Amount set to dynamic-ram preview DOES affect rendering! :-/

[Steve Rhoden]

Now that is important info Dave!
Have to run some test first.

Steve Rhoden
(Cow Leader)
Film Maker
Filmex Creative Media.
1-876-832-4956
https://filmex-creative-media.blogspot.com/

[Mike Kujbida]

Dave, I remember reading on a Vegas forum somewhere the reason why that works like it does but, for the life of me, I can’t remember what it was.
I will make one suggestion though, based on a lot of folks saying the same thing and that is to set it to a low number like 128 MB., not 0.
Once again I can’t remember the reason but give it a try and see if your times don’t get even better.

[Dave Lozinski]

Mike,

Yeah, I remember reading something here as well but couldn’t find it.

Anyway, will try your suggestion about the 128MB, see what difference that makes, and let you guys know.

Personally, I have 16GB of ram in my machine so setting the dynamic ram preview amount to 8GB, logically to me, shouldn’t make that much difference!

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https://www.davelozinski.com
https://www.davelozinski.com/DemoReel/
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[Mike Kujbida]

Dave, the following explanation on another Vegas forum made the most sense to me.
It was from June of 2009 so it’s pre-Windows 7 days.

If your preview RAM setting is too high it can starve your system for memory. Remember that Windows also needs RAM. If your setting is so high that it forces something (it doesn’t even have to be Vegas) to be shunted off to the page file then you’re creating unnecessary disk activity. If your preview RAM is WAY, WAY too high then you could force a system to constantly thrash the page file as it puts away and then retrieves needed parts of Vegas or the OS.

[Dave Haynie]

That’s basically it. The Preview RAM is a static allocation… Vegas grabs that RAM and holds on to it. The main use is RAM preview during editing, but it also seems to be used as buffer memory during rendering. It would kind of be a crime if it wasn’t.

A couple of problems occur. You’re more sensitive to memory-related slowdowns during rendering, and the rendering algorithms have to everything you see during editing, and then some. So you might think you’re ok with N MB set aside during editing, but you run short during editing.

“Run Short” of memory is a very bad thing. The render doesn’t fail, but Windows’ virtual memory system kicks in. Code may be dumped from memory and reloaded as needed, data may be paged to the swap file on your disc. Even with today’s fastest hard drives, paged memory is thousands of times slower than real memory. What I found was that too much preview RAM and you’ll get VM thrashing… memory, memory all around, and not a drop to drink.

You probably don’t want to drop the preview buffer entirely, though. For hard drives to hit their peak speed, they need to do reasonably large loads. It seems that Vegas is counting on this memory for some amount of buffering during rendering. With no memory, it’s forced to do more small reads. You’ll see rendering performance drop noticably, and CPU percentage drop way down, too, as the render speed gets dominated by hard drive access. Not likely an issue on single projects, but put something complex into Vegas, and you’ll see it.

-Dave

[Matt Carlson]

I can put forth a theory here after reading several weeks of better than average PC builds choking on renders. The facts in this instance are pretty straightforward. System Ram = 12GB. Setting preview ram to 8GB seems reasonable since most only have 4GB to begin with (although 8GB preview ram is probably unnecessary in most work flows.) Once the preview ram is set to 0 or 128mb render times are cut buy a factor of ten or twenty.

A GTX 460 is a reasonable card and miles ahead of say a 9800gt and the 9800gt does a serviceable job. A difference of 50+ minutes down to 2 minutes suggests something to me. Vegas may be walling off CUDA cores to run the preview ram. When it comes to final rendering CUDA is not being released and whatever small amount Vegas is leaving open is being seen as the total of CUDA cores available. This may be some small amount like ten percent or less. With only a small percentage of CUDA cores available Vegas then begins to render inefficiently because the graphics card is seen as capable but has no power left. Under these circumstances the graphics card would actually be a major hindrance. Once the preview ram is optioned back to being insignificant the GTX 460 gets back to chewing on the render the way it should.

This is only a theory but it would explain the massive inconsistency in render times.

[Steve Rhoden]

Best then setting it at 0 when you are ready to render.
And putting it back up when editing and need ram previews.

