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Status

Current state:  [One of "Under Discussion", "Accepted", "Rejected"]

Discussion thread: here [Change the link from the KIP proposal email archive to your own email thread]
JIRA: here [Change the link from KAFKA-1 to your own ticket]

Voting thread: https://lists.apache.org/thread/xxyb5yyqrsdxsyxxbjhvnlxw5fl8xd0c

JIRA:

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

Motivation

Describe the problems you are trying to solve.

Public Interfaces

Briefly list any new interfaces that will be introduced as part of this proposal or any existing interfaces that will be removed or changed. The purpose of this section is to concisely call out the public contract that will come along with this feature.

A public interface is any change to the following:

• Binary log format

• The network protocol and api behavior

• Any class in the public packages under clientsConfiguration, especially client configuration

  • org/apache/kafka/common/serialization

  • org/apache/kafka/common

  • org/apache/kafka/common/errors

  • org/apache/kafka/clients/producer

  • org/apache/kafka/clients/consumer (eventually, once stable)

• Monitoring

• Command line tools and arguments

• Anything else that will likely break existing users in some way when they upgrade

Proposed Changes

Describe the new thing you want to do in appropriate detail. This may be fairly extensive and have large subsections of its own. Or it may be a few sentences. Use judgement based on the scope of the change.

Compatibility, Deprecation, and Migration Plan

• What impact (if any) will there be on existing users?
• If we are changing behavior how will we phase out the older behavior?
• If we need special migration tools, describe them here.
• When will we remove the existing behavior?

Test Plan

Describe in few sentences how the KIP will be tested. We are mostly interested in system tests (since unit-tests are specific to implementation details). How will we know that the implementation works as expected? How will we know nothing broke?

Rejected Alternatives

...

The concepts of reverseRange and reverseAll are not tied to any specific method or class. Rather, they represent functionalities we wish to achieve. Currently, with RangeQuery, we can use methods like withRange(), withLowerBound(), withUpperBound(), and withNoBounds().

Utilizing these, the query results are ordered based on the serialized byte[] of the keys, not the 'logical' key order.

Take IQv2StoreIntegrationTest as an example: we have two partitions with four key-value pairs:

• <0,0> in Partition0
• <1,1> in Partition1
• <2,2> in Partition0
• <3,3> in Partition1

When we use RangeQuery.withRange(1,3), the returned result is:

• Partition0: [2]
• Partition1: [1, 3]

To achieve the functionalities of reverseRange and reverseAll, we can introduce a method named withDescendingKeys() for reversed queries. For example, by using RangeQuery.withRange(1,3).withDescendingKeys(), the expected result would be:

• Partition0: [2]
• Partition1: [3, 1]

This means the results are in the reverse order of their keys.

To ensure that we can achieve this functionality, the keys in both RocksDB  and InMemoryKeyValueStore  should be sorted. We know that RocksDB  keys are inherently sorted. After investigation, we found that InMemoryKeyValueStore  uses a TreeMap, implying its keys are also sorted. Therefore, performing the aforementioned queries is feasible.

Proposed Changes

According to KIP-968, this KIP introduces the public enum ResultOrder to determine whether keys are sorted in ascending or descending  or unordered order. Order is based on the serialized byte[] of the keys, not the 'logical' key order. employs the withDescendingKeys() and withAscendingKeys() methods to specify that the keys should be ordered in descending or ascending or unordered sequence, and the resultOrder() method to retrieve the value of enum value in  ResultOrder. I've incorporated these variables and methods into the RangeQuery class and modified some method inputs. As a result, we can now use withDescendingKeys() to obtain results in reverse order and use withAscendingKeys to obtain the result in ascending order.

/**
 * Interactive query for issuing range queries and scans over KeyValue stores.
 * <p>
 *  A range query retrieves a set of records, specified using an upper and/or lower bound on the keys.
 * <p>
 * A scan query retrieves all records contained in the store.
 * <p>
 */
@Evolving
public final class RangeQuery<K, V> implements Query<KeyValueIterator<K, V>> {
    ...  

	/**
     * Determines if the serialized byte[] of the keys in ascending or descending or unordered order.
     * Order is based on the serialized byte[] of the keys, not the 'logical' key order.
     * @return return the order of returned records based on the serialized byte[] of the keys (can be unordered, or in ascending or in descending order).
     */
    public ResultOrder resultOrder() 

    /**
     * Set the query to return the serialized byte[] of the keys in descending order.
     * Order is based on the serialized byte[] of the keys, not the 'logical' key order.
     * @return a new RangeQuery instance with descending flag set.
     */
    public RangeQuery<K, V> withDescendingKeys() 

    /**
     * Set the query to return the serialized byte[] of the keys in ascending order.
     * Order is based on the serialized byte[] of the keys, not the 'logical' key order.
     * @return a new RangeQuery instance with ascending flag set.
     */
    public RangeQuery<K, V> withAscendingKeys()
      ...
}

According to KIP-968, we introduce a public enum ResultOrder.

