[GitHub] [incubator-pinot] mqliang commented on a change in pull request #6710: Add a trailer section to data table and measure data table serialization cost on server

[GitBox <gi...@apache.org>]

mqliang commented on a change in pull request #6710:
URL: https://github.com/apache/incubator-pinot/pull/6710#discussion_r600925212



##########
File path: pinot-core/src/main/java/org/apache/pinot/core/common/datatable/DataTableImplV3.java
##########
@@ -0,0 +1,702 @@
+/**
+ * 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.common.datatable;
+
+import com.google.common.primitives.Ints;
+import com.google.common.primitives.Longs;
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.DataInputStream;
+import java.io.DataOutputStream;
+import java.io.IOException;
+import java.nio.ByteBuffer;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.TreeMap;
+import org.apache.pinot.common.response.ProcessingException;
+import org.apache.pinot.common.utils.DataSchema;
+import org.apache.pinot.common.utils.DataTable;
+import org.apache.pinot.common.utils.StringUtil;
+import org.apache.pinot.core.common.ObjectSerDeUtils;
+import org.apache.pinot.core.query.request.context.ThreadTimer;
+import org.apache.pinot.spi.utils.ByteArray;
+import org.apache.pinot.spi.utils.BytesUtils;
+
+import static org.apache.pinot.core.common.datatable.DataTableUtils.*;
+
+
+public class DataTableImplV3 implements DataTable {
+  private static final int VERSION = 3;
+
+  // VERSION
+  // NUM_ROWS
+  // NUM_COLUMNS
+  // EXCEPTIONS (START|SIZE)
+  // DICTIONARY_MAP (START|SIZE)
+  // DATA_SCHEMA (START|SIZE)
+  // FIXED_SIZE_DATA (START|SIZE)
+  // VARIABLE_SIZE_DATA (START|SIZE)
+  // TRAILER (START|SIZE)
+  private static final int HEADER_SIZE = Integer.BYTES * 15;
+
+  private final int _numRows;
+  private final int _numColumns;
+  private final DataSchema _dataSchema;
+  private final int[] _columnOffsets;
+  private final int _rowSizeInBytes;
+  private final Map<String, Map<Integer, String>> _dictionaryMap;
+  private final byte[] _fixedSizeDataBytes;
+  private final ByteBuffer _fixedSizeData;
+  private final byte[] _variableSizeDataBytes;
+  private final ByteBuffer _variableSizeData;
+  // _exceptions stores exceptions as a map of errorCode->errorMessage
+  private final Map<Integer, String> _exceptions;
+  /**
+   * _metadata stores KV pairs for metadata. Metadata is actually a part of _trailer in V3 when serialize DataTable
+   * into bytes. When deserialize, we extract metadata from _trailer into this _metadata map to provide the same
+   * interface with V2. There are many code use
+   * datatable.getMetadata().get("key")/datatable.getMetadata().put("key", "value") to get/set metadata.
+   * TODO(@mqliang): revise this if we decide to get/set metadata by
+   *  datable.getTailerData(key)/datable.setTailer(key, value).
+   */
+  private final Map<String, String> _metadata;
+  private Map<TrailerKeys, String> _trailer;
+
+  private long _responseSerializationCpuTimeNs;
+  private int _responseSerializationCpuTimeNsValueOffset;
+
+  /**
+   * Construct data table with results. (Server side)
+   */
+  public DataTableImplV3(int numRows, DataSchema dataSchema, Map<String, Map<Integer, String>> dictionaryMap,
+      byte[] fixedSizeDataBytes, byte[] variableSizeDataBytes) {
+    _numRows = numRows;
+    _numColumns = dataSchema.size();
+    _dataSchema = dataSchema;
+    _columnOffsets = new int[_numColumns];
+    _rowSizeInBytes = DataTableUtils.computeColumnOffsets(dataSchema, _columnOffsets);
+    _dictionaryMap = dictionaryMap;
+    _fixedSizeDataBytes = fixedSizeDataBytes;
+    _fixedSizeData = ByteBuffer.wrap(fixedSizeDataBytes);
+    _variableSizeDataBytes = variableSizeDataBytes;
+    _variableSizeData = ByteBuffer.wrap(variableSizeDataBytes);
+    _exceptions = new HashMap<>();
+    _metadata = new HashMap<>();
+    _trailer = new TreeMap<>();
+  }
+
+  /**
+   * Construct empty data table. (Server side)
+   */
+  public DataTableImplV3() {
+    _numRows = 0;
+    _numColumns = 0;
+    _dataSchema = null;
+    _columnOffsets = null;
+    _rowSizeInBytes = 0;
+    _dictionaryMap = null;
+    _fixedSizeDataBytes = null;
+    _fixedSizeData = null;
+    _variableSizeDataBytes = null;
+    _variableSizeData = null;
+    _exceptions = new HashMap<>();
+    _metadata = new HashMap<>();
+    _trailer = new TreeMap<>();
+  }
+
+  @Override
+  public void addException(ProcessingException processingException) {
+    _exceptions.put(processingException.getErrorCode(), processingException.getMessage());
+  }
+
+  @Override
+  public Map<Integer, String> getExceptions() {
+    return _exceptions;
+  }
+
+  @Override
+  public byte[] toBytes()
+      throws IOException {
+    _trailer.put(TrailerKeys.RESPONSE_SERIALIZATION_CPU_TIME_NS_METADATA_KEY, String.valueOf(-1));
+    ThreadTimer threadTimer = new ThreadTimer();
+    threadTimer.start();
+    byte[] bytes = toBytesInternal();
+    _responseSerializationCpuTimeNs = threadTimer.stopAndGetThreadTimeNs();
+    // Replace the value of "responseSerializationCpuTimeNs" as actual value
+    System.arraycopy(Longs.toByteArray(_responseSerializationCpuTimeNs), 0, bytes,
+        _responseSerializationCpuTimeNsValueOffset, Long.BYTES);
+    return bytes;
+  }
+
+  private byte[] toBytesInternal()
+      throws IOException {
+    ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
+    DataOutputStream dataOutputStream = new DataOutputStream(byteArrayOutputStream);
+    dataOutputStream.writeInt(VERSION);
+    dataOutputStream.writeInt(_numRows);
+    dataOutputStream.writeInt(_numColumns);
+    int dataOffset = HEADER_SIZE;
+
+    // Write exceptions (START|SIZE).
+    dataOutputStream.writeInt(dataOffset);
+    byte[] exceptionsBytes;
+    exceptionsBytes = serializeExceptions();
+    dataOutputStream.writeInt(exceptionsBytes.length);
+    dataOffset += exceptionsBytes.length;
+
+    // Write dictionary (START|SIZE).
+    dataOutputStream.writeInt(dataOffset);
+    byte[] dictionaryMapBytes = null;
+    if (_dictionaryMap != null) {
+      dictionaryMapBytes = serializeDictionaryMap(_dictionaryMap);
+      dataOutputStream.writeInt(dictionaryMapBytes.length);
+      dataOffset += dictionaryMapBytes.length;
+    } else {
+      dataOutputStream.writeInt(0);
+    }
+
+    // Write data schema (START|SIZE).
+    dataOutputStream.writeInt(dataOffset);
+    byte[] dataSchemaBytes = null;
+    if (_dataSchema != null) {
+      dataSchemaBytes = _dataSchema.toBytes();
+      dataOutputStream.writeInt(dataSchemaBytes.length);
+      dataOffset += dataSchemaBytes.length;
+    } else {
+      dataOutputStream.writeInt(0);
+    }
+
+    // Write fixed size data (START|SIZE).
+    dataOutputStream.writeInt(dataOffset);
+    if (_fixedSizeDataBytes != null) {
+      dataOutputStream.writeInt(_fixedSizeDataBytes.length);
+      dataOffset += _fixedSizeDataBytes.length;
+    } else {
+      dataOutputStream.writeInt(0);
+    }
+
+    // Write variable size data (START|SIZE).
+    dataOutputStream.writeInt(dataOffset);
+    if (_variableSizeDataBytes != null) {
+      dataOutputStream.writeInt(_variableSizeDataBytes.length);
+      dataOffset += _variableSizeDataBytes.length;
+    } else {
+      dataOutputStream.writeInt(0);
+    }
+
+    // Write trailer data (START|SIZE).
+    dataOutputStream.writeInt(dataOffset);
+    // Put all meta data into trailer.
+    _trailer = putAllMetaDataIntoTrailer();

Review comment:
       @mcvsubbu Before serialize _trailer, we need copy all KV pairs in metadata in to trailer.

##########
File path: pinot-core/src/main/java/org/apache/pinot/core/common/datatable/DataTableImplV3.java
##########
@@ -0,0 +1,702 @@
+/**
+ * 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.common.datatable;
+
+import com.google.common.primitives.Ints;
+import com.google.common.primitives.Longs;
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.DataInputStream;
+import java.io.DataOutputStream;
+import java.io.IOException;
+import java.nio.ByteBuffer;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.TreeMap;
+import org.apache.pinot.common.response.ProcessingException;
+import org.apache.pinot.common.utils.DataSchema;
+import org.apache.pinot.common.utils.DataTable;
+import org.apache.pinot.common.utils.StringUtil;
+import org.apache.pinot.core.common.ObjectSerDeUtils;
+import org.apache.pinot.core.query.request.context.ThreadTimer;
+import org.apache.pinot.spi.utils.ByteArray;
+import org.apache.pinot.spi.utils.BytesUtils;
+
+import static org.apache.pinot.core.common.datatable.DataTableUtils.*;
+
+
+public class DataTableImplV3 implements DataTable {
+  private static final int VERSION = 3;
+
+  // VERSION
+  // NUM_ROWS
+  // NUM_COLUMNS
+  // EXCEPTIONS (START|SIZE)

Review comment:
       @mcvsubbu V3 has a dedicate exceptions section to store exceptions. The reason is in V3, all key are enum value, which must be defined statically, we can not use "Exception"+errCode to create new keys

