kafka-streams-Windows.adoc

Windows — Window Specification For Time-Windowed Streaming Aggregations

Windows is the abstraction of window specifications that describe windows of fixed size and grace period.

Windows are used in KGroupedStream.windowedBy streaming operator (for time-windowed streaming aggregations).

Table 1. Windows API / Operators

Method	Description
gracePeriodMs	long gracePeriodMs() Grace period (in milliseconds) New events are added to windows until their grace period ends
size	long size() Window size (in milliseconds)
windowsFor	Map<Long, W> windowsFor(final long timestamp) Returns all the windows that contain the given timestamp, indexed by non-negative window start timestamps. Used when KStreamWindowAggregateProcessor is requested to process a record

Table 2. Windows

Windows	Description
JoinWindows
TimeWindows	Time-bound window specification for tumbling or hopping windows
UnlimitedWindows

Windows takes no arguments when created and simply initializes the internal registries and counters.

Note	Windows is a Java abstract class and cannot be created directly. It is created indirectly when the concrete Windows are.

Windows defines a window maintain duration (aka retention time). The default window maintain duration is 1 day.