org.apache.beam.sdk.transforms.windowing

Class OutputTimeFn.Defaults<W extends BoundedWindow>

java.lang.Object

org.apache.beam.sdk.transforms.windowing.OutputTimeFn<W>

org.apache.beam.sdk.transforms.windowing.OutputTimeFn.Defaults<W>

All Implemented Interfaces:

Serializable

Enclosing class:

OutputTimeFn<W extends BoundedWindow>

public abstract static class OutputTimeFn.Defaults<W extends BoundedWindow>
extends OutputTimeFn<W>

(Experimental) Default method implementations for OutputTimeFn where the output time depends on the input element timestamps and possibly the window.

To complete an implementation, override OutputTimeFn.assignOutputTime(org.joda.time.Instant, W), at a minimum.

By default, combine(org.joda.time.Instant, org.joda.time.Instant) and merge(W, java.lang.Iterable<? extends org.joda.time.Instant>) return the earliest timestamp of their inputs.

See Also:

Serialized Form

Nested Class Summary

Nested classes/interfaces inherited from class org.apache.beam.sdk.transforms.windowing.OutputTimeFn

OutputTimeFn.Defaults<W extends BoundedWindow>, OutputTimeFn.DependsOnlyOnWindow<W extends BoundedWindow>

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	Defaults()

Method Summary

Modifier and Type	Method and Description
Instant	combine(Instant outputTimestamp, Instant otherOutputTimestamp) Combines the given output times, which must be from the same window, into an output time for a computed value.
boolean	dependsOnlyOnEarliestInputTimestamp() Returns true if the result of combination of many output timestamps actually depends only on the earliest.
boolean	dependsOnlyOnWindow() Returns true if the result does not depend on what outputs were combined but only the window they are in.
boolean	equals(Object other)
int	hashCode()
Instant	merge(W resultWindow, Iterable<? extends Instant> mergingTimestamps) Merges the given output times, presumed to be combined output times for windows that are merging, into an output time for the resultWindow.

Methods inherited from class org.apache.beam.sdk.transforms.windowing.OutputTimeFn

assignOutputTime

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Defaults

protected Defaults()

Method Detail

combine

public Instant combine(Instant outputTimestamp,
                       Instant otherOutputTimestamp)

Combines the given output times, which must be from the same window, into an output time for a computed value.

• combine must be commutative: combine(a, b).equals(combine(b, a)).
• combine must be associative: combine(a, combine(b, c)).equals(combine(combine(a, b), c)).

Specified by:

combine in class OutputTimeFn<W extends BoundedWindow>

Returns:

the earlier of the two timestamps.

merge

public Instant merge(W resultWindow,
                     Iterable<? extends Instant> mergingTimestamps)

Merges the given output times, presumed to be combined output times for windows that are merging, into an output time for the resultWindow.

When windows w1 and w2 merge to become a new window w1plus2, then OutputTimeFn.merge(W, java.lang.Iterable<? extends org.joda.time.Instant>) must be implemented such that the output time is the same as if all timestamps were assigned in w1plus2. Formally:

fn.merge(w, fn.assignOutputTime(t1, w1), fn.assignOutputTime(t2, w2))

must be equal to

fn.combine(fn.assignOutputTime(t1, w1plus2), fn.assignOutputTime(t2, w1plus2))

If the assigned time depends only on the window, the correct implementation of merge() necessarily returns the result of assignOutputTime(t1, w1plus2) (which equals assignOutputTime(t2, w1plus2). Defaults for this case are provided by OutputTimeFn.DependsOnlyOnWindow.

For many other OutputTimeFn implementations, such as taking the earliest or latest timestamp, this will be the same as combine(). Defaults for this case are provided by OutputTimeFn.Defaults.

Specified by:

merge in class OutputTimeFn<W extends BoundedWindow>

Returns:

the result of combine(outputTimstamp, otherOutputTimestamp), by default.

dependsOnlyOnWindow

public boolean dependsOnlyOnWindow()

Returns true if the result does not depend on what outputs were combined but only the window they are in. The canonical example is if all timestamps are sure to be the end of the window.

This may allow optimizations, since it is typically very efficient to retrieve the window and combining output timestamps is not necessary.

If the assigned output time for an implementation depends only on the window, consider extending OutputTimeFn.DependsOnlyOnWindow, which returns true here and also provides a framework for easily implementing a correct OutputTimeFn.merge(W, java.lang.Iterable<? extends org.joda.time.Instant>), OutputTimeFn.combine(org.joda.time.Instant, org.joda.time.Instant) and OutputTimeFn.assignOutputTime(org.joda.time.Instant, W).

Specified by:

dependsOnlyOnWindow in class OutputTimeFn<W extends BoundedWindow>

Returns:

false by default. An OutputTimeFn that is known to depend only on the window should extend OutputTimeFn.DependsOnlyOnWindow.

dependsOnlyOnEarliestInputTimestamp

public boolean dependsOnlyOnEarliestInputTimestamp()

Returns true if the result of combination of many output timestamps actually depends only on the earliest.

This may allow optimizations when it is very efficient to retrieve the earliest timestamp to be combined.

Specified by:

dependsOnlyOnEarliestInputTimestamp in class OutputTimeFn<W extends BoundedWindow>

Returns:

true by default.

equals

public boolean equals(Object other)

Overrides:

equals in class Object

Returns:

true if the two OutputTimeFn instances have the same class, by default.

hashCode

public int hashCode()

Overrides:

hashCode in class Object