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0fe8b55427
Introduces the rate_limiter, a replica-side data structure meant for tracking the frequence with which each partition is being accessed (separately for reads and writes) and deciding whether the request should be accepted and processed further or rejected. The limiter is implemented as a statically allocated hashmap which keeps track of the frequency with which partitions are accessed. Its entries are incremented when an operation is admitted and are decayed exponentially over time. If a partition is detected to be accessed more than its limit allows, requests are rejected with a probability calculated in such a way that, on average, the number of accepted requests is kept at the limit. The structure currently weights a bit above 1MB and each shard is meant to keep a separate instance. All operations are O(1), including the periodic timer.