Jackie-Jiang commented on code in PR #8979:
URL: https://github.com/apache/pinot/pull/8979#discussion_r925008347
##########
pinot-core/src/main/java/org/apache/pinot/core/operator/blocks/IntermediateResultsBlock.java:
##########
@@ -80,9 +81,8 @@ public IntermediateResultsBlock() {
/**
* Constructor for selection result.
*/
- public IntermediateResultsBlock(DataSchema dataSchema, Collection<Object[]>
selectionResult) {
+ public IntermediateResultsBlock(DataSchema dataSchema) {
Review Comment:
The change in this class can be simplified by adding a `@Nullable
Comparator<? super Object[]> comparator`, then we may add a new method `public
PriorityQueue<Object[]> getSelectionResultAsPriorityQueue()`. I feel the
current change is a little bit too complicated, and we might not want to extend
this block
##########
pinot-core/src/main/java/org/apache/pinot/core/operator/query/SelectionPartiallyOrderedByDescOperation.java:
##########
@@ -0,0 +1,105 @@
+/**
+ * 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.List;
+import org.apache.pinot.common.request.context.ExpressionContext;
+import org.apache.pinot.core.common.BlockValSet;
+import org.apache.pinot.core.common.RowBasedBlockValueFetcher;
+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 void fetch(ListBuilder listBuilder) {
+
+ List<TransformBlock> blocks = new ArrayList<>();
+
+ TransformBlock transformBlock;
+ int numColumnsProjected = _transformOperator.getNumColumnsProjected();
+ try {
+ while ((transformBlock = _transformOperator.nextBlock()) != null) {
+ int numDocsFetched = transformBlock.getNumDocs();
+ _numDocsScanned += numDocsFetched;
+ blocks.add(transformBlock);
Review Comment:
(MAJOR) We cannot store all blocks here because the `ProjectionBlock` shares
the same `DataBlockCache` underlying, where the previous value is overridden.
For descending order, the best we can do currently is to iterate in reverse
order from each block, and keep up to `LIMIT` rows per block. When getting the
next block, if we gathered enough rows, we can throw away the rows from the
previous block.
##########
pinot-core/src/main/java/org/apache/pinot/core/operator/query/LinearSelectionOrderByOperator.java:
##########
@@ -0,0 +1,388 @@
+/**
+ * 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.Arrays;
+import java.util.Collections;
+import java.util.Comparator;
+import java.util.Iterator;
+import java.util.List;
+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.IntermediateResultsBlock;
+import org.apache.pinot.core.operator.blocks.TransformBlock;
+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.segment.spi.IndexSegment;
+
+
+/**
+ * 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<IntermediateResultsBlock> {
+ protected final IndexSegment _indexSegment;
+
+ // 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 ListBuilder _listBuilder;
+ protected boolean _used = false;
+ 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(ListBuilder)}
+ */
+ public LinearSelectionOrderByOperator(IndexSegment indexSegment,
QueryContext queryContext,
+ List<ExpressionContext> expressions, TransformOperator transformOperator,
+ int sortedExpr) {
+ _indexSegment = indexSegment;
+ _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);
+ _listBuilder = new TotallySortedListBuilder(expectedSize);
+ } else {
+ int expectedSize =
Math.min(SelectionOperatorUtils.MAX_ROW_HOLDER_INITIAL_CAPACITY, _numRowsToKeep
* 2);
+
+ Comparator<Object[]> sortedComparator =
+ OrderByComparatorFactory.getComparator(_orderByExpressions,
_expressionsMetadata, true, 0, sortedExpr);
+ Comparator<Object[]> unsortedComparator =
+ OrderByComparatorFactory.getComparator(_orderByExpressions,
_expressionsMetadata, true, sortedExpr,
+ numOrderByExpressions);
+ _listBuilder = new PartiallySortedListBuilder(expectedSize,
sortedComparator, unsortedComparator);
+ }
+
+ _comparator = OrderByComparatorFactory.getComparator(_orderByExpressions,
_expressionsMetadata, false);
+ }
+
+ @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 RowBasedBlockValueFetcher 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);
+ }
+ return new RowBasedBlockValueFetcher(blockValSets);
+ }
+
+ protected abstract long getNumEntriesScannedPostFilter();
+
+ protected abstract int getNumDocsScanned();
+
+ /**
+ * Modifies the given {@link ListBuilder} adding rows in an order compatible
with the constructor used until the
+ * implementation considers that no more rows need to be added.
