Lightroom cache files

<p>I'm still using LR 2.7, and in preparation for installing LR 3.0, I decided to clean up some files.</p>

<p>I have ~800 LR Cache files (Cachennnnnnnn.dat) dating from January to May, each ~8MB in size.</p>

<p>Which of these can I delete? Can I just delete them in the OS (Win Vista), or do I need to tell LR about removing them in some way?</p>

<p>Thanks,</p>

<p><Chas><br /><br /></p>

<p>Based on the filename these are in the Camera Raw cache (right?). Yes, you can just delete them, though you don't need to -- LR3 may use them, improving your performance in the Develop module (and for other image rendering tasks such as printing, exports, and preview generation).</p>

<p>The Camera Raw cache includes partially-cooked image files -- the raw files are demosaiced and some initial processing is done. The rendering engine reads these files rather than the original disk files. If you clean out the Camera Raw cache, it will recreate these files as needed.</p>

<blockquote>

<p>..and for other image rendering tasks such as printing, exports, and preview generation)</p>

</blockquote>

<p>My understanding, and I could easily be wrong, is the cache is only used in Develop. I thought the other tasks mentioned were using the irdata data. </p>

<p>You're not completely wrong. <em>User interaction</em> in the other modules uses the rendered previews in the Previews database (the .lrdata file (note that's a lower-case L as in LightRoom, not a lower-case I as in InfraRed)).</p>

<p>However, when you Export, Print (except draft mode), or generate previews, the data is rendered from the original data, not from the previews. If it's already in the Camera Raw cache it'll start there, otherwise the original file will be read, partially processed into the Camera Raw cache, and the rest of the process will work from there.</p>

<p>Think of it this way -- if the largest preview you've got is a 1680 pixel wide "standard preview" but you're exporting or printing a file bigger than that, the data has to come from somewhere...</p>

<blockquote>

 

<p>Think of it this way -- if the largest preview you've got is a 1680 pixel wide "standard preview" but you're exporting or printing a file bigger than that, the data has to come from somewhere...</p>

 

</blockquote>

<p>That makes sense of course. So if (using your example), I have preference’s set for 1680, smaller requests would use the .lrdata data and naturally, if something needed to be bigger, it would have to go to the ACR cache. <br>

One thing I’ve done recently is update the location of the ACR cache from where it normally is (on the Mac, it was deep in the Library), to the same drive as the images and other LR files so that when I clone this data to take on location, its available. I still keep it kind of on the low side as tests I did after comments from Ian Lyons about the speed it in having to build em from scratch seemed to indicate that keeping 200 gigs isn’t a good use of space. I have it set for 20 gigs which I think should be plenty for a rolling cache.</p>

<p>Not exactly. The rendering engine will always go for the ACR cache (and will populate it if it doesn't find what it needs). Develop, Export and Print (except draft) always go to the rendering engine.</p>

<p>Draft-mode printing and Library go to the preview cache (the .lrdata database) first. If what they need isn't in there, it is populated using the rendering engine (see above).</p>

<blockquote>

<p>Export and Print (except draft) always go to the rendering engine.</p>

</blockquote>

<p>Got it.</p>

<p>Seems pretty definitive to me. I'm going to delete all but the most recent.</p>

<p>Thanks Mark and Andrew</p>

<p><Chas><br /><br /></p>

<p>Let me amend what I wrote above: When you work in the Print module, you're working with previews. When you press the Print button (except draft mode), it goes to the rendering engine just as it does for Export. The same is true for Slideshow and Web. I apologize for any confusion that may have caused...</p>

<p>Thanks Mark. I understand. I appreciate, and like, LRs process of "rendering to order" and go so far as to not keep exported images, knowing that I can recreate them at will.<br>

<Chas></p>