##########
File path: pinot-core/src/main/java/org/apache/pinot/core/common/datatable/DataTableImplV3.java
##########
@@ -0,0 +1,702 @@
+/**
+ * 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.common.datatable;
+
+import com.google.common.primitives.Ints;
+import com.google.common.primitives.Longs;
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.DataInputStream;
+import java.io.DataOutputStream;
+import java.io.IOException;
+import java.nio.ByteBuffer;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.TreeMap;
+import org.apache.pinot.common.response.ProcessingException;
+import org.apache.pinot.common.utils.DataSchema;
+import org.apache.pinot.common.utils.DataTable;
+import org.apache.pinot.common.utils.StringUtil;
+import org.apache.pinot.core.common.ObjectSerDeUtils;
+import org.apache.pinot.core.query.request.context.ThreadTimer;
+import org.apache.pinot.spi.utils.ByteArray;
+import org.apache.pinot.spi.utils.BytesUtils;
+
+import static org.apache.pinot.core.common.datatable.DataTableUtils.*;
+
+
+public class DataTableImplV3 implements DataTable {
+  private static final int VERSION = 3;
+
+  // VERSION
+  // NUM_ROWS
+  // NUM_COLUMNS
+  // EXCEPTIONS (START|SIZE)
+  // DICTIONARY_MAP (START|SIZE)
+  // DATA_SCHEMA (START|SIZE)
+  // FIXED_SIZE_DATA (START|SIZE)
+  // VARIABLE_SIZE_DATA (START|SIZE)
+  // TRAILER (START|SIZE)
+  private static final int HEADER_SIZE = Integer.BYTES * 15;
+
+  private final int _numRows;
+  private final int _numColumns;
+  private final DataSchema _dataSchema;
+  private final int[] _columnOffsets;
+  private final int _rowSizeInBytes;
+  private final Map<String, Map<Integer, String>> _dictionaryMap;
+  private final byte[] _fixedSizeDataBytes;
+  private final ByteBuffer _fixedSizeData;
+  private final byte[] _variableSizeDataBytes;
+  private final ByteBuffer _variableSizeData;
+  // _exceptions stores exceptions as a map of errorCode->errorMessage
+  private final Map<Integer, String> _exceptions;
+  /**
+   * _metadata stores KV pairs for metadata. Metadata is actually a part of _trailer in V3 when serialize DataTable
+   * into bytes. When deserialize, we extract metadata from _trailer into this _metadata map to provide the same
+   * interface with V2. There are many code use
+   * datatable.getMetadata().get("key")/datatable.getMetadata().put("key", "value") to get/set metadata.
+   * TODO(@mqliang): revise this if we decide to get/set metadata by
+   *  datable.getTailerData(key)/datable.setTailer(key, value).
+   */
+  private final Map<String, String> _metadata;
+  private Map<TrailerKeys, String> _trailer;
+
+  private long _responseSerializationCpuTimeNs;
+  private int _responseSerializationCpuTimeNsValueOffset;
+
+  /**
+   * Construct data table with results. (Server side)
+   */
+  public DataTableImplV3(int numRows, DataSchema dataSchema, Map<String, Map<Integer, String>> dictionaryMap,
+      byte[] fixedSizeDataBytes, byte[] variableSizeDataBytes) {
+    _numRows = numRows;
+    _numColumns = dataSchema.size();
+    _dataSchema = dataSchema;
+    _columnOffsets = new int[_numColumns];
+    _rowSizeInBytes = DataTableUtils.computeColumnOffsets(dataSchema, _columnOffsets);
+    _dictionaryMap = dictionaryMap;
+    _fixedSizeDataBytes = fixedSizeDataBytes;
+    _fixedSizeData = ByteBuffer.wrap(fixedSizeDataBytes);
+    _variableSizeDataBytes = variableSizeDataBytes;
+    _variableSizeData = ByteBuffer.wrap(variableSizeDataBytes);
+    _exceptions = new HashMap<>();
+    _metadata = new HashMap<>();
+    _trailer = new TreeMap<>();
+  }
+
+  /**
+   * Construct empty data table. (Server side)
+   */
+  public DataTableImplV3() {
+    _numRows = 0;
+    _numColumns = 0;
+    _dataSchema = null;
+    _columnOffsets = null;
+    _rowSizeInBytes = 0;
+    _dictionaryMap = null;
+    _fixedSizeDataBytes = null;
+    _fixedSizeData = null;
+    _variableSizeDataBytes = null;
+    _variableSizeData = null;
+    _exceptions = new HashMap<>();
+    _metadata = new HashMap<>();
+    _trailer = new TreeMap<>();
+  }
+
+  @Override
+  public void addException(ProcessingException processingException) {
+    _exceptions.put(processingException.getErrorCode(), processingException.getMessage());
+  }
+
+  @Override
+  public Map<Integer, String> getExceptions() {
+    return _exceptions;
+  }
+
+  @Override
+  public byte[] toBytes()
+      throws IOException {
+    _trailer.put(TrailerKeys.RESPONSE_SERIALIZATION_CPU_TIME_NS_METADATA_KEY, String.valueOf(-1));
+    ThreadTimer threadTimer = new ThreadTimer();
+    threadTimer.start();
+    byte[] bytes = toBytesInternal();
+    _responseSerializationCpuTimeNs = threadTimer.stopAndGetThreadTimeNs();
+    // Replace the value of "responseSerializationCpuTimeNs" as actual value
+    System.arraycopy(Longs.toByteArray(_responseSerializationCpuTimeNs), 0, bytes,
+        _responseSerializationCpuTimeNsValueOffset, Long.BYTES);
+    return bytes;
+  }
+
+  private byte[] toBytesInternal()
+      throws IOException {
+    ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
+    DataOutputStream dataOutputStream = new DataOutputStream(byteArrayOutputStream);
+    dataOutputStream.writeInt(VERSION);
+    dataOutputStream.writeInt(_numRows);
+    dataOutputStream.writeInt(_numColumns);
+    int dataOffset = HEADER_SIZE;
+
+    // Write exceptions (START|SIZE).
+    dataOutputStream.writeInt(dataOffset);
+    byte[] exceptionsBytes;
+    exceptionsBytes = serializeExceptions();
+    dataOutputStream.writeInt(exceptionsBytes.length);
+    dataOffset += exceptionsBytes.length;
+
+    // Write dictionary (START|SIZE).
+    dataOutputStream.writeInt(dataOffset);
+    byte[] dictionaryMapBytes = null;
+    if (_dictionaryMap != null) {
+      dictionaryMapBytes = serializeDictionaryMap(_dictionaryMap);
+      dataOutputStream.writeInt(dictionaryMapBytes.length);
+      dataOffset += dictionaryMapBytes.length;
+    } else {
+      dataOutputStream.writeInt(0);
+    }
+
+    // Write data schema (START|SIZE).
+    dataOutputStream.writeInt(dataOffset);
+    byte[] dataSchemaBytes = null;
+    if (_dataSchema != null) {
+      dataSchemaBytes = _dataSchema.toBytes();
+      dataOutputStream.writeInt(dataSchemaBytes.length);
+      dataOffset += dataSchemaBytes.length;
+    } else {
+      dataOutputStream.writeInt(0);
+    }
+
+    // Write fixed size data (START|SIZE).
+    dataOutputStream.writeInt(dataOffset);
+    if (_fixedSizeDataBytes != null) {
+      dataOutputStream.writeInt(_fixedSizeDataBytes.length);
+      dataOffset += _fixedSizeDataBytes.length;
+    } else {
+      dataOutputStream.writeInt(0);
+    }
+
+    // Write variable size data (START|SIZE).
+    dataOutputStream.writeInt(dataOffset);
+    if (_variableSizeDataBytes != null) {
+      dataOutputStream.writeInt(_variableSizeDataBytes.length);
+      dataOffset += _variableSizeDataBytes.length;
+    } else {
+      dataOutputStream.writeInt(0);
+    }
+
+    // Write trailer data (START|SIZE).
+    dataOutputStream.writeInt(dataOffset);
+    // Put all meta data into trailer.
+    _trailer = putAllMetaDataIntoTrailer();
+    _responseSerializationCpuTimeNsValueOffset = dataOffset;
+    byte[] trailerBytes = serializeTrailer();
+    dataOutputStream.writeInt(trailerBytes.length);
+
+    // Write actual data.
+    dataOutputStream.write(exceptionsBytes);
+    if (dictionaryMapBytes != null) {
+      dataOutputStream.write(dictionaryMapBytes);
+    }
+    if (dataSchemaBytes != null) {
+      dataOutputStream.write(dataSchemaBytes);
+    }
+    if (_fixedSizeDataBytes != null) {
+      dataOutputStream.write(_fixedSizeDataBytes);
+    }
+    if (_variableSizeDataBytes != null) {
+      dataOutputStream.write(_variableSizeDataBytes);
+    }
+    dataOutputStream.write(trailerBytes);
+
+    return byteArrayOutputStream.toByteArray();
+  }
+
+  /**
+   * Construct data table from byte array. (broker side)
+   */
+  public DataTableImplV3(ByteBuffer byteBuffer)
+      throws IOException {
+    // Read header.
+    _numRows = byteBuffer.getInt();
+    _numColumns = byteBuffer.getInt();
+    int exceptionsStart = byteBuffer.getInt();
+    int exceptionsLength = byteBuffer.getInt();
+    int dictionaryMapStart = byteBuffer.getInt();
+    int dictionaryMapLength = byteBuffer.getInt();
+    int dataSchemaStart = byteBuffer.getInt();
+    int dataSchemaLength = byteBuffer.getInt();
+    int fixedSizeDataStart = byteBuffer.getInt();
+    int fixedSizeDataLength = byteBuffer.getInt();
+    int variableSizeDataStart = byteBuffer.getInt();
+    int variableSizeDataLength = byteBuffer.getInt();
+    int trailerStart = byteBuffer.getInt();
+    int trailerLength = byteBuffer.getInt();
+
+    // Read exceptions.
+    if (exceptionsLength != 0) {
+      byte[] exceptionsBytes = new byte[exceptionsLength];
+      byteBuffer.position(exceptionsStart);
+      byteBuffer.get(exceptionsBytes);
+      _exceptions = deserializeExceptions(exceptionsBytes);
+    } else {
+      _exceptions = new HashMap<>();
+    }
+
+    // Read dictionary.
+    if (dictionaryMapLength != 0) {
+      byte[] dictionaryMapBytes = new byte[dictionaryMapLength];
+      byteBuffer.position(dictionaryMapStart);
+      byteBuffer.get(dictionaryMapBytes);
+      _dictionaryMap = deserializeDictionaryMap(dictionaryMapBytes);
+    } else {
+      _dictionaryMap = null;
+    }
+
+    // Read data schema.
+    if (dataSchemaLength != 0) {
+      byte[] schemaBytes = new byte[dataSchemaLength];
+      byteBuffer.position(dataSchemaStart);
+      byteBuffer.get(schemaBytes);
+      _dataSchema = DataSchema.fromBytes(schemaBytes);
+      _columnOffsets = new int[_dataSchema.size()];
+      _rowSizeInBytes = DataTableUtils.computeColumnOffsets(_dataSchema, _columnOffsets);
+    } else {
+      _dataSchema = null;
+      _columnOffsets = null;
+      _rowSizeInBytes = 0;
+    }
+
+    // Read fixed size data.
+    if (fixedSizeDataLength != 0) {
+      _fixedSizeDataBytes = new byte[fixedSizeDataLength];
+      byteBuffer.position(fixedSizeDataStart);
+      byteBuffer.get(_fixedSizeDataBytes);
+      _fixedSizeData = ByteBuffer.wrap(_fixedSizeDataBytes);
+    } else {
+      _fixedSizeDataBytes = null;
+      _fixedSizeData = null;
+    }
+
+    // Read variable size data.
+    if (variableSizeDataLength != 0) {
+      _variableSizeDataBytes = new byte[variableSizeDataLength];
+      byteBuffer.position(variableSizeDataStart);
+      byteBuffer.get(_variableSizeDataBytes);
+      _variableSizeData = ByteBuffer.wrap(_variableSizeDataBytes);
+    } else {
+      _variableSizeDataBytes = null;
+      _variableSizeData = null;
+    }
+
+    // Read trailer.
+    byte[] trailerBytes = new byte[trailerLength];
+    byteBuffer.position(trailerStart);
+    byteBuffer.get(trailerBytes);
+    _trailer = deserializeTrailer(trailerBytes);
+
+    /**
+     * Extract metadata from trailer.
+     * Metadata is actually a part of _trailer in V3 when serialize DataTable into bytes. When deserialize,
+     * we extract metadata from _trailer into this _metadata map to provide the same interface with V2.
+     * */
+    _metadata = extractMetadataFormTrailer();
+  }
+
+  /**
+   * Construct data table from V2 byte array. (broker side)
+   */
+  public DataTableImplV3(ByteBuffer byteBuffer, boolean isV2)
+      throws IOException {
+    // Read header.
+    _numRows = byteBuffer.getInt();
+    _numColumns = byteBuffer.getInt();
+    int dictionaryMapStart = byteBuffer.getInt();
+    int dictionaryMapLength = byteBuffer.getInt();
+    int metadataStart = byteBuffer.getInt();
+    int metadataLength = byteBuffer.getInt();
+    int dataSchemaStart = byteBuffer.getInt();
+    int dataSchemaLength = byteBuffer.getInt();
+    int fixedSizeDataStart = byteBuffer.getInt();
+    int fixedSizeDataLength = byteBuffer.getInt();
+    int variableSizeDataStart = byteBuffer.getInt();
+    int variableSizeDataLength = byteBuffer.getInt();
+
+    // Read dictionary.
+    if (dictionaryMapLength != 0) {
+      byte[] dictionaryMapBytes = new byte[dictionaryMapLength];
+      byteBuffer.position(dictionaryMapStart);
+      byteBuffer.get(dictionaryMapBytes);
+      _dictionaryMap = deserializeDictionaryMap(dictionaryMapBytes);
+    } else {
+      _dictionaryMap = null;
+    }
+
+    // Read metadata.
+    byte[] metadataBytes = new byte[metadataLength];
+    byteBuffer.position(metadataStart);
+    byteBuffer.get(metadataBytes);
+    _metadata = deserializeV2Metadata(metadataBytes);
+
+    // Read data schema.
+    if (dataSchemaLength != 0) {
+      byte[] schemaBytes = new byte[dataSchemaLength];
+      byteBuffer.position(dataSchemaStart);
+      byteBuffer.get(schemaBytes);
+      _dataSchema = DataSchema.fromBytes(schemaBytes);
+      _columnOffsets = new int[_dataSchema.size()];
+      _rowSizeInBytes = DataTableUtils.computeColumnOffsets(_dataSchema, _columnOffsets);
+    } else {
+      _dataSchema = null;
+      _columnOffsets = null;
+      _rowSizeInBytes = 0;
+    }
+
+    // Read fixed size data.
+    if (fixedSizeDataLength != 0) {
+      _fixedSizeDataBytes = new byte[fixedSizeDataLength];
+      byteBuffer.position(fixedSizeDataStart);
+      byteBuffer.get(_fixedSizeDataBytes);
+      _fixedSizeData = ByteBuffer.wrap(_fixedSizeDataBytes);
+    } else {
+      _fixedSizeDataBytes = null;
+      _fixedSizeData = null;
+    }
+
+    // Read variable size data.
+    if (variableSizeDataLength != 0) {
+      _variableSizeDataBytes = new byte[variableSizeDataLength];
+      byteBuffer.position(variableSizeDataStart);
+      byteBuffer.get(_variableSizeDataBytes);
+      _variableSizeData = ByteBuffer.wrap(_variableSizeDataBytes);
+    } else {
+      _variableSizeDataBytes = null;
+      _variableSizeData = null;
+    }
+
+    _trailer = null;
+    /**
+     * V2 stores exceptions as a bunch of KV pairs in metadata, all exceptions has key of "Exception"+errCode.
+     * To interpret V2 bytes as V3 object, extract exceptions from metadata.
+     */
+    _exceptions = extractExceptionsFormV2Metadata();
+  }
+
+  /**
+   * Serialize trailer section to bytes.
+   * Format of the bytes looks:
+   * [numEntries, bytesOfKV2, bytesOfKV2, bytesOfKV3]
+   * For each KV pairs:
+   * - if value is int/long, encode it as: [keyOrdinal, bigEndianRepresentationOfValue]
+   * - if value is string, encode it as: [keyOrdinal, valueLength, Utf8EncodedValue]
+   */
+  private byte[] serializeTrailer()