+ */
+ protected abstract void fetch(ListBuilder listBuilder);
+
+ @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 IntermediateResultsBlock getNextBlock() {
+ Preconditions.checkState(!_used, "nextBlock was called more than once");
+ _used = true;
+ fetch(_listBuilder);
+
+ DataSchema dataSchema = createDataSchema();
+
+ List<Object[]> list = _listBuilder.build();
+ if (list.size() > _numRowsToKeep) {
+ list = new ArrayList<>(list.subList(0, _numRowsToKeep));
+ }
+
+ return new IntermediateResultsBlock.ListSelection(dataSchema, list,
_comparator);
+ }
+
+ 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 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()}. Once this method is called, the behavior of
this object is undefined and therefore it
+ * should not be used.
+ *
+ * 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.
+ *
+ * Some implementations, like {@link PartiallySortedListBuilder} accepts a
second comparator that is used to sort rows
+ * inside each partition.
+ * When calling {@link #add(Object[])} with a row that doesn't belong to the
current partition, a new one is started
+ * and the previous one is sorted. Therefore, this object maintains the
invariant that at any moment there are at
+ * least {@link #sortedSize()} elements that are completely sorted, which
means that no matter which elements are
+ * added after that, these elements are going to be smallest.
+ */
+ protected interface ListBuilder {
+
+ /**
+ * Adds the given row to this object. The new column must be equal or
higher than 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 returned list will be sorted, even if a
previous call t o {@link #sortedSize()}
+ * returned a number lower than the number of elements that have been
added.
+ *
+ * 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. Therefore it 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 is the more versatile {@link ListBuilder} that requires two
comparators: The first defines the order on which
+ * {@link #add(Object[])} is called and defines the partitions. The second
one is used to sort rows in the same
+ * paritition. 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.
+ *
+ * In this implementation the {@link #add(Object[])} method has a log(P)
cost, where P is the number of elements in
+ * each partition. In normal cases we can consider P a constant. In some
degenerated cases like having an ordering by
+ * a sorted column whose values are all equal, P may tend to the number of
elements in the segment, which would make
+ * the cost of this method log(N).
+ */
+ private static class PartiallySortedListBuilder implements ListBuilder {
+ private final ArrayList<Object[]> _rows;
+ /**
+ * 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;
+ /**
+ * The index where the current (and still not sorted) partition starts.
+ */
+ private int _lastSorted;
+
+ public PartiallySortedListBuilder(int expectedSize, Comparator<Object[]>
partitionComparator,
+ Comparator<Object[]> unsortedComparator) {
+ _rows = new ArrayList<>(expectedSize);
+ _partitionComparator = partitionComparator;
+ _unsortedComparator = unsortedComparator;
+ }
+
+ @Override
+ public boolean add(Object[] row) {
+ boolean result;
+ if (_lastPartitionRow == null) {
+ _lastSorted = 0;
+ _lastPartitionRow = row;
+ result = false;
+ } else {
+ int cmp = _partitionComparator.compare(row, _lastPartitionRow);
+ if (cmp < 0) {
+ throw new IllegalArgumentException("Row " + Arrays.toString(row) + "
is lower than previously added row"
+ + Arrays.toString(_lastPartitionRow));
+ }
+ if (cmp > 0) {
Review Comment:
In some corner case, we might gather too many rows with sorted columns the
same value, and cause memory issue. We might want to use a priority queue and
only keep the `LIMIT` rows
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