[GitHub] [pinot] ankitsultana commented on a diff in pull request #10286: [multistage] Initial (phase 1) Query runtime for window functions - empty OVER() and OVER(PARTITION BY)

["ankitsultana (via GitHub)" <gi...@apache.org>]

ankitsultana commented on code in PR #10286:
URL: https://github.com/apache/pinot/pull/10286#discussion_r1110298242


##########
pinot-query-runtime/src/main/java/org/apache/pinot/query/runtime/operator/WindowAggregateOperator.java:
##########
@@ -0,0 +1,431 @@
+/**
+ * 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.query.runtime.operator;
+
+import com.google.common.annotations.VisibleForTesting;
+import com.google.common.base.Preconditions;
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.ImmutableMap;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.function.Function;
+import java.util.stream.Collectors;
+import javax.annotation.Nullable;
+import org.apache.calcite.rel.RelFieldCollation;
+import org.apache.pinot.common.datablock.DataBlock;
+import org.apache.pinot.common.utils.DataSchema;
+import org.apache.pinot.core.data.table.Key;
+import org.apache.pinot.query.planner.logical.RexExpression;
+import org.apache.pinot.query.runtime.blocks.TransferableBlock;
+import org.apache.pinot.query.runtime.blocks.TransferableBlockUtils;
+import org.apache.pinot.spi.data.FieldSpec;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+
+/**
+ * The WindowAggregateOperator is used to compute window function aggregations over a set of optional
+ * PARTITION BY keys, ORDER BY keys and a FRAME clause. The output data will include the projected
+ * columns and in addition will add the aggregation columns to the output data.
+ * [input columns, aggregate result1, ... aggregate resultN]
+ *
+ * The window functions supported today are SUM/COUNT/MIN/MAX aggregations. Window functions also include
+ * other types of functions such as rank and value functions.
+ *
+ * Unlike the AggregateOperator which will output one row per group, the WindowAggregateOperator
+ * will output as many rows as input rows.
+ *
+ * TODO:
+ *     1. Add support for OVER() clause with ORDER BY only or PARTITION BY ORDER BY
+ *     2. Add support for rank window functions
+ *     3. Add support for value window functions
+ *     4. Add support for custom frames
+ */
+public class WindowAggregateOperator extends MultiStageOperator {
+  private static final String EXPLAIN_NAME = "WINDOW";
+  private static final Logger LOGGER = LoggerFactory.getLogger(WindowAggregateOperator.class);
+
+  private final MultiStageOperator _inputOperator;
+  private final List<RexExpression> _groupSet;
+  private final OrderSetInfo _orderSetInfo;
+  private final WindowFrame _windowFrame;
+  private final List<RexExpression.FunctionCall> _aggCalls;
+  private final List<RexExpression> _constants;
+  private final DataSchema _resultSchema;
+  private final WindowAccumulator[] _windowAccumulators;
+  private final Map<Key, List<Object[]>> _partitionRows;
+
+  private TransferableBlock _upstreamErrorBlock;
+
+  private int _numRows;
+  private boolean _readyToConstruct;
+  private boolean _hasReturnedWindowAggregateBlock;
+
+  public WindowAggregateOperator(MultiStageOperator inputOperator, List<RexExpression> groupSet,
+      List<RexExpression> orderSet, List<RelFieldCollation.Direction> orderSetDirection,
+      List<RelFieldCollation.NullDirection> orderSetNullDirection, List<RexExpression> aggCalls, int lowerBound,
+      int upperBound, boolean isRows, List<RexExpression> constants, DataSchema resultSchema, DataSchema inputSchema,
+      long requestId, int stageId) {
