# Operating limitations

# Background

If there are no limitations on connection numbers or data transmission, users may experience reduced MQTT broker performance, such as a slow network connection or operation response, prolonged message latency, message accumulation, or even message discards, and other issues. On the other hand, the protocol limitation also specify the usage limits.

EMQX has therefore specified the following quotas and usage limits for some of the major features.

# Reference List

The operating limitations can be classified into:

  • Broker resource limitation: Theoretically, there is no maximum limit. The actual limit varies with the server specification.
  • Hard coding or protocol limitation: EMQX has set these limitations to comply with the protocols or to ensure stable performance. In some projects, EMQX has modified the default setting (as specified in the protocol) to a more reasonable value. You can change the setting with our configuration file.
Client Connection
Maximum concurrent connection devicesUnlimited
Maximum device connection rateUnlimited
Maximum MQTT client ID length65535
Maximum subscriptionsUnlimited
Maximum subscription rateUnlimited
Per device subscriptionsUnlimited
Per device subscription rateUnlimited
Maximum bandwidthUnlimited
Per device bandwidthUnlimited
MQTT Message
Message BytesDefault 1024KB, Max 256MB
Maximum QoS2
MQTT Keepalive
Maximun Keepalive65535 seconds
MQTT Topic
Number of topicsUnlimited
Topic level65535
Topic lengthUnlimited
Number of topic aliases65535
MQTT Retained Message
Single Message SizeDefault 1204KB, Max 256MB
Number of messagesUnlimited
Total messages sizeUnlimited
MQTT 5.0
Number of User Properity65535
MQTT Add-ons
Number of topic rewrite rules30
Number of auto subscription rules30
Number of delayed publishUnlimited
Delayed maximum duration4294967 seconds
Number of rulesUnlimited
Rule execution timeoutUnlimited
Number of single rule outputsUnlimited
Data Bridge
Number of data bridgesUnlimited
Max page size10000
Number of API Keys100
Dashboard usersUnlimited