iOS 5 brought a lot of changes for users and application developers, but a good part of them were not presented by the Apple company. A very important one has to do with how applications save data in the cache and how this cache is deleted. Apple has in iOS 5 a system for automatically deleting the cache when the available space on our terminals falls below a certain value. When that value is reached, the system goes into operation and deletes all the cache together with all the data in it. Until iOS 5, this did not happen and important data such as articles saved by Instapaper, for example, were saved in the cache to be read offline.
A common scenario: an Instapaper customer is stocking up on an iPad for a long flight. She syncs a bunch of movies and podcasts, downloads some magazines, and buys a few new games, leaving very little free space. Right before boarding, she remembers to download the latest issue of The Economist. (I think highly of my customers.) This causes free space to fall below the threshold that triggers the cleaner, which — in the background, unbeknownst to her — deletes everything that was saved in Instapaper. Later in the flight, with no internet connectivity, she goes to launch Instapaper and finds it completely empty.
In practice, iOS 5 deleted all the cache together with the data in it when the space available on the terminals reached a certain value. In iOS 5.0.1 Apple solved the problem by giving users and developers the possibility to mark certain files so that the deletion system will pass over them and leave them in the system. The change is important because articles saved in applications like Instapaper will remain there, but the same thing will happen to many other types of data available in our iDevices.
