# MQTT Options

## Retry Interval

Set the time in seconds after a `QoS=1 or QoS=2` message has been sent that VerneMQ will wait before retrying when no response is received.

```
retry_interval = 20
```

This option default to `20` seconds.

## Inflight Messages

This option defines the maximum number of QoS 1 or 2 messages that can be in the process of being transmitted simultaneously.

```
max_inflight_messages = 20
```

Defaults to `20` messages, use `0` for no limit. The inflight window serves as a protection for sessions, on the incoming side.

## Load Shedding

The maximum number of messages to hold in the queue above those messages that are currently in flight. Defaults to `1000`. Set to `-1` for no limit. This option protects a client session from overload by dropping messages (of any QoS).

```
max_online_messages = 1000
```

Defaults to `1000` messages, use `-1` for no limit. This parameter was named `max_queued_messages` in `0.10.*`. Note that `0` will totally block message delivery from any queue!

This option specifies the maximum number of QoS 1 and 2 messages to hold in the offline queue.

```
max_offline_messages = 1000
```

Defaults to `1000` messages, use `-1` for no limit, use `0` if no messages should be stored.

In contrast to the session based inflight window, max\_online\_messages and max\_offline\_messages serves as a protection of queues, on the outgoing side.