+    this(inputOperator, groupSet, orderSet, orderSetDirection, orderSetNullDirection, aggCalls, lowerBound,
+        upperBound, isRows, constants, resultSchema, inputSchema, WindowAccumulator.WINDOW_MERGERS,
+        requestId, stageId);
+  }
+
+  @VisibleForTesting
+  public WindowAggregateOperator(MultiStageOperator inputOperator, List<RexExpression> groupSet,
+      List<RexExpression> orderSet, List<RelFieldCollation.Direction> orderSetDirection,
+      List<RelFieldCollation.NullDirection> orderSetNullDirection, List<RexExpression> aggCalls, int lowerBound,
+      int upperBound, boolean isRows, List<RexExpression> constants, DataSchema resultSchema, DataSchema inputSchema,
+      Map<String, Function<DataSchema.ColumnDataType, WindowMerger>> mergers, long requestId, int stageId) {
+    super(requestId, stageId);
+
+    boolean isPartitionByOnly = isPartitionByOnlyQuery(groupSet, orderSet, orderSetDirection, orderSetNullDirection);
+    // TODO: add support for ORDER BY in the OVER() clause
+    Preconditions.checkState(orderSet == null || orderSet.isEmpty() || isPartitionByOnly,
+        "Order by is not yet supported in window functions");
+
+    _inputOperator = inputOperator;
+    _groupSet = groupSet;
+    _orderSetInfo = new OrderSetInfo(orderSet, orderSetDirection, orderSetNullDirection);
+    _windowFrame = new WindowFrame(lowerBound, upperBound, isRows);
+
+    // TODO: add support for custom frames, and for ORDER BY default frame (upperBound => currentRow)
+    Preconditions.checkState(!_windowFrame.isRows(), "Only RANGE type frames are supported at present");
+    Preconditions.checkState(_windowFrame.isUnboundedPreceding(),
+        "Only default frame is supported, lowerBound must be UNBOUNDED PRECEDING");
+    Preconditions.checkState(_windowFrame.isUnboundedFollowing()
+            || (_windowFrame.isUpperBoundCurrentRow() && isPartitionByOnly),
+        "Only default frame is supported, upperBound must be UNBOUNDED FOLLOWING or CURRENT ROW");
+
+    // we expect all agg calls to be aggregate function calls
+    _aggCalls = aggCalls.stream().map(RexExpression.FunctionCall.class::cast).collect(Collectors.toList());
+    _constants = constants;
+    _resultSchema = resultSchema;
+
+    // TODO: Not all window functions (e.g. ROW_NUMBER, LAG, etc) need aggregations. Such functions should be handled
+    //       differently.
+    _windowAccumulators = new WindowAccumulator[_aggCalls.size()];
+    for (int i = 0; i < _aggCalls.size(); i++) {
+      RexExpression.FunctionCall agg = _aggCalls.get(i);
+      String functionName = agg.getFunctionName();
+      if (!mergers.containsKey(functionName)) {
+        throw new IllegalStateException("Unexpected value: " + functionName);
+      }
+      _windowAccumulators[i] = new WindowAccumulator(agg, mergers, functionName, inputSchema);
+    }
+
+    _partitionRows = new HashMap<>();
+
+    _numRows = 0;
+    _readyToConstruct = false;
+    _hasReturnedWindowAggregateBlock = false;
+  }
+
+  @Override
+  public List<MultiStageOperator> getChildOperators() {
+    return ImmutableList.of(_inputOperator);
+  }
+
+  @Nullable
+  @Override
+  public String toExplainString() {
+    return EXPLAIN_NAME;
+  }
+
+  @Override
+  protected TransferableBlock getNextBlock() {
+    try {
+      if (!_readyToConstruct && !consumeInputBlocks()) {
+        return TransferableBlockUtils.getNoOpTransferableBlock();
+      }
+
+      if (_upstreamErrorBlock != null) {
+        return _upstreamErrorBlock;
+      }
+
+      if (!_hasReturnedWindowAggregateBlock) {
+        return produceWindowAggregateBlock();
+      } else {
+        // TODO: Move to close call.
