This patch adds a timed LRU cache implementation and a compute node info cache on top of that.
Cache entries might expire on their own (default ttl=5mins) or become invalid due to real-world events,
e.g. compute node scale-to-zero event, so we add a connection retry loop with a wake-up call.
Solved problems:
- [x] Find a decent LRU implementation.
- [x] Implement timed LRU on top of that.
- [x] Cache results of `proxy_wake_compute` API call.
- [x] Don't invalidate newer cache entries for the same key.
- [x] Add cmdline configuration knobs (requires some refactoring).
- [x] Add failed connection estab metric.
- [x] Refactor auth backends to make things simpler (retries, cache
placement, etc).
- [x] Address review comments (add code comments + cleanup).
- [x] Retry `/proxy_wake_compute` if we couldn't connect to a compute
(e.g. stalled cache entry).
- [x] Add high-level description for `TimedLru`.
TODOs (will be addressed later):
- [ ] Add cache metrics (hit, spurious hit, miss).
- [ ] Synchronize http requests across concurrent per-client tasks
(https://github.com/neondatabase/neon/pull/3331#issuecomment-1399216069).
- [ ] Cache results of `proxy_get_role_secret` API call.
