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Posted to commits@pinot.apache.org by GitBox <gi...@apache.org> on 2022/10/19 19:34:43 UTC
[GitHub] [pinot] Jackie-Jiang commented on a diff in pull request #8979: optimize `order by sorted ASC, unsorted` and `order by DESC` cases
Jackie-Jiang commented on code in PR #8979:
URL: https://github.com/apache/pinot/pull/8979#discussion_r999853860
##########
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);
+
+ Comparator<Object[]> sortedComparator = OrderByComparatorFactory.getComparator(_orderByExpressions,
+ _expressionsMetadata, false, _nullHandlingEnabled, 0, sortedExpr);
+ Comparator<Object[]> unsortedComparator = OrderByComparatorFactory.getComparator(_orderByExpressions,
+ _expressionsMetadata, false, _nullHandlingEnabled, sortedExpr, numOrderByExpressions);
+ _listBuilderSupplier = () -> new PartiallySortedListBuilder(maxSize, sortedComparator, unsortedComparator);
+ }
+
+ _comparator =
+ OrderByComparatorFactory.getComparator(_orderByExpressions, _expressionsMetadata, true, _nullHandlingEnabled);
+ }
+
+ @Override
+ public IndexSegment getIndexSegment() {
+ return _indexSegment;
+ }
+
+ @Override
+ public ExecutionStatistics getExecutionStatistics() {
+ long numEntriesScannedInFilter = _transformOperator.getExecutionStatistics().getNumEntriesScannedInFilter();
+ int numTotalDocs = _indexSegment.getSegmentMetadata().getTotalDocs();
+ return new ExecutionStatistics(getNumDocsScanned(), numEntriesScannedInFilter, getNumEntriesScannedPostFilter(),
+ numTotalDocs);
+ }
+
+ protected IntFunction<Object[]> fetchBlock(TransformBlock transformBlock, BlockValSet[] blockValSets) {
+ int numExpressions = _expressions.size();
+
+ for (int i = 0; i < numExpressions; i++) {
+ ExpressionContext expression = _expressions.get(i);
+ blockValSets[i] = transformBlock.getBlockValueSet(expression);
+ }
+ RowBasedBlockValueFetcher blockValueFetcher = new RowBasedBlockValueFetcher(blockValSets);
+
+ if (!_nullHandlingEnabled) {
+ return blockValueFetcher::getRow;
+ }
+ RoaringBitmap[] nullBitmaps = new RoaringBitmap[numExpressions];
+ for (int i = 0; i < numExpressions; i++) {
+ nullBitmaps[i] = blockValSets[i].getNullBitmap();
+ }
+ return (docId) -> {
+ Object[] row = blockValueFetcher.getRow(docId);
+ for (int colId = 0; colId < nullBitmaps.length; colId++) {
+ if (nullBitmaps[colId] != null && nullBitmaps[colId].contains(docId)) {
+ row[colId] = null;
+ }
+ }
+ return row;
+ };
+ }
+
+ protected abstract long getNumEntriesScannedPostFilter();
+
+ protected abstract int getNumDocsScanned();
+
+ /**
+ * Returns a list of rows sorted that:
+ * <ul>
+ * <li>At least contains all the rows that fulfill the predicate</li>
+ * <li>Rows are sorted in a way that is compatible with the given list builder supplier</li>
+ * </ul>
+ *
+ * That means that the result may contain more rows than required.
+ *
+ * @param listBuilderSupplier a {@link ListBuilder} supplier that should be used to create the result. Each time is
+ * called a new {@link ListBuilder} will be returned. All returned instances use the same
+ * comparator logic.
+ */
+ protected abstract List<Object[]> fetch(Supplier<ListBuilder> listBuilderSupplier);
+
+ @Override
+ public List<Operator> getChildOperators() {
+ return Collections.singletonList(_transformOperator);
+ }
+
+ protected abstract String getExplainName();
+
+ @Override
+ public String toExplainString() {
+ StringBuilder sb = new StringBuilder(getExplainName());
+
+ sb.append("(sortedList: ");
+ concatList(sb, _alreadySorted);
+
+ sb.append(", unsortedList: ");
+ concatList(sb, _toSort);
+
+ sb.append(", rest: ");
+ concatList(sb, _expressions.subList(_alreadySorted.size() + _toSort.size(), _expressions.size()));
+
+ sb.append(')');
+ return sb.toString();
+ }
+
+ private void concatList(StringBuilder sb, List<?> list) {
+ sb.append('(');
+ Iterator<?> it = list.iterator();
+ if (it.hasNext()) {
+ sb.append(it.next());
+ while (it.hasNext()) {
+ sb.append(", ").append(it.next());
+ }
+ }
+ sb.append(')');
+ }
+
+ @Override
+ protected SelectionResultsBlock getNextBlock() {
+ Preconditions.checkState(!_used, "nextBlock was called more than once");
+ _used = true;
+ List<Object[]> list = fetch(_listBuilderSupplier);
+
+ DataSchema dataSchema = createDataSchema();
+
+ if (list.size() > _numRowsToKeep) {
+ list = new ArrayList<>(list.subList(0, _numRowsToKeep));
+ }
+
+ SelectionResultsBlock resultsBlock = new SelectionResultsBlock(dataSchema, list, _comparator);
+
+ return resultsBlock;
+ }
+
+ protected DataSchema createDataSchema() {
+ int numExpressions = _expressions.size();
+
+ // Create the data schema
+ String[] columnNames = new String[numExpressions];
+ DataSchema.ColumnDataType[] columnDataTypes = new DataSchema.ColumnDataType[numExpressions];
+ for (int i = 0; i < columnNames.length; i++) {
+ columnNames[i] = _expressions.get(i).toString();
+ }
+ for (int i = 0; i < numExpressions; i++) {
+ TransformResultMetadata expressionMetadata = _expressionsMetadata[i];
+ columnDataTypes[i] =
+ DataSchema.ColumnDataType.fromDataType(expressionMetadata.getDataType(), expressionMetadata.isSingleValue());
+ }
+ return new DataSchema(columnNames, columnDataTypes);
+ }
+
+ /**
+ * A private class used to build a partially sorted list by adding partially sorted data.
