Package org.apache.kafka.streams.kstream

Class SlidingWindows

java.lang.Object
org.apache.kafka.streams.kstream.SlidingWindows
public final class SlidingWindows
extends Object
A sliding window used for aggregating events.

Sliding Windows are defined based on a record's timestamp, the window size based on the given maximum time difference (inclusive) between records in the same window, and the given window grace period. While the window is sliding over the input data stream, a new window is created each time a record enters the sliding window or a record drops out of the sliding window.

Records that come after set grace period will be ignored, i.e., a window is closed when stream-time > window-end + grace-period.

For example, if we have a time difference of 5000ms and the following data arrives: 

 +--------------------------------------+
 |    key    |    value    |    time    |
 +-----------+-------------+------------+
 |    A      |     1       |    8000    |
 +-----------+-------------+------------+
 |    A      |     2       |    9200    |
 +-----------+-------------+------------+
 |    A      |     3       |    12400   |
 +-----------+-------------+------------+
We'd have the following 5 windows:
  • window [3000;8000] contains [1] (created when first record enters the window)
  • window [4200;9200] contains [1,2] (created when second record enters the window)
  • window [7400;12400] contains [1,2,3] (created when third record enters the window)
  • window [8001;13001] contains [2,3] (created when the first record drops out of the window)
  • window [9201;14201] contains [3] (created when the second record drops out of the window)

Note that while SlidingWindows are of a fixed size, as are TimeWindows, the start and end points of the window depend on when events occur in the stream (i.e., event timestamps), similar to SessionWindows.

For time semantics, see TimestampExtractor.

See Also:
TimeWindows, SessionWindows, UnlimitedWindows, JoinWindows, KGroupedStream.windowedBy(SlidingWindows), CogroupedKStream.windowedBy(SlidingWindows), TimestampExtractor

  • Method Details

    • ofTimeDifferenceWithNoGrace

      public static SlidingWindows ofTimeDifferenceWithNoGrace​(Duration timeDifference) throws IllegalArgumentException
      Return a window definition with the window size based on the given maximum time difference (inclusive) between records in the same window and given window grace period. Reject out-of-order events that arrive after grace. A window is closed when stream-time > window-end + grace-period.

      CAUTION: Using this method implicitly sets the grace period to zero, which means that any out-of-order records arriving after the window ends are considered late and will be dropped.

      Parameters:
      timeDifference - the max time difference (inclusive) between two records in a window
      Returns:
      a new window definition with no grace period. Note that this means out-of-order records arriving after the window end will be dropped
      Throws:
      IllegalArgumentException - if the timeDifference is negative or can't be represented as long milliseconds

    • ofTimeDifferenceAndGrace

      public static SlidingWindows ofTimeDifferenceAndGrace​(Duration timeDifference, Duration afterWindowEnd) throws IllegalArgumentException
      Return a window definition with the window size based on the given maximum time difference (inclusive) between records in the same window and given window grace period. Reject out-of-order events that arrive after afterWindowEnd. A window is closed when stream-time > window-end + grace-period.
      Parameters:
      timeDifference - the max time difference (inclusive) between two records in a window
      afterWindowEnd - the grace period to admit out-of-order events to a window
      Returns:
      a new window definition with the specified grace period
      Throws:
      IllegalArgumentException - if the timeDifference or afterWindowEnd (grace period) is negative or can't be represented as long milliseconds

    • withTimeDifferenceAndGrace

      @Deprecated public static SlidingWindows withTimeDifferenceAndGrace​(Duration timeDifference, Duration grace) throws IllegalArgumentException
      Deprecated.
      since 3.0. Use ofTimeDifferenceWithNoGrace(Duration) or ofTimeDifferenceAndGrace(Duration, Duration) instead
      Return a window definition with the window size based on the given maximum time difference (inclusive) between records in the same window and given window grace period. Reject out-of-order events that arrive after grace. A window is closed when stream-time > window-end + grace-period.
      Parameters:
      timeDifference - the max time difference (inclusive) between two records in a window
      grace - the grace period to admit out-of-order events to a window
      Returns:
      a new window definition
      Throws:
      IllegalArgumentException - if the specified window size is < 0 or grace < 0, or either can't be represented as long milliseconds

    • timeDifferenceMs

      public long timeDifferenceMs()

    • gracePeriodMs

      public long gracePeriodMs()

    • equals

      public boolean equals​(Object o)
      Overrides:
      equals in class Object

    • hashCode

      public int hashCode()
      Overrides:
      hashCode in class Object

    • toString

      public String toString()
      Overrides:
      toString in class Object