ekuiper-new/docs/en_US/rules/overview.md

Rules

Rules are defined by JSON, below is an example.

{
  "id": "rule1",
  "sql": "SELECT demo.temperature, demo1.temp FROM demo left join demo1 on demo.timestamp = demo1.timestamp where demo.temperature > demo1.temp GROUP BY demo.temperature, HOPPINGWINDOW(ss, 20, 10)",
  "actions": [
    {
      "log": {}
    },
    {
      "mqtt": {
        "server": "tcp://47.52.67.87:1883",
        "topic": "demoSink"
      }
    }
  ]
}

The following 3 parameters are required for creating a rule.

Parameters

Parameter name	Optional	Description
id	false	The id of the rule
sql	false	The sql query to run for the rule
actions	false	An array of sink actions
options	true	A map of options

id

The identification of the rule. The rule name cannot be duplicated in the same Kuiper instance.

sql

The sql query to run for the rule.

• Kuiper provides embeded following 2 sources,
  • MQTT source, see MQTT source stream for more detailed info.
  • EdgeX source by default is shipped in docker images, but NOT included in single download binary files, you use make pkg_with_edgex command to build a binary package that supports EdgeX source. Please see EdgeX source stream for more detailed info.
• See SQL for more info of Kuiper SQL.
• Sources can be customized, see extension for more detailed info.

actions

Currently, 3 kinds of actions are supported: log, mqtt and rest. Each action can define its own properties. There are 3 common properties:

property name	Type & Default Value	Description
concurrency	int: 1	Specify how many instances of the sink will be run. If the value is bigger than 1, the order of the messages may not be retained.
bufferLength	int: 1024	Specify how many messages can be buffered in memory. If the buffered messages exceed the limit, the sink will block message receiving until the buffered messages have been sent out so that the buffered size is less than the limit.
runAsync	bool:false	Whether the sink will run asynchronously for better performance. If it is true, the sink result order is not promised.
retryInterval	int:1000	Specify how many milliseconds will the sink retry to send data out if the previous send failed
cacheLength	int:10240	Specify how many messages can be cached. The cached messages will be resent to external system until the data sent out successfully. The cached message will be sent in order except in runAsync or concurrent mode. The cached message will be saved to disk in fixed intervals.
cacheSaveInterval	int:1000	Specify the interval to save cached message to the disk. Notice that, if the rule is closed in plan, all the cached messages will be saved at close. A larger value can reduce the saving overhead but may lose more cache messages when the system is interrupted in error.

Actions could be customized to support different kinds of outputs, see extension for more detailed info.

options

The current options includes:

Option name	Type & Default Value	Description
isEventTime	boolean: false	Whether to use event time or processing time as the timestamp for an event. If event time is used, the timestamp will be extracted from the payload. The timestamp filed must be specified by the stream definition.
lateTolerance	int64:0	When working with event-time windowing, it can happen that elements arrive late. LateTolerance can specify by how much time(unit is millisecond) elements can be late before they are dropped. By default, the value is 0 which means late elements are dropped.
concurrency	int: 1	A rule is processed by several phases of plans according to the sql statement. This option will specify how many instances will be run for each plan. If the value is bigger than 1, the order of the messages may not be retained.
bufferLength	int: 1024	Specify how many messages can be buffered in memory for each plan. If the buffered messages exceed the limit, the plan will block message receiving until the buffered messages have been sent out so that the buffered size is less than the limit. A bigger value will accommodate more throughput but will also take up more memory footprint.