All The Get Alls

[jnunemaker]

In testing preload_all with Flipper::Cloud, I found that the memoizing and caching adapters weren't working correctly with get_all (which preload_all uses). Several things were subtly not right causing extra net/http calls. I added several specs that verify the number of network calls and tested externally with a few apps I control. This also adds get_all to all the adapters flipper supports out of the box. This ensures that when possible preload_all and get_all do the fewest network calls.

There is some funny business with caching and get_all. The trick with get_all and caching is you don't know the features so you can't do a get_multi for all features. This left two obvious options:

1. wrap the entire get_all call with its own cache fetch block.
2. add an extra network call to avoid calling get_all more than necessary when using a caching adapter.

Option 1 meant get_all would be 1 network call which was dope. The downside was it would not share the primed caches from get and get_multi. Additionally, it would mean that all features would need to fit in a single cache value (usually 1MB with memcached). Probably fine, but I didn't want to make assumptions.

Option 2 was to do an unless exists get_all key. If the key was present, then we are moderately sure that both the set of feature keys and each feature is cached, so the cache adapters do at least 2 network calls (get the set of feature keys and then get_multi all the individual feature cache values). The upside is this shares the per feature cache values with get and get_multi. Another upside is that because the cache is per feature, having a lot of features won't overflow a single value like option 1. The downside of this is a minimum of 3 network calls. I guess I'm assuming that cache calls are super fast, so 3 small ones that share between many adapter methods is better than potentially 1 big one that doesn't share.

[jnunemaker]

Looks like rails 3.2 failures... I'll look at them, get this merged and release 0.11

[jnunemaker]

It seems unless_exist wasn't added until rails 4, which is why rails 3 tests are failing.

xref rails/rails@b5005b6