+        return TransferableBlockUtils.getEndOfStreamTransferableBlock();
+      }
+    } catch (Exception e) {
+      return TransferableBlockUtils.getErrorTransferableBlock(e);
+    }
+  }
+
+  private boolean isPartitionByOnlyQuery(List<RexExpression> groupSet, List<RexExpression> orderSet,
+      List<RelFieldCollation.Direction> orderSetDirection,
+      List<RelFieldCollation.NullDirection> orderSetNullDirection) {
+    if (orderSet == null || orderSet.isEmpty()) {
+      return true;
+    }
+
+    if (groupSet == null || groupSet.isEmpty() || (groupSet.size() != orderSet.size())) {
+      return false;
+    }
+
+    Set<Integer> partitionByInputRefIndexes = new HashSet<>();
+    Set<Integer> orderByInputRefIndexes = new HashSet<>();
+    for (int i = 0; i < groupSet.size(); i++) {
+      partitionByInputRefIndexes.add(((RexExpression.InputRef) groupSet.get(i)).getIndex());
+      orderByInputRefIndexes.add(((RexExpression.InputRef) orderSet.get(i)).getIndex());
+    }
+
+    boolean isPartitionByOnly = partitionByInputRefIndexes.equals(orderByInputRefIndexes);
+    if (isPartitionByOnly) {
+      // Check the direction and null direction to ensure default ordering on the order by keys, which are:
+      // Direction: ASC
+      // Null Direction: LAST
+      for (int i = 0; i < orderSet.size(); i++) {
+        if (orderSetDirection.get(i) == RelFieldCollation.Direction.DESCENDING
+            || orderSetNullDirection.get(i) == RelFieldCollation.NullDirection.FIRST) {
+          isPartitionByOnly = false;
+          break;
+        }
+      }
+    }
+    return isPartitionByOnly;
+  }
+
+  private TransferableBlock produceWindowAggregateBlock() {
+    List<Object[]> rows = new ArrayList<>(_numRows);
+    for (Map.Entry<Key, List<Object[]>> e : _partitionRows.entrySet()) {
+      Key partitionKey = e.getKey();
+      List<Object[]> rowList = e.getValue();
+      for (Object[] existingRow : rowList) {
+        Object[] row = new Object[existingRow.length + _aggCalls.size()];
+        System.arraycopy(existingRow, 0, row, 0, existingRow.length);
+        for (int i = 0; i < _windowAccumulators.length; i++) {
+          row[i + existingRow.length] = _windowAccumulators[i]._results.get(partitionKey);
+        }
+        rows.add(row);
+      }
+    }
+    _hasReturnedWindowAggregateBlock = true;
+    if (rows.size() == 0) {

Review Comment:
   If there are no rows I think we should still return a regular `TransferableBlock` (not EOS), so that the upstream operators have at least one block that they can process, which may be needed to handle scenarios like aggregations without group-by.



##########
pinot-query-runtime/src/main/java/org/apache/pinot/query/runtime/operator/WindowAggregateOperator.java:
##########
@@ -0,0 +1,431 @@
+/**
+ * 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.query.runtime.operator;
+
+import com.google.common.annotations.VisibleForTesting;
+import com.google.common.base.Preconditions;
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.ImmutableMap;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.function.Function;
+import java.util.stream.Collectors;
+import javax.annotation.Nullable;
+import org.apache.calcite.rel.RelFieldCollation;
+import org.apache.pinot.common.datablock.DataBlock;
+import org.apache.pinot.common.utils.DataSchema;
+import org.apache.pinot.core.data.table.Key;
+import org.apache.pinot.query.planner.logical.RexExpression;
+import org.apache.pinot.query.runtime.blocks.TransferableBlock;
+import org.apache.pinot.query.runtime.blocks.TransferableBlockUtils;
+import org.apache.pinot.spi.data.FieldSpec;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+
+/**
+ * The WindowAggregateOperator is used to compute window function aggregations over a set of optional
+ * PARTITION BY keys, ORDER BY keys and a FRAME clause. The output data will include the projected
+ * columns and in addition will add the aggregation columns to the output data.
+ * [input columns, aggregate result1, ... aggregate resultN]
+ *
+ * The window functions supported today are SUM/COUNT/MIN/MAX aggregations. Window functions also include
+ * other types of functions such as rank and value functions.
+ *
+ * Unlike the AggregateOperator which will output one row per group, the WindowAggregateOperator
+ * will output as many rows as input rows.
