Message Queue (MQ)
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Usage Restrictions
MQ usage restrictions are as follows:
Service Restrictions
| Item | Limit Value | Description |
|---|---|---|
| Total number of topics that users can create for a message queuing service | 5 | |
| Total number of subscriptions that users can create to a topic | 5 | |
| Message body size | 256KB | Over-quota messages will be discarded. |
| Expiration time of messages on a topic | 30s-7days | Messages that are enqueued for more than the expiration time will be reclaimed |
| topic cache size | 1G | 1G by default, where configuration is not supported yet. When queue data volume exceeds the limit, the service will reclaim the space occupied by unexpired messages from the head. |
| Rate of messages consumed per topic | 5000 pcs/sec | How to calculate the number of messages: measured in 1KB and rounded up Example 1: 1.5KB enqueued is consumed by one client, and the number of messages is counted as 2. Example 2: 1KB enqueued is consumed by 3 clients, and the number of messages is counted as 3. |
| Subscribe message lock time | 10-60s | 0 by default, that is, not locked. If set to > 0, message locking is enabled. For example, if it is set to 10s and no ack is returned after data are consumed by the client, any unacknowledged messages will be consumed again after 10s |
| Position of consumer subscribed | None | 0 by default, that is, it starts consuming messages from the head of the queue. |
| Frequency limit to non-business messages per client | 60/s | In terms of frequency limit to Ping, Subscribe and Unsubscribe messages, the client will disconnect if it exceeds the limit. |
MQTT Protocol Restrictions
| Function | Supported or Not | Description |
|---|---|---|
| Connect | Supported | A CONNECT message that a client sends to MQ contains a connect flag that must be set to 0xC2, otherwise the client will disconnect. |
| ConnAck | Supported | MQ’s response to CONNECT received from the client. If response in reverse order, the client will disconnect |
| Publish | Supported | MQ pushes messages to the client |
| PubAck | Supported | A reply from the client after receiving MQ’s push. |
| Subscribe | Supported | A message sent by the client to MQ that subscribes to a topic When the instance is in arrears, subscribe failed and the server will disconnect |
| SubAck | Supported | A response that Q sends to a client that subscribes to a topic. If response in reverse order, the client will disconnect |
| Unsubscribe | Supported | A message that a client sends to MQ to unsubscribe from a topic |
| UnsubAck | Supported | A response that MQ sends to the client that unsubscribes from a topic. If response in reverse order, the client will disconnect |
| Ping | Supported | Ping message that the client sends to MQ |
| PingResp | Supported | A response that MQ sends to the Ping message from the client |
| Disconnect | Supported | An off-line message that the client sends to MQ |
| PubRec | Not Supported | When the client sends this type of message, it will disconnect |
| PubRel | Not Supported | When the client sends this type of message, it will disconnect |
| PubComp | Not Supported | When the client sends this type of message, it will disconnect |