which gives you a fire exit http://forums.cgsociety.org/showthread.php?f=87&t=721362 (http://forums.cgsociety.org/showthread.php?f=87&t=721362)

mgkaplan

05-05-2009, 08:49 PM

I've had this problem as well at times (it doesn't seem consistent though from project to project.) Would love some info!

Galakgorr

05-05-2009, 09:59 PM

that long pause is the translation time... where mental ray takes all of your maya DAG nodes and translates them into its own language.

the slowdown after the first frame has to do with how mental ray handles memory, what gets purged between frames and what doesn't. you can try messing around with your memory settings in the render, maybe use the -mem flag to change how much RAM you're willing to allocate. it doesn't always work, though.

i haven't found any consistent fix for the problem, except to just batch render one frame at a time when it happens. if you're using a render farm you can just set your batch size to one, and maybe render one layer at a time if it's still hanging.

if you don't have a render farm, you could always use MEL to generate a long batch file which calls one "render.exe" after the next. if you're familiar with using the command line renderer it should be a pretty straightforward script.

Samizdat

05-05-2009, 10:26 PM

Thanks to everyone for responding. That script sounds very helpful.

About the mental ray translation - normally, I would suspect something like that - but in this case, almost all of the render layers are only using the Maya Software renderer. These Software layers have the same problem.

Thanks again.

JayHoo

05-07-2009, 09:49 AM

Are you using SP1a?

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