Swift/ideas/memoize lookups

Reduce memcache network lookups

Each Swift proxy server normally shares a single (per-region) memcache pool. The proxy checks this pool for account and container info. While faster than going to disk to get this, it's a common operation that has a (1 - 1/N) chance of going to a different proxy server, where N is the number of proxy servers.

We already have an LRU cache that can be used as a decorator to memoize functions. We could use this to store account and container info in the local proxy, similar to https://gist.github.com/notmyname/c4ca69c1ebf85079b673b6b153bb5bb9

Obviously this needs to be profiled to see if there's any benefit whatsoever (I haven't done that yet). Also, the idea of tiering caches has likely side effects about when the cache is invalidated or when data is expected to be accurate in the cluster. Some things like ratelimiting or quotas might be adversely affected. Other operations like normal reads and writes may be improved.

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