# sqlalchemy.exc.TimeoutError: QueuePool limit of size 5 overflow 10 reached, connection timed out, timeout 30

- **ID:** `python/sqlalchemy-connection-timeout`
- **Domain:** python
- **Category:** network_error
- **Verification:** ai_generated
- **Fix Rate:** 80%

## Root Cause

The connection pool is exhausted because too many connections are in use, and the timeout is exceeded waiting for a free connection.

## Version Compatibility

| Version | Status | Introduced | Deprecated |
|---------|--------|------------|------------|
| 3.x | active | — | — |

## Workarounds

1. **Increase pool_size and overflow, and ensure connections are closed** (85% success)
   ```
   engine = create_engine('postgresql://user:pass@localhost/db', pool_size=20, max_overflow=40, pool_timeout=60)
   ```
2. **Use context managers for sessions to ensure closure** (95% success)
   ```
   with Session() as session:
    session.query(User).all()
   ```

## Dead Ends

- **Increasing pool_size without monitoring usage** — This may mask the underlying issue of connection leaks. (50% fail)
- **Restarting the application** — Connections may leak again if not properly closed. (70% fail)