Browser storage/cache size limits?

[sleidig]

How are offline applications handled by the browsers in regards to cache size? Could it become a problem if our database grows too large, so the browsers decide they need some space and delete our offline replication? This would be the absolute worst case if the user hasn't synchronized his work yet.

[sleidig]

more details citing from #54 (comment) (h/t @fschoell )

researched a bit about the cache handling of firefox and chrome (you can find some information on firefox here and about chrome here).

First, caching the application/database should be no problem in general, as the browsers mostly have a large quota limit for the cache (like 20% of the free hdd storage). However, there are a couple of possible issues with using the browsers cache to store the database:

• Firefox does offer persistent storage for an IndexedDB, but Chrome does not (see the link above). As of now, persistent storage in Chrome is only available for the file system API.
• The quota limit for the temporary cache is configurable by the user, we shouldn't rely on the default settings. If a user decides that 200 MB is enough for the cache then we could run into problems really fast.
• Even the persistent storage will be deleted if the user chooses to clean the cache.

Now, this won't be an issue most of the times. However, it can become a real nightmare if a database would be somehow deleted by either the user or the browser - this could mean that the users work is lost if he hasn't synchronized the database for a certain time. As for now we can instruct the social workers on how to setup their browsers and sensitize them to never clean the cache - but in my opinion we should not rely on the users technical understanding in the future.