iOS 8 caching bug

2016-11-25 13:51:49 UTC

Denne artikel findes pt. kun på engelsk.

 

Recently we have received incident reports from users stating that the app takes up too much disk space. This happens even though a user deletes all newspapers in an app.

After investigating the issue we have now found the cause.
First of all the issue is not critical - since the used disk space resides in a place where the OS is allowed to purge the data at any time.
Secondly the problem lies in iOS 8 and is observed by many developers and users. 

Here is a detailed explanation of the issue:

When the app downloads content from the web, the internal mechanism is ‘smart’ enough to cache the contents, so that the same request repeated does not need to ask the server, but can be fulfilled with the cached contents.
This is good for many purposes, but when downloading the contents of your newspapers, this caching is both unnecessary and unwanted.
Apple has made functionality to control the caching in a very fine grained manner. This functionality has been available since iOS 2.0. With the release of iOS 8, however, it stopped working properly.
The following pages describe the exact nature of the iOS 8 caching bugs in high detail with code examples that allows us to reproduce and verify the OS bugs.

http://blog.airsource.co.uk/2014/10/11/nsurlcache-ios8-broken/

http://blog.airsource.co.uk/2014/10/13/nsurlcache-ios8-broken-2/

As you can read from the above links, the complete control over the caching behavior got broken with iOS 8. 

With the release of iOS 8.1 Apple has fixed a lot of the functionality of the caching mechanism. Unfortunately there is still an issue related to caching which have not been fixed yet. We have executed a test with a Visiolink app which shows the improvement and difference between iOS 8 and iOS 8.1:

Results from the app running iOS 8.0.2:

- App downloaded but not opened: 11,1 mb

- App opened: 17,2 mb

- Five newspapers downloaded: 703 mb

- All newspapers deleted: 283 mb

- App closed on device: 281 mb

- App opened 284 mb

Total added mb: 272,9 mb

Results from the app running iOS 8.1:

- App downloaded but not opened: 12,5 mb

- App opened: 15,4 mb

- Five newspapers downloaded: 347 mb

- All newspapers deleted: 30,7 mb

- App closed on device: 29,2 mb 

- App opened: 29,7 mb

Total added mb: 17,2 mb

We recommend all users of iOS 8 to upgrade their devices to iOS 8.1 and hope that Apple will fix the last caching issue with their next OS release. 

If you have any questions in relation to the above, please feel free to send our Customer Care an email on support@visiolink.com

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