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Table of Contents

Status

Current state: Under DiscussionAccepted

Discussion thread: here

JIRA: here

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Code Block
titleJoined.java
linenumberstrue
public class Joined {
   /**
	* Set the grace period on the stream side of the join. Records will enter a buffer before being processed. Out of order records in the grace period will be processed in timestamp order. Late records, out of the grace period, will be dropped executed right as they come in, if it is past the table history retention this could result in joins on the wrong version or a null join. Long gaps in stream side arriving records will cause records to be delayed in processing, even resulting in be processed out of the grace period window.
	*  
	*
	* @param gracePeriod the duration of the grace period. If zero, no buffer will be used. Must be less than the joining table's history retention.
	* @return new {@code Joined} instance configured with the gracePeriod
	*/
	public Joined withGracePeriod(Duration gracePeriod);

   /**
     * Create an instance of {@code Joined} with key, value, and otherValue {@link Serde} instances.
     * {@code null} values are accepted and will be replaced by the default serdes as defined in
     * config.
     *
     * @param keySerde the key serde to use. If {@code null} the default key serde from config will be
     * used
     * @param valueSerde the value serde to use. If {@code null} the default value serde from config
     * will be used
     * @param otherValueSerde the otherValue serde to use. If {@code null} the default value serde
     * from config will be used
     * @param name the name used as the base for naming components of the join including any
     * repartition topics
	 * @param gracePeriod Duration of the stream side buffer
     * @param <K> key type
     * @param <V> value type
     * @param <VO> other value type
     * @return new {@code Joined} instance with the provided serdes
     */
    public static <K, V, VO> Joined<K, V, VO> with(final Serde<K> keySerde,
                                                   final Serde<V> valueSerde,
                                                   final Serde<VO> otherValueSerde,
                                                   final String name,
                                                   final Duration gracePeriod);

    public Duration gracePeriod() {
        return gracePeriod;
    }
}

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If a grace period is not set the join will execute as before, using the same logic in the stream table join node. If a grace period of zero is set the join will execute as a normal join will drop all out of order records from the stream side operationsas each record comes it will try to join to the point of time in the versioned table. If the grace period is non zero, the record will enter a stream buffer and will dequeue when the record timestamp is greater lees than or equal to than stream time plus minus the grace period.  Late records, out of the grace period, will be executed right as they come in.

The buffer will be checked whenever stream time is advanced. Stream time will be advanced whenever a new record enters the node from the stream. From then the record records will be evicted and sent down to the next processor, the join node. The buffer will use an on disk implementation of TimeOrderedKeyValueBuffer.

Setting the grace period will only be allowed for already materialized tables with a table history retention that is greater than the stream buffer's grace period. All other configurations will result in an Exception.

When a failure occurs the buffer will try to recover from an OffsetCheckpoint if possible. If not it will reload the buffer from a compacted change-log topic.

Adding a buffer to the stream will increase the latency of the join by at least the grace period. It will also take the time to serialize and store the record as well as retrieve and deserialize.

Compatibility, Deprecation, and Migration Plan

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