+ *
+ * Specifically, this class has been designed to receive successive calls to {@link #add(Object[])} follow by a single
+ * call to {@link #build()}.
+ *
+ * Rows must be inserted in ascending order accordingly to the partial order specified by a comparator.
+ * This comparator will define <i>partitions</i> of rows. All the rows in the same partition same are considered equal
+ * by that comparator.
+ *
+ * When calling {@link #add(Object[])} with a row that doesn't belong to the current partition, the previous partition
+ * is <em>closed</em> and a new one is started.
+ *
+ * The method {@link #sortedSize()} returns the number of elements stored in all closed partitions.
+ */
+ protected interface ListBuilder {
+
+ /**
+ * Adds the given row to this object. The new column must be equal or higher than previous inserted elements
+ * according to the partition comparator.
+ *
+ * @param row The row to add. The values of the already sorted columns must be equal or higher than the last added
+ * row, if any.
+ * @return true if and only if the previous partition was closed.
+ */
+ boolean add(Object[] row);
+
+ /**
+ * Builds the sorted list. The current partition will be <em>closed</em>.
+ *
+ * Once this method is called, the builder should not be used. There is no guaranteed on whether
+ * {@link #sortedSize()} is updated or not.
+ */
+ List<Object[]> build();
+
+ /**
+ * How many elements are actually sorted. This number is lower or equal to the number of elements that has been
+ * added.
+ */
+ int sortedSize();
+ }
+
+ /**
+ * This is the faster {@link ListBuilder} but also the most restrictive one. It can only be used when data is inserted
+ * in total order and therefore each element belong to its own partition.
+ *
+ * This builder cannot be used to implement order-by queries where there is at least one expression
+ * that is not sorted. In such case {@link PartiallySortedListBuilder} should be used.
+ *
+ * This implementation is just a wrapper over an ArrayList and therefore the average costs of its methods is constant.
+ */
+ protected static class TotallySortedListBuilder implements ListBuilder {
+ private final ArrayList<Object[]> _list;
+
+ public TotallySortedListBuilder(int expectedSize) {
+ _list = new ArrayList<>(expectedSize);
+ }
+
+ @Override
+ public boolean add(Object[] row) {
+ _list.add(row);
+ return true;
+ }
+
+ @Override
+ public List<Object[]> build() {
+ return _list;
+ }
+
+ @Override
+ public int sortedSize() {
+ return _list.size();
+ }
+ }
+
+ /**
+ * This {@link ListBuilder} is size bound and requires two comparators: The first defines the partitions and the
+ * second defines an order inside each partition.
+ *
+ * This class does never store more than the requested number of elements. In case more elements are inserted:
+ * <ul>
+ * <li>If the new element belongs to a higher partition, it is discarded.</li>
+ * <li>If the new element belongs to the last included partition, the last partition is treated as a priority queue
+ * sorted by the in-partition comparator. If the new element is lower than some of the already inserted elements,
+ * the new replace the older.</li>
+ * </ul>
+ *
+ * This class can be used to implement order-by queries that include one or more not sorted expressions.
+ * In cases where all expressions are sorted, {@link TotallySortedListBuilder} should be used because its performance
+ * is better.
+ *
+ * As usual, elements are sorted by partition and there is no order guarantee inside each partition. The second
+ * comparator is only used to keep the lower elements in the last partition.
+ */
+ private static class PartiallySortedListBuilder implements ListBuilder {
+ /**
+ * A list with all the elements that have been already sorted.
+ */
+ private final ArrayList<Object[]> _sorted;
+ /**
+ * This attribute is used to store the last partition when the builder already contains {@link #_maxSize} elements.
+ */
+ private PriorityQueue<Object[]> _lastPartitionQueue = null;
+ /**
+ * The comparator that defines the partitions and the one that impose in which order add has to be called.
+ */
+ private final Comparator<Object[]> _partitionComparator;
+ /**
+ * The comparator that sorts different rows on each partition.
