Limit Item | Limit Description | Behavior After Exceeding the Limit | Recommendation |
Cluster TPS Limit | Strictly limited according to the specifications selected on the purchase page. Note: The settings of the QoS and cleanSession parameters affect TPS calculations. One TPS is not equivalent to producing or sending one message. For details, see Billing Overview. | After the TPS limit is exceeded, message production or consumption requests will be rejected and result in errors. For details, see Quota and Flow Control Instructions. You can view the relevant throttling metrics in the console. For details, see Monitoring Instructions. | When making a purchase, estimate traffic based on the actual situation. When traffic throttling occurs, you can choose to upgrade cluster specifications to handle sudden traffic spikes. |
Number of Client Connections to the Cluster | Strictly limited according to the specifications selected on the purchase page. | Client connections will be rejected, and CONNECT requests will return an error. | When making a purchase, estimate the number of clients based on the actual situation. When the number of clients reaches the upper limit, you can choose to upgrade cluster specifications. |
Number of Cluster Subscriptions | 30 x Maximum number of client connections. The number of cluster subscriptions includes shared subscriptions and automatic subscriptions. | New client subscriptions will be rejected, and SUBSCRIBE requests will return an error. When quota conflicts occur across multiple subscription scenarios, subscriptions are throttled according to the following priority: non-clean-session subscriptions > Auto Subscribe rules > manual subscriptions added by clients. For details, see Auto Subscribe Instructions. | |
Number of Topic Filters Subscribed per Client (Client ID) | 30. The number of cluster subscriptions includes shared subscriptions and automatic subscriptions. | New client subscriptions will be rejected, and SUBSCRIBE requests will return an error. When quota conflicts occur across multiple subscription scenarios, subscriptions are throttled according to the following priority: non-clean-session subscriptions > Auto Subscribe rules > manual subscriptions added by clients. For details, see Auto Subscribe Instructions. | |
Cluster Subscription Rate | Maximum number of subscription requests (MQTT SUBSCRIBE requests) that a cluster can accept per second, whose value is the greater of 100 and 1/100 of the number of client connections in the cluster specification, that is, max(100, ClientNum/100). | New client subscriptions will be rejected, and SUBSCRIBE requests will return an error. | |
Cluster Unsubscription Rate | Maximum number of unsubscription requests (MQTT UNSUBSCRIBE requests) that a cluster can accept per second, whose value is the greater of 100 and 1/100 of the number of client connections in the cluster specification, that is, max(100, ClientNum/100). | New client unsubscriptions will be rejected, and UNSUBSCRIBE requests will return an error. | |
Cluster Connection Creation Rate | max(100, ClientNum/100). If the maximum number of connections for a cluster is 10000, the number of new client connections allowed per second is 100. Up to 100 new connections can be established per second. | Client connections will be rejected, and CONNECT requests will return an error. | |
Rate of Connections with Will Messages | 100. Number of new client connections with Will messages allowed per second. | Client connections will be rejected, and CONNECT requests will return an error. | |
Limit Item Category | Limit Item | Limit Item Description | Behavior after Exceeding the Limit | Recommendation |
Resource Naming | Client ID and Alias | Unique within a single cluster. If multiple clients or devices use the same Client ID, they may take over each other, causing disconnections. Supported characters: digits 0–9, lowercase letters a–z, uppercase letters A–Z, and three special characters: Hyphen (-), Underscore (_), and At sign (@).Length: 128 bytes. | Client connections will be rejected, and CONNECT requests will be rejected. | |
| Topic Name | Channel and path for message transmission defined in the MQTT protocol. Supported characters: UTF-8 encoded characters. Length: 256 bytes. | Once the quota is reached, client PUBLISH requests will be rejected. | |
| Number of Topic Levels | 10. A topic name can contain up to 9 forward slashes (/). | Once the quota is reached, client PUBLISH or SUBSCRIBE requests will be rejected. | |
| Number of Topic Prefixes | Default: 20. | Once the quota is reached, new topic prefixes cannot be created. | |
Message Properties and Body | Message Size | 4MiB, which is the size of a complete packet. | An error will occur if the message sent exceeds the allowed quota. | |
| Content Type Property Length | 256 bytes, applicable only to MQTT 5.0. | Client connections (CONNECT) will be rejected, and PUBLISH requests will return an error. | |
| User Property Length | 8KB, applicable only to MQTT 5.0. | An error will occur if the message sent exceeds the allowed quota. | |
| Correlation Data Property Length | 8KB, applicable only to MQTT 5.0. | An error will occur if the message sent exceeds the allowed quota. | |
| Length of Message Properties (Excluding Message Body) | 16KB | An error will occur if the message sent exceeds the allowed quota. | |
