Trigger¶

Trigger defines how often a streaming query should be executed (triggered) and emit a new data (which StreamExecution uses to resolve a TriggerExecutor).

[[available-implementations]] [[available-triggers]] [[triggers]] .Trigger's Factory Methods [cols="1m,2",options="header",width="100%"] |=== | Trigger | Creating Instance

| ContinuousTrigger a| [[ContinuousTrigger]][[Continuous]]

[source, java]¶

Trigger Continuous(long intervalMs) Trigger Continuous(long interval, TimeUnit timeUnit) Trigger Continuous(Duration interval) Trigger Continuous(String interval)

| OneTimeTrigger a| [[OneTimeTrigger]][[Once]]

[source, java]¶

Trigger Once()¶

| ProcessingTime a| [[ProcessingTime]]

[source, java]¶

Trigger ProcessingTime(Duration interval) Trigger ProcessingTime(long intervalMs) Trigger ProcessingTime(long interval, TimeUnit timeUnit) Trigger ProcessingTime(String interval)

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NOTE: You specify the trigger for a streaming query using DataStreamWriter's trigger method.

[source, scala]¶

import org.apache.spark.sql.streaming.Trigger val query = spark. readStream. format("rate"). load. writeStream. format("console"). option("truncate", false). trigger(Trigger.Once). // ← execute once and stop queryName("rate-once"). start

assert(query.isActive == false)

scala> println(query.lastProgress) { "id" : "2ae4b0a4-434f-4ca7-a523-4e859c07175b", "runId" : "24039ce5-906c-4f90-b6e7-bbb3ec38a1f5", "name" : "rate-once", "timestamp" : "2017-07-04T18:39:35.998Z", "numInputRows" : 0, "processedRowsPerSecond" : 0.0, "durationMs" : { "addBatch" : 1365, "getBatch" : 29, "getOffset" : 0, "queryPlanning" : 285, "triggerExecution" : 1742, "walCommit" : 40 }, "stateOperators" : [ ], "sources" : [ { "description" : "RateSource[rowsPerSecond=1, rampUpTimeSeconds=0, numPartitions=8]", "startOffset" : null, "endOffset" : 0, "numInputRows" : 0, "processedRowsPerSecond" : 0.0 } ], "sink" : { "description" : "org.apache.spark.sql.execution.streaming.ConsoleSink@7dbf277" } }

NOTE: Although Trigger allows for custom implementations, StreamExecution StreamExecution.md#triggerExecutor[refuses such attempts] and reports an IllegalStateException.

[source, scala]¶

import org.apache.spark.sql.streaming.Trigger case object MyTrigger extends Trigger scala> val sq = spark .readStream .format("rate") .load .writeStream .format("console") .trigger(MyTrigger) // ← use custom trigger .queryName("rate-custom-trigger") .start java.lang.IllegalStateException: Unknown type of trigger: MyTrigger at org.apache.spark.sql.execution.streaming.MicroBatchExecution.(MicroBatchExecution.scala:60) at org.apache.spark.sql.streaming.StreamingQueryManager.createQuery(StreamingQueryManager.scala:275) at org.apache.spark.sql.streaming.StreamingQueryManager.startQuery(StreamingQueryManager.scala:316) at org.apache.spark.sql.streaming.DataStreamWriter.start(DataStreamWriter.scala:325) ... 57 elided

NOTE: Trigger was introduced in https://github.com/apache/spark/commit/855ed44ed31210d2001d7ce67c8fa99f8416edd3[the commit for [SPARK-14176][SQL] Add DataFrameWriter.trigger to set the stream batch period].

=== [[ProcessingTime-examples]] Examples of ProcessingTime

ProcessingTime is a Trigger that assumes that milliseconds is the minimum time unit.

You can create an instance of ProcessingTime using the following constructors:

• ProcessingTime(Long) that accepts non-negative values that represent milliseconds. +

  ProcessingTime(10)
  

• ProcessingTime(interval: String) or ProcessingTime.create(interval: String) that accept CalendarInterval instances with or without leading interval string. +

  ProcessingTime("10 milliseconds")
  ProcessingTime("interval 10 milliseconds")
  

• ProcessingTime(Duration) that accepts scala.concurrent.duration.Duration instances. +

  ProcessingTime(10.seconds)
  

• ProcessingTime.create(interval: Long, unit: TimeUnit) for Long and java.util.concurrent.TimeUnit instances. +

  ProcessingTime.create(10, TimeUnit.SECONDS)