#rust

Rust language and Tokio

1. Connection pooling vs read replicas for a 50k-member forum

   We used to raise `max_connections` whenever p99 login latency spiked. After about 4_000 concurrent sessions that stopped working — the wait moved to row locks on `topic_subscript...

2. Caching UserSummary in Valkey without stale display names

   UserSummary on every comment used to cost 3 SQL round-trips. We cache it in Valkey for 45s keyed by `user:{id}:summary`. The failure mode is a display-name change that stays stale...