| Maximum Number of Topic Aliases | Disabled by default. Up to 10 per client. | Client connections exceeding the limit will be disconnected. | |
Message Retention Rules | Retention Time for Unconsumed Messages (Including Retained Messages) | 3 days. | Messages will be deleted if they exceed the retention period. | |
| Maximum Number of Retained Messages per Cluster | 10000 | Once this limit is reached, new PUBLISH requests for retained messages will be rejected by the server. | |
Message Sending and Receiving | Maximum Number of Unacknowledged Messages (QoS > 0) Received by the Server per Session | For QoS 1 and 2 messages, the maximum number of unacknowledged messages per client is 32. | The server will disconnect the client if it receives messages exceeding the quota. | |
| Maximum Number of Unacknowledged Messages (QoS > 0) Sent by the Server per Session | For QoS 1 and 2 messages, the maximum number of unacknowledged messages per client is 16. For clients using the MQTT 5 protocol, the limit can be adjusted via the Receive Maximum setting, with a maximum of 1024. | Once the quota is reached, the server stops sending messages to the client. | |
| HTTP API | Each HTTP connection consumes one connection from the quota. Each call is counted as a QoS 1 message for TPS calculation. For details, see API Usage Details. | Once the quota is reached, any calls will return an error. | |
| Number of Queued Messages per Cluster | No quantity limit, but subject to the message retention period. | - | |
| Rate of Retained Message Publishing and Consumption per Cluster | 100 messages per second. | Once the quota is reached, message publish requests will return an error. The server will stop sending messages to the client. | |
Client Connection | Client Heartbeat Check Cycle (Keep Alive Interval) | 30–1200 seconds. According to the protocol, if the server does not receive any message within 1.5 times the Keep Alive interval, it will consider the current connection invalid. | If the interval set by the client exceeds this limit (default: 1200s), 1200s is applied. If the interval set by the client is less than 30s, 30s is applied. | - |
| Number of New Connections per Client ID | 1 per second, 10 per minute. | Client connections will be rejected, and CONNECT requests will return an error. | - |
| HTTP Query for Client Online Status | Each HTTP connection consumes one connection from the quota. Each message call is counted as a QoS 1 message for TPS calculation. For details, see API Usage Details. | API calls will fail once the limit is exceeded. | When making a purchase, estimate the number of clients based on the actual situation. When the number of clients reaches the upper limit, you can choose to upgrade cluster specifications. |
| WebSocket Connection Time | 24 hours. | Automatically disconnects when the connection time is exceeded. | - |
| Offline Client Status Retention Time | Retained for 3 days by default. For clients using the MQTT 5 protocol, the retention period can be adjusted by setting Session Expiry Interval, up to 3 days. | Client status will be deleted if it exceeds the retention period. | |
| Offline Client Status Count Limit | The cluster connection limit applies to both offline and online clients. | When the total number of online and offline clients exceeds the cluster's client connection limit, additional client connections will be rejected. | |
Certificate | Number of Server Certificates per Cluster | 3, up to 10. | - | |
| Number of CA Certificates per Cluster | 32 | Automatic or manual registration will fail once the limit is exceeded. | |
Automatic Subscription | Number of Automatic Subscription Rules | Defaults to 10, with a maximum of 20. | New automatic subscription rules cannot be created. | |
| Number of Subscriptions per Automatic Subscription Rule | Defaults to 20, with a maximum of 30. | New subscriptions cannot be added to the rule. Any additions will not take effect. | |
Shared Subscription | Maximum Number of Shared Subscription Groups per Cluster | 20 | Once the quota is reached, client subscription (SUBSCRIBE) requests will return an error. | |
| Maximum Number of Subscription Expressions per Shared Subscription Group | 10, that is, the number of filters in $share/{ShareName}/{filter}. | Once the quota is reached, client subscription (SUBSCRIBE) requests will return an error. | |
| Number of Clients per Shared Subscription Group | 1024 | Once the quota is reached, client subscription (SUBSCRIBE) requests will return an error. | |
Message Enhancement Rules | Number of Message Enhancement Rules per Cluster | 10. Each rule can have up to 10 key-value user properties, with each property value not exceeding 8KB. | Once the limit is exceeded, any requests to add new message enhancement rules will fail. | |
Other Features | Number of Propagation Properties per Client | Once the limit is exceeded, any requests to add new propagation properties will fail. You need to call the API to delete existing properties before adding new ones. | | |
| Number of Device Identities per Cluster | The limit is equal to the number of client connections to the cluster. For example, a cluster with 2000 TPS and 2000 connections supports up to 2000 device identities. | Once the limit is exceeded, calling the device identity registration API will result in an error. | |
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