[GitHub] [pinot] klsince commented on a change in pull request #7661: implement size balanced V4 raw chunk format

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

klsince commented on a change in pull request #7661:
URL: https://github.com/apache/pinot/pull/7661#discussion_r741338323



##########
File path: pinot-segment-local/src/main/java/org/apache/pinot/segment/local/segment/index/readers/forward/VarByteChunkSVForwardIndexReaderV4.java
##########
@@ -0,0 +1,299 @@
+/**
+ * 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.segment.local.segment.index.readers.forward;
+
+import java.io.IOException;
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
+import java.nio.charset.StandardCharsets;
+import javax.annotation.Nullable;
+import org.apache.pinot.segment.local.io.compression.ChunkCompressorFactory;
+import org.apache.pinot.segment.local.io.writer.impl.VarByteChunkSVForwardIndexWriterV4;
+import org.apache.pinot.segment.spi.compression.ChunkCompressionType;
+import org.apache.pinot.segment.spi.compression.ChunkDecompressor;
+import org.apache.pinot.segment.spi.index.reader.ForwardIndexReader;
+import org.apache.pinot.segment.spi.index.reader.ForwardIndexReaderContext;
+import org.apache.pinot.segment.spi.memory.CleanerUtil;
+import org.apache.pinot.segment.spi.memory.PinotDataBuffer;
+import org.apache.pinot.spi.data.FieldSpec;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+
+public class VarByteChunkSVForwardIndexReaderV4
+    implements ForwardIndexReader<VarByteChunkSVForwardIndexReaderV4.ReaderContext> {
+
+  private static final Logger LOGGER = LoggerFactory.getLogger(VarByteChunkSVForwardIndexReaderV4.class);
+
+  private static final int METADATA_ENTRY_SIZE = 8;

Review comment:
       nit: add a comment that the two metadata entries are the starting docId of the chunk and the chunk offset.

##########
File path: pinot-segment-local/src/main/java/org/apache/pinot/segment/local/io/writer/impl/VarByteChunkSVForwardIndexWriterV4.java
##########
@@ -0,0 +1,222 @@
+/**
+ * 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.segment.local.io.writer.impl;
+
+import java.io.File;
+import java.io.IOException;
+import java.io.RandomAccessFile;
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
+import java.nio.channels.FileChannel;
+import java.nio.charset.StandardCharsets;
+import javax.annotation.concurrent.NotThreadSafe;
+import org.apache.commons.io.FileUtils;
+import org.apache.pinot.segment.local.io.compression.ChunkCompressorFactory;
+import org.apache.pinot.segment.spi.compression.ChunkCompressionType;
+import org.apache.pinot.segment.spi.compression.ChunkCompressor;
+import org.apache.pinot.segment.spi.memory.CleanerUtil;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+
+/**
+ * Class to write out variable length bytes into a single column.
+ *
+ *
+ * Only sequential writes are supported.
+ */
+@NotThreadSafe
+public class VarByteChunkSVForwardIndexWriterV4 implements VarByteChunkWriter {
+
+  private static final Logger LOGGER = LoggerFactory.getLogger(VarByteChunkSVForwardIndexWriterV4.class);
+
+  public static final int VERSION = 4;
+
+  private static final String DATA_BUFFER_SUFFIX = ".buf";
+
+  private final File _dataBuffer;
+  private final RandomAccessFile _output;
+  private final FileChannel _dataChannel;
+  private final ByteBuffer _chunkBuffer;
+  private final ChunkCompressor _chunkCompressor;
+
+  private int _docIdOffset = 0;
+  private int _nextDocId = 0;
+  private int _metadataSize = 0;
+  private long _chunkOffset = 0;
+
+  public VarByteChunkSVForwardIndexWriterV4(File file, ChunkCompressionType compressionType, int chunkSize)
+      throws IOException {
+    _dataBuffer = new File(file.getName() + DATA_BUFFER_SUFFIX);
+    _output = new RandomAccessFile(file, "rw");
+    _dataChannel = new RandomAccessFile(_dataBuffer, "rw").getChannel();
+    _chunkCompressor = ChunkCompressorFactory.getCompressor(compressionType, true);
+    _chunkBuffer = ByteBuffer.allocateDirect(chunkSize).order(ByteOrder.LITTLE_ENDIAN);
+    // reserve space for numDocs
+    _chunkBuffer.position(Integer.BYTES);
+    writeHeader(_chunkCompressor.compressionType(), chunkSize);
+  }
+
+  private void writeHeader(ChunkCompressionType compressionType, int targetDecompressedChunkSize)
+      throws IOException {
+    // keep metadata BE for backwards compatibility
+    // (e.g. the version needs to be read by a factory which assumes BE)
+    _output.writeInt(VERSION);
+    _output.writeInt(targetDecompressedChunkSize);
+    _output.writeInt(compressionType.getValue());
+    // reserve a slot to write the data offset into
+    _output.writeInt(0);
+    _metadataSize += 4 * Integer.BYTES;
+  }
+
+  @Override
+  public void putString(String string) {
+    putBytes(string.getBytes(StandardCharsets.UTF_8));
+  }
+
+  @Override
+  public void putBytes(byte[] bytes) {
+    int sizeRequired = Integer.BYTES + bytes.length;
+    if (_chunkBuffer.position() >= _chunkBuffer.capacity() - sizeRequired) {
+      writeChunk();
+      if (sizeRequired >= _chunkBuffer.capacity() - Integer.BYTES) {
+        writeHugeChunk(bytes);
+        return;
+      }
+    }
+    _chunkBuffer.putInt(bytes.length);
+    _chunkBuffer.put(bytes);
+    _nextDocId++;
+  }
+
+  private void writeHugeChunk(byte[] bytes) {
+    // huge values where the bytes and their length prefix don't fit in to the remainder of the buffer after the prefix
+    // for the number of documents in a regular chunk are written as a single value without metadata, and these chunks
+    // are detected by marking the MSB in the doc id offset
+    final ByteBuffer buffer;
+    if (_chunkCompressor.compressionType() == ChunkCompressionType.SNAPPY
+        || _chunkCompressor.compressionType() == ChunkCompressionType.ZSTANDARD) {
+      buffer = ByteBuffer.allocateDirect(bytes.length);
+      buffer.put(bytes);
+      buffer.flip();
+    } else {
+      // cast for JDK8 javac compatibility
+      buffer = (ByteBuffer) ByteBuffer.wrap(bytes);
+    }
+    try {
+      _nextDocId++;
+      write(buffer, true);
+    } finally {
+      CleanerUtil.cleanQuietly(buffer);
+    }
+  }
+
+  private void writeChunk() {
+    if (_nextDocId > _docIdOffset) {

Review comment:
       It may help to understand this method to describe a bit about the data layout before and after in method comment.
   
   nit: save a few indents
   ```
   if (_nextDocId <= _docIdOffset) {
     return;
   }
   ...
   ```




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