+ */
+ private final Comparator<Object[]> _unsortedComparator;
+ @Nullable
+ private Object[] _lastPartitionRow;
+ private final int _maxSize;
+ private int _alreadySorted;
+
+ public PartiallySortedListBuilder(int maxSize, Comparator<Object[]> partitionComparator,
+ Comparator<Object[]> unsortedComparator) {
+ Preconditions.checkArgument(maxSize > 0, "Max size must be greater than 0");
+ _maxSize = maxSize;
+ _sorted = new ArrayList<>(maxSize);
+ _partitionComparator = partitionComparator;
+ _unsortedComparator = unsortedComparator;
+ }
+
+ @Override
+ public boolean add(Object[] row) {
+ if (_lastPartitionRow == null) {
+ _lastPartitionRow = row;
+ _sorted.add(row);
+ return false;
+ }
+ int cmp = _partitionComparator.compare(row, _lastPartitionRow);
+ if (cmp < 0) {
+ throw new IllegalArgumentException(
+ "Row with docId " + _sorted.size() + " is not sorted compared to the previous one");
+ }
+
+ boolean newPartition = cmp > 0;
+ if (_sorted.size() < _maxSize) { // we don't have _maxSize elements yet
+ if (newPartition) {
+ _lastPartitionRow = row;
+ _alreadySorted = _sorted.size();
+ }
+ // just add the new row to the result list
+ _sorted.add(row);
+ return newPartition;
+ }
+ // at least _maxSize have been added
+ if (newPartition) { // and the new element belongs to a new partition, so we can just ignore it
+ return true;
+ }
+ // new element doesn't belong to a new partition, so we may need to add it
+ if (_lastPartitionQueue == null) { // we have exactly _maxSize elements, and the new belongs to the last partition
+ // we need to prepare the priority queue
+ buildPriorityQueue();
+ }
+ // add the new element if it is lower than the greatest element stored in the partition
Review Comment:
The logic of adding row to the priority queue is missing
##########
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:
Why do we need this `*2`?
##########
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);
+
+ Comparator<Object[]> sortedComparator = OrderByComparatorFactory.getComparator(_orderByExpressions,
+ _expressionsMetadata, false, _nullHandlingEnabled, 0, sortedExpr);
+ Comparator<Object[]> unsortedComparator = OrderByComparatorFactory.getComparator(_orderByExpressions,
+ _expressionsMetadata, false, _nullHandlingEnabled, sortedExpr, numOrderByExpressions);
+ _listBuilderSupplier = () -> new PartiallySortedListBuilder(maxSize, sortedComparator, unsortedComparator);
+ }
+
+ _comparator =
+ OrderByComparatorFactory.getComparator(_orderByExpressions, _expressionsMetadata, true, _nullHandlingEnabled);
+ }
+
+ @Override
+ public IndexSegment getIndexSegment() {
+ return _indexSegment;
+ }
+
+ @Override
+ public ExecutionStatistics getExecutionStatistics() {
+ long numEntriesScannedInFilter = _transformOperator.getExecutionStatistics().getNumEntriesScannedInFilter();
+ int numTotalDocs = _indexSegment.getSegmentMetadata().getTotalDocs();
+ return new ExecutionStatistics(getNumDocsScanned(), numEntriesScannedInFilter, getNumEntriesScannedPostFilter(),
+ numTotalDocs);
+ }
+
+ protected IntFunction<Object[]> fetchBlock(TransformBlock transformBlock, BlockValSet[] blockValSets) {
+ int numExpressions = _expressions.size();
+
+ for (int i = 0; i < numExpressions; i++) {
+ ExpressionContext expression = _expressions.get(i);
+ blockValSets[i] = transformBlock.getBlockValueSet(expression);
+ }
+ RowBasedBlockValueFetcher blockValueFetcher = new RowBasedBlockValueFetcher(blockValSets);
+
+ if (!_nullHandlingEnabled) {
+ return blockValueFetcher::getRow;
+ }
+ RoaringBitmap[] nullBitmaps = new RoaringBitmap[numExpressions];
+ for (int i = 0; i < numExpressions; i++) {
+ nullBitmaps[i] = blockValSets[i].getNullBitmap();
+ }
+ return (docId) -> {
+ Object[] row = blockValueFetcher.getRow(docId);
+ for (int colId = 0; colId < nullBitmaps.length; colId++) {
+ if (nullBitmaps[colId] != null && nullBitmaps[colId].contains(docId)) {
+ row[colId] = null;
+ }
+ }
+ return row;
+ };
+ }
+
+ protected abstract long getNumEntriesScannedPostFilter();
+
+ protected abstract int getNumDocsScanned();
+
+ /**
+ * Returns a list of rows sorted that:
+ * <ul>
+ * <li>At least contains all the rows that fulfill the predicate</li>
+ * <li>Rows are sorted in a way that is compatible with the given list builder supplier</li>
+ * </ul>
+ *
+ * That means that the result may contain more rows than required.
