Camera Cache function and it's relationship to XMP files

[MSA]

Hi,

I’ve been an LR user since 1.3 was available. I’m now using LR2 and have a few technical questions, al least one of which is not LR2 specific. I’ll address that one first:

I just noticed that as of mid-April (2''8), there are no xmp files in my import directories. I just realized this and found that the option “Automatically write changes into XMP” was unchecked. I’ve rechecked that option and LR2 is writing the XMP files as I type.

Also, after a time of using LR2, it became very sluggish, especially when using the adjustment brush. CS3 was also having issues, especially using the Burn Brush. Having read up on the issue, I told LR2 to relocate my cache file to a separate drive and enlarged it to 2'GB. This seemed to resolve the issues in both programs.

So now the questions:

') I kind of like the option of having the XMP files so that I can ‘take my edits’ to other programs if the need arises. Are there any disadvantages to using XMP as opposed to the LR catalog to track edits? Is DNG a better option, and if so, why?

1) What function does the Cache perform, and what is its relationship to the XMP files (if any). Does allowing XMP files lessen the impact on the cache?

2) When I re-located the cache file, I noticed that it was at .99GB, which was just .'1 GB from its max limit. Since this seemed to be the problem with the performance issues I was having, why didn’t LR flush the cache (or CS3, given that it impacted its performance as well)? It also left the .99 GB worth of .DAT files in the directory. Should one intermittently purge the cache file, or can LR be normally expected to handle this?

3) After relocating the Cache, I set the max limit to 2' GB. Is this a practical limit?

Any information at all about the cache file would be appreciated. Forgive the ‘helter-skelter’ post, as I am in the middle of my business day. Thanks for any information!

MSA

System Specs:
X2 44''+
3 GB DDR RAM
SATA HDs
ATI 18''XL
Vista Ultimate, SP1

 

[Brad Snyder]

MSA, Welcome to LR Forums.

Hi,



So now the questions:

') I kind of like the option of having the XMP files so that I can ‘take my edits’ to other programs if the need arises. Are there any disadvantages to using XMP as opposed to the LR catalog to track edits? Is DNG a better option, and if so, why?

The LR catalog will always track the edits. XMP has two primary advantages, it provides a fall-back catalog back-up strategy, even if your catalog is damaged, and recovery from backup fails, with XMP, you'll still be able to recreate your adjustments. Often called the 'Belt and Suspenders' approach. In addition, as you noted, there is some abiltity to exchange some data with XMP aware applications, (at present only Adobe Camera Raw-ACR, and LR are completely compatible). As an example, our Guru Victoria post-processes wedding images for other photographers. They send her raws, she sends back just the XMP sidecars, since they already have the originals. Drastically saves bandwidth, etc. There are numerous threads here already discussing DNG vs raw. In fact I wrote something just yesterday. If you can't find the pertinent threads, follow-up. One gotcha to look out for, the XMP autowrite settings are selected on a per catalog basis, rather than global, so if you have more than one catalog, and should you create a new catalog(s) make sure to turn it on, if that's what you want. [I always leave it on]
1) What function does the Cache perform, and what is its relationship to the XMP files (if any). Does allowing XMP files lessen the impact on the cache?

[COLOR=#''''ff]I don't completely understand all I know about this. There are two caches, in fact. There is a preview cache, which lives in a folder which by default is parallel and alongside your catalog. I believe these are used for expediting display updates/scrolling outside the Develop module. There is also the Camera Raw cache, which I believe you are referring to, which is speculated to be used for expediting scrolling/image navigation within the Develop module. If this is clearly documented somewhere, I'd love to see the reference. This is my current take on how it works. XMP settings have no effect, other that the potential for shared I/O bandwidth. But XMP data is tiny <1' kB per image.
[/COLOR]
2) When I re-located the cache file, I noticed that it was at .99GB, which was just .'1 GB from its max limit. Since this seemed to be the problem with the performance issues I was having, why didn’t LR flush the cache (or CS3, given that it impacted its performance as well)? It also left the .99 GB worth of .DAT files in the directory. Should one intermittently purge the cache file, or can LR be normally expected to handle this?

[COLOR=#''''ff]No idea. Anybody? [/COLOR]

3) After relocating the Cache, I set the max limit to 2' GB. Is this a practical limit?

[COLOR=#''''ff]I've seen numbers of 1' to 3' GB bandied about as an effective size.[/COLOR]



System Specs:
X2 44''+
3 GB DDR RAM
SATA HDs
ATI 18''XL
Vista Ultimate, SP1

 

[MSA]

MSA, Welcome to LR Forums.

Thanks, Brad, for the welcome and the response and pointers. Subsequent research has revealed that, as you have stated, there is no real relationship between xmp files and the CR Cache. I still haven't found out why LR2 didn't maintain the CR Cache to avoid these issues. Hopefully Adobe will come up with an update that will resolve many of these issues and the point will become moot.

Thanks again for your response,

MSA

 

[Brad Snyder]

Yes, it's probably further down on the priority list. Each change is not just about writing the code, but about all the QA and documentation that has to go with it. In this case, it's at least twice as bad, because Adobe Camera Raw, is a separate product, and a separate development team, so that all has to be coordinated, not always a straight-forward task in a large corporation.

I'm sure it all makes sense somewhere, but it sure seems like sometimes the hard stuff is easy, and the easy stuff is hard.

 

[Victoria Bampton]

1) What function does the Cache perform, and what is its relationship to the XMP files (if any). Does allowing XMP files lessen the impact on the cache?

[COLOR=#''''ff]I don't completely understand all I know about this. There are two caches, in fact. There is a preview cache, which lives in a folder which by default is parallel and alongside your catalog. I believe these are used for expediting display updates/scrolling outside the Develop module. There is also the Camera Raw cache, which I believe you are referring to, which is speculated to be used for expediting scrolling/image navigation within the Develop module. If this is clearly documented somewhere, I'd love to see the reference. This is my current take on how it works. XMP settings have no effect, other that the potential for shared I/O bandwidth. But XMP data is tiny <1' kB per image.
[/COLOR]
2) When I re-located the cache file, I noticed that it was at .99GB, which was just .'1 GB from its max limit. Since this seemed to be the problem with the performance issues I was having, why didn’t LR flush the cache (or CS3, given that it impacted its performance as well)? It also left the .99 GB worth of .DAT files in the directory. Should one intermittently purge the cache file, or can LR be normally expected to handle this?

[COLOR=#''''ff]No idea. Anybody? [/COLOR]

Hi, welcome to the forum!

The cache speeds the loading of raw data into Develop module when viewing a photo that you've recently viewed. It flushes as it goes, so once it reaches its limit, it'll throw away the earliest preview and replace with a new one, so imagine a conveyor belt. The bigger the cache, the more recent photos you can load from the cache (quicker than original file).

 

[MSA]

Thanks for the Welcome and the information, Victoria!