PostgreSQL Advisory Locks for Distributed Rate Limiting

Using pg_try_advisory_xact_lock with connection pooling (PgBouncer in transaction mode) to implement sliding-window rate limiting directly in PostgreSQL, eliminating the Redis dependency for startups running lean infrastructure. Covers the lock namespace design for per-user and per-endpoint buckets, the gotchas of advisory locks with prepared statements in Ktor/Exposed, and benchmarks showing where this pattern breaks down (spoiler: around 15k req/s per node) versus where it saves you $200/mo and an entire failure domain.