+ *
+ * @param listBuilderSupplier a {@link ListBuilder} supplier that should be used to create the result. Each time is
+ * called a new {@link ListBuilder} will be returned. All returned instances use the same
+ * comparator logic.
+ */
+ protected abstract List<Object[]> fetch(Supplier<ListBuilder> listBuilderSupplier);
+
+ @Override
+ public List<Operator> getChildOperators() {
+ return Collections.singletonList(_transformOperator);
+ }
+
+ protected abstract String getExplainName();
+
+ @Override
+ public String toExplainString() {
+ StringBuilder sb = new StringBuilder(getExplainName());
+
+ sb.append("(sortedList: ");
+ concatList(sb, _alreadySorted);
+
+ sb.append(", unsortedList: ");
+ concatList(sb, _toSort);
+
+ sb.append(", rest: ");
+ concatList(sb, _expressions.subList(_alreadySorted.size() + _toSort.size(), _expressions.size()));
+
+ sb.append(')');
+ return sb.toString();
+ }
+
+ private void concatList(StringBuilder sb, List<?> list) {
+ sb.append('(');
+ Iterator<?> it = list.iterator();
+ if (it.hasNext()) {
+ sb.append(it.next());
+ while (it.hasNext()) {
+ sb.append(", ").append(it.next());
+ }
+ }
+ sb.append(')');
+ }
+
+ @Override
+ protected SelectionResultsBlock getNextBlock() {
+ Preconditions.checkState(!_used, "nextBlock was called more than once");
+ _used = true;
+ List<Object[]> list = fetch(_listBuilderSupplier);
+
+ DataSchema dataSchema = createDataSchema();
+
+ if (list.size() > _numRowsToKeep) {
+ list = new ArrayList<>(list.subList(0, _numRowsToKeep));
+ }
+
+ SelectionResultsBlock resultsBlock = new SelectionResultsBlock(dataSchema, list, _comparator);
+
+ return resultsBlock;
+ }
+
+ protected DataSchema createDataSchema() {
+ int numExpressions = _expressions.size();
+
+ // Create the data schema
+ String[] columnNames = new String[numExpressions];
+ DataSchema.ColumnDataType[] columnDataTypes = new DataSchema.ColumnDataType[numExpressions];
+ for (int i = 0; i < columnNames.length; i++) {
+ columnNames[i] = _expressions.get(i).toString();
+ }
+ for (int i = 0; i < numExpressions; i++) {
+ TransformResultMetadata expressionMetadata = _expressionsMetadata[i];
+ columnDataTypes[i] =
+ DataSchema.ColumnDataType.fromDataType(expressionMetadata.getDataType(), expressionMetadata.isSingleValue());
+ }
+ return new DataSchema(columnNames, columnDataTypes);
+ }
+
+ /**
+ * A private class used to build a partially sorted list by adding partially sorted data.
+ *
+ * Specifically, this class has been designed to receive successive calls to {@link #add(Object[])} follow by a single
+ * call to {@link #build()}.
+ *
+ * Rows must be inserted in ascending order accordingly to the partial order specified by a comparator.
+ * This comparator will define <i>partitions</i> of rows. All the rows in the same partition same are considered equal
+ * by that comparator.
+ *
+ * When calling {@link #add(Object[])} with a row that doesn't belong to the current partition, the previous partition
+ * is <em>closed</em> and a new one is started.
+ *
+ * The method {@link #sortedSize()} returns the number of elements stored in all closed partitions.
+ */
+ protected interface ListBuilder {
+
+ /**
+ * Adds the given row to this object. The new column must be equal or higher than previous inserted elements
+ * according to the partition comparator.
+ *
+ * @param row The row to add. The values of the already sorted columns must be equal or higher than the last added
+ * row, if any.
+ * @return true if and only if the previous partition was closed.
+ */
+ boolean add(Object[] row);
+
+ /**
+ * Builds the sorted list. The current partition will be <em>closed</em>.
+ *
+ * Once this method is called, the builder should not be used. There is no guaranteed on whether
+ * {@link #sortedSize()} is updated or not.
+ */
+ List<Object[]> build();
+
+ /**
+ * How many elements are actually sorted. This number is lower or equal to the number of elements that has been
+ * added.
+ */
+ int sortedSize();
+ }
+
+ /**
+ * This is the faster {@link ListBuilder} but also the most restrictive one. It can only be used when data is inserted
+ * in total order and therefore each element belong to its own partition.
+ *
+ * This builder cannot be used to implement order-by queries where there is at least one expression
+ * that is not sorted. In such case {@link PartiallySortedListBuilder} should be used.
+ *
+ * This implementation is just a wrapper over an ArrayList and therefore the average costs of its methods is constant.
+ */
+ protected static class TotallySortedListBuilder implements ListBuilder {
+ private final ArrayList<Object[]> _list;
+
+ public TotallySortedListBuilder(int expectedSize) {
+ _list = new ArrayList<>(expectedSize);
+ }
+
+ @Override
+ public boolean add(Object[] row) {
+ _list.add(row);
+ return true;
+ }
+
+ @Override
+ public List<Object[]> build() {
+ return _list;
+ }
+
+ @Override
+ public int sortedSize() {
+ return _list.size();
+ }
+ }
+
+ /**
+ * This {@link ListBuilder} is size bound and requires two comparators: The first defines the partitions and the
+ * second defines an order inside each partition.
