connections

Use the connections { ... } block to configure the SQL pool.

server "primary" {
    url "mysql://radiator:secret@db.example.com:3306/radiator";
    connections {
        max 25;
        idle-timeout 5m;
        min 2;
        min-timeout 1s;
        min-retry 250ms;
    }
}

Parameters:

• max: Maximum pool size. Default: 10.
• idle-timeout: Maximum time an idle connection above min stays in the pool. Default: 5m.
• min: Warm-pool floor. Default: 0.
• min-timeout: Warm-pool maintenance probe timeout. Default: 1s.
• min-retry: Delay between warm-pool maintenance retries. Default: 250ms.

idle-timeout accepts duration units such as 5s, 500ms, and 1m.

Idle connections at or below the configured min value are kept open. Idle connections above min are closed after idle-timeout.

Setting min to a value greater than 0 keeps a warm-pool floor of established connections, enables unreachable-server fast-skip during request routing, and starts background maintenance probes.

min-timeout accepts duration units such as 1s, 500ms, and 2s. If the timeout is too short, slow connection establishment can be treated as a failure. If it is too long, recovery from unreachable servers becomes slower.

min-retry accepts duration units such as 250ms, 500ms, and 2s. Smaller values retry warm-pool probes more aggressively. Larger values reduce probe traffic, but slow down detection and recovery.

The default min value is 0, which disables all three. Set min 1; (or higher) on production servers where fast failover and warm pools matter.

See Backend Load Balancing for further information.

Error: Setting min greater than max is a hard configuration error.

When every configured MySQL pool appears full, Radiator returns a pool-exhausted error instead of intentionally queueing behind a saturated pool.