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Status

Current state: "Under Discussion"

Discussion thread: here 

JIRA: KAFKA-13494

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

Motivation

Provide an implementation of the Query interface, introduced in KIP-796: Interactive Query v2 , to support session and window queries.

Public Interfaces

In this KIP we propose two new public classes:

  • WindowKeyQuery: used to search occurrences of keys in window stores in combination with IQv2
  • WindowRangeQuery: used to search per window aggregates of keys in window and session stores in combination with IQv2

Proposed Changes

The WindowKeyQuery class:

public class WindowKeyQuery<K, V> implements Query<V> {

    private final K key;
    private final Optional<Long> windowLower;

    private WindowKeyQuery(final K key, final Optional<Long> windowLower) {
        this.key = key;
        this.windowLower = windowLower;
    }

    public static <K, V> WindowKeyQuery<K, V> withKey(final K key) {
        return new WindowKeyQuery<>(key, Optional.empty());
    }

    public static <K, V> WindowKeyQuery<K, V> withKeyAndWindowLowerBound(final K key, final long time) {
        return new WindowKeyQuery<>(key, Optional.of(time));
    }

    public K getKey() {
        return key;
    }

    public Optional<Long> getWindowLower() {
        return windowLower;
    }
}

The WindowRangeQuery class:

public class WindowRangeQuery<K, V> implements Query<KeyValueIterator<K, V>> {

    private final Optional<K> lower;
    private final Optional<K> upper;
    private final Optional<Long> windowLower;
    private final Optional<Long> windowUpper;

    private WindowRangeQuery(final Optional<K> lower, final Optional<K> upper, final Optional<Long> windowLower, final Optional<Long> windowUpper) {
        this.lower = lower;
        this.upper = upper;
        this.windowLower = windowLower;
        this.windowUpper = windowUpper;
    }

    public static <K, V> WindowRangeQuery<K, V> withKeyRange(final K lower, final K upper, final Optional<Long> windowLower, final Optional<Long> windowUpper) {
        return new WindowRangeQuery<>(Optional.of(lower), Optional.of(upper), windowLower, windowUpper);
    }

    public static <K, V> WindowRangeQuery<K, V> withKeyUpperBound(final K upper, final Optional<Long> windowLower, final Optional<Long> windowUpper) {
        return new WindowRangeQuery<>(Optional.empty(), Optional.of(upper), windowLower, windowUpper);
    }

    public static <K, V> WindowRangeQuery<K, V> withKeyLowerBound(final K lower, final Optional<Long> windowLower, final Optional<Long> windowUpper) {
        return new WindowRangeQuery<>(Optional.of(lower), Optional.empty(), windowLower, windowUpper);
    }

    public static <K, V> WindowRangeQuery<K, V> withNoKeyBounds(final Optional<Long> windowLower, final Optional<Long> windowUpper) {
        return new WindowRangeQuery<>(Optional.empty(), Optional.empty(), windowLower, windowUpper);
    }

    public Optional<K> getKeyLowerBound() {
        return lower;
    }

    public Optional<K> getKeyUpperBound() {
        return upper;
    }

    public Optional<Long> getWindowLowerBound() {
        return windowLower;
    }

    public Optional<Long> getWindowUpperBound() {
        return windowUpper;
    }
}

Examples

The following example illustrates the use of the WindowKeyQuey class.

Integer key = 1;
long lowerBound = beginningOfDay();
 
StateQueryRequest<byte[]> query =
  inStore("rocksdbwindowstore")
  .withQuery(WindowKeyQuery.withKey(key, lowerBound));
       
// run the query
StateQueryResult<byte[]> result = kafkaStreams.query(query);

The following example illustrates the use of the WindowQuery class.

Integer key1 = 1;
Integer key2 = 2;
long lowerBound = beginningOfDay();
long upperBound = now();
 
StateQueryRequest<KeyValueIterator<Windowed<Bytes>, byte[]>>, byte[]> query =
  inStore("rocksdbsessionstore")
  .withQuery(WindowQuery.withRange(key1, key2, lowerBound, upperBound));
       
// run the query
StateQueryResult<KeyValueIterator<Windowed<Bytes>>, byte[]> result = kafkaStreams.query(query);
  
// Get the results from all partitions.
final Map<Integer, QueryResult<KeyValueIterator<Windowed<Bytes>>, byte[]> partitionResults = rangeResult.getPartitionResults();
for (final Entry<Integer, QueryResult<KeyValueIterator<Windowed<Bytes>>, byte[]> entry : partitionResults.entrySet()) {
    try (final KeyValueIterator<Windowed<Bytes>>, byte[] keyValueIterator = entry.getValue().getResult()) {
        while (keyValueIterator.hasNext()) {
            final KeyValue<Bytes, byte[]> next = keyValueIterator.next();
            Bytes key = next.key.get;
            byte[] value = next.value;
        }
     }
}

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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