While discussing with :baku about bug 1115820 he suggested to add telemetry to Service Worker Cache as well so here is the bug. I could take it once I finish bug 1115820. :bkelly, it would be nice if you could add a list of what things you find interesting to know about (e.g. :baku proposed something like 'from a fetch request to the actually response, how long does it take').

Statistics about the number of entries stored in the cache and whether for example they include URLs with query string (and other things that we treat specially in cache) would be nice to have.

I thought I had a bug for this, but can't find it. I think there are a few classes of things to capture here: * Time performance (time to match, time to put, etc) * Database usage info (how many Cache objects, how many entries per Cache, how large is the security info column in practice, etc.) * API usage info (do people really use ignoreSearch, how often do we really see VARY headers, etc) To be honest, I have no experience with the telemetry system. It strikes me, though, that it could be difficult to get stats on the database structure. We can't just up a counter when a request comes through. Instead we have to open the database and inspect it in detail. This could be challenging to do efficiently, etc.