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Refactor GroupBy and TopN code to relax the constraint of dimensions …
…being comparable (#15559) The code in the groupBy engine and the topN engine assume that the dimensions are comparable and can call dimA.compareTo(dimB) to sort the dimensions and group them together. This works well for the primitive dimensions, because they are Comparable, however falls apart when the dimensions can be arrays (or in future scenarios complex columns). In cases when the dimensions are not comparable, Druid resorts to having a wrapper type ComparableStringArray and ComparableList, which is a Comparable, based on the list comparator.
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128
processing/src/main/java/org/apache/druid/query/DimensionComparisonUtils.java
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| /* | ||
| * Licensed to the Apache Software Foundation (ASF) under one | ||
| * or more contributor license agreements. See the NOTICE file | ||
| * distributed with this work for additional information | ||
| * regarding copyright ownership. The ASF licenses this file | ||
| * to you under the Apache License, Version 2.0 (the | ||
| * "License"); you may not use this file except in compliance | ||
| * with the License. You may obtain a copy of the License at | ||
| * | ||
| * http://www.apache.org/licenses/LICENSE-2.0 | ||
| * | ||
| * Unless required by applicable law or agreed to in writing, | ||
| * software distributed under the License is distributed on an | ||
| * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY | ||
| * KIND, either express or implied. See the License for the | ||
| * specific language governing permissions and limitations | ||
| * under the License. | ||
| */ | ||
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| package org.apache.druid.query; | ||
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| import org.apache.druid.query.ordering.StringComparator; | ||
| import org.apache.druid.query.ordering.StringComparators; | ||
| import org.apache.druid.segment.column.ColumnCapabilities; | ||
| import org.apache.druid.segment.column.ValueType; | ||
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| import java.util.Comparator; | ||
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| /** | ||
| * Utility class to compare dimensions | ||
| */ | ||
| public class DimensionComparisonUtils | ||
| { | ||
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| /** | ||
| * Checks if the comparator is the natural comparator for the given type. Natural comparator for a type is the | ||
| * comparator that will yield the same results as a.compareTo(b) for objects a, b belonging to that valueType. In such | ||
| * cases, it'll be faster to directly use the comparison methods provided by Java or the library, as using the | ||
| * StringComparator would be slow. | ||
| * MSQ only supports natural comparators | ||
| */ | ||
| public static boolean isNaturalComparator(final ValueType type, final StringComparator comparator) | ||
| { | ||
| if (StringComparators.NATURAL.equals(comparator)) { | ||
| return true; | ||
| } | ||
| return ((type == ValueType.STRING && StringComparators.LEXICOGRAPHIC.equals(comparator)) | ||
| || (type.isNumeric() && StringComparators.NUMERIC.equals(comparator))) | ||
| && !type.isArray(); | ||
| } | ||
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| /** | ||
| * Creates a list comparator with custom comparator for the elements. This is used to support weird usecases where the | ||
| * list dimensions can have custom comparators, and cannot be handled with | ||
| * {@link ColumnCapabilities#getNullableStrategy()}. These queries can only be generated with native queries. | ||
| */ | ||
| public static class ArrayComparator<T> implements Comparator<Object[]> | ||
| { | ||
| /** | ||
| * Custom element comparator. The comparator should handle null types as well | ||
| */ | ||
| private final Comparator<T> elementComparator; | ||
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| public ArrayComparator(Comparator<T> elementComparator) | ||
| { | ||
| this.elementComparator = elementComparator; | ||
| } | ||
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| @Override | ||
| public int compare(Object[] lhs, Object[] rhs) | ||
| { | ||
| //noinspection ArrayEquality | ||
| if (lhs == rhs) { | ||
| return 0; | ||
| } | ||
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| if (lhs == null) { | ||
| return -1; | ||
| } | ||
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| if (rhs == null) { | ||
| return 1; | ||
| } | ||
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| final int minSize = Math.min(lhs.length, rhs.length); | ||
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| for (int index = 0; index < minSize; ++index) { | ||
| Object lhsElement = lhs[index]; | ||
| Object rhsElement = rhs[index]; | ||
| int cmp = elementComparator.compare(coerceElement(lhsElement), coerceElement(rhsElement)); | ||
| if (cmp != 0) { | ||
| return cmp; | ||
| } | ||
| } | ||
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| if (lhs.length == rhs.length) { | ||
| return 0; | ||
| } else if (lhs.length < rhs.length) { | ||
| return -1; | ||
| } | ||
| return 1; | ||
| } | ||
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| protected T coerceElement(Object element) | ||
| { | ||
| return (T) element; | ||
| } | ||
| } | ||
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| /** | ||
| * Array comparator that converts the elements to their string representation, before comparing the values using | ||
| * the provided {@link StringComparator}. It can be used when the user provides weird comparators for their | ||
| * string arrays | ||
| */ | ||
| public static class ArrayComparatorForUnnaturalStringComparator extends ArrayComparator<String> | ||
| { | ||
| public ArrayComparatorForUnnaturalStringComparator(StringComparator elementComparator) | ||
| { | ||
| super(elementComparator); | ||
| } | ||
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| @Override | ||
| protected String coerceElement(Object element) | ||
| { | ||
| return String.valueOf(element); | ||
| } | ||
| } | ||
| } |
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