List cache keys

[albertforweb]

i don't see an api for listing keys in cache, and think such api will be helpful for determining whether desired keys exist or not.

[thibaultcha]

This does not make much sense to me given the multiple layers of caching, multiple possible states of cached items (e.g. fresh, stale, re-validating, negative vs. positive cache, etc...), the discrepancies that may exist between these layers (e.g. item in L2 but evicted from L1), the performance or feasibility challenges in retrieving/building this list even for L1/L2. Not opposed to the feature if the API is really well designed, keeps it simple, and is well implemented (e.g. perf), but I doubt anybody will implement this.