Found a significant LR4 speedup - regenerate ACR cache

Question

Like many others here, after I upgraded to LR4, my performance went completely to hell.  It would literally take 9-10 seconds just to advance to the next image in the Develop module.  Marking an image for deletion would take 15 seconds.  I'm running a Q6600 - quadcore processor at 2.4GHz with 4GB RAM on Vista 32-bit.  By today's standards, it's not a terrific speed demon, but no slouch either and it worked fine for several years with LR3.  I mostly process D300 RAW files.
After reading a lot of posts here about crummy performance, I wasn't able to find any tips that might help so I started poking around in the preferences/settings.  One thing I discovered was that my ACR cache was perhaps getting starved a bit for size.  It was set to 50GB, but it was on a drive that might not have that much free space.  I reasoned that if the cache couldn't quite be large enough to hold my working directory of images, then it might be thrashing and pretty much never loading from the cache.
So, I moved my ACR cache to a new drive with lots of free space, increased the cache size to 100GB and then proceeded to regenerate the cache for the directory of 500 images I was working on by making a 2 point change in sharpening on all images and then regenerating all previews.  It took awhile to make all new previews for all the images, but after doing so - WOW my old performance was back again, even running on the new 2012 process.  I could move from one image to the next in the develop module in under a second.
So, I don't know if it was low disk space, some sort of general caching problem, a corrupted cache or what, but after making those ACR cache changes, my LR4 performance is back neaer where the LR3 performance was.

Answer 1

rosalynsam wrote:
I have significant problems with near lock up in LR4 and have posted a discussion (it takes HOURS to import a couple hundred photos, minutes to load a photo just to view sometimes).  There have been no suggestions in reply to my original post -so maybe I can tag along here for some assistance?  Please? In LR, I opened the preferences (in Edit) and found that my Camera Raw Cache Settings were set at 1. GB maximum size, with the Video Cache set at 3.0 GB.  Hate to be dense, but I want to be sure I am not causing with more problems.....so, I should purge cache on each first, then change maximum size to 100? Since mine is set on 1. that seems pretty drastic, since my system says it has 308 GB free out of 465. 
I have an HP server which I can can use (instead of the default C drive which it is set to). My system is less than 2 years old,  Windows 7- my processor is AMD Phenon(tm)  II x 4 925 Processor.  My hard drive back up has plenty of space -  4 terabytes.  Could Purge Cache and change these settings in any way cause another problem?  Should I change this to my hard drive -if so, would I use the same file location, except change to my server? 
I have a Mac with the same cache settings, and it is lightening fast with LR3 compared to this.  I really don't know how to ask the right questions -my knowlege about computer systems, etc. is limited.
One of my symptoms before fixing my cache was that importing was ridiculously slow (hours to import a few hundred images) so my experience does overlap with your symptoms.   How big a cache you need depends upon what you're processing and how many you work on at a time.  I presume the ACR cache (which is what I wrote about here) is mostly (or perhaps only) used for RAW images so it's most applicable if you shoot RAW.  Secondly, you need to think about your working set of images (how many you work on at a time).  What you want is a cache that is big enough to hold cached versions of every image in the set you work on.  That way, you can import the images into LR which will build previews and fill the cache in the process and then you can go back and work on your images and they will all be precached.  If your cache size is a little smaller that the working set, then by the time it gets to the end of building previews, the cache is full and it's kicking your first images out of the cache.  Then, you go to start working on the first images and there's nothing cached so it keeps having to back to the RAW file for every new image.  This is when it's going to be really slow.  OTOH, if your cache is larger than your working set, then all images you are working on in a particular shoot can stay in the cache for the duration of working on them.
I think the norm for the ACR cache is around 50GB just to make sure it's big enough for a large shoot.  1GB is miniscule and won't be doing you much good at all.