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The exclusive subscription allows mutually exclusive subscriptions to topics. Only one subscriber is allowed to subscribe to a topic at a time. Other subscribers will not be able to subscribe to the corresponding topic until the current subscriber unsubscribe the subscription.
The prefix and example of exclusive subscriptions:
| Example | Prefix | Real Topic Name |
|---|---|---|
| $exclusive/t/1 | $exclusive/ | t/1 |
When a client A subscribes to $exclusive/t/1, other clients will fail to subscribe to $exclusive/t/1 until A cancels the subscription to $exclusive/t/1 .
Note: Exclusive subscriptions must be prefixed with $exclusive/, in the above example, other clients can still successfully subscribe via t/1.
Subscription error code
| Code | Reason |
|---|---|
| 0x8F | use $exclusive/ without exclusive subscription enable |
| 0x97 | A client has already subscribed to this topic |
Configuration settings
Exclusive subscription is disabled by default and can be configured in etc/emqx.conf:
| configuration | type | default | description |
|---|---|---|---|
| mqtt.exclusive_subscription | boolean | false | default switch for exclusive subscription |
| zone.external.exclusive_subscription | boolean | not set | switch for exclusive subscription on external zone |
| zone.internal.exclusive_subscription | boolean | not set | switch for exclusive subscription on internal zone |
If the value of exclusive_subscription is not set on the zone, EMQX will use mqtt.exclusive_subscription to determine whether the function is enable.
