# sqlalchemy.exc.OperationalError: (psycopg2.OperationalError) connection to server … failed

**Code:** `SQLAlchemy OperationalError` · **Category:** Python · **Seen on:** Python

SQLAlchemy’s DB driver raised an operational error — connection failures, lost connections or locked SQLite databases.

## Meaning

The text in parentheses is the driver’s own error: connection refused, password authentication failed, server closed the connection, or “database is locked” for SQLite.

## Common causes

- Database unreachable / credentials wrong
- Connection dropped by the server (idle timeout)
- SQLite locked by another writer
- Too many connections

## Quick fix

1. Read the driver error in parentheses
2. Use pool_pre_ping=True and pool_recycle to avoid stale connections
3. Check DATABASE_URL
4. For SQLite, avoid concurrent writers or use WAL

## Detailed fix by platform

### Python

1. `engine = create_engine(url, pool_pre_ping=True, pool_recycle=1800)`

## How to diagnose

1. **Driver error** — Text inside the parentheses
2. **Timing** — At startup or after idle?

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Source: [WhatIsMyError](https://whatismyerror.com/errors/python/sqlalchemy-operationalerror)