Review comment:
       @mcvsubbu This is the code to serialize trailer.

##########
File path: pinot-core/src/main/java/org/apache/pinot/core/common/datatable/DataTableImplV3.java
##########
@@ -0,0 +1,702 @@
+/**
+ * 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.common.datatable;
+
+import com.google.common.primitives.Ints;
+import com.google.common.primitives.Longs;
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.DataInputStream;
+import java.io.DataOutputStream;
+import java.io.IOException;
+import java.nio.ByteBuffer;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.TreeMap;
+import org.apache.pinot.common.response.ProcessingException;
+import org.apache.pinot.common.utils.DataSchema;
+import org.apache.pinot.common.utils.DataTable;
+import org.apache.pinot.common.utils.StringUtil;
+import org.apache.pinot.core.common.ObjectSerDeUtils;
+import org.apache.pinot.core.query.request.context.ThreadTimer;
+import org.apache.pinot.spi.utils.ByteArray;
+import org.apache.pinot.spi.utils.BytesUtils;
+
+import static org.apache.pinot.core.common.datatable.DataTableUtils.*;
+
+
+public class DataTableImplV3 implements DataTable {
+  private static final int VERSION = 3;
+
+  // VERSION
+  // NUM_ROWS
+  // NUM_COLUMNS
+  // EXCEPTIONS (START|SIZE)
+  // DICTIONARY_MAP (START|SIZE)
+  // DATA_SCHEMA (START|SIZE)
+  // FIXED_SIZE_DATA (START|SIZE)
+  // VARIABLE_SIZE_DATA (START|SIZE)
+  // TRAILER (START|SIZE)
+  private static final int HEADER_SIZE = Integer.BYTES * 15;
+
+  private final int _numRows;
+  private final int _numColumns;
+  private final DataSchema _dataSchema;
+  private final int[] _columnOffsets;
+  private final int _rowSizeInBytes;
+  private final Map<String, Map<Integer, String>> _dictionaryMap;
+  private final byte[] _fixedSizeDataBytes;
+  private final ByteBuffer _fixedSizeData;
+  private final byte[] _variableSizeDataBytes;
+  private final ByteBuffer _variableSizeData;
+  // _exceptions stores exceptions as a map of errorCode->errorMessage
+  private final Map<Integer, String> _exceptions;
+  /**
+   * _metadata stores KV pairs for metadata. Metadata is actually a part of _trailer in V3 when serialize DataTable
+   * into bytes. When deserialize, we extract metadata from _trailer into this _metadata map to provide the same
+   * interface with V2. There are many code use
+   * datatable.getMetadata().get("key")/datatable.getMetadata().put("key", "value") to get/set metadata.
+   * TODO(@mqliang): revise this if we decide to get/set metadata by
+   *  datable.getTailerData(key)/datable.setTailer(key, value).
+   */
+  private final Map<String, String> _metadata;
+  private Map<TrailerKeys, String> _trailer;
+
+  private long _responseSerializationCpuTimeNs;
+  private int _responseSerializationCpuTimeNsValueOffset;
+
+  /**
+   * Construct data table with results. (Server side)
+   */
+  public DataTableImplV3(int numRows, DataSchema dataSchema, Map<String, Map<Integer, String>> dictionaryMap,
+      byte[] fixedSizeDataBytes, byte[] variableSizeDataBytes) {
+    _numRows = numRows;
+    _numColumns = dataSchema.size();
+    _dataSchema = dataSchema;
+    _columnOffsets = new int[_numColumns];
+    _rowSizeInBytes = DataTableUtils.computeColumnOffsets(dataSchema, _columnOffsets);
+    _dictionaryMap = dictionaryMap;
+    _fixedSizeDataBytes = fixedSizeDataBytes;
+    _fixedSizeData = ByteBuffer.wrap(fixedSizeDataBytes);
+    _variableSizeDataBytes = variableSizeDataBytes;
+    _variableSizeData = ByteBuffer.wrap(variableSizeDataBytes);
+    _exceptions = new HashMap<>();
+    _metadata = new HashMap<>();
+    _trailer = new TreeMap<>();
+  }
+
+  /**
+   * Construct empty data table. (Server side)
+   */
+  public DataTableImplV3() {
+    _numRows = 0;
+    _numColumns = 0;
+    _dataSchema = null;
+    _columnOffsets = null;
+    _rowSizeInBytes = 0;
+    _dictionaryMap = null;
+    _fixedSizeDataBytes = null;
+    _fixedSizeData = null;
+    _variableSizeDataBytes = null;
+    _variableSizeData = null;
+    _exceptions = new HashMap<>();
+    _metadata = new HashMap<>();
+    _trailer = new TreeMap<>();
+  }
+
+  @Override
+  public void addException(ProcessingException processingException) {
+    _exceptions.put(processingException.getErrorCode(), processingException.getMessage());
+  }
+
+  @Override
+  public Map<Integer, String> getExceptions() {
+    return _exceptions;
+  }
+
+  @Override
+  public byte[] toBytes()
+      throws IOException {
+    _trailer.put(TrailerKeys.RESPONSE_SERIALIZATION_CPU_TIME_NS_METADATA_KEY, String.valueOf(-1));
+    ThreadTimer threadTimer = new ThreadTimer();
+    threadTimer.start();
+    byte[] bytes = toBytesInternal();
+    _responseSerializationCpuTimeNs = threadTimer.stopAndGetThreadTimeNs();
+    // Replace the value of "responseSerializationCpuTimeNs" as actual value
+    System.arraycopy(Longs.toByteArray(_responseSerializationCpuTimeNs), 0, bytes,
+        _responseSerializationCpuTimeNsValueOffset, Long.BYTES);
+    return bytes;
+  }
+
+  private byte[] toBytesInternal()
+      throws IOException {
+    ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
+    DataOutputStream dataOutputStream = new DataOutputStream(byteArrayOutputStream);
+    dataOutputStream.writeInt(VERSION);
+    dataOutputStream.writeInt(_numRows);
+    dataOutputStream.writeInt(_numColumns);
+    int dataOffset = HEADER_SIZE;
+
+    // Write exceptions (START|SIZE).
+    dataOutputStream.writeInt(dataOffset);
+    byte[] exceptionsBytes;
+    exceptionsBytes = serializeExceptions();
+    dataOutputStream.writeInt(exceptionsBytes.length);
+    dataOffset += exceptionsBytes.length;
+
+    // Write dictionary (START|SIZE).
+    dataOutputStream.writeInt(dataOffset);
+    byte[] dictionaryMapBytes = null;
+    if (_dictionaryMap != null) {
+      dictionaryMapBytes = serializeDictionaryMap(_dictionaryMap);
+      dataOutputStream.writeInt(dictionaryMapBytes.length);
+      dataOffset += dictionaryMapBytes.length;
+    } else {
+      dataOutputStream.writeInt(0);
+    }
+
+    // Write data schema (START|SIZE).
+    dataOutputStream.writeInt(dataOffset);
+    byte[] dataSchemaBytes = null;
+    if (_dataSchema != null) {
+      dataSchemaBytes = _dataSchema.toBytes();
+      dataOutputStream.writeInt(dataSchemaBytes.length);
+      dataOffset += dataSchemaBytes.length;
+    } else {
+      dataOutputStream.writeInt(0);
+    }
+
+    // Write fixed size data (START|SIZE).
+    dataOutputStream.writeInt(dataOffset);
+    if (_fixedSizeDataBytes != null) {
+      dataOutputStream.writeInt(_fixedSizeDataBytes.length);
+      dataOffset += _fixedSizeDataBytes.length;
+    } else {
+      dataOutputStream.writeInt(0);
+    }
+
+    // Write variable size data (START|SIZE).
+    dataOutputStream.writeInt(dataOffset);
+    if (_variableSizeDataBytes != null) {
+      dataOutputStream.writeInt(_variableSizeDataBytes.length);
+      dataOffset += _variableSizeDataBytes.length;
+    } else {
+      dataOutputStream.writeInt(0);
+    }
+
+    // Write trailer data (START|SIZE).
+    dataOutputStream.writeInt(dataOffset);
+    // Put all meta data into trailer.
+    _trailer = putAllMetaDataIntoTrailer();
+    _responseSerializationCpuTimeNsValueOffset = dataOffset;
+    byte[] trailerBytes = serializeTrailer();
+    dataOutputStream.writeInt(trailerBytes.length);
+
+    // Write actual data.
+    dataOutputStream.write(exceptionsBytes);
+    if (dictionaryMapBytes != null) {
+      dataOutputStream.write(dictionaryMapBytes);
+    }
+    if (dataSchemaBytes != null) {
+      dataOutputStream.write(dataSchemaBytes);
+    }
+    if (_fixedSizeDataBytes != null) {
+      dataOutputStream.write(_fixedSizeDataBytes);
+    }
+    if (_variableSizeDataBytes != null) {
+      dataOutputStream.write(_variableSizeDataBytes);
+    }
+    dataOutputStream.write(trailerBytes);
+
+    return byteArrayOutputStream.toByteArray();
+  }
+
+  /**
+   * Construct data table from byte array. (broker side)
+   */
+  public DataTableImplV3(ByteBuffer byteBuffer)
+      throws IOException {
+    // Read header.
+    _numRows = byteBuffer.getInt();
+    _numColumns = byteBuffer.getInt();
+    int exceptionsStart = byteBuffer.getInt();
+    int exceptionsLength = byteBuffer.getInt();
+    int dictionaryMapStart = byteBuffer.getInt();
+    int dictionaryMapLength = byteBuffer.getInt();
+    int dataSchemaStart = byteBuffer.getInt();
+    int dataSchemaLength = byteBuffer.getInt();
+    int fixedSizeDataStart = byteBuffer.getInt();
+    int fixedSizeDataLength = byteBuffer.getInt();
+    int variableSizeDataStart = byteBuffer.getInt();
