# ERROR 53300: Too many connections

Source: https://www.bytebase.com/reference/postgres/error/53300-too-many-connections/

---

## Error Message

```sql
ERROR: sorry, too many clients already
DETAIL: All connection slots are currently in use.
HINT: Consider increasing max_connections (currently 100).
```

## Description

This error occurs when you try to connect to a PostgreSQL server that has already reached its maximum number of concurrent connections. The server rejects new connections to prevent overloading system resources.

## Causes

- Application connection leaks (connections not properly closed)
- Insufficient connection pooling
- Database under heavy load with many clients
- `max_connections` parameter set too low for your workload
- Long-running queries or transactions holding connections

## Solutions

1. **Implement connection pooling** with tools like PgBouncer:

   ```bash
   # Example PgBouncer configuration in pgbouncer.ini
   [databases]
   mydb = host=localhost port=5432 dbname=mydb

   [pgbouncer]
   pool_mode = transaction
   max_client_conn = 1000
   default_pool_size = 20
   ```

2. **Terminate idle connections** to free up connection slots:

   ```sql
   -- Find idle connections
   SELECT pid, datname, usename, state
   FROM pg_stat_activity
   WHERE state = 'idle' AND current_timestamp - state_change > interval '10 minutes';

   -- Terminate specific connection
   SELECT pg_terminate_backend(pid);
   ```

3. **Increase the maximum connections** (requires server restart):

   ```sql
   -- Check current setting
   SHOW max_connections;

   -- In postgresql.conf:
   # max_connections = 200
   ```

4. **Fix connection leaks** in your application code:
   - Ensure connections are closed in finally blocks
   - Use connection pooling libraries
   - Set appropriate connection timeouts

## Prevention

- Use connection pooling in your application
- Monitor connection usage regularly
- Set appropriate timeouts for idle connections
- Design applications to use fewer connections (batch operations, shorter transactions)