+ *
+ * This class does never store more than the requested number of elements. In case more elements are inserted:
+ * <ul>
+ * <li>If the new element belongs to a higher partition, it is discarded.</li>
+ * <li>If the new element belongs to the last included partition, the last partition is treated as a priority queue
+ * sorted by the in-partition comparator. If the new element is lower than some of the already inserted elements,
+ * the new replace the older.</li>
+ * </ul>
+ *
+ * This class can be used to implement order-by queries that include one or more not sorted expressions.
+ * In cases where all expressions are sorted, {@link TotallySortedListBuilder} should be used because its performance
+ * is better.
+ *
+ * As usual, elements are sorted by partition and there is no order guarantee inside each partition. The second
+ * comparator is only used to keep the lower elements in the last partition.
+ */
+ private static class PartiallySortedListBuilder implements ListBuilder {
+ /**
+ * A list with all the elements that have been already sorted.
+ */
+ private final ArrayList<Object[]> _sorted;
+ /**
+ * This attribute is used to store the last partition when the builder already contains {@link #_maxSize} elements.
+ */
+ private PriorityQueue<Object[]> _lastPartitionQueue = null;
+ /**
+ * The comparator that defines the partitions and the one that impose in which order add has to be called.
+ */
+ private final Comparator<Object[]> _partitionComparator;
+ /**
+ * The comparator that sorts different rows on each partition.
+ */
+ private final Comparator<Object[]> _unsortedComparator;
+ @Nullable
+ private Object[] _lastPartitionRow;
+ private final int _maxSize;
+ private int _alreadySorted;
+
+ public PartiallySortedListBuilder(int maxSize, Comparator<Object[]> partitionComparator,
+ Comparator<Object[]> unsortedComparator) {
+ Preconditions.checkArgument(maxSize > 0, "Max size must be greater than 0");
+ _maxSize = maxSize;
+ _sorted = new ArrayList<>(maxSize);
+ _partitionComparator = partitionComparator;
+ _unsortedComparator = unsortedComparator;
+ }
+
+ @Override
+ public boolean add(Object[] row) {
+ if (_lastPartitionRow == null) {
+ _lastPartitionRow = row;
+ _sorted.add(row);
+ return false;
+ }
+ int cmp = _partitionComparator.compare(row, _lastPartitionRow);
+ if (cmp < 0) {
+ throw new IllegalArgumentException(
+ "Row with docId " + _sorted.size() + " is not sorted compared to the previous one");
+ }
+
+ boolean newPartition = cmp > 0;
+ if (_sorted.size() < _maxSize) { // we don't have _maxSize elements yet
+ if (newPartition) {
+ _lastPartitionRow = row;
+ _alreadySorted = _sorted.size();
+ }
+ // just add the new row to the result list
+ _sorted.add(row);
+ return newPartition;
+ }
+ // at least _maxSize have been added
+ if (newPartition) { // and the new element belongs to a new partition, so we can just ignore it
+ return true;
Review Comment:
`_alreadySorted` is not updated, which can cause the while check for `sortedSize()` never able to reach
##########
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);
+
+ Comparator<Object[]> sortedComparator = OrderByComparatorFactory.getComparator(_orderByExpressions,
+ _expressionsMetadata, false, _nullHandlingEnabled, 0, sortedExpr);
+ Comparator<Object[]> unsortedComparator = OrderByComparatorFactory.getComparator(_orderByExpressions,
+ _expressionsMetadata, false, _nullHandlingEnabled, sortedExpr, numOrderByExpressions);
+ _listBuilderSupplier = () -> new PartiallySortedListBuilder(maxSize, sortedComparator, unsortedComparator);
+ }
+
+ _comparator =
+ OrderByComparatorFactory.getComparator(_orderByExpressions, _expressionsMetadata, true, _nullHandlingEnabled);
+ }
+
+ @Override
+ public IndexSegment getIndexSegment() {
+ return _indexSegment;
+ }
+
+ @Override
+ public ExecutionStatistics getExecutionStatistics() {
+ long numEntriesScannedInFilter = _transformOperator.getExecutionStatistics().getNumEntriesScannedInFilter();
+ int numTotalDocs = _indexSegment.getSegmentMetadata().getTotalDocs();
+ return new ExecutionStatistics(getNumDocsScanned(), numEntriesScannedInFilter, getNumEntriesScannedPostFilter(),
+ numTotalDocs);
+ }
+
+ protected IntFunction<Object[]> fetchBlock(TransformBlock transformBlock, BlockValSet[] blockValSets) {
+ int numExpressions = _expressions.size();
+
+ for (int i = 0; i < numExpressions; i++) {
+ ExpressionContext expression = _expressions.get(i);
+ blockValSets[i] = transformBlock.getBlockValueSet(expression);
+ }
+ RowBasedBlockValueFetcher blockValueFetcher = new RowBasedBlockValueFetcher(blockValSets);
+
+ if (!_nullHandlingEnabled) {
+ return blockValueFetcher::getRow;
+ }
+ RoaringBitmap[] nullBitmaps = new RoaringBitmap[numExpressions];
+ for (int i = 0; i < numExpressions; i++) {
+ nullBitmaps[i] = blockValSets[i].getNullBitmap();
+ }
+ return (docId) -> {
+ Object[] row = blockValueFetcher.getRow(docId);
+ for (int colId = 0; colId < nullBitmaps.length; colId++) {
+ if (nullBitmaps[colId] != null && nullBitmaps[colId].contains(docId)) {
+ row[colId] = null;
+ }
+ }
+ return row;
+ };
+ }
+
+ protected abstract long getNumEntriesScannedPostFilter();
+
+ protected abstract int getNumDocsScanned();
+
+ /**
+ * Returns a list of rows sorted that:
+ * <ul>
+ * <li>At least contains all the rows that fulfill the predicate</li>
+ * <li>Rows are sorted in a way that is compatible with the given list builder supplier</li>
+ * </ul>
+ *
+ * That means that the result may contain more rows than required.
