Maybe it's you, or your library...
Great to see issues fixed, but I am still amazed at how absolutely inefficient Aperture is.
Incredibly slow. Yes. I have a large library. Yes, the images are large. But, isn't this the professional-level library management tool?
The issue I have here is that I know it is possible to do much better. Software can (and does) scale much better - and it isn't the hardware I'm running on

.
I think performance, scalability, and responsiveness is the next thing Apple needs to focus on here.
Have no clue what you are running A3 on, or how much ram you have, and where your library is stored, so I will leave that alone (but could be obvious culprits). I have a large library, of large images and recently just topped the 100,0000 mark on my main library.
Previously I was running A3 on an iMac 24" with 3gb of ram, or thereabouts. It ran fine, not amazingly, but adequate. Last year I upgraded to a 27" iMac with 16gb ram. I also moved the image library to the internal hard drive. Obviously the more ram the better, so max it out. It isn't that expensive when you buy it third party from Crucial or elsewhere.
About a month ago, I noticed A3 starting to creep, and bog down a bit. If I made an album with selections it would lag and stall for increasingly longer bits of time. After I hit the 3-4 minutes for the album to render, I knew there were issues. Faces & Places were off, so I knew it wasn't that.
First off, I made sure I backed up the library before I started mucking about. Then I repaired my permissions with Disk Utility.
Then using Aperture's First Aid tools, I repaired the Aperture library Permissions, followed by a Repair of the Database. (see
http://support.apple.com/kb/HT3805).
I also, deleted and rebuilt my thumbnails (see here:
http://brettgrossphotography.com/2008/04/24/aperture-library-slimming-the-size).
Or you can easily do it by "You can easily do the same thing for aperture 3 by right clicking the library, select open package contents, then delete the thumbnail folder within the package.... no terminal commands required. Then the next time you open the library, aperture will rebuild thumbnails for any photos still in the library." (
https://forums.macrumors.com/threads/911505/).
I also deleted my previews & regenerated new ones... which took a few clicks, and a bit of time to generate the new ones (see below).
Click for large view -
Uploaded with Skitch
and then to generate new ones...
Click for large view -
Uploaded with Skitch
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There is a good deal of discussion about whether using Aperture's First Aid fixes the previews & thumbnails. I have no idea, however, just doing the First Aid didn't solve my issue, and so continued on with the other steps. I suspect that choice number three (Rebuild Database) would do all of it, by is a LAST choice for good reason, and avoided in my case.
All of this took a good bit of time to accomplish, about half a day or six hours. However, the end result was a resounding success for me. A3 was as zippy as the first day I installed it on my 27" iMac. I could create albums in seconds, and scrolling about was a breeze again, with nary a beach ball in sight. A I would also point out, if you can break up your library into smaller ones, do so. I have three now, and switching between them is a click away. Aperture is an amazing, mostly rock solid PROFESSIONAL app for me. I use it every single day, and have shifted vast chunks of my workflow away from Photoshop (all for the better) .
Cheers & good luck,
Michael