Cached items now periodically cleaned out
The reasoning behind the change in iOS 5 is sound; the cleaning isn't triggered until an iOS device begins to run too low on space (the exact definition of that known only to Apple) and thus removes what it considers are (or should be) temporary items to reclaim space in those situations. Content that was "cleaned" but is needed again can simply be re-downloaded. Cleaning out temporary files can also be considered a security improvement.
The problem arises, however, if needed content can't be re-downloaded -- either because the user is no longer connected to the internet, or because the only download option is using 3G, which most users have strict limits on. Long articles, large maps, downloadable graphic novels, alternative podcasts not handled by iTunes and offline Wikipedia apps, as examples, now have to put their data in the "Caches" directory, which will be deleted without the user's knowledge when the device gets too full, making them think the app was to blame for lost content.
The only alternative -- placing the data in the app's internal "Documents" directory -- means the large files will be periodically and automatically synced with iCloud, which may use up 3G data and will count against a user's 5GB of storage. Apple has begun "cracking down" on apps that try to store too much data in the "Documents" directory. As Arment explains, "There needs to be a file storage location that behaves the way Caches did before iOS 5: it's not backed up to iTunes or iCloud, it's not synced, but it's also never deleted unless the app is deleted."
Although he does not specify it, Arment and other developers have undoubtedly been in conversation with Apple about the changes in iOS 5 since before its public release (it went through an extensive beta period). A solution may be forthcoming, but Arment complains that in the meantime, users are going to be upset with apps and developers rather than Apple, even though the issue was created by a system change. This may increase support requests and cause other problems, including an eroded user experience for users who routinely keep their iDevice relatively full. [Photo of Marco Arment via Lucius Kwok]