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Status

Current state: Under Discussion

Discussion thread: here [Change the link from the KIP proposal email archive to your own email thread]

JIRA: Unable to render Jira issues macro, execution error.

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 reverseRange and reverseAll

Proposed Changes

The ReverseRangeQuery  class will be used for both reverseRange and reverseAll queries. A reverseAll is performed when no lower and no upper bound is specified. A reverseRange query retrieves a set of keys, specified using an upper and/or lower bound, from the underlying KV store. A reverseAll, on the other hand, retrieves all keys contained in the KV store.

ReverseRangeQuery
@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;
    }
}



Compatibility, Deprecation, and Migration Plan

  • Because we have already have RangeQuery, so we can achieve the ReverseRangeQuery following RangeQuery.
  • Since nothing is deprecated in this KIP, users have no need to migrate unless they want to.

Rejected Alternatives

Initially, we want to reuse the code in RangeQuery , but in the end, we find reuse the code will lead some problem, so we rewrite some methods to achieve ReverseRangeQuery .

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