ResultOrder enum
It helps with specifying the order of the returned results by the query.

package org.apache.kafka.streams.query;
 
public enum ResultOrder {
    ANY,
    ASCENDING,
    DESCENDING
}

Test Plan

This time, our goal is to implement reverseRange and reverseAll functionalities. While these terms are used for clarity, in practice, they correspond to RangeQuery.withRange().withDescendingKeys() and RangeQuery.withNoBounds().withDescendingKeys(), respectively. To ensure the accurate retrieval of results for both functionalities, adjustments to IQv2StoreIntegrationTest are required. In our previous approach, we stored query results in a set, which doesn't maintain order. I've transitioned to using a list for storing query results, enabling us to distinguish between rangeQuery and reverseQuery. Here, rangeQuery refers to standard queries (those not using withDescendingKeys()) such as withRange(), withLowerBound(), withUpperBound(), and withNoBounds(). In contrast, reverseQuery denotes queries that employ the withDescendingKeys() method.

We've transitioned the expectedValue from a Set to a List and arranged the partition numbers in order. This organization assists us in predicting the results. If the partition numbers were random, predicting the outcome would be challenging. Ultimately, this enables us to obtain and store the answer in the expectedValue. Consequently, the results between rangeQuery and reverseQuery will differ.

public class IQv2StoreIntegrationTest {
...
 @SuppressWarnings("unchecked")
    public <V> void shouldHandleRangeQuery(
		final Optional<Integer> lower,
        final Optional<Integer> upper,
        final boolean isKeyAscending,
        final Function<V, Integer> valueExtactor,
        final List<Integer> expectedValue) {

        final RangeQuery<Integer, V> query;

        if (isKeyAscending) {
            query = RangeQuery.withRange(lower.orElse(null), upper.orElse(null));
        } else {
            query = (RangeQuery<Integer, V>) RangeQuery.withRange(lower.orElse(null), upper.orElse(null)).withDescendingKeys();
        }
        ...
        } else {
            final List<Integer> actualValue = new ArrayList<>();
           ...
            final List<Integer> partitions = new ArrayList<>(queryResult.keySet());
            partitions.sort(null);
            for (final int partition : partitions) {
		...
		}
   ...
}

Compatibility, Deprecation, and Migration Plan

• Utilizing the existing RangeQuery class, we can make some modifications to realize the concepts of reverseRange  and reverseAll . To reiterate, reverseRange  and reverseAll  are not classes or methods but merely concepts.
• Since nothing is deprecated in this KIP, users have no need to migrate unless they want to.

Rejected Alternatives

After initial plans to create a ReverseRangeQuery from the ground up, we opted to leverage existing code from the RangeQuery class following further discussions.

@Evolving
public final class ReverseRangeQuery<K, V> implements Query<KeyValueIterator<K, V>> {

    private final Optional<K> lower;
    private final Optional<K> upper;

    private ReverseRangeQuery(final Optional<K> lower, final Optional<K> upper) {
        this.lower = lower;
        this.upper = upper;
    }

    /**
     * Interactive range query using a lower and upper bound to filter the keys returned.
     * @param lower The key that specifies the lower bound of the range
     * @param upper The key that specifies the upper bound of the range
     * @param <K> The key type
     * @param <V> The value type
     */
    public static <K, V> ReverseRangeQuery<K, V> withRange(final K lower, final K upper) {
        return new ReverseRangeQuery<>(Optional.ofNullable(lower), Optional.ofNullable(upper));
    }

    /**
     * Interactive range query using an upper bound to filter the keys returned.
     * If both <K,V> are null, RangQuery returns a full range scan.
     * @param upper The key that specifies the upper bound of the range
     * @param <K> The key type
     * @param <V> The value type
     */
    public static <K, V> ReverseRangeQuery<K, V> withUpperBound(final K upper) {
        return new ReverseRangeQuery<>(Optional.empty(), Optional.of(upper));
    }

    /**
     * Interactive range query using a lower bound to filter the keys returned.
     * @param lower The key that specifies the lower bound of the range
     * @param <K> The key type
     * @param <V> The value type
     */
    public static <K, V> ReverseRangeQuery<K, V> withLowerBound(final K lower) {
        return new ReverseRangeQuery<>(Optional.of(lower), Optional.empty());
    }

    /**
     * Interactive scan query that returns all records in the store.
     * @param <K> The key type
     * @param <V> The value type
     */
    public static <K, V> ReverseRangeQuery<K, V> withNoBounds() {
        return new ReverseRangeQuery<>(Optional.empty(), Optional.empty());
    }

    /**
     * The lower bound of the query, if specified.
     */
    public Optional<K> getLowerBound() {
        return lower;
    }

    /**
     * The upper bound of the query, if specified
     */
    public Optional<K> getUpperBound() {
        return upper;
    }
}