+    int variableSizeDataLength = byteBuffer.getInt();
+    int trailerStart = byteBuffer.getInt();
+    int trailerLength = byteBuffer.getInt();
+
+    // Read exceptions.
+    if (exceptionsLength != 0) {
+      byte[] exceptionsBytes = new byte[exceptionsLength];
+      byteBuffer.position(exceptionsStart);
+      byteBuffer.get(exceptionsBytes);
+      _exceptions = deserializeExceptions(exceptionsBytes);
+    } else {
+      _exceptions = new HashMap<>();
+    }
+
+    // Read dictionary.
+    if (dictionaryMapLength != 0) {
+      byte[] dictionaryMapBytes = new byte[dictionaryMapLength];
+      byteBuffer.position(dictionaryMapStart);
+      byteBuffer.get(dictionaryMapBytes);
+      _dictionaryMap = deserializeDictionaryMap(dictionaryMapBytes);
+    } else {
+      _dictionaryMap = null;
+    }
+
+    // Read data schema.
+    if (dataSchemaLength != 0) {
+      byte[] schemaBytes = new byte[dataSchemaLength];
+      byteBuffer.position(dataSchemaStart);
+      byteBuffer.get(schemaBytes);
+      _dataSchema = DataSchema.fromBytes(schemaBytes);
+      _columnOffsets = new int[_dataSchema.size()];
+      _rowSizeInBytes = DataTableUtils.computeColumnOffsets(_dataSchema, _columnOffsets);
+    } else {
+      _dataSchema = null;
+      _columnOffsets = null;
+      _rowSizeInBytes = 0;
+    }
+
+    // Read fixed size data.
+    if (fixedSizeDataLength != 0) {
+      _fixedSizeDataBytes = new byte[fixedSizeDataLength];
+      byteBuffer.position(fixedSizeDataStart);
+      byteBuffer.get(_fixedSizeDataBytes);
+      _fixedSizeData = ByteBuffer.wrap(_fixedSizeDataBytes);
+    } else {
+      _fixedSizeDataBytes = null;
+      _fixedSizeData = null;
+    }
+
+    // Read variable size data.
+    if (variableSizeDataLength != 0) {
+      _variableSizeDataBytes = new byte[variableSizeDataLength];
+      byteBuffer.position(variableSizeDataStart);
+      byteBuffer.get(_variableSizeDataBytes);
+      _variableSizeData = ByteBuffer.wrap(_variableSizeDataBytes);
+    } else {
+      _variableSizeDataBytes = null;
+      _variableSizeData = null;
+    }
+
+    // Read trailer.
+    byte[] trailerBytes = new byte[trailerLength];
+    byteBuffer.position(trailerStart);
+    byteBuffer.get(trailerBytes);
+    _trailer = deserializeTrailer(trailerBytes);
+
+    /**
+     * Extract metadata from trailer.
+     * Metadata is actually a part of _trailer in V3 when serialize DataTable into bytes. When deserialize,
+     * we extract metadata from _trailer into this _metadata map to provide the same interface with V2.
+     * */
+    _metadata = extractMetadataFormTrailer();
+  }
+
+  /**
+   * Construct data table from V2 byte array. (broker side)
+   */
+  public DataTableImplV3(ByteBuffer byteBuffer, boolean isV2)
+      throws IOException {
+    // Read header.
+    _numRows = byteBuffer.getInt();
+    _numColumns = byteBuffer.getInt();
+    int dictionaryMapStart = byteBuffer.getInt();
+    int dictionaryMapLength = byteBuffer.getInt();
+    int metadataStart = byteBuffer.getInt();
+    int metadataLength = byteBuffer.getInt();
+    int dataSchemaStart = byteBuffer.getInt();
+    int dataSchemaLength = byteBuffer.getInt();
+    int fixedSizeDataStart = byteBuffer.getInt();
+    int fixedSizeDataLength = byteBuffer.getInt();
+    int variableSizeDataStart = byteBuffer.getInt();
+    int variableSizeDataLength = byteBuffer.getInt();
+
+    // Read dictionary.
+    if (dictionaryMapLength != 0) {
+      byte[] dictionaryMapBytes = new byte[dictionaryMapLength];
+      byteBuffer.position(dictionaryMapStart);
+      byteBuffer.get(dictionaryMapBytes);
+      _dictionaryMap = deserializeDictionaryMap(dictionaryMapBytes);
+    } else {
+      _dictionaryMap = null;
+    }
+
+    // Read metadata.
+    byte[] metadataBytes = new byte[metadataLength];
+    byteBuffer.position(metadataStart);
+    byteBuffer.get(metadataBytes);
+    _metadata = deserializeV2Metadata(metadataBytes);
+
+    // Read data schema.
+    if (dataSchemaLength != 0) {
+      byte[] schemaBytes = new byte[dataSchemaLength];
+      byteBuffer.position(dataSchemaStart);
+      byteBuffer.get(schemaBytes);
+      _dataSchema = DataSchema.fromBytes(schemaBytes);
+      _columnOffsets = new int[_dataSchema.size()];
+      _rowSizeInBytes = DataTableUtils.computeColumnOffsets(_dataSchema, _columnOffsets);
+    } else {
+      _dataSchema = null;
+      _columnOffsets = null;
+      _rowSizeInBytes = 0;
+    }
+
+    // Read fixed size data.
+    if (fixedSizeDataLength != 0) {
+      _fixedSizeDataBytes = new byte[fixedSizeDataLength];
+      byteBuffer.position(fixedSizeDataStart);
+      byteBuffer.get(_fixedSizeDataBytes);
+      _fixedSizeData = ByteBuffer.wrap(_fixedSizeDataBytes);
+    } else {
+      _fixedSizeDataBytes = null;
+      _fixedSizeData = null;
+    }
+
+    // Read variable size data.
+    if (variableSizeDataLength != 0) {
+      _variableSizeDataBytes = new byte[variableSizeDataLength];
+      byteBuffer.position(variableSizeDataStart);
+      byteBuffer.get(_variableSizeDataBytes);
+      _variableSizeData = ByteBuffer.wrap(_variableSizeDataBytes);
+    } else {
+      _variableSizeDataBytes = null;
+      _variableSizeData = null;
+    }
+
+    _trailer = null;
+    /**
+     * V2 stores exceptions as a bunch of KV pairs in metadata, all exceptions has key of "Exception"+errCode.
+     * To interpret V2 bytes as V3 object, extract exceptions from metadata.
+     */
+    _exceptions = extractExceptionsFormV2Metadata();

Review comment:
       @mcvsubbu  V2 stores exceptions as a bunch of KV pairs in metadata, all exceptions has key of "Exception"+errCode. To interpret V2 bytes as V3 object, extract exceptions from metadata and put them into _exceptions

##########
File path: pinot-core/src/main/java/org/apache/pinot/core/common/datatable/DataTableImplV3.java
##########
@@ -0,0 +1,702 @@
+/**
+ * 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.common.datatable;
+
+import com.google.common.primitives.Ints;
+import com.google.common.primitives.Longs;
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.DataInputStream;
+import java.io.DataOutputStream;
+import java.io.IOException;
+import java.nio.ByteBuffer;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.TreeMap;
+import org.apache.pinot.common.response.ProcessingException;
+import org.apache.pinot.common.utils.DataSchema;
+import org.apache.pinot.common.utils.DataTable;
+import org.apache.pinot.common.utils.StringUtil;
+import org.apache.pinot.core.common.ObjectSerDeUtils;
+import org.apache.pinot.core.query.request.context.ThreadTimer;
+import org.apache.pinot.spi.utils.ByteArray;
+import org.apache.pinot.spi.utils.BytesUtils;
+
+import static org.apache.pinot.core.common.datatable.DataTableUtils.*;
+
+
+public class DataTableImplV3 implements DataTable {
+  private static final int VERSION = 3;
+
+  // VERSION
+  // NUM_ROWS
+  // NUM_COLUMNS
+  // EXCEPTIONS (START|SIZE)
+  // DICTIONARY_MAP (START|SIZE)
+  // DATA_SCHEMA (START|SIZE)
+  // FIXED_SIZE_DATA (START|SIZE)
+  // VARIABLE_SIZE_DATA (START|SIZE)
+  // TRAILER (START|SIZE)
+  private static final int HEADER_SIZE = Integer.BYTES * 15;
+
+  private final int _numRows;
+  private final int _numColumns;
+  private final DataSchema _dataSchema;
+  private final int[] _columnOffsets;
+  private final int _rowSizeInBytes;
+  private final Map<String, Map<Integer, String>> _dictionaryMap;
+  private final byte[] _fixedSizeDataBytes;
+  private final ByteBuffer _fixedSizeData;
+  private final byte[] _variableSizeDataBytes;
+  private final ByteBuffer _variableSizeData;
+  // _exceptions stores exceptions as a map of errorCode->errorMessage
+  private final Map<Integer, String> _exceptions;
+  /**
+   * _metadata stores KV pairs for metadata. Metadata is actually a part of _trailer in V3 when serialize DataTable
+   * into bytes. When deserialize, we extract metadata from _trailer into this _metadata map to provide the same
+   * interface with V2. There are many code use
+   * datatable.getMetadata().get("key")/datatable.getMetadata().put("key", "value") to get/set metadata.
+   * TODO(@mqliang): revise this if we decide to get/set metadata by
+   *  datable.getTailerData(key)/datable.setTailer(key, value).
+   */
+  private final Map<String, String> _metadata;

Review comment:
       All metadata KV pairs are stored in trailer in V3,  however, to provide the same interface with V2, V3 also implement the `Map<String, String> getMedadata()` method. We need to copy KV paird between _metadata and _trailer during serializaion/deserialization.

