# max\_ack\_pending

Aliases:

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`max_pending`, `max_inflight`

Hot Reloadable

Existing sessions pick up the new value, but each subscription captures its own limit when it is created, so only subscriptions made after the reload are governed by it.

This is the amount of QoS 1 messages the server can send to a subscription without receiving any `PUBACK` for those messages. The valid range is \[0..65535].

The total of subscriptions' max\_ack\_pending on a given session cannot exceed 65535. Attempting to create a subscription that would bring the total above the limit would result in the server returning `0x80` in the `SUBACK` for this subscription.

Due to how the NATS Server handles the MQTT `#` wildcard, each subscription ending with `#` will use 2 times the `max_ack_pending` value. Note that changes to this option is applied only to new subscriptions.

## Types

| Type      | Description | Choices |
| --------- | ----------- | ------- |
| `integer` | -           | -       |