+ *
+ * TODO:
+ *     1. Add support for OVER() clause with ORDER BY only or PARTITION BY ORDER BY
+ *     2. Add support for rank window functions
+ *     3. Add support for value window functions
+ *     4. Add support for custom frames
+ */
+public class WindowAggregateOperator extends MultiStageOperator {
+  private static final String EXPLAIN_NAME = "WINDOW";
+  private static final Logger LOGGER = LoggerFactory.getLogger(WindowAggregateOperator.class);
+
+  private final MultiStageOperator _inputOperator;
+  private final List<RexExpression> _groupSet;
+  private final OrderSetInfo _orderSetInfo;
+  private final WindowFrame _windowFrame;
+  private final List<RexExpression.FunctionCall> _aggCalls;
+  private final List<RexExpression> _constants;
+  private final DataSchema _resultSchema;
+  private final WindowAccumulator[] _windowAccumulators;
+  private final Map<Key, List<Object[]>> _partitionRows;
+
+  private TransferableBlock _upstreamErrorBlock;
+
+  private int _numRows;
+  private boolean _readyToConstruct;
+  private boolean _hasReturnedWindowAggregateBlock;
+
+  public WindowAggregateOperator(MultiStageOperator inputOperator, List<RexExpression> groupSet,
+      List<RexExpression> orderSet, List<RelFieldCollation.Direction> orderSetDirection,
+      List<RelFieldCollation.NullDirection> orderSetNullDirection, List<RexExpression> aggCalls, int lowerBound,
+      int upperBound, boolean isRows, List<RexExpression> constants, DataSchema resultSchema, DataSchema inputSchema,
+      long requestId, int stageId) {
+    this(inputOperator, groupSet, orderSet, orderSetDirection, orderSetNullDirection, aggCalls, lowerBound,
+        upperBound, isRows, constants, resultSchema, inputSchema, WindowAccumulator.WINDOW_MERGERS,
+        requestId, stageId);
+  }
+
+  @VisibleForTesting
+  public WindowAggregateOperator(MultiStageOperator inputOperator, List<RexExpression> groupSet,
+      List<RexExpression> orderSet, List<RelFieldCollation.Direction> orderSetDirection,
+      List<RelFieldCollation.NullDirection> orderSetNullDirection, List<RexExpression> aggCalls, int lowerBound,
+      int upperBound, boolean isRows, List<RexExpression> constants, DataSchema resultSchema, DataSchema inputSchema,
+      Map<String, Function<DataSchema.ColumnDataType, WindowMerger>> mergers, long requestId, int stageId) {
+    super(requestId, stageId);
+
+    boolean isPartitionByOnly = isPartitionByOnlyQuery(groupSet, orderSet, orderSetDirection, orderSetNullDirection);
+    // TODO: add support for ORDER BY in the OVER() clause
+    Preconditions.checkState(orderSet == null || orderSet.isEmpty() || isPartitionByOnly,
+        "Order by is not yet supported in window functions");
+
+    _inputOperator = inputOperator;
+    _groupSet = groupSet;
+    _orderSetInfo = new OrderSetInfo(orderSet, orderSetDirection, orderSetNullDirection);
+    _windowFrame = new WindowFrame(lowerBound, upperBound, isRows);
+
+    // TODO: add support for custom frames, and for ORDER BY default frame (upperBound => currentRow)
+    Preconditions.checkState(!_windowFrame.isRows(), "Only RANGE type frames are supported at present");
+    Preconditions.checkState(_windowFrame.isUnboundedPreceding(),
+        "Only default frame is supported, lowerBound must be UNBOUNDED PRECEDING");
+    Preconditions.checkState(_windowFrame.isUnboundedFollowing()
+            || (_windowFrame.isUpperBoundCurrentRow() && isPartitionByOnly),
+        "Only default frame is supported, upperBound must be UNBOUNDED FOLLOWING or CURRENT ROW");
+
+    // we expect all agg calls to be aggregate function calls
+    _aggCalls = aggCalls.stream().map(RexExpression.FunctionCall.class::cast).collect(Collectors.toList());
+    _constants = constants;
+    _resultSchema = resultSchema;
+
+    // TODO: Not all window functions (e.g. ROW_NUMBER, LAG, etc) need aggregations. Such functions should be handled
+    //       differently.
+    _windowAccumulators = new WindowAccumulator[_aggCalls.size()];
+    for (int i = 0; i < _aggCalls.size(); i++) {
+      RexExpression.FunctionCall agg = _aggCalls.get(i);
+      String functionName = agg.getFunctionName();
+      if (!mergers.containsKey(functionName)) {
+        throw new IllegalStateException("Unexpected value: " + functionName);
+      }
+      _windowAccumulators[i] = new WindowAccumulator(agg, mergers, functionName, inputSchema);
+    }
+
+    _partitionRows = new HashMap<>();
+
+    _numRows = 0;
+    _readyToConstruct = false;
+    _hasReturnedWindowAggregateBlock = false;
+  }
+
+  @Override
+  public List<MultiStageOperator> getChildOperators() {
+    return ImmutableList.of(_inputOperator);
+  }
+
+  @Nullable
+  @Override
+  public String toExplainString() {
+    return EXPLAIN_NAME;
+  }
+
+  @Override
+  protected TransferableBlock getNextBlock() {
+    try {
+      if (!_readyToConstruct && !consumeInputBlocks()) {
+        return TransferableBlockUtils.getNoOpTransferableBlock();
+      }
+
+      if (_upstreamErrorBlock != null) {
+        return _upstreamErrorBlock;
+      }
+
+      if (!_hasReturnedWindowAggregateBlock) {
+        return produceWindowAggregateBlock();
+      } else {
+        // TODO: Move to close call.
