apache/hadoop · error · IOException

Got wrong length during writeBlock({}) from {} at offset {}:

Error message

Got wrong length during writeBlock({}) from {} at offset {}: {}

What it means

Error "Got wrong length during writeBlock({}) from {} at offset {}: {}" thrown in apache/hadoop.

Source

Thrown at hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/BlockReceiver.java:568

   * returns the number of data bytes that the packet has.
   */
  private int receivePacket() throws IOException {
    // read the next packet
    packetReceiver.receiveNextPacket(in);

    PacketHeader header = packetReceiver.getHeader();
    long seqno = header.getