聊聊flink Table的Group Windows

序

本文主要研究一下flink Table的Group Windows

实例

Table table = input
  .window([Window w].as("w"))  // define window with alias w
  .groupBy("w")  // group the table by window w
  .select("b.sum");  // aggregate

Table table = input
  .window([Window w].as("w"))  // define window with alias w
  .groupBy("w, a")  // group the table by attribute a and window w 
  .select("a, b.sum");  // aggregate

Table table = input
  .window([Window w].as("w"))  // define window with alias w
  .groupBy("w, a")  // group the table by attribute a and window w 
  .select("a, w.start, w.end, w.rowtime, b.count"); // aggregate and add window start, end, and rowtime timestamps

• window操作可以对Window进行别名，然后可以在groupBy及select中引用，window有start、end、rowtime属性可以用，其中start及rowtime是inclusive的，而end为exclusive

Tumbling Windows实例

// Tumbling Event-time Window
.window(Tumble.over("10.minutes").on("rowtime").as("w"));

// Tumbling Processing-time Window (assuming a processing-time attribute "proctime")
.window(Tumble.over("10.minutes").on("proctime").as("w"));

// Tumbling Row-count Window (assuming a processing-time attribute "proctime")
.window(Tumble.over("10.rows").on("proctime").as("w"));

• Tumbling Windows按固定窗口大小来移动，因而窗口不重叠；over方法用于指定窗口大小；窗口大小可以基于event-time、processing-time、row-count来定义

Sliding Windows实例

// Sliding Event-time Window
.window(Slide.over("10.minutes").every("5.minutes").on("rowtime").as("w"));

// Sliding Processing-time window (assuming a processing-time attribute "proctime")
.window(Slide.over("10.minutes").every("5.minutes").on("proctime").as("w"));

// Sliding Row-count window (assuming a processing-time attribute "proctime")
.window(Slide.over("10.rows").every("5.rows").on("proctime").as("w"));

• Sliding Windows在slide interval小于window size的时候，窗口会有重叠，因而rows可能归属多个窗口；over方法用于指定窗口大小，窗口大小可以基于event-time、processing-time、row-count来定义；every方法用于指定slide interval

Session Windows实例

// Session Event-time Window
.window(Session.withGap("10.minutes").on("rowtime").as("w"));

// Session Processing-time Window (assuming a processing-time attribute "proctime")
.window(Session.withGap("10.minutes").on("proctime").as("w"));

• Session Windows没有固定的窗口大小，它基于inactivity的程度来关闭窗口，withGap方法用于指定两个窗口的gap，作为time interval；Session Windows只能使用event-time或者processing-time

Table.window

flink-table_2.11-1.7.0-sources.jar!/org/apache/flink/table/api/table.scala

class Table(
    private[flink] val tableEnv: TableEnvironment,
    private[flink] val logicalPlan: LogicalNode) {

  //......
  
  def window(window: Window): WindowedTable = {
    new WindowedTable(this, window)
  }
  
  //......
}

• Table提供了window操作，接收Window参数，创建的是WindowedTable

WindowedTable

flink-table_2.11-1.7.0-sources.jar!/org/apache/flink/table/api/table.scala

class WindowedTable(
    private[flink] val table: Table,
    private[flink] val window: Window) {

  def groupBy(fields: Expression*): WindowGroupedTable = {
    val fieldsWithoutWindow = fields.filterNot(window.alias.equals(_))
    if (fields.size != fieldsWithoutWindow.size + 1) {
      throw new ValidationException("GroupBy must contain exactly one window alias.")
    }

    new WindowGroupedTable(table, fieldsWithoutWindow, window)
  }

  def groupBy(fields: String): WindowGroupedTable = {
    val fieldsExpr = ExpressionParser.parseExpressionList(fields)
    groupBy(fieldsExpr: _*)
  }

}

• WindowedTable只提供groupBy操作，其中groupBy可以接收String类型的参数，也可以接收Expression类型的参数；String类型的参数会被转换为Expression类型，最后调用的是Expression类型参数的groupBy方法；如果groupBy除了window没有其他属性，则其parallelism为1，只会在单一task上执行；groupBy方法创建的是WindowGroupedTable

WindowGroupedTable

flink-table_2.11-1.7.0-sources.jar!/org/apache/flink/table/api/table.scala

class WindowGroupedTable(
    private[flink] val table: Table,
    private[flink] val groupKeys: Seq[Expression],
    private[flink] val window: Window) {

  def select(fields: Expression*): Table = {
    val expandedFields = expandProjectList(fields, table.logicalPlan, table.tableEnv)
    val (aggNames, propNames) = extractAggregationsAndProperties(expandedFields, table.tableEnv)

    val projectsOnAgg = replaceAggregationsAndProperties(
      expandedFields, table.tableEnv, aggNames, propNames)

    val projectFields = extractFieldReferences(expandedFields ++ groupKeys :+ window.timeField)

    new Table(table.tableEnv,
      Project(
        projectsOnAgg,
        WindowAggregate(
          groupKeys,
          window.toLogicalWindow,
          propNames.map(a => Alias(a._1, a._2)).toSeq,
          aggNames.map(a => Alias(a._1, a._2)).toSeq,
          Project(projectFields, table.logicalPlan).validate(table.tableEnv)
        ).validate(table.tableEnv),
        // required for proper resolution of the time attribute in multi-windows
        explicitAlias = true
      ).validate(table.tableEnv))
  }

  def select(fields: String): Table = {
    val fieldExprs = ExpressionParser.parseExpressionList(fields)
    //get the correct expression for AggFunctionCall
    val withResolvedAggFunctionCall = fieldExprs.map(replaceAggFunctionCall(_, table.tableEnv))
    select(withResolvedAggFunctionCall: _*)
  }
}

• WindowGroupedTable只提供select操作，其中select可以接收String类型的参数，也可以接收Expression类型的参数；String类型的参数会被转换为Expression类型，最后调用的是Expression类型参数的select方法；select方法创建了新的Table，其Project的child为WindowAggregate

小结

• window操作可以对Window进行别名，然后可以在groupBy及select中引用，window有start、end、rowtime属性可以用，其中start及rowtime是inclusive的，而end为exclusive
• Tumbling Windows按固定窗口大小来移动，因而窗口不重叠；over方法用于指定窗口大小；窗口大小可以基于event-time、processing-time、row-count来定义；Sliding Windows在slide interval小于window size的时候，窗口会有重叠，因而rows可能归属多个窗口；over方法用于指定窗口大小，窗口大小可以基于event-time、processing-time、row-count来定义；every方法用于指定slide interval；Session Windows没有固定的窗口大小，它基于inactivity的程度来关闭窗口，withGap方法用于指定两个窗口的gap，作为time interval；Session Windows只能使用event-time或者processing-time
• Table提供了window操作，接收Window参数，创建的是WindowedTable；WindowedTable只提供groupBy操作，其中groupBy可以接收String类型的参数，也可以接收Expression类型的参数；String类型的参数会被转换为Expression类型，最后调用的是Expression类型参数的groupBy方法；如果groupBy除了window没有其他属性，则其parallelism为1，只会在单一task上执行；groupBy方法创建的是WindowGroupedTable；WindowGroupedTable只提供select操作，其中select可以接收String类型的参数，也可以接收Expression类型的参数；String类型的参数会被转换为Expression类型，最后调用的是Expression类型参数的select方法；select方法创建了新的Table，其Project的child为WindowAggregate

doc

• Group Windows