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+---
+title: Use Connection Pooling for All Applications
+impact: CRITICAL
+impactDescription: Handle 10-100x more concurrent users
+tags: connection-pooling, pgbouncer, performance, scalability
+---
+
+## Use Connection Pooling for All Applications
+
+Postgres connections are expensive (1-3MB RAM each). Without pooling, applications exhaust connections under load.
+
+**Incorrect (new connection per request):**
+
+```sql
+-- Each request creates a new connection
+-- Application code: db.connect() per request
+-- Result: 500 concurrent users = 500 connections = crashed database
+
+-- Check current connections
+select count(*) from pg_stat_activity;  -- 487 connections!
+```
+
+**Correct (connection pooling):**
+
+```sql
+-- Use a pooler like PgBouncer between app and database
+-- Application connects to pooler, pooler reuses a small pool to Postgres
+
+-- Configure pool_size based on: (CPU cores * 2) + spindle_count
+-- Example for 4 cores: pool_size = 10
+
+-- Result: 500 concurrent users share 10 actual connections
+select count(*) from pg_stat_activity;  -- 10 connections
+```
+
+Pool modes:
+
+- **Transaction mode**: connection returned after each transaction (best for most apps)
+- **Session mode**: connection held for entire session (needed for prepared statements, temp tables)
+
+Reference: [Connection Pooling](https://supabase.com/docs/guides/database/connecting-to-postgres#connection-pooler)