gortiz commented on code in PR #8979: URL: https://github.com/apache/pinot/pull/8979#discussion_r1000205202
########## pinot-core/src/main/java/org/apache/pinot/core/operator/query/LinearSelectionOrderByOperator.java: ########## @@ -0,0 +1,452 @@ +/** + * 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. + */ +package org.apache.pinot.core.operator.query; + +import com.google.common.base.Preconditions; +import java.util.ArrayList; +import java.util.Collections; +import java.util.Comparator; +import java.util.Iterator; +import java.util.List; +import java.util.PriorityQueue; +import java.util.function.IntFunction; +import java.util.function.Supplier; +import javax.annotation.Nullable; +import org.apache.pinot.common.request.context.ExpressionContext; +import org.apache.pinot.common.request.context.OrderByExpressionContext; +import org.apache.pinot.common.utils.DataSchema; +import org.apache.pinot.core.common.BlockValSet; +import org.apache.pinot.core.common.Operator; +import org.apache.pinot.core.common.RowBasedBlockValueFetcher; +import org.apache.pinot.core.operator.BaseOperator; +import org.apache.pinot.core.operator.ExecutionStatistics; +import org.apache.pinot.core.operator.blocks.TransformBlock; +import org.apache.pinot.core.operator.blocks.results.SelectionResultsBlock; +import org.apache.pinot.core.operator.transform.TransformOperator; +import org.apache.pinot.core.operator.transform.TransformResultMetadata; +import org.apache.pinot.core.query.request.context.QueryContext; +import org.apache.pinot.core.query.selection.SelectionOperatorUtils; +import org.apache.pinot.core.query.utils.OrderByComparatorFactory; +import org.apache.pinot.segment.spi.IndexSegment; +import org.roaringbitmap.RoaringBitmap; + + +/** + * A selection Operator used when the first expressions in the order by are identifier expressions of columns that are + * already sorted (either ascendingly or descendingly), even if the tail of order by expressions are not sorted. + * + * ie: SELECT ... FROM Table WHERE predicates ORDER BY sorted_column DESC LIMIT 10 OFFSET 5 + * or: SELECT ... FROM Table WHERE predicates ORDER BY sorted_column, not_sorted LIMIT 10 OFFSET 5 + * but not SELECT ... FROM Table WHERE predicates ORDER BY not_sorted, sorted_column LIMIT 10 OFFSET 5 + * + * Operators that derives from this class are going to have an almost linear cost instead of the usual NlogN when actual + * sorting must be done, where N is the number of rows in the segment. + * There is a degraded scenario when the cost is actually NlogL (where L is the limit of the query) when all the first L + * rows have the exact same value for the prefix of the sorted columns. Even in that case, L should be quite smaller + * than N, so this implementation is algorithmically better than the normal solution. + */ +public abstract class LinearSelectionOrderByOperator extends BaseOperator<SelectionResultsBlock> { + protected final IndexSegment _indexSegment; + + protected final boolean _nullHandlingEnabled; + // Deduped order-by expressions followed by output expressions from SelectionOperatorUtils.extractExpressions() + protected final List<ExpressionContext> _expressions; + protected final List<ExpressionContext> _alreadySorted; + protected final List<ExpressionContext> _toSort; + + protected final TransformOperator _transformOperator; + protected final List<OrderByExpressionContext> _orderByExpressions; + protected final TransformResultMetadata[] _expressionsMetadata; + protected final int _numRowsToKeep; + private final Supplier<ListBuilder> _listBuilderSupplier; + protected boolean _used = false; + /** + * The comparator used to build the resulting {@link SelectionResultsBlock}, which sorts rows in reverse order to the + * one specified in the query. + */ + protected Comparator<Object[]> _comparator; + + /** + * + * @param expressions order by expressions must be at the head of the list. + * @param sortedExpr How many expressions at the head of the expression list are going to be considered sorted by + * {@link #fetch(Supplier<ListBuilder>)} + */ + public LinearSelectionOrderByOperator(IndexSegment indexSegment, QueryContext queryContext, + List<ExpressionContext> expressions, TransformOperator transformOperator, + int sortedExpr) { + _indexSegment = indexSegment; + _nullHandlingEnabled = queryContext.isNullHandlingEnabled(); + _expressions = expressions; + _transformOperator = transformOperator; + + _orderByExpressions = queryContext.getOrderByExpressions(); + assert _orderByExpressions != null; + int numOrderByExpressions = _orderByExpressions.size(); + + _alreadySorted = expressions.subList(0, sortedExpr); + _toSort = expressions.subList(sortedExpr, numOrderByExpressions); + + _expressionsMetadata = new TransformResultMetadata[_expressions.size()]; + for (int i = 0; i < _expressionsMetadata.length; i++) { + ExpressionContext expression = _expressions.get(i); + _expressionsMetadata[i] = _transformOperator.getResultMetadata(expression); + } + + _numRowsToKeep = queryContext.getOffset() + queryContext.getLimit(); + + if (_toSort.isEmpty()) { + int expectedSize = Math.min(SelectionOperatorUtils.MAX_ROW_HOLDER_INITIAL_CAPACITY, _numRowsToKeep); + _listBuilderSupplier = () -> new TotallySortedListBuilder(expectedSize); + } else { + int maxSize = Math.min(SelectionOperatorUtils.MAX_ROW_HOLDER_INITIAL_CAPACITY, _numRowsToKeep * 2); Review Comment: We don't actually needed it, but previous implementations used that list to add unsorted elements, so it was useful to increase the size a little bit to avoid resizings. -- This is an automated message from the Apache Git Service. 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