+ *
+ * @param listBuilderSupplier a {@link ListBuilder} supplier that should be used to create the result. Each time is
+ * called a new {@link ListBuilder} will be returned. All returned instances use the same
+ * comparator logic.
+ */
+ protected abstract List<Object[]> fetch(Supplier<ListBuilder> listBuilderSupplier);
+
+ @Override
+ public List<Operator> getChildOperators() {
+ return Collections.singletonList(_transformOperator);
+ }
+
+ protected abstract String getExplainName();
+
+ @Override
+ public String toExplainString() {
+ StringBuilder sb = new StringBuilder(getExplainName());
+
+ sb.append("(sortedList: ");
+ concatList(sb, _alreadySorted);
+
+ sb.append(", unsortedList: ");
+ concatList(sb, _toSort);
+
+ sb.append(", rest: ");
+ concatList(sb, _expressions.subList(_alreadySorted.size() + _toSort.size(), _expressions.size()));
+
+ sb.append(')');
+ return sb.toString();
+ }
+
+ private void concatList(StringBuilder sb, List<?> list) {
+ sb.append('(');
+ Iterator<?> it = list.iterator();
+ if (it.hasNext()) {
+ sb.append(it.next());
+ while (it.hasNext()) {
+ sb.append(", ").append(it.next());
+ }
+ }
+ sb.append(')');
+ }
+
+ @Override
+ protected SelectionResultsBlock getNextBlock() {
+ Preconditions.checkState(!_used, "nextBlock was called more than once");
+ _used = true;
+ List<Object[]> list = fetch(_listBuilderSupplier);
+
+ DataSchema dataSchema = createDataSchema();
+
+ if (list.size() > _numRowsToKeep) {
+ list = new ArrayList<>(list.subList(0, _numRowsToKeep));
+ }
+
+ SelectionResultsBlock resultsBlock = new SelectionResultsBlock(dataSchema, list, _comparator);
+
+ return resultsBlock;
+ }
+
+ protected DataSchema createDataSchema() {
+ int numExpressions = _expressions.size();
+
+ // Create the data schema
+ String[] columnNames = new String[numExpressions];
+ DataSchema.ColumnDataType[] columnDataTypes = new DataSchema.ColumnDataType[numExpressions];
+ for (int i = 0; i < columnNames.length; i++) {
+ columnNames[i] = _expressions.get(i).toString();
+ }
+ for (int i = 0; i < numExpressions; i++) {
+ TransformResultMetadata expressionMetadata = _expressionsMetadata[i];
+ columnDataTypes[i] =
+ DataSchema.ColumnDataType.fromDataType(expressionMetadata.getDataType(), expressionMetadata.isSingleValue());
+ }
+ return new DataSchema(columnNames, columnDataTypes);
+ }
+
+ /**
+ * A private class used to build a partially sorted list by adding partially sorted data.
+ *
+ * Specifically, this class has been designed to receive successive calls to {@link #add(Object[])} follow by a single
+ * call to {@link #build()}.
+ *
+ * Rows must be inserted in ascending order accordingly to the partial order specified by a comparator.
+ * This comparator will define <i>partitions</i> of rows. All the rows in the same partition same are considered equal
+ * by that comparator.
+ *
+ * When calling {@link #add(Object[])} with a row that doesn't belong to the current partition, the previous partition
+ * is <em>closed</em> and a new one is started.
+ *
+ * The method {@link #sortedSize()} returns the number of elements stored in all closed partitions.
+ */
+ protected interface ListBuilder {
+
+ /**
+ * Adds the given row to this object. The new column must be equal or higher than previous inserted elements
+ * according to the partition comparator.
+ *
+ * @param row The row to add. The values of the already sorted columns must be equal or higher than the last added
+ * row, if any.
+ * @return true if and only if the previous partition was closed.