##########
File path: pinot-core/src/main/java/org/apache/pinot/core/common/datatable/DataTableImplV3.java
##########
@@ -0,0 +1,702 @@
+/**
+ * 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.common.datatable;
+
+import com.google.common.primitives.Ints;
+import com.google.common.primitives.Longs;
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.DataInputStream;
+import java.io.DataOutputStream;
+import java.io.IOException;
+import java.nio.ByteBuffer;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.TreeMap;
+import org.apache.pinot.common.response.ProcessingException;
+import org.apache.pinot.common.utils.DataSchema;
+import org.apache.pinot.common.utils.DataTable;
+import org.apache.pinot.common.utils.StringUtil;
+import org.apache.pinot.core.common.ObjectSerDeUtils;
+import org.apache.pinot.core.query.request.context.ThreadTimer;
+import org.apache.pinot.spi.utils.ByteArray;
+import org.apache.pinot.spi.utils.BytesUtils;
+
+import static org.apache.pinot.core.common.datatable.DataTableUtils.*;
+
+
+public class DataTableImplV3 implements DataTable {
+  private static final int VERSION = 3;
+
+  // VERSION
+  // NUM_ROWS
+  // NUM_COLUMNS
+  // EXCEPTIONS (START|SIZE)
+  // DICTIONARY_MAP (START|SIZE)
+  // DATA_SCHEMA (START|SIZE)
+  // FIXED_SIZE_DATA (START|SIZE)
+  // VARIABLE_SIZE_DATA (START|SIZE)
+  // TRAILER (START|SIZE)
+  private static final int HEADER_SIZE = Integer.BYTES * 15;
+
+  private final int _numRows;
+  private final int _numColumns;
+  private final DataSchema _dataSchema;
+  private final int[] _columnOffsets;
+  private final int _rowSizeInBytes;
+  private final Map<String, Map<Integer, String>> _dictionaryMap;
+  private final byte[] _fixedSizeDataBytes;
+  private final ByteBuffer _fixedSizeData;
+  private final byte[] _variableSizeDataBytes;
+  private final ByteBuffer _variableSizeData;
+  // _exceptions stores exceptions as a map of errorCode->errorMessage
+  private final Map<Integer, String> _exceptions;
+  /**
+   * _metadata stores KV pairs for metadata. Metadata is actually a part of _trailer in V3 when serialize DataTable
+   * into bytes. When deserialize, we extract metadata from _trailer into this _metadata map to provide the same
+   * interface with V2. There are many code use
+   * datatable.getMetadata().get("key")/datatable.getMetadata().put("key", "value") to get/set metadata.
+   * TODO(@mqliang): revise this if we decide to get/set metadata by
+   *  datable.getTailerData(key)/datable.setTailer(key, value).
+   */
+  private final Map<String, String> _metadata;
+  private Map<TrailerKeys, String> _trailer;
+
+  private long _responseSerializationCpuTimeNs;
+  private int _responseSerializationCpuTimeNsValueOffset;
+
+  /**
+   * Construct data table with results. (Server side)
+   */
+  public DataTableImplV3(int numRows, DataSchema dataSchema, Map<String, Map<Integer, String>> dictionaryMap,
+      byte[] fixedSizeDataBytes, byte[] variableSizeDataBytes) {
+    _numRows = numRows;
+    _numColumns = dataSchema.size();
+    _dataSchema = dataSchema;
+    _columnOffsets = new int[_numColumns];
+    _rowSizeInBytes = DataTableUtils.computeColumnOffsets(dataSchema, _columnOffsets);
+    _dictionaryMap = dictionaryMap;
+    _fixedSizeDataBytes = fixedSizeDataBytes;
+    _fixedSizeData = ByteBuffer.wrap(fixedSizeDataBytes);
+    _variableSizeDataBytes = variableSizeDataBytes;
+    _variableSizeData = ByteBuffer.wrap(variableSizeDataBytes);
+    _exceptions = new HashMap<>();
+    _metadata = new HashMap<>();
+    _trailer = new TreeMap<>();
+  }
+
+  /**
+   * Construct empty data table. (Server side)
+   */
+  public DataTableImplV3() {
+    _numRows = 0;
+    _numColumns = 0;
+    _dataSchema = null;
+    _columnOffsets = null;
+    _rowSizeInBytes = 0;
+    _dictionaryMap = null;
+    _fixedSizeDataBytes = null;
+    _fixedSizeData = null;
+    _variableSizeDataBytes = null;
+    _variableSizeData = null;
+    _exceptions = new HashMap<>();
+    _metadata = new HashMap<>();
+    _trailer = new TreeMap<>();
+  }
+
+  @Override
+  public void addException(ProcessingException processingException) {
+    _exceptions.put(processingException.getErrorCode(), processingException.getMessage());
+  }
+
+  @Override
+  public Map<Integer, String> getExceptions() {
+    return _exceptions;
+  }
+
+  @Override
+  public byte[] toBytes()
+      throws IOException {
+    _trailer.put(TrailerKeys.RESPONSE_SERIALIZATION_CPU_TIME_NS_METADATA_KEY, String.valueOf(-1));
+    ThreadTimer threadTimer = new ThreadTimer();
+    threadTimer.start();
+    byte[] bytes = toBytesInternal();
+    _responseSerializationCpuTimeNs = threadTimer.stopAndGetThreadTimeNs();
+    // Replace the value of "responseSerializationCpuTimeNs" as actual value
+    System.arraycopy(Longs.toByteArray(_responseSerializationCpuTimeNs), 0, bytes,
+        _responseSerializationCpuTimeNsValueOffset, Long.BYTES);
+    return bytes;
+  }
+
+  private byte[] toBytesInternal()
+      throws IOException {
+    ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
+    DataOutputStream dataOutputStream = new DataOutputStream(byteArrayOutputStream);
+    dataOutputStream.writeInt(VERSION);
+    dataOutputStream.writeInt(_numRows);
+    dataOutputStream.writeInt(_numColumns);
+    int dataOffset = HEADER_SIZE;
+
+    // Write exceptions (START|SIZE).
+    dataOutputStream.writeInt(dataOffset);
+    byte[] exceptionsBytes;
+    exceptionsBytes = serializeExceptions();
+    dataOutputStream.writeInt(exceptionsBytes.length);
+    dataOffset += exceptionsBytes.length;
+
+    // Write dictionary (START|SIZE).
+    dataOutputStream.writeInt(dataOffset);
+    byte[] dictionaryMapBytes = null;
+    if (_dictionaryMap != null) {
+      dictionaryMapBytes = serializeDictionaryMap(_dictionaryMap);
+      dataOutputStream.writeInt(dictionaryMapBytes.length);
+      dataOffset += dictionaryMapBytes.length;
+    } else {
+      dataOutputStream.writeInt(0);
+    }
+
+    // Write data schema (START|SIZE).
+    dataOutputStream.writeInt(dataOffset);
+    byte[] dataSchemaBytes = null;
+    if (_dataSchema != null) {
+      dataSchemaBytes = _dataSchema.toBytes();
+      dataOutputStream.writeInt(dataSchemaBytes.length);
+      dataOffset += dataSchemaBytes.length;
+    } else {
+      dataOutputStream.writeInt(0);
+    }
+
+    // Write fixed size data (START|SIZE).
+    dataOutputStream.writeInt(dataOffset);
+    if (_fixedSizeDataBytes != null) {
+      dataOutputStream.writeInt(_fixedSizeDataBytes.length);
+      dataOffset += _fixedSizeDataBytes.length;
+    } else {
+      dataOutputStream.writeInt(0);
+    }
+
+    // Write variable size data (START|SIZE).
+    dataOutputStream.writeInt(dataOffset);
+    if (_variableSizeDataBytes != null) {
+      dataOutputStream.writeInt(_variableSizeDataBytes.length);
+      dataOffset += _variableSizeDataBytes.length;
+    } else {
+      dataOutputStream.writeInt(0);
+    }
+
+    // Write trailer data (START|SIZE).
+    dataOutputStream.writeInt(dataOffset);
+    // Put all meta data into trailer.
+    _trailer = putAllMetaDataIntoTrailer();
+    _responseSerializationCpuTimeNsValueOffset = dataOffset;
+    byte[] trailerBytes = serializeTrailer();
+    dataOutputStream.writeInt(trailerBytes.length);
+
+    // Write actual data.
+    dataOutputStream.write(exceptionsBytes);
+    if (dictionaryMapBytes != null) {
+      dataOutputStream.write(dictionaryMapBytes);
+    }
+    if (dataSchemaBytes != null) {
+      dataOutputStream.write(dataSchemaBytes);
+    }
+    if (_fixedSizeDataBytes != null) {
+      dataOutputStream.write(_fixedSizeDataBytes);
+    }
+    if (_variableSizeDataBytes != null) {
+      dataOutputStream.write(_variableSizeDataBytes);
+    }
+    dataOutputStream.write(trailerBytes);
+
+    return byteArrayOutputStream.toByteArray();
+  }
+
+  /**
+   * Construct data table from byte array. (broker side)
+   */
+  public DataTableImplV3(ByteBuffer byteBuffer)
+      throws IOException {
+    // Read header.
+    _numRows = byteBuffer.getInt();
+    _numColumns = byteBuffer.getInt();
+    int exceptionsStart = byteBuffer.getInt();
+    int exceptionsLength = byteBuffer.getInt();
+    int dictionaryMapStart = byteBuffer.getInt();
+    int dictionaryMapLength = byteBuffer.getInt();
+    int dataSchemaStart = byteBuffer.getInt();
+    int dataSchemaLength = byteBuffer.getInt();
+    int fixedSizeDataStart = byteBuffer.getInt();
+    int fixedSizeDataLength = byteBuffer.getInt();
+    int variableSizeDataStart = byteBuffer.getInt();
+    int variableSizeDataLength = byteBuffer.getInt();
+    int trailerStart = byteBuffer.getInt();
+    int trailerLength = byteBuffer.getInt();
+
+    // Read exceptions.
+    if (exceptionsLength != 0) {
+      byte[] exceptionsBytes = new byte[exceptionsLength];
+      byteBuffer.position(exceptionsStart);
+      byteBuffer.get(exceptionsBytes);
+      _exceptions = deserializeExceptions(exceptionsBytes);
+    } else {
+      _exceptions = new HashMap<>();
+    }
+
+    // Read dictionary.
+    if (dictionaryMapLength != 0) {
+      byte[] dictionaryMapBytes = new byte[dictionaryMapLength];
+      byteBuffer.position(dictionaryMapStart);
+      byteBuffer.get(dictionaryMapBytes);
+      _dictionaryMap = deserializeDictionaryMap(dictionaryMapBytes);
+    } else {
+      _dictionaryMap = null;
+    }
+
+    // Read data schema.
+    if (dataSchemaLength != 0) {
+      byte[] schemaBytes = new byte[dataSchemaLength];
+      byteBuffer.position(dataSchemaStart);
+      byteBuffer.get(schemaBytes);
+      _dataSchema = DataSchema.fromBytes(schemaBytes);
+      _columnOffsets = new int[_dataSchema.size()];
+      _rowSizeInBytes = DataTableUtils.computeColumnOffsets(_dataSchema, _columnOffsets);
+    } else {
+      _dataSchema = null;
+      _columnOffsets = null;
+      _rowSizeInBytes = 0;
+    }
+
+    // Read fixed size data.
+    if (fixedSizeDataLength != 0) {
+      _fixedSizeDataBytes = new byte[fixedSizeDataLength];
+      byteBuffer.position(fixedSizeDataStart);
+      byteBuffer.get(_fixedSizeDataBytes);
+      _fixedSizeData = ByteBuffer.wrap(_fixedSizeDataBytes);
+    } else {
+      _fixedSizeDataBytes = null;
+      _fixedSizeData = null;
+    }
+
+    // Read variable size data.
+    if (variableSizeDataLength != 0) {
+      _variableSizeDataBytes = new byte[variableSizeDataLength];
+      byteBuffer.position(variableSizeDataStart);
+      byteBuffer.get(_variableSizeDataBytes);
+      _variableSizeData = ByteBuffer.wrap(_variableSizeDataBytes);
+    } else {
+      _variableSizeDataBytes = null;
+      _variableSizeData = null;
+    }
+
+    // Read trailer.
+    byte[] trailerBytes = new byte[trailerLength];
+    byteBuffer.position(trailerStart);
+    byteBuffer.get(trailerBytes);
+    _trailer = deserializeTrailer(trailerBytes);
+
+    /**
+     * Extract metadata from trailer.
+     * Metadata is actually a part of _trailer in V3 when serialize DataTable into bytes. When deserialize,
+     * we extract metadata from _trailer into this _metadata map to provide the same interface with V2.
+     * */
+    _metadata = extractMetadataFormTrailer();
+  }
+
+  /**
+   * Construct data table from V2 byte array. (broker side)
+   */
+  public DataTableImplV3(ByteBuffer byteBuffer, boolean isV2)

