Question

I want to know, when Apple AppStore pushes an application updates to the user, and when the user chooses to download that application update, is it a partial updates or is it a complete reinstall for the application?

Assuming an extreme case, the developer only updated one image in the application and he submitted the updates to the app store, does apple smartly delivers the updated portion of the app, or it blindly redeliver the whole new application to the end user as an update?

Answer 1

It is a complete download and reinstall of the entire application binary, with only user data being preserved. This is to mitigate any otherwise irreversible corruptions during the update, since if the update itself is corrupted then it’s just a matter of rolling back to what was previously installed on a device, preventing user data loss.

From Apple’s developer docs:

When a user downloads an application update, iTunes installs the update in a new application directory. It then moves the user’s data files from the old installation over to the new application directory before deleting the old installation. Files in the following directories are guaranteed to be preserved during the update process:

• <Application_Home>/Documents

• <Application_Home>/Library

Although files in other user directories may also be moved over, you should not rely on them being present after an update.

It doesn’t say out loud that it’s a complete reinstall, however the first paragraph makes it quite clear why it is.