+ */
+ boolean add(Object[] row);
+
+ /**
+ * Builds the sorted list. The current partition will be <em>closed</em>.
+ *
+ * Once this method is called, the builder should not be used. There is no guaranteed on whether
+ * {@link #sortedSize()} is updated or not.
+ */
+ List<Object[]> build();
+
+ /**
+ * How many elements are actually sorted. This number is lower or equal to the number of elements that has been
+ * added.
+ */
+ int sortedSize();
+ }
+
+ /**
+ * This is the faster {@link ListBuilder} but also the most restrictive one. It can only be used when data is inserted
+ * in total order and therefore each element belong to its own partition.
+ *
+ * This builder cannot be used to implement order-by queries where there is at least one expression
+ * that is not sorted. In such case {@link PartiallySortedListBuilder} should be used.
+ *
+ * This implementation is just a wrapper over an ArrayList and therefore the average costs of its methods is constant.
+ */
+ protected static class TotallySortedListBuilder implements ListBuilder {
+ private final ArrayList<Object[]> _list;
+
+ public TotallySortedListBuilder(int expectedSize) {
+ _list = new ArrayList<>(expectedSize);
+ }
+
+ @Override
+ public boolean add(Object[] row) {
+ _list.add(row);
+ return true;
+ }
+
+ @Override
+ public List<Object[]> build() {
+ return _list;
+ }
+
+ @Override
+ public int sortedSize() {
+ return _list.size();
+ }
+ }
+
+ /**
+ * This {@link ListBuilder} is size bound and requires two comparators: The first defines the partitions and the
+ * second defines an order inside each partition.
+ *
+ * This class does never store more than the requested number of elements. In case more elements are inserted:
+ * <ul>
+ * <li>If the new element belongs to a higher partition, it is discarded.</li>
+ * <li>If the new element belongs to the last included partition, the last partition is treated as a priority queue
+ * sorted by the in-partition comparator. If the new element is lower than some of the already inserted elements,
+ * the new replace the older.</li>
+ * </ul>
+ *
+ * This class can be used to implement order-by queries that include one or more not sorted expressions.
+ * In cases where all expressions are sorted, {@link TotallySortedListBuilder} should be used because its performance
+ * is better.
+ *
+ * As usual, elements are sorted by partition and there is no order guarantee inside each partition. The second
+ * comparator is only used to keep the lower elements in the last partition.
+ */
+ private static class PartiallySortedListBuilder implements ListBuilder {
+ /**
+ * A list with all the elements that have been already sorted.
+ */
+ private final ArrayList<Object[]> _sorted;
+ /**
+ * This attribute is used to store the last partition when the builder already contains {@link #_maxSize} elements.
+ */
+ private PriorityQueue<Object[]> _lastPartitionQueue = null;
+ /**
+ * The comparator that defines the partitions and the one that impose in which order add has to be called.
+ */
+ private final Comparator<Object[]> _partitionComparator;
+ /**
+ * The comparator that sorts different rows on each partition.
+ */
+ private final Comparator<Object[]> _unsortedComparator;
+ @Nullable
+ private Object[] _lastPartitionRow;
+ private final int _maxSize;
+ private int _alreadySorted;
+
+ public PartiallySortedListBuilder(int maxSize, Comparator<Object[]> partitionComparator,
+ Comparator<Object[]> unsortedComparator) {
+ Preconditions.checkArgument(maxSize > 0, "Max size must be greater than 0");
+ _maxSize = maxSize;
+ _sorted = new ArrayList<>(maxSize);
+ _partitionComparator = partitionComparator;
+ _unsortedComparator = unsortedComparator;
+ }
+
+ @Override
+ public boolean add(Object[] row) {
+ if (_lastPartitionRow == null) {
+ _lastPartitionRow = row;
+ _sorted.add(row);
+ return false;
+ }
+ int cmp = _partitionComparator.compare(row, _lastPartitionRow);
+ if (cmp < 0) {
+ throw new IllegalArgumentException(
+ "Row with docId " + _sorted.size() + " is not sorted compared to the previous one");
+ }
+
+ boolean newPartition = cmp > 0;
+ if (_sorted.size() < _maxSize) { // we don't have _maxSize elements yet
+ if (newPartition) {
+ _lastPartitionRow = row;
+ _alreadySorted = _sorted.size();
+ }
+ // just add the new row to the result list
+ _sorted.add(row);
+ return newPartition;
+ }
+ // at least _maxSize have been added
+ if (newPartition) { // and the new element belongs to a new partition, so we can just ignore it
+ return true;
+ }
+ // new element doesn't belong to a new partition, so we may need to add it
+ if (_lastPartitionQueue == null) { // we have exactly _maxSize elements, and the new belongs to the last partition
+ // we need to prepare the priority queue
+ buildPriorityQueue();
+ }
+ // add the new element if it is lower than the greatest element stored in the partition
+ return false;
+ }
+
+ private void buildPriorityQueue() {
+ int maxPriorityQueueValues = _maxSize - _alreadySorted;
+ _lastPartitionQueue = new PriorityQueue<>(maxPriorityQueueValues, _unsortedComparator.reversed());
+ _lastPartitionQueue.addAll(_sorted.subList(_alreadySorted, _sorted.size()));
+ }
+
+ /**
+ * Sorts the rows and returns the sorted list.
