Scaling PostgreSQL to power 800 million ChatGPT users

OpenAI scaled PostgreSQL to handle millions of queries per second for 800 million ChatGPT users using a single primary Azure PostgreSQL instance with nearly 50 read replicas across multiple regions. Key optimizations included offloading reads to replicas, migrating write-heavy workloads to sharded systems like CosmosDB, implementing PgBouncer for connection pooling, deploying cache locking to prevent cache-miss storms, isolating workloads to prevent noisy neighbor issues, and enforcing strict rate limiting. The architecture achieved five-nines availability with low double-digit millisecond p99 latency despite PostgreSQL's MVCC limitations for write-heavy workloads.