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Status

Current state: Under Discussion

Discussion thread: here

JIRA: KAFKA-15346

Please keep the discussion on the mailing list rather than commenting on the wiki (wiki discussions get unwieldy fast).

Motivation

The main goal is supporting interactive queries in presence of versioned state stores (KIP-889) in AK. For this KIP, the following query types are considered to be implemented. This KIP discusses single-key, single-timestamp queries. Other types of IQs are explained in the following KIPs (KIP-968 and KIP-969)  

Key Queries with single timestamp:

  1. single-key latest-value lookup
  2. single-key lookup with timestamp (upper) bound


Proposed Changes

In this KIP we propose a new Optional field in VersionedKeyQuery to store the asOfTimestamp value. Moreover, the method asOf is added to the class in order to create key queries having asOfTimestamp value as well.  
Defining the latest() method is not needed since returning the latest value has been always the default assumption.

VersionedKeyQuery.java
package org.apache.kafka.streams.query;

/**
 * Interactive query for retrieving a single record  from a versioned state store based on its key and timestamp.
 * <p>
 * See KIP-960 for more details.
 */
@Evolving
public final class VersionedKeyQuery<K, V> implements Query<VersionedRecord<V>> {

    private final K key;
    private final Optional<Instant> asOfTimestamp;

    private VersionedKeyQuery(final K key, final Optional<Instant> asOfTimestamp) {
        this.key = Objects.requireNonNull(key);
        this.asOfTimestamp = asOfTimestamp;
    }

    /**
     * Creates a query that will retrieve the record from a versioned state store identified by {@code key} if it exists
     * (or {@code null} otherwise).
     * @param key The key to retrieve
     * @param <K> The type of the key
     * @param <V> The type of the value that will be retrieved
     */
    public static <K, V> VersionedKeyQuery<K, V> withKey(final K key);

    /**
     * Specifies the upper inclusive bound for the key query. The key query returns the record
     * with the greatest timestamp <= asOfTimestamp
     * @param asOfTimestamp The upper inclusive bound for timestamp
     */
    public VersionedKeyQuery<K, V> asOf(final Instant asOfTimestamp);

    /**
     * The key that was specified for this query.
     */
    public K getKey();

    /**
     * The timestamp of the query, if specified
     */
    public Optional<Instant> getAsOfTimestamp();
}


Examples

The following example illustrates the use of the VersionedKeyQuery class to query a versioned state store.

builder.table(
            "my_topic",
            Consumed.with(Serdes.Integer(), Serdes.Integer()),
            Materialized.as(Stores.persistentVersionedKeyValueStore(
                "my_store",
                Duration.ofMillis(HISTORY_RETENTION)
            ))
        );

final VersionedKeyQuery<Integer, Integer> query = VersionedKeyQuery.withKey(1).asOf(Instant.parse("2023-08-03T10:37:30.00Z");

final StateQueryRequest<VersionedRecord<Integer>> request =
        inStore("my_store").withQuery(query);

final StateQueryResult<VersionedRecord<Integer>> result = kafkaStreams.query(request);


Compatibility, Deprecation, and Migration Plan

  • Since this is a completely new set of APIs, no backward compatibility concerns are anticipated. 
  • Since nothing is deprecated in this KIP, users have no need to migrate unless they want to.




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