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Create Triggers

Triggers allow events to be periodically generated. A trigger also works like a Stream Source with a predefined schema.

Purpose​

For some use cases, the system should be able to periodically generate events based on a specified time interval to periodically execute queries.

A trigger can be performed for a 'start' operation, for a given <time interval>, or for a given '<cron expression>'.

Syntax​

The syntax for a trigger definition is as follows:

CREATE TRIGGER <trigger name> at ('start'| every <time interval>| '<cron expression>');

Similar to streams, triggers can be used as inputs. They adhere to the following stream definition and produce the triggered_time attribute of the long type.

CREATE STREAM <trigger name> (triggered_time long);

Supported Triggers​

The following types of triggers are currently supported:

Trigger typeDescription
startAn event is triggered when a stream is started.
every <time interval>An event is triggered periodically at the given time interval. Minimum supported time interval is millisecond.
<cron expression>An event is triggered periodically based on the given cron expression. For configuration details, see CronTrigger.

Examples​

  • Trigger an event when the stream is started.

    The following query triggers an event when the stream is started:

    CREATE TRIGGER InitTrigger WITH (expression = 'start');

  • Trigger events regularly at specific time intervals.

    The following query triggers events every five minutes:

    CREATE TRIGGER FiveMinTriggerStream WITH(interval = 5 min);

  • Trigger events at a specific time on specified days.

    The following query triggers an event at 10.15 AM every weekday:

    CREATE TRIGGER FiveMinTriggerStream1 WITH (expression = '0 15 10 ? * MON-FRI');

  • The following stream worker uses a trigger that runs a query worker every minute as the source.

    @App:name("runQueryWorker")
    @App:description("Execute a query worker every minute.")
    @App:qlVersion("2")

    CREATE TRIGGER InitTrigger WITH (interval = 1 minute);

    -- query.worker.name is the name of a query worker that already exists in the fabric.
    CREATE SINK queryWorkerStream WITH (type='query-worker', query.worker.name='queryWorkerSample')(startTime string);

    INSERT INTO queryWorkerStream
    SELECT time:dateFormat(eventTimestamp(), 'yyyy/MM/dd HH:mm:ss') as startTime
    FROM InitTrigger