LR4 and Camera RAW Cache folder

Question

Hi all,
I know many are complaining about LR4 responsiveness and how LR3 was faster in response.
Like many others, I have a new and very fast PC, however it seems that LR4 is crawling when it comes to navigtaing through images.
I've done my share bit of tweaking LR4 to get the best optimized results such as, Optimize catalogs, Render 1:1 previews, Increase Camera Raw cache size to 30GB, move the Camera Raw Cache folder next to the catalog folder as Adobe recommends and what not.
LR4 didn't become more responsive, however I did notice something strange, which is the topic of this post.
While filddeling around with LR4 performance issues on my PC, I've noticed that even though I have over 20,000 images in my PC and some folders are rendered with 1:1 previews, the Camera Raw Cache folder is empty.
This might explain why rendering 1:1 previews didn't affect LR4 while browsing images.
For example, right after I've created the 1:1 previews (whether it's straight from import or after the fact) I'm browsing back and forth during this browsing action, LR4 renders the 2 images each and every single time I view them - that beats the purpose of using the cache folder.
So one comes to think how could it be that with such a catalog size and 1:1 previews, the camera raw cache folder remains empty? And could this be the cause that makes LR4 render each and every single image time and time again regardless if I viewed the image a second ago?
Thanks.
Gil.

Answer 1

Firstly, to clarify, Previews and Camera RAW files are not the same thing. Previews are simple, just jpeg representations of the raw file, at various resolutions used principally in the Library module and filmstrip.
Camera RAW cache files are used by the Develop module and contain the output from some initial RAW processing. I don’t remember exactly what processing but about half that LR needs to do to render an image. This processing is done regardless of what you actually do in the Develop module so it is done once, then cached. This is why the “Loading” appears to take longer when you initially browse to an image in the Develop module. The rest of the RAW processing (about half) is done every single time you browse away from the image and back again. This is why you always get CPU spikes when browsing through images in the Develop module. So you can create as many 1:1 previews as you like, this will have no impact whatsoever on image rendering performance in the Develop module.
So to answer your question specifically,
Can you be more specific about when exactly does this folder being populated?
A camera raw cache file is generated when you browse to an image whilst in the Develop module. Files continue to be generated until the cache size limit is reached, then as new files are generated, the oldest are deleted.