+        return TransferableBlockUtils.getEndOfStreamTransferableBlock();
+      }
+    } catch (Exception e) {
+      return TransferableBlockUtils.getErrorTransferableBlock(e);
+    }
+  }
+
+  private boolean isPartitionByOnlyQuery(List<RexExpression> groupSet, List<RexExpression> orderSet,
+      List<RelFieldCollation.Direction> orderSetDirection,
+      List<RelFieldCollation.NullDirection> orderSetNullDirection) {
+    if (orderSet == null || orderSet.isEmpty()) {

Review Comment:
   nit: `CollectionUtils.isEmpty`.



##########
pinot-query-runtime/src/main/java/org/apache/pinot/query/runtime/operator/WindowAggregateOperator.java:
##########
@@ -0,0 +1,431 @@
+/**
+ * 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.query.runtime.operator;
+
+import com.google.common.annotations.VisibleForTesting;
+import com.google.common.base.Preconditions;
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.ImmutableMap;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.function.Function;
+import java.util.stream.Collectors;
+import javax.annotation.Nullable;
+import org.apache.calcite.rel.RelFieldCollation;
+import org.apache.pinot.common.datablock.DataBlock;
+import org.apache.pinot.common.utils.DataSchema;
+import org.apache.pinot.core.data.table.Key;
+import org.apache.pinot.query.planner.logical.RexExpression;
+import org.apache.pinot.query.runtime.blocks.TransferableBlock;
+import org.apache.pinot.query.runtime.blocks.TransferableBlockUtils;
+import org.apache.pinot.spi.data.FieldSpec;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+
+/**
+ * The WindowAggregateOperator is used to compute window function aggregations over a set of optional
+ * PARTITION BY keys, ORDER BY keys and a FRAME clause. The output data will include the projected
+ * columns and in addition will add the aggregation columns to the output data.
+ * [input columns, aggregate result1, ... aggregate resultN]
+ *
+ * The window functions supported today are SUM/COUNT/MIN/MAX aggregations. Window functions also include
+ * other types of functions such as rank and value functions.
+ *
+ * Unlike the AggregateOperator which will output one row per group, the WindowAggregateOperator
+ * will output as many rows as input rows.
+ *
+ * TODO:
+ *     1. Add support for OVER() clause with ORDER BY only or PARTITION BY ORDER BY
+ *     2. Add support for rank window functions
+ *     3. Add support for value window functions
+ *     4. Add support for custom frames
+ */
+public class WindowAggregateOperator extends MultiStageOperator {
+  private static final String EXPLAIN_NAME = "WINDOW";
+  private static final Logger LOGGER = LoggerFactory.getLogger(WindowAggregateOperator.class);
+
+  private final MultiStageOperator _inputOperator;
+  private final List<RexExpression> _groupSet;
+  private final OrderSetInfo _orderSetInfo;
+  private final WindowFrame _windowFrame;
+  private final List<RexExpression.FunctionCall> _aggCalls;
+  private final List<RexExpression> _constants;
+  private final DataSchema _resultSchema;
+  private final WindowAccumulator[] _windowAccumulators;
+  private final Map<Key, List<Object[]>> _partitionRows;
+
+  private TransferableBlock _upstreamErrorBlock;
+
+  private int _numRows;
+  private boolean _readyToConstruct;
+  private boolean _hasReturnedWindowAggregateBlock;
+
+  public WindowAggregateOperator(MultiStageOperator inputOperator, List<RexExpression> groupSet,
+      List<RexExpression> orderSet, List<RelFieldCollation.Direction> orderSetDirection,
+      List<RelFieldCollation.NullDirection> orderSetNullDirection, List<RexExpression> aggCalls, int lowerBound,
+      int upperBound, boolean isRows, List<RexExpression> constants, DataSchema resultSchema, DataSchema inputSchema,
+      long requestId, int stageId) {
