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Old 02-07-2009, 02:15 AM   #1
ben hobden
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Default Frustration vent on mental ray memory errors!

Just wanted to express my annoyance over the last few hours!! I have been working some more on my bee scene...a couple of days ago, I started getting those horrible 'no memory, fatal error, system unstable messages when trying to render. My scenes got all of about 125,000 polys! Im not particularly a technical person, but my computer is very new and pretty nice. Luckily, I have worked on enough maya projects now to know to duplicate a scene file every now and then as backup. Which I did in this case.

But then this evening...again!... one minute my scene was rendering at around 5 and a half minutes (less than it had been doing in the original file), then suddenly it was 53 minutes. Then back to 7, then it was running out of memory on me. Don't understand why it does this, I wasn't making any dramatic changes to the scene, no change in render settings.

I don't know. Can have you walking on eggshells can't she sometimes. :headbang:
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Old 02-07-2009, 07:47 PM   #2
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I don't know about the random render times, unless you juiced up settings on a light or shader, I can't see how that happens without messing with the render settings.

How much RAM do you have and what OS are you running? I was getting that out of memory issue a while back, I wasn't surprised as Vista is a resource hog, and then running Maya and MR ate up what was left so I just got more RAM and didn't have that problem again. I did however, turn this notebook into a lab rat to test out Windows 7 to see what all the hullabaloo was about and so far its pretty damn good.
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Old 02-07-2009, 10:18 PM   #3
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It's 32 bit, 4 gig. I may have added a shader, like today, ive been trying to add materials to the books on the book shelf in that bee scene Ive been doing. I rendered on loading - about 7 minutes. Then I made 5 or 6 new lambert materials, each with its own texture, just the spine of a book, add one to each book. So I click render again. Exactly the same, just 6 books, 6 tiny books, have a new lambert on them. 1 hour 40 minutes.

I have vista, and I have other stuff open at the same time, but it's happening when I don't have stuff open aswell. And whats open isn't really heavy duty, Im not downloading, or surfing the web, I might have a couple of notepad files open, or photoshop on standby. But it's why one minute, generally after loading maya, it renders without trouble, then next time, its like cluttered itself up and takes so much longer. I've been restarting my computer to reopen maya cause the patterns emerged that the first render is reasonable, and thereafter my computer seems to struggle. I don't want to sound immaturely impatient, I just don't understand the drastic fluctuation.

I would say that I dont think my scenes that 'expensive' because from google-searching I've done people seem to get the memory issues when they're in the millions of polys, and Im nowhere near that. But then I guess I have some particles, and a couple of bits of n-cloth. The render settings are pretty high, but they have been throughout.
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Old 02-07-2009, 10:56 PM   #4
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Not too sure the problem, sounds though like its more to do with the scene over the comp or MR, maybe have clean up.

Also if you've got a lot of single procedural textures there convert them to textures as they hog RAM, there quite afew ways round taming that RAM and speeding up renders, have a google for em

Though saying that aint a clue why its going up and down so much, you sure thres not a process running in the backround? Maybe start the task manager up and have a look?
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Old 02-07-2009, 11:46 PM   #5
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how big are your textures? ....also your bee is maya fur.

I believe mental ray is a scanline render algorithm... (someone correct me if i'm wrong!) do you know how a scanline renderer breaks down a scene?
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Old 02-07-2009, 11:54 PM   #6
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is convert to file texture a viable option when rendering with mental ray?
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Old 03-07-2009, 12:08 AM   #7
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yeah, hammer you are right the bee is fur. I now have a broom in there which has fur aswell, a couple of dialectric materials, mia_x, light fog, a little displacement too. All of which I could understand if the consistency in the rendering time was there. It's the way, it will render all that in the time it takes me to make a cup of tea one minute, and then has me keeled over silently cursing the world the next. If it always took an hour or more, no worries. When its fluctuating, and occasionally running out of memory, it makes me feel a little out of control, and unhappy about putting more time into it.
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Old 03-07-2009, 12:12 AM   #8
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(I apologise for multiple posting.)

hammer, my textures are actually unnecessarily big. I should scale them down.

I don't know how the scanline works. I enabled the raytracing option after I put the dialectric material in there.
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Old 03-07-2009, 07:33 AM   #9
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Yes you can convert and its a good thing to do as it saves RAM.

Hammer got to ask, how would knowing how a scanline renderer works help to solve the fluctuations in the render time?
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Old 03-07-2009, 10:28 AM   #10
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i just thought that as it works on a row by row basis, it decides on a box size and goes along rendering. if it comes to an area of high detail then it will stop if the box is too big and make a new smaller box and then go again.
If the scene has lots of areas of varying detail it would be doing this lots and maybe this would be the reason for long render times? I might be wrong i'm not that technical, but i do like numbers.
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Old 03-07-2009, 11:21 AM   #11
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I think you and gster are both on the right line regarding texture issues. I got a straightforward render off last night. Then just now I wanted to finish the last few books off on the middle shelf. Created four new lamberts, one texture for each and put them on the books. Fatal error: out of memory. Unfortunately this means I might have to retxture everything I've textured with non-procedurals, which isn't actually that much, just a pain isn't it. Unless I can convert my textures as gster suggests. From the googling I did, and even in the help files actually, the info all seems to point to converting file textures when using maya software, but I'm sure if I look a little harder the info will be about somewhere. I wonder if converting the textures would bypass the resolution issue, or whether it'd still be best to scale them down before converting?

I would tone down the render settings but I think it would be at the cost of the glass and the fur. Im sure some people would know a workaround with render layers, but that's beyond me at the moment.
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Old 03-07-2009, 12:13 PM   #12
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Hammer, scanline is an accelerator that is used within MR its not the actual render itself, MR relys on Raytracing as the underlying render and will use this when it cant use scanline as scanline is limited to lenses, so its only used to speed up the render where it can, though as I say it will go to raytracing when it cant use scanline.

Having lots and lots of detail would ofcourse slow a render down but I highly doubt it would cause such high differences.
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Old 03-07-2009, 12:20 PM   #13
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cool, i get it... i think.
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Old 03-07-2009, 01:24 PM   #14
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gster, so does that mean that all mental ray renders are at heart, raytracing? and if so, does that mean when using the scanline option it means more work for the computer? I always think that raytracing is a more complex job for the computer than a scanline render.
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Old 03-07-2009, 01:40 PM   #15
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Yes.

Mental ray is a raytracer that incorporates scanline rendering.

Scanline rendering is a faster way of calculating where objects are and what light hits them.

Basically raytracing is the hardest (longest) on the computer but gives better and more accurate results, scanline is easier and faster. So using scanline will (or should) speed up the render time.
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