Review comment:
       @mcvsubbu This function is used to deserialize a V2 bytes into V3 datatable object

##########
File path: pinot-core/src/main/java/org/apache/pinot/core/common/datatable/DataTableImplV3.java
##########
@@ -0,0 +1,702 @@
+/**
+ * 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.common.datatable;
+
+import com.google.common.primitives.Ints;
+import com.google.common.primitives.Longs;
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.DataInputStream;
+import java.io.DataOutputStream;
+import java.io.IOException;
+import java.nio.ByteBuffer;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.TreeMap;
+import org.apache.pinot.common.response.ProcessingException;
+import org.apache.pinot.common.utils.DataSchema;
+import org.apache.pinot.common.utils.DataTable;
+import org.apache.pinot.common.utils.StringUtil;
+import org.apache.pinot.core.common.ObjectSerDeUtils;
+import org.apache.pinot.core.query.request.context.ThreadTimer;
+import org.apache.pinot.spi.utils.ByteArray;
+import org.apache.pinot.spi.utils.BytesUtils;
+
+import static org.apache.pinot.core.common.datatable.DataTableUtils.*;
+
+
+public class DataTableImplV3 implements DataTable {
+  private static final int VERSION = 3;
+
+  // VERSION
+  // NUM_ROWS
+  // NUM_COLUMNS
+  // EXCEPTIONS (START|SIZE)
+  // DICTIONARY_MAP (START|SIZE)
+  // DATA_SCHEMA (START|SIZE)
+  // FIXED_SIZE_DATA (START|SIZE)
+  // VARIABLE_SIZE_DATA (START|SIZE)
+  // TRAILER (START|SIZE)
+  private static final int HEADER_SIZE = Integer.BYTES * 15;
+
+  private final int _numRows;
+  private final int _numColumns;
+  private final DataSchema _dataSchema;
+  private final int[] _columnOffsets;
+  private final int _rowSizeInBytes;
+  private final Map<String, Map<Integer, String>> _dictionaryMap;
+  private final byte[] _fixedSizeDataBytes;
+  private final ByteBuffer _fixedSizeData;
+  private final byte[] _variableSizeDataBytes;
+  private final ByteBuffer _variableSizeData;
+  // _exceptions stores exceptions as a map of errorCode->errorMessage
+  private final Map<Integer, String> _exceptions;
+  /**
+   * _metadata stores KV pairs for metadata. Metadata is actually a part of _trailer in V3 when serialize DataTable
+   * into bytes. When deserialize, we extract metadata from _trailer into this _metadata map to provide the same
+   * interface with V2. There are many code use
+   * datatable.getMetadata().get("key")/datatable.getMetadata().put("key", "value") to get/set metadata.
+   * TODO(@mqliang): revise this if we decide to get/set metadata by
+   *  datable.getTailerData(key)/datable.setTailer(key, value).
+   */
+  private final Map<String, String> _metadata;
+  private Map<TrailerKeys, String> _trailer;
+
+  private long _responseSerializationCpuTimeNs;
+  private int _responseSerializationCpuTimeNsValueOffset;
+
+  /**
+   * Construct data table with results. (Server side)
+   */
+  public DataTableImplV3(int numRows, DataSchema dataSchema, Map<String, Map<Integer, String>> dictionaryMap,
+      byte[] fixedSizeDataBytes, byte[] variableSizeDataBytes) {
+    _numRows = numRows;
+    _numColumns = dataSchema.size();
+    _dataSchema = dataSchema;
+    _columnOffsets = new int[_numColumns];
+    _rowSizeInBytes = DataTableUtils.computeColumnOffsets(dataSchema, _columnOffsets);
+    _dictionaryMap = dictionaryMap;
+    _fixedSizeDataBytes = fixedSizeDataBytes;
+    _fixedSizeData = ByteBuffer.wrap(fixedSizeDataBytes);
+    _variableSizeDataBytes = variableSizeDataBytes;
+    _variableSizeData = ByteBuffer.wrap(variableSizeDataBytes);
+    _exceptions = new HashMap<>();
+    _metadata = new HashMap<>();
+    _trailer = new TreeMap<>();
+  }
+
+  /**
+   * Construct empty data table. (Server side)
+   */
+  public DataTableImplV3() {
+    _numRows = 0;
+    _numColumns = 0;
+    _dataSchema = null;
+    _columnOffsets = null;
+    _rowSizeInBytes = 0;
+    _dictionaryMap = null;
+    _fixedSizeDataBytes = null;
+    _fixedSizeData = null;
+    _variableSizeDataBytes = null;
+    _variableSizeData = null;
+    _exceptions = new HashMap<>();
+    _metadata = new HashMap<>();
+    _trailer = new TreeMap<>();
+  }
+
+  @Override
+  public void addException(ProcessingException processingException) {
+    _exceptions.put(processingException.getErrorCode(), processingException.getMessage());
+  }
+
+  @Override
+  public Map<Integer, String> getExceptions() {
+    return _exceptions;
+  }
+
+  @Override
+  public byte[] toBytes()
+      throws IOException {
+    _trailer.put(TrailerKeys.RESPONSE_SERIALIZATION_CPU_TIME_NS_METADATA_KEY, String.valueOf(-1));
+    ThreadTimer threadTimer = new ThreadTimer();
+    threadTimer.start();
+    byte[] bytes = toBytesInternal();
+    _responseSerializationCpuTimeNs = threadTimer.stopAndGetThreadTimeNs();
+    // Replace the value of "responseSerializationCpuTimeNs" as actual value
+    System.arraycopy(Longs.toByteArray(_responseSerializationCpuTimeNs), 0, bytes,
+        _responseSerializationCpuTimeNsValueOffset, Long.BYTES);
+    return bytes;
+  }
+
+  private byte[] toBytesInternal()
+      throws IOException {
+    ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
+    DataOutputStream dataOutputStream = new DataOutputStream(byteArrayOutputStream);
+    dataOutputStream.writeInt(VERSION);
+    dataOutputStream.writeInt(_numRows);
+    dataOutputStream.writeInt(_numColumns);
+    int dataOffset = HEADER_SIZE;
+
+    // Write exceptions (START|SIZE).
+    dataOutputStream.writeInt(dataOffset);
+    byte[] exceptionsBytes;
+    exceptionsBytes = serializeExceptions();
+    dataOutputStream.writeInt(exceptionsBytes.length);
+    dataOffset += exceptionsBytes.length;
+
+    // Write dictionary (START|SIZE).
+    dataOutputStream.writeInt(dataOffset);
+    byte[] dictionaryMapBytes = null;
+    if (_dictionaryMap != null) {
+      dictionaryMapBytes = serializeDictionaryMap(_dictionaryMap);
+      dataOutputStream.writeInt(dictionaryMapBytes.length);
+      dataOffset += dictionaryMapBytes.length;
+    } else {
+      dataOutputStream.writeInt(0);
+    }
+
+    // Write data schema (START|SIZE).
+    dataOutputStream.writeInt(dataOffset);
+    byte[] dataSchemaBytes = null;
+    if (_dataSchema != null) {
+      dataSchemaBytes = _dataSchema.toBytes();
+      dataOutputStream.writeInt(dataSchemaBytes.length);
+      dataOffset += dataSchemaBytes.length;
+    } else {
+      dataOutputStream.writeInt(0);
+    }
+
+    // Write fixed size data (START|SIZE).
+    dataOutputStream.writeInt(dataOffset);
+    if (_fixedSizeDataBytes != null) {
+      dataOutputStream.writeInt(_fixedSizeDataBytes.length);
+      dataOffset += _fixedSizeDataBytes.length;
+    } else {
+      dataOutputStream.writeInt(0);
+    }
+
+    // Write variable size data (START|SIZE).
+    dataOutputStream.writeInt(dataOffset);
+    if (_variableSizeDataBytes != null) {
+      dataOutputStream.writeInt(_variableSizeDataBytes.length);
+      dataOffset += _variableSizeDataBytes.length;
+    } else {
+      dataOutputStream.writeInt(0);
+    }
+
+    // Write trailer data (START|SIZE).
+    dataOutputStream.writeInt(dataOffset);
+    // Put all meta data into trailer.
+    _trailer = putAllMetaDataIntoTrailer();
+    _responseSerializationCpuTimeNsValueOffset = dataOffset;
+    byte[] trailerBytes = serializeTrailer();
+    dataOutputStream.writeInt(trailerBytes.length);
+
+    // Write actual data.
+    dataOutputStream.write(exceptionsBytes);
+    if (dictionaryMapBytes != null) {
+      dataOutputStream.write(dictionaryMapBytes);
+    }
+    if (dataSchemaBytes != null) {
+      dataOutputStream.write(dataSchemaBytes);
+    }
+    if (_fixedSizeDataBytes != null) {
+      dataOutputStream.write(_fixedSizeDataBytes);
+    }
+    if (_variableSizeDataBytes != null) {
+      dataOutputStream.write(_variableSizeDataBytes);
+    }
+    dataOutputStream.write(trailerBytes);
+
+    return byteArrayOutputStream.toByteArray();
+  }
+
+  /**
+   * Construct data table from byte array. (broker side)
+   */
+  public DataTableImplV3(ByteBuffer byteBuffer)
+      throws IOException {
+    // Read header.
+    _numRows = byteBuffer.getInt();
+    _numColumns = byteBuffer.getInt();
+    int exceptionsStart = byteBuffer.getInt();
+    int exceptionsLength = byteBuffer.getInt();
+    int dictionaryMapStart = byteBuffer.getInt();
+    int dictionaryMapLength = byteBuffer.getInt();
+    int dataSchemaStart = byteBuffer.getInt();
+    int dataSchemaLength = byteBuffer.getInt();
+    int fixedSizeDataStart = byteBuffer.getInt();
+    int fixedSizeDataLength = byteBuffer.getInt();
+    int variableSizeDataStart = byteBuffer.getInt();
+    int variableSizeDataLength = byteBuffer.getInt();
+    int trailerStart = byteBuffer.getInt();
+    int trailerLength = byteBuffer.getInt();
+
+    // Read exceptions.
+    if (exceptionsLength != 0) {
+      byte[] exceptionsBytes = new byte[exceptionsLength];
+      byteBuffer.position(exceptionsStart);
+      byteBuffer.get(exceptionsBytes);
+      _exceptions = deserializeExceptions(exceptionsBytes);
+    } else {
+      _exceptions = new HashMap<>();
+    }
+
+    // Read dictionary.
+    if (dictionaryMapLength != 0) {
+      byte[] dictionaryMapBytes = new byte[dictionaryMapLength];
+      byteBuffer.position(dictionaryMapStart);
+      byteBuffer.get(dictionaryMapBytes);
+      _dictionaryMap = deserializeDictionaryMap(dictionaryMapBytes);
+    } else {
+      _dictionaryMap = null;
+    }
+
+    // Read data schema.
+    if (dataSchemaLength != 0) {
+      byte[] schemaBytes = new byte[dataSchemaLength];
+      byteBuffer.position(dataSchemaStart);
+      byteBuffer.get(schemaBytes);
+      _dataSchema = DataSchema.fromBytes(schemaBytes);
+      _columnOffsets = new int[_dataSchema.size()];
+      _rowSizeInBytes = DataTableUtils.computeColumnOffsets(_dataSchema, _columnOffsets);
+    } else {
+      _dataSchema = null;
+      _columnOffsets = null;
+      _rowSizeInBytes = 0;
+    }
+
+    // Read fixed size data.
+    if (fixedSizeDataLength != 0) {
+      _fixedSizeDataBytes = new byte[fixedSizeDataLength];
+      byteBuffer.position(fixedSizeDataStart);
+      byteBuffer.get(_fixedSizeDataBytes);
+      _fixedSizeData = ByteBuffer.wrap(_fixedSizeDataBytes);
+    } else {
+      _fixedSizeDataBytes = null;
+      _fixedSizeData = null;
+    }
+
+    // Read variable size data.
+    if (variableSizeDataLength != 0) {
+      _variableSizeDataBytes = new byte[variableSizeDataLength];
+      byteBuffer.position(variableSizeDataStart);
+      byteBuffer.get(_variableSizeDataBytes);
+      _variableSizeData = ByteBuffer.wrap(_variableSizeDataBytes);
+    } else {
+      _variableSizeDataBytes = null;
+      _variableSizeData = null;
+    }
+
+    // Read trailer.
+    byte[] trailerBytes = new byte[trailerLength];
+    byteBuffer.position(trailerStart);
+    byteBuffer.get(trailerBytes);
+    _trailer = deserializeTrailer(trailerBytes);
+
+    /**
+     * Extract metadata from trailer.
+     * Metadata is actually a part of _trailer in V3 when serialize DataTable into bytes. When deserialize,
+     * we extract metadata from _trailer into this _metadata map to provide the same interface with V2.
+     * */
+    _metadata = extractMetadataFormTrailer();