Steve Rhoden
(Cow Leader)
Film Maker
Filmex Creative Media.
1-876-832-4956
https://filmex-creative-media.blogspot.com/

[Dave Lozinski]

I ran a few tests tonight. I downloaded the latest version of Vegas too (they released version 511).

If I have the memory set to 128mb or 256mb, Vegas zips through the video with GPU accelerated encoding.

If I set any value higher than 256MB, it slows down tremendously.

I do not understand why because I have 16GB of memory in my machine, and the only thing I have up and running besides Windows is Vegas. It seriously is just a 5 minute short video with no effects other than a fade-out.

The other interesting thing is if I increase the amount of dynamic ram for the preview to number like 9000MB, generate a dynamic ram preview (which takes a long time in itself! Go figure?!), and then try to render it takes even longer.

Going to reply to another post in this thread, but I guess the lesson here is if it’s taking too long, for whatever reason try decreasing the amount of dynamic ram!

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https://www.davelozinski.com
https://www.davelozinski.com/DemoReel/
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[Dave Lozinski]

[Dave Haynie] “A couple of problems occur. You’re more sensitive to memory-related slowdowns during rendering, and the rendering algorithms have to everything you see during editing, and then some. So you might think you’re ok with N MB set aside during editing, but you run short during editing.”

Hey Dave:

I guess I don’t understand this at all. Because in my mind if I set my dynamic ram to say 8GB, I still have 8GB left (of which about 3GB is used by Windows). So there shouldn’t be any thrashing per-se.

Also, while watching the task manager during the render, the memory usage never gets close to peaking. So in my mind Vegas should be able to load large clips into memory, and then perform the render.

Having to decrease the amount of dynamic ram to 256MB when I have a machine with 16GB to speed up encoding is completely counter intuitive.

There must be something else going on of which I don’t have any idea at the moment.

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https://www.davelozinski.com
https://www.davelozinski.com/DemoReel/
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[Dave Lozinski]

[Matt Carlson] “I can put forth a theory here after reading several weeks of better than average PC builds choking on renders. The facts in this instance are pretty straightforward. System Ram = 12GB. Setting preview ram to 8GB seems reasonable since most only have 4GB to begin with (although 8GB preview ram is probably unnecessary in most work flows.) Once the preview ram is set to 0 or 128mb render times are cut buy a factor of ten or twenty.

A GTX 460 is a reasonable card and miles ahead of say a 9800gt and the 9800gt does a serviceable job. A difference of 50+ minutes down to 2 minutes suggests something to me. Vegas may be walling off CUDA cores to run the preview ram. When it comes to final rendering CUDA is not being released and whatever small amount Vegas is leaving open is being seen as the total of CUDA cores available. This may be some small amount like ten percent or less. With only a small percentage of CUDA cores available Vegas then begins to render inefficiently because the graphics card is seen as capable but has no power left. Under these circumstances the graphics card would actually be a major hindrance. Once the preview ram is optioned back to being insignificant the GTX 460 gets back to chewing on the render the way it should.

This is only a theory but it would explain the massive inconsistency in render times.”

Hey Matt:

Interesting theory! However I would say that’s not the case here because (and you wouldn’t have known this from what I’ve posted) when I first start rendering, Vegas zips through the video up until about the first 18%. Then it starts to slow down before doing like 1 frame per second.

So either it’s using the full amount of CUDA cores when it starts, or it always has the “reduced” amount as per your theory and for some reason stops using them later through the process?

One other thing I checked last night is in Task Manager I used the Resource Monitor to watch disk activity. There didn’t seem to be any noticeable difference whether I had the amount of dynamic preview ram set to 128MB or 9000MB. Eg, the disk queue length was always small. So to me, that says my hard drives aren’t being thrashed about either.

Two other changes I made to my system to see what that does is:
1) turned off the Windows Indexing Service
2) had it render out to my C drive

In both cases, with the dynamic ram set to 9000MB it eventually ground to a snails pace rendering; with 128MB it kept chugging along.

Hmmm… any other theories?

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https://www.davelozinski.com
https://www.davelozinski.com/DemoReel/
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