com.hazelcast.jet.core

Interface WatermarkPolicy

public interface WatermarkPolicy

This object tracks and determines the current Watermark given the event timestamps as they occur for a single input stream. Typically the watermark will be advanced with a fixed lag behind the top observed timestamp so far.

This object is used by source processors to determine the current watermark. The processor may choose to create several of these objects to track each source partition separately and each processor will also have their own instance. The implementation does not need to be thread-safe.

Since:

Jet 3.0

See Also:

EventTimePolicy, EventTimeMapper

Method Summary

Modifier and Type	Method and Description
long	getCurrentWatermark() Called to get the current watermark.
static SupplierEx<WatermarkPolicy>	limitingLag(long lag) Maintains a watermark that lags behind the top observed timestamp by the given amount.
static SupplierEx<WatermarkPolicy>	limitingRealTimeLag(long lag) Maintains a watermark that lags behind the real time by the given amount.
void	reportEvent(long timestamp) Called to report the observation of an event with the given timestamp.

Method Detail

reportEvent

void reportEvent(long timestamp)

Called to report the observation of an event with the given timestamp. The next call to getCurrentWatermark() should reflect this.

Parameters:

timestamp - event's timestamp

getCurrentWatermark

long getCurrentWatermark()

Called to get the current watermark. The watermark may advance based just on the passage of time.

limitingLag

@Nonnull
static SupplierEx<WatermarkPolicy> limitingLag(long lag)

Maintains a watermark that lags behind the top observed timestamp by the given amount.

Note: if Jet stops receiving events at some point (e.g., at the end of a business day), the watermark will stop advancing and stay behind the most recent events. Jet will not output the results of aggregating these events until it starts receiving events again (e.g., at the start of the next business day).

Parameters:

lag - the desired difference between the top observed timestamp and the watermark

limitingRealTimeLag

@Nonnull
static SupplierEx<WatermarkPolicy> limitingRealTimeLag(long lag)

Maintains a watermark that lags behind the real time by the given amount. Doesn't consider the event timestamp at all.

Parameters:

lag - the desired difference between the top observed timestamp and the watermark

Since:

Jet 4.3