Review comment:
       @mcvsubbu After de-serialize _trailer, we need copy all metadata KV pairs in _trailer into _metadata.

##########
File path: pinot-core/src/main/java/org/apache/pinot/core/common/datatable/DataTableImplV3.java
##########
@@ -0,0 +1,702 @@
+/**
+ * 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.common.datatable;
+
+import com.google.common.primitives.Ints;
+import com.google.common.primitives.Longs;
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.DataInputStream;
+import java.io.DataOutputStream;
+import java.io.IOException;
+import java.nio.ByteBuffer;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.TreeMap;
+import org.apache.pinot.common.response.ProcessingException;
+import org.apache.pinot.common.utils.DataSchema;
+import org.apache.pinot.common.utils.DataTable;
+import org.apache.pinot.common.utils.StringUtil;
+import org.apache.pinot.core.common.ObjectSerDeUtils;
+import org.apache.pinot.core.query.request.context.ThreadTimer;
+import org.apache.pinot.spi.utils.ByteArray;
+import org.apache.pinot.spi.utils.BytesUtils;
+
+import static org.apache.pinot.core.common.datatable.DataTableUtils.*;
+
+
+public class DataTableImplV3 implements DataTable {
+  private static final int VERSION = 3;
+
+  // VERSION
+  // NUM_ROWS
+  // NUM_COLUMNS
+  // EXCEPTIONS (START|SIZE)
+  // DICTIONARY_MAP (START|SIZE)
+  // DATA_SCHEMA (START|SIZE)
+  // FIXED_SIZE_DATA (START|SIZE)
+  // VARIABLE_SIZE_DATA (START|SIZE)
+  // TRAILER (START|SIZE)
+  private static final int HEADER_SIZE = Integer.BYTES * 15;
+
+  private final int _numRows;
+  private final int _numColumns;
+  private final DataSchema _dataSchema;
+  private final int[] _columnOffsets;
+  private final int _rowSizeInBytes;
+  private final Map<String, Map<Integer, String>> _dictionaryMap;
+  private final byte[] _fixedSizeDataBytes;
+  private final ByteBuffer _fixedSizeData;
+  private final byte[] _variableSizeDataBytes;
+  private final ByteBuffer _variableSizeData;
+  // _exceptions stores exceptions as a map of errorCode->errorMessage
+  private final Map<Integer, String> _exceptions;
+  /**
+   * _metadata stores KV pairs for metadata. Metadata is actually a part of _trailer in V3 when serialize DataTable
+   * into bytes. When deserialize, we extract metadata from _trailer into this _metadata map to provide the same
+   * interface with V2. There are many code use
+   * datatable.getMetadata().get("key")/datatable.getMetadata().put("key", "value") to get/set metadata.
+   * TODO(@mqliang): revise this if we decide to get/set metadata by
+   *  datable.getTailerData(key)/datable.setTailer(key, value).
+   */
+  private final Map<String, String> _metadata;
+  private Map<TrailerKeys, String> _trailer;
+
+  private long _responseSerializationCpuTimeNs;
+  private int _responseSerializationCpuTimeNsValueOffset;
+
+  /**
+   * Construct data table with results. (Server side)
+   */
+  public DataTableImplV3(int numRows, DataSchema dataSchema, Map<String, Map<Integer, String>> dictionaryMap,
+      byte[] fixedSizeDataBytes, byte[] variableSizeDataBytes) {
+    _numRows = numRows;
+    _numColumns = dataSchema.size();
+    _dataSchema = dataSchema;
+    _columnOffsets = new int[_numColumns];
+    _rowSizeInBytes = DataTableUtils.computeColumnOffsets(dataSchema, _columnOffsets);
+    _dictionaryMap = dictionaryMap;
+    _fixedSizeDataBytes = fixedSizeDataBytes;
+    _fixedSizeData = ByteBuffer.wrap(fixedSizeDataBytes);
+    _variableSizeDataBytes = variableSizeDataBytes;
+    _variableSizeData = ByteBuffer.wrap(variableSizeDataBytes);
+    _exceptions = new HashMap<>();
+    _metadata = new HashMap<>();
+    _trailer = new TreeMap<>();
+  }
+
+  /**
+   * Construct empty data table. (Server side)
+   */
+  public DataTableImplV3() {
+    _numRows = 0;
+    _numColumns = 0;
+    _dataSchema = null;
+    _columnOffsets = null;
+    _rowSizeInBytes = 0;
+    _dictionaryMap = null;
+    _fixedSizeDataBytes = null;
+    _fixedSizeData = null;
+    _variableSizeDataBytes = null;
+    _variableSizeData = null;
+    _exceptions = new HashMap<>();
+    _metadata = new HashMap<>();
+    _trailer = new TreeMap<>();
+  }
+
+  @Override
+  public void addException(ProcessingException processingException) {
+    _exceptions.put(processingException.getErrorCode(), processingException.getMessage());
+  }
+
+  @Override
+  public Map<Integer, String> getExceptions() {
+    return _exceptions;
+  }
+
+  @Override
+  public byte[] toBytes()
+      throws IOException {
+    _trailer.put(TrailerKeys.RESPONSE_SERIALIZATION_CPU_TIME_NS_METADATA_KEY, String.valueOf(-1));
+    ThreadTimer threadTimer = new ThreadTimer();
+    threadTimer.start();
+    byte[] bytes = toBytesInternal();
+    _responseSerializationCpuTimeNs = threadTimer.stopAndGetThreadTimeNs();
+    // Replace the value of "responseSerializationCpuTimeNs" as actual value
+    System.arraycopy(Longs.toByteArray(_responseSerializationCpuTimeNs), 0, bytes,
+        _responseSerializationCpuTimeNsValueOffset, Long.BYTES);
+    return bytes;
+  }
+
+  private byte[] toBytesInternal()
+      throws IOException {
+    ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
+    DataOutputStream dataOutputStream = new DataOutputStream(byteArrayOutputStream);
+    dataOutputStream.writeInt(VERSION);
+    dataOutputStream.writeInt(_numRows);
+    dataOutputStream.writeInt(_numColumns);
+    int dataOffset = HEADER_SIZE;
+
+    // Write exceptions (START|SIZE).
+    dataOutputStream.writeInt(dataOffset);
+    byte[] exceptionsBytes;
+    exceptionsBytes = serializeExceptions();
+    dataOutputStream.writeInt(exceptionsBytes.length);
+    dataOffset += exceptionsBytes.length;
+
+    // Write dictionary (START|SIZE).
+    dataOutputStream.writeInt(dataOffset);
+    byte[] dictionaryMapBytes = null;
+    if (_dictionaryMap != null) {
+      dictionaryMapBytes = serializeDictionaryMap(_dictionaryMap);
+      dataOutputStream.writeInt(dictionaryMapBytes.length);
+      dataOffset += dictionaryMapBytes.length;
+    } else {
+      dataOutputStream.writeInt(0);
+    }
+
+    // Write data schema (START|SIZE).
+    dataOutputStream.writeInt(dataOffset);
+    byte[] dataSchemaBytes = null;
+    if (_dataSchema != null) {
+      dataSchemaBytes = _dataSchema.toBytes();
+      dataOutputStream.writeInt(dataSchemaBytes.length);
+      dataOffset += dataSchemaBytes.length;
+    } else {
+      dataOutputStream.writeInt(0);
+    }
+
+    // Write fixed size data (START|SIZE).
+    dataOutputStream.writeInt(dataOffset);
+    if (_fixedSizeDataBytes != null) {
+      dataOutputStream.writeInt(_fixedSizeDataBytes.length);
+      dataOffset += _fixedSizeDataBytes.length;
+    } else {
+      dataOutputStream.writeInt(0);
+    }
+
+    // Write variable size data (START|SIZE).
+    dataOutputStream.writeInt(dataOffset);
+    if (_variableSizeDataBytes != null) {
+      dataOutputStream.writeInt(_variableSizeDataBytes.length);
+      dataOffset += _variableSizeDataBytes.length;
+    } else {
+      dataOutputStream.writeInt(0);
+    }
+
+    // Write trailer data (START|SIZE).
+    dataOutputStream.writeInt(dataOffset);
+    // Put all meta data into trailer.
+    _trailer = putAllMetaDataIntoTrailer();
+    _responseSerializationCpuTimeNsValueOffset = dataOffset;
+    byte[] trailerBytes = serializeTrailer();
+    dataOutputStream.writeInt(trailerBytes.length);
+
+    // Write actual data.
+    dataOutputStream.write(exceptionsBytes);
+    if (dictionaryMapBytes != null) {
+      dataOutputStream.write(dictionaryMapBytes);
+    }
+    if (dataSchemaBytes != null) {
+      dataOutputStream.write(dataSchemaBytes);
+    }
+    if (_fixedSizeDataBytes != null) {
+      dataOutputStream.write(_fixedSizeDataBytes);
+    }
+    if (_variableSizeDataBytes != null) {
+      dataOutputStream.write(_variableSizeDataBytes);
+    }
+    dataOutputStream.write(trailerBytes);
+
+    return byteArrayOutputStream.toByteArray();
+  }
+
+  /**
+   * Construct data table from byte array. (broker side)
+   */
