“WTF”, I muttered to myself sometime during the last year when I ran OmniDiskSweeper, and discovered that the Thumbnails folder inside my Aperture Library was well over 150GB. So I started looking around for what to do about it.

These posts on Aperture performance and Thumbnail disk usage, in particular, helped me get to courage to take the steps I outline below.

• In April this year, Klaus posted, Tip: Reduce Thumbnail File Sizes in Aperture 3
• Just previously, Klaus had also posted Aperture 3 Performance Fix – Make Slow Aperture Run Faster (and referenced Matthew Bergsma’s work at the Apple Discussions board.)
• In May, Mike Comeau’s ApertureLand Blog posted 12 Easy Ways to Make Aperture 3 Run Faster (and this referenced Klaus’s ‘Clear out your Cache’ tips!)

OK.  So these are the steps I followed:

1. First of all, my Aperture Library began in early 2007 as a import from iPhoto to Aperture 1.5, and has been upgraded to Aperture 2, Aperture 3 (man, that was a long wait) and now, 3.1.1.  I’m running on a 2.3GHz MacBook Pro, maxed out with 3GB of memory. I mostly use Referenced Masters with my Aperture Library on my Macbook Pro, and my Masters on external drives (a Drobo, but that’s another story….)  My Aperture Library had about 213K images across 754 projects.
2. I backed up my Macbook Pro’s hard drive using SuperDuper.
3. I followed Klaus’s steps and cleared out my cache.
4. Then on Sunday, November 28th, yikes, following Klaus’s steps, I deleted the Thumbnails folder inside my Aperture Library (and the available space on my hard drive when from about 15GB to 171GB!)
5. Then I started Aperture, noticed the ‘Processing’ indicator and opened the Activity window, and saw a status count incrementing (to 212,787!)
6. I mostly let Aperture alone as it generated new Thumbnails.  Over the course of the next two weeks, it did occasionally seem to freeze on me.  I’d do a Force Quit, and restarted it, and the Activity Window would show it counting forward, this time to a reduced target.
7. On weekends, when I just left the machine otherwise idle, it would seem to generate about 15K thumbnails.  On weekdays during the day, I’d need to do my daytime job (email, web, powerpoint), so it would keep running, but generate the Thumbnails at a slower rate.
8. I was due to leave on business travel on Monday, December 13th, and, based on my  estimates, it would have been completed, but for most of that Friday evening, Saturday, and Sunday, was working in Aperture producing Photo Books for Christmas gifts, and I cancelled the Thumbnail regeneration activity while working on the books.
9. When I left on Monday midday for my business travel (taking my old 12” Macbook Pro) I left my machine cranking away generating Thumbnails with 51K still to complete.
10. I returned Saturday, December 16, to find the Activity Window empty of activities, with all Thumbnails finally regenerated.  When I selected Aperture to poke around, it froze.  I did a Force Quit on it, rebooted the Macbook Pro, and everything seems fine  and fast.
11. The Thumbnails folder in my Aperture Library went from 155GB to 95GB, still a pig, but with about 16 days of continuous processing, I had reduced it by 60GB!!  And my hard drive now had just under 75GB head room.   It was a long and tedious journey, but worth it.

Special Thanks to @TechPatio, @ApertureLand and Matthew Bergsma of the Pacific Northwest.