Status
Current state: "Under Discussion"
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Please keep the discussion on the mailing list rather than commenting on the wiki (wiki discussions get unwieldy fast).
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| Code Block |
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| language | java |
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| title | TimestampAssigner |
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/**
* A {@code TimestampAssigner} assigns event time timestamps to elements.
* These timestamps are used by all functions that operate on event time,
* for example event time windows.
*
* <p>Timestamps can be an arbitrary {@code long} value, but all built-in implementations
* represent it as the milliseconds since the Epoch (midnight, January 1, 1970 UTC),
* the same way as {@link System#currentTimeMillis()} does it.
*
* @param <T> The type of the elements to which this assigner assigns timestamps.
*/
@PublicEvolving
@FunctionalInterface
public interface TimestampAssigner<T> extends Function {
/**
* Assigns a timestamp to an element, in milliseconds since the Epoch.
*
* <p>The method is passed the previously assigned timestamp of the element.
* That previous timestamp may have been assigned from a previous assigner. If the element did
* not carry a timestamp before, this value is {@code Long.MIN_VALUE}.
*
* @param element The element that the timestamp will be assigned to.
* @param currentTimestamp The current internal timestamp of the element,
* or a negative value, if no timestamp has been assigned yet.
* @return The new timestamp.
*/
long extractTimestamp(T element, long currentTimestamprecordTimestamp);
} |
| Code Block |
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| language | java |
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| title | WatermarkGenerator |
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/**
* The {@code WatermarkGenerator} generates watermarks either based on events or
* periodically (in a fixed interval).
*
* <p><b>Note:</b> This WatermarkGenerator subsumes the previous distinction between the
* {@code AssignerWithPunctuatedWatermarks} and the {@code AssignerWithPeriodicWatermarks}.
*/
@PublicEvolving
public interface WatermarkGenerator<T> {
/**
* Called for every event, allows the watermark generator to examine and remember the
* event timestamps, or to emit a watermark based on the event itself.
*/
void onEvent(T event, long eventTimestamp, WatermarkOutput output);
/**
* Called periodically, and might emit a new watermark, or not.
*
* <p>The interval in which this method is called and Watermarks are generated
* depends on {@link ExecutionConfig#getAutoWatermarkInterval()}.
*/
void onPeriodicEmit(WatermarkOutput output);
} |
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| Code Block |
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| language | java |
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| title | WatermarkStrategy |
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/**
* The WatermarkStrategy defines how to generate {@link Watermark}s in the stream sources.
* The WatermarkStrategy is a builder/factory for the {@link WatermarkGenerator} that
* generates the watermarks and the {@link TimestampAssigner} which assigns the internal timestamp
* of a record.
*
* <p>This interface is {@link Serializable} because watermark strategies may be shipped
* to workers during distributed execution.
*/
@PublicEvolving
public interface WatermarkStrategy<T> extends Serializable {
/**
* Instantiates a {@link TimestampAssigner} for assigning timestamps according to this
* strategy.
*/
default TimestampAssigner<T> createTimestampAssigner() {
// By default, this is {@link IdentityTimestampAssignerRecordTimestampAssigner},
// forwhich casestakes wherethe recordstimestamp comethat out of a sourcerecord withalready valid timestampshas, for example from Kafka.
return new IdentityTimestampAssigner<>RecordTimestampAssigner<>();
}
/**
* Instantiates a WatermarkGenerator that generates watermarks according to this strategy.
*/
WatermarkGenerator<T> createWatermarkGenerator();
} |
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