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## Problem A user can perform many database connections at the same instant of time - these will all cache miss and materialise as requests to the control plane. #5705 ## Summary of changes I am using a `DashMap` (a sharded `RwLock<HashMap>`) of endpoints -> semaphores to apply a limiter. If the limiter is enabled (permits > 0), the semaphore will be retrieved per endpoint and a permit will be awaited before continuing to call the wake_compute endpoint. ### Important details This dashmap would grow uncontrollably without maintenance. It's not a cache so I don't think an LRU-based reclamation makes sense. Instead, I've made use of the sharding functionality of DashMap to lock a single shard and clear out unused semaphores periodically. I ran a test in release, using 128 tokio tasks among 12 threads each pushing 1000 entries into the map per second, clearing a shard every 2 seconds (64 second epoch with 32 shards). The endpoint names were sampled from a gamma distribution to make sure some overlap would occur, and each permit was held for 1ms. The histogram for time to clear each shard settled between 256-512us without any variance in my testing. Holding a lock for under a millisecond for 1 of the shards does not concern me as blocking