Database Connection Pooling at Scale: PgBouncer + Multi-Tenant Postgres (10K Concurrent Connections)

Last month, I watched our production Postgres cluster melt down at 3 AM. We’d hit 8,000 concurrent connections, memory usage spiked to 94%, and our carefully tuned indexes became irrelevant. The database was spending more time managing connections than executing queries. Sound familiar? Here’s what the PgBouncer documentation won’t tell you: simply throwing connection pooling at the problem doesn’t magically solve high-concurrency issues. I’ve seen teams install PgBouncer, pat themselves on the back, and then wonder why their database still chokes under load. The reality? Most connection-pooling implementations are fundamentally flawed for multi-tenant architectures at scale.