fix review issue

Signed-off-by: OneSizeFitQuorum <[email protected]>

iotdb-core/datanode/src/main/java/org/apache/iotdb/db/storageengine/dataregion/wal/io/LogWriter.java

@@ -50,15 +50,22 @@ public abstract class LogWriter implements ILogWriter {
   protected final FileChannel logChannel;
   protected long size = 0;
   protected long originalSize = 0;
+
+  /**
+   * 1 byte for whether enable compression, 4 byte for compressedSize, 4 byte for uncompressedSize
+   */
   private final int COMPRESSED_HEADER_SIZE = Byte.BYTES + Integer.BYTES * 2;
+
+  /** 1 byte for whether enable compression, 4 byte for uncompressedSize */
   private final int UN_COMPRESSED_HEADER_SIZE = Byte.BYTES + Integer.BYTES;
+
   private final ByteBuffer headerBuffer = ByteBuffer.allocate(COMPRESSED_HEADER_SIZE);
   private ICompressor compressor =
       ICompressor.getCompressor(
           IoTDBDescriptor.getInstance().getConfig().getWALCompressionAlgorithm());
   private ByteBuffer compressedByteBuffer;
 
-  /** Minimum size to compress, default is 32 KB */
+  /** Minimum size to compress, use magic number 32 KB */
   private static long MIN_COMPRESSION_SIZE = 32 * 1024L;
 
   protected LogWriter(File logFile, WALFileVersion version) throws IOException {

iotdb-core/datanode/src/main/java/org/apache/iotdb/db/storageengine/dataregion/wal/io/WALInputStream.java

@@ -39,9 +39,12 @@ public class WALInputStream extends InputStream implements AutoCloseable {
 
   private static final Logger logger = LoggerFactory.getLogger(WALInputStream.class);
   private final FileChannel channel;
+
+  /** 1 byte for whether enable compression, 4 byte for compressedSize */
   private final ByteBuffer segmentHeaderWithoutCompressedSizeBuffer =
       ByteBuffer.allocate(Integer.BYTES + Byte.BYTES);
-  private final ByteBuffer compressedSizeHeaderBuffer = ByteBuffer.allocate(Integer.BYTES);
+
+  private final ByteBuffer compressedSizeBuffer = ByteBuffer.allocate(Integer.BYTES);
   private ByteBuffer dataBuffer = null;
   private ByteBuffer compressedBuffer = null;
   private final long fileSize;
@@ -335,10 +338,10 @@ private SegmentInfo getNextSegmentInfo() throws IOException {
         CompressionType.deserialize(segmentHeaderWithoutCompressedSizeBuffer.get());
     info.dataInDiskSize = segmentHeaderWithoutCompressedSizeBuffer.getInt();
     if (info.compressionType != CompressionType.UNCOMPRESSED) {
-      compressedSizeHeaderBuffer.clear();
-      channel.read(compressedSizeHeaderBuffer);
-      compressedSizeHeaderBuffer.flip();
-      info.uncompressedSize = compressedSizeHeaderBuffer.getInt();
+      compressedSizeBuffer.clear();
+      channel.read(compressedSizeBuffer);
+      compressedSizeBuffer.flip();
+      info.uncompressedSize = compressedSizeBuffer.getInt();
     } else {
       info.uncompressedSize = info.dataInDiskSize;
     }