+  public DataTableImplV3(ByteBuffer byteBuffer)
+      throws IOException {
+    // Read header.
+    _numRows = byteBuffer.getInt();
+    _numColumns = byteBuffer.getInt();
+    int exceptionsStart = byteBuffer.getInt();
+    int exceptionsLength = byteBuffer.getInt();
+    int dictionaryMapStart = byteBuffer.getInt();
+    int dictionaryMapLength = byteBuffer.getInt();
+    int dataSchemaStart = byteBuffer.getInt();
+    int dataSchemaLength = byteBuffer.getInt();
+    int fixedSizeDataStart = byteBuffer.getInt();
+    int fixedSizeDataLength = byteBuffer.getInt();
+    int variableSizeDataStart = byteBuffer.getInt();
+    int variableSizeDataLength = byteBuffer.getInt();
+    int trailerStart = byteBuffer.getInt();
+    int trailerLength = byteBuffer.getInt();
+
+    // Read exceptions.
+    if (exceptionsLength != 0) {
+      byte[] exceptionsBytes = new byte[exceptionsLength];
+      byteBuffer.position(exceptionsStart);
+      byteBuffer.get(exceptionsBytes);
+      _exceptions = deserializeExceptions(exceptionsBytes);
+    } else {
+      _exceptions = new HashMap<>();
+    }
+
+    // Read dictionary.
+    if (dictionaryMapLength != 0) {
+      byte[] dictionaryMapBytes = new byte[dictionaryMapLength];
+      byteBuffer.position(dictionaryMapStart);
+      byteBuffer.get(dictionaryMapBytes);
+      _dictionaryMap = deserializeDictionaryMap(dictionaryMapBytes);
+    } else {
+      _dictionaryMap = null;
+    }
+
+    // Read data schema.
+    if (dataSchemaLength != 0) {
+      byte[] schemaBytes = new byte[dataSchemaLength];
+      byteBuffer.position(dataSchemaStart);
+      byteBuffer.get(schemaBytes);
+      _dataSchema = DataSchema.fromBytes(schemaBytes);
+      _columnOffsets = new int[_dataSchema.size()];
+      _rowSizeInBytes = DataTableUtils.computeColumnOffsets(_dataSchema, _columnOffsets);
+    } else {
+      _dataSchema = null;
+      _columnOffsets = null;
+      _rowSizeInBytes = 0;
+    }
+
+    // Read fixed size data.
+    if (fixedSizeDataLength != 0) {
+      _fixedSizeDataBytes = new byte[fixedSizeDataLength];
+      byteBuffer.position(fixedSizeDataStart);
+      byteBuffer.get(_fixedSizeDataBytes);
+      _fixedSizeData = ByteBuffer.wrap(_fixedSizeDataBytes);
+    } else {
+      _fixedSizeDataBytes = null;
+      _fixedSizeData = null;
+    }
+
+    // Read variable size data.
+    if (variableSizeDataLength != 0) {
+      _variableSizeDataBytes = new byte[variableSizeDataLength];
+      byteBuffer.position(variableSizeDataStart);
+      byteBuffer.get(_variableSizeDataBytes);
+      _variableSizeData = ByteBuffer.wrap(_variableSizeDataBytes);
+    } else {
+      _variableSizeDataBytes = null;
+      _variableSizeData = null;
+    }
+
+    // Read trailer.
+    byte[] trailerBytes = new byte[trailerLength];
+    byteBuffer.position(trailerStart);
+    byteBuffer.get(trailerBytes);
+    _trailer = deserializeTrailer(trailerBytes);
+
+    /**
+     * Extract metadata from trailer.
+     * Metadata is actually a part of _trailer in V3 when serialize DataTable into bytes. When deserialize,
+     * we extract metadata from _trailer into this _metadata map to provide the same interface with V2.
+     * */
+    _metadata = extractMetadataFormTrailer();
+  }
+
+  /**
+   * Construct data table from V2 byte array. (broker side)
+   */
+  public DataTableImplV3(ByteBuffer byteBuffer, boolean isV2)
+      throws IOException {
+    // Read header.
+    _numRows = byteBuffer.getInt();
+    _numColumns = byteBuffer.getInt();
+    int dictionaryMapStart = byteBuffer.getInt();
+    int dictionaryMapLength = byteBuffer.getInt();
+    int metadataStart = byteBuffer.getInt();
+    int metadataLength = byteBuffer.getInt();
+    int dataSchemaStart = byteBuffer.getInt();
+    int dataSchemaLength = byteBuffer.getInt();
+    int fixedSizeDataStart = byteBuffer.getInt();
+    int fixedSizeDataLength = byteBuffer.getInt();
+    int variableSizeDataStart = byteBuffer.getInt();
+    int variableSizeDataLength = byteBuffer.getInt();
+
+    // Read dictionary.
+    if (dictionaryMapLength != 0) {
+      byte[] dictionaryMapBytes = new byte[dictionaryMapLength];
+      byteBuffer.position(dictionaryMapStart);
+      byteBuffer.get(dictionaryMapBytes);
+      _dictionaryMap = deserializeDictionaryMap(dictionaryMapBytes);
+    } else {
+      _dictionaryMap = null;
+    }
+
+    // Read metadata.
+    byte[] metadataBytes = new byte[metadataLength];
+    byteBuffer.position(metadataStart);
+    byteBuffer.get(metadataBytes);
+    _metadata = deserializeV2Metadata(metadataBytes);
+
+    // Read data schema.
+    if (dataSchemaLength != 0) {
+      byte[] schemaBytes = new byte[dataSchemaLength];
+      byteBuffer.position(dataSchemaStart);
+      byteBuffer.get(schemaBytes);
+      _dataSchema = DataSchema.fromBytes(schemaBytes);
+      _columnOffsets = new int[_dataSchema.size()];
+      _rowSizeInBytes = DataTableUtils.computeColumnOffsets(_dataSchema, _columnOffsets);
+    } else {
+      _dataSchema = null;
+      _columnOffsets = null;
+      _rowSizeInBytes = 0;
+    }
+
+    // Read fixed size data.
+    if (fixedSizeDataLength != 0) {
+      _fixedSizeDataBytes = new byte[fixedSizeDataLength];
+      byteBuffer.position(fixedSizeDataStart);
+      byteBuffer.get(_fixedSizeDataBytes);
+      _fixedSizeData = ByteBuffer.wrap(_fixedSizeDataBytes);
+    } else {
+      _fixedSizeDataBytes = null;
+      _fixedSizeData = null;
+    }
+
+    // Read variable size data.
+    if (variableSizeDataLength != 0) {
+      _variableSizeDataBytes = new byte[variableSizeDataLength];
+      byteBuffer.position(variableSizeDataStart);
+      byteBuffer.get(_variableSizeDataBytes);
+      _variableSizeData = ByteBuffer.wrap(_variableSizeDataBytes);
+    } else {
+      _variableSizeDataBytes = null;
+      _variableSizeData = null;
+    }
+
+    _trailer = null;
+    /**
+     * V2 stores exceptions as a bunch of KV pairs in metadata, all exceptions has key of "Exception"+errCode.
+     * To interpret V2 bytes as V3 object, extract exceptions from metadata.
+     */
+    _exceptions = extractExceptionsFormV2Metadata();
+  }
+
+  /**
+   * Serialize trailer section to bytes.
+   * Format of the bytes looks:
+   * [numEntries, bytesOfKV2, bytesOfKV2, bytesOfKV3]
+   * For each KV pairs:
+   * - if value is int/long, encode it as: [keyOrdinal, bigEndianRepresentationOfValue]
+   * - if value is string, encode it as: [keyOrdinal, valueLength, Utf8EncodedValue]
+   */
+  private byte[] serializeTrailer()
+      throws IOException {
+    ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
+    DataOutputStream dataOutputStream = new DataOutputStream(byteArrayOutputStream);
+    int offset = 0;
+    dataOutputStream.writeInt(_trailer.size());
+    offset += Integer.BYTES;
+    for (Map.Entry<TrailerKeys, String> entry : _trailer.entrySet()) {
+      TrailerKeys key = entry.getKey();
+      String value = entry.getValue();
+      dataOutputStream.writeInt(key.ordinal());
+      offset += Integer.BYTES;
+      if (key == TrailerKeys.RESPONSE_SERIALIZATION_CPU_TIME_NS_METADATA_KEY) {
+        _responseSerializationCpuTimeNsValueOffset += offset;
+      }
+      if (IntValueTrailerKeys.contains(key)) {
+        byte[] valueBytes = Ints.toByteArray(Integer.parseInt(value));
+        dataOutputStream.write(valueBytes);
+        offset += valueBytes.length;
+      } else if (LongValueTrailerKeys.contains(key)) {
+        byte[] valueBytes = Longs.toByteArray(Long.parseLong(value));
+        dataOutputStream.write(valueBytes);
+        offset += valueBytes.length;
+      } else {
+        byte[] valueBytes = StringUtil.encodeUtf8(value);
+        dataOutputStream.writeInt(valueBytes.length);
+        dataOutputStream.write(valueBytes);
+        offset += Integer.BYTES + valueBytes.length;
+      }
+    }
+    return byteArrayOutputStream.toByteArray();
+  }
+
+  private Map<TrailerKeys, String> deserializeTrailer(byte[] bytes)

Review comment:
       @mcvsubbu This is the code to de-serialize trailer.




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