PostgreSQL Connection Pooling at Scale

Every .NET developer knows Npgsql connection pooling. At 200+ application instances, client-side pooling isn’t enough — you exhaust PostgreSQL’s max_connections.

Architecture

App (pool: 10) → PgBouncer (pool: 100) → PostgreSQL (max: 200)

PgBouncer Config

[databases]
app = host=postgres port=5432 dbname=app

[pgbouncer]
pool_mode = transaction
max_client_conn = 1000
default_pool_size = 20
reserve_pool_size = 5

Transaction pooling works for our read-heavy workload. Avoid for apps using prepared statements or session-level settings.

Numbers

Setup	Max concurrent apps	PG connections used
Direct	~20	200 (saturated)
PgBouncer	200+	~80 average

Pitfalls

• DISCARD ALL after each transaction in transaction mode
• Long-running transactions block pool slots
• Monitor pgbouncer_pools for waiting clients