THIS IS A TEST INSTANCE. ALL YOUR CHANGES WILL BE LOST!!!!
Status
Current state: Accepted
Discussion thread: here [Change the link from the KIP proposal email archive to your own email thread]
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
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-969, this KIP introduces the isKeyAscending variable to determine whether keys are sorted in ascending order. It employs the withDescendingKeys() method to specify that the keys should be ordered in descending sequence, and the isKeyAscending() method to retrieve the value of isKeyAscending. 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.
/**
* 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>> {
...
private final boolean isKeyAscending;
/**
* Determines if the query keys are in ascending order.
* @return true if ascending, false otherwise.
*/
public boolean isKeyAscending();
...
/**
* Set the query to return keys in descending order.
* @return a new RangeQuery instance with descending flag set.
*/
public RangeQuery<K, V> withDescendingKeys();
...
}
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.
IQv2StoreIntegrationTest
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
RangeQueryclass, we can make some modifications to realize the concepts ofreverseRangeandreverseAll. To reiterate,reverseRangeandreverseAllare 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.
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;
}
}