+ *
+ * This object should not be used once this method is called.
+ *
+ * @return the list of all added rows, sorted by {@link #_partitionComparator} and then by
+ * {@link #_unsortedComparator}
+ */
+ @Override
+ public List<Object[]> build() {
+ if (_lastPartitionQueue != null) {
+ assert _lastPartitionQueue.size() == _sorted.size() - _alreadySorted;
+ Iterator<Object[]> lastPartitionIt = _lastPartitionQueue.iterator();
+ for (int i = _alreadySorted; i < _sorted.size(); i++) {
+ _sorted.set(i, lastPartitionIt.next());
+ }
+ }
+ return _sorted;
+ }
+
+ @Override
+ public int sortedSize() {
Review Comment:
Tracking this on the caller side and use it to decide whether to add more rows can be hard to manage. Instead, this logic can be managed internally
##########
pinot-core/src/main/java/org/apache/pinot/core/operator/query/SelectionPartiallyOrderedByDescOperation.java:
##########
@@ -0,0 +1,126 @@
+/**
+ * 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.Iterator;
+import java.util.List;
+import java.util.function.IntFunction;
+import java.util.function.Supplier;
+import org.apache.pinot.common.request.context.ExpressionContext;
+import org.apache.pinot.core.common.BlockValSet;
+import org.apache.pinot.core.operator.blocks.TransformBlock;
+import org.apache.pinot.core.operator.transform.TransformOperator;
+import org.apache.pinot.core.query.request.context.QueryContext;
+import org.apache.pinot.segment.spi.IndexSegment;
+
+
+/**
+ * An operator for order-by queries DESC that are partially sorted over the sorting keys.
+ *
+ * @see LinearSelectionOrderByOperator
+ */
+public class SelectionPartiallyOrderedByDescOperation extends LinearSelectionOrderByOperator {
+
+ private static final String EXPLAIN_NAME = "SELECT_PARTIAL_ORDER_BY_DESC";
+
+ private int _numDocsScanned = 0;
+ private long _numEntriesScannedPostFilter = 0;
+
+ public SelectionPartiallyOrderedByDescOperation(IndexSegment indexSegment, QueryContext queryContext,
+ List<ExpressionContext> expressions, TransformOperator transformOperator, int sortedExpr) {
+ super(indexSegment, queryContext, expressions, transformOperator, sortedExpr);
+ assert queryContext.getOrderByExpressions() != null;
+ Preconditions.checkArgument(queryContext.getOrderByExpressions().stream()
+ .filter(expr -> expr.getExpression().getType() == ExpressionContext.Type.IDENTIFIER)
+ .findFirst()
+ .orElseThrow(() -> new IllegalArgumentException("The query is not order by identifiers"))
+ .isDesc(),
+ "%s can only be used when the first column in order by is DESC", EXPLAIN_NAME);
+ }
+
+ @Override
+ protected List<Object[]> fetch(Supplier<ListBuilder> listBuilderSupplier) {
+
+ // Ideally we would use a descending cursor, but we don't actually have them
+ // Alternatively, we could store all blocks in a list and iterate them in reverse order, but ProjectionBlocks share
+ // the same DataBlockCache, so they may be ephemeral and being overridden by the next block.
+ // The only alternative we have right now is to retrieve the last LIMIT elements from each block
+
+ TransformBlock block;
+ int numColumnsProjected = _transformOperator.getNumColumnsProjected();
+ int numExpressions = _expressions.size();
+ BlockValSet[] blockValSets = new BlockValSet[numExpressions];
+
+ List<Object[]> localBestRows = new ArrayList<>();
+
+ try {
+ while ((block = _transformOperator.nextBlock()) != null) {
+ int numDocsFetched = block.getNumDocs();
+ _numDocsScanned += numDocsFetched;
+
+ IntFunction<Object[]> rowFetcher = fetchBlock(block, blockValSets);
+
+ ListBuilder listBuilder = listBuilderSupplier.get();
+
+ if (block.getNumDocs() == 0) {
+ continue;
+ }
+
+ // first, calculate the best rows on this block
+ boolean newPartition = false;
+ for (int docId = block.getNumDocs() - 1; docId >= 0; docId--) {
+ newPartition = listBuilder.add(rowFetcher.apply(docId));
+ if (newPartition && listBuilder.sortedSize() >= _numRowsToKeep) {
+ // We changed to a new partition and we have more values than required.
+ // Therefore, we can stop the execution of this block here.
+ break;
+ }
+ }
+ // then try to add the best rows from previous block
+ Iterator<Object[]> localBestRowIt = localBestRows.iterator();
+ while (localBestRowIt.hasNext() && !newPartition && listBuilder.sortedSize() < _numRowsToKeep) {
Review Comment:
This logic doesn't seem correct to me. E.g. when it is new partition, but not enough rows collected, we should still add the row.
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