+    this(inputOperator, groupSet, orderSet, orderSetDirection, orderSetNullDirection, aggCalls, lowerBound,
+        upperBound, isRows, constants, resultSchema, inputSchema, WindowAccumulator.WINDOW_MERGERS,
+        requestId, stageId);
+  }
+
+  @VisibleForTesting
+  public WindowAggregateOperator(MultiStageOperator inputOperator, List<RexExpression> groupSet,
+      List<RexExpression> orderSet, List<RelFieldCollation.Direction> orderSetDirection,
+      List<RelFieldCollation.NullDirection> orderSetNullDirection, List<RexExpression> aggCalls, int lowerBound,
+      int upperBound, boolean isRows, List<RexExpression> constants, DataSchema resultSchema, DataSchema inputSchema,
+      Map<String, Function<DataSchema.ColumnDataType, WindowMerger>> mergers, long requestId, int stageId) {
+    super(requestId, stageId);
+
+    boolean isPartitionByOnly = isPartitionByOnlyQuery(groupSet, orderSet, orderSetDirection, orderSetNullDirection);
+    // TODO: add support for ORDER BY in the OVER() clause
+    Preconditions.checkState(orderSet == null || orderSet.isEmpty() || isPartitionByOnly,
+        "Order by is not yet supported in window functions");
+
+    _inputOperator = inputOperator;
+    _groupSet = groupSet;
+    _orderSetInfo = new OrderSetInfo(orderSet, orderSetDirection, orderSetNullDirection);
+    _windowFrame = new WindowFrame(lowerBound, upperBound, isRows);
+
+    // TODO: add support for custom frames, and for ORDER BY default frame (upperBound => currentRow)
+    Preconditions.checkState(!_windowFrame.isRows(), "Only RANGE type frames are supported at present");
+    Preconditions.checkState(_windowFrame.isUnboundedPreceding(),
+        "Only default frame is supported, lowerBound must be UNBOUNDED PRECEDING");
+    Preconditions.checkState(_windowFrame.isUnboundedFollowing()
+            || (_windowFrame.isUpperBoundCurrentRow() && isPartitionByOnly),
+        "Only default frame is supported, upperBound must be UNBOUNDED FOLLOWING or CURRENT ROW");
+
+    // we expect all agg calls to be aggregate function calls
+    _aggCalls = aggCalls.stream().map(RexExpression.FunctionCall.class::cast).collect(Collectors.toList());
+    _constants = constants;
+    _resultSchema = resultSchema;
+
+    // TODO: Not all window functions (e.g. ROW_NUMBER, LAG, etc) need aggregations. Such functions should be handled
+    //       differently.
+    _windowAccumulators = new WindowAccumulator[_aggCalls.size()];
+    for (int i = 0; i < _aggCalls.size(); i++) {
+      RexExpression.FunctionCall agg = _aggCalls.get(i);
+      String functionName = agg.getFunctionName();
+      if (!mergers.containsKey(functionName)) {
+        throw new IllegalStateException("Unexpected value: " + functionName);
+      }
+      _windowAccumulators[i] = new WindowAccumulator(agg, mergers, functionName, inputSchema);
+    }
+
+    _partitionRows = new HashMap<>();
+
+    _numRows = 0;
+    _readyToConstruct = false;
+    _hasReturnedWindowAggregateBlock = false;
+  }
+
+  @Override
+  public List<MultiStageOperator> getChildOperators() {
+    return ImmutableList.of(_inputOperator);
+  }
+
+  @Nullable
+  @Override
+  public String toExplainString() {
+    return EXPLAIN_NAME;
+  }
+
+  @Override
+  protected TransferableBlock getNextBlock() {
+    try {
+      if (!_readyToConstruct && !consumeInputBlocks()) {
+        return TransferableBlockUtils.getNoOpTransferableBlock();
+      }
+
+      if (_upstreamErrorBlock != null) {
+        return _upstreamErrorBlock;
+      }
+
+      if (!_hasReturnedWindowAggregateBlock) {
+        return produceWindowAggregateBlock();
+      } else {
+        // TODO: Move to close call.
+        return TransferableBlockUtils.getEndOfStreamTransferableBlock();
+      }
+    } catch (Exception e) {

Review Comment:
   Can you also log the exception here?



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