Mac App Store sometimes downloads whole apps, instead of downloading just the differential update needed.
Take the latest iMovie update which is a bug-fix update and shouldn't be larger than a couple hundred megabytes, but instead it downloads the whole 2 GB app. (This happened for Xcode 6.3.1 and downloaded the whole 2.6 GB app, while 6.3 which was a major update was OK and downloaded much less than 2.6 GB)
Recent minor updates of Pages, Keynote and Numbers were OK and each was a 30~40 MB update.
I'm aware that if the process of downloading the differential update fails (network error, etc.), Mac App Store starts to download the whole app, which is a strange behaviour itself. But in my case, it doesn't even try to download the differential update.
One observation I made, was that when I click on update in Mac App Store Updates page, it goes to 'waiting' state for a minute or two, the Launchpad icon on the Deck jumps up once (which is the case of failed download.) and then starts to download the whole app.
Measures I've already taken:
- Deleted Mac App Store temp directory (opening
$TMPDIR../C/and deleting com.apple.appstore folder)
- Restarting Mac App Store (Quitting and opening again)
- Resetting Mac App Store (using Debug menu)
- Signing out of my Apple ID and signing in again
Although occasionally downloading 2~3 GBs won't hurt me, but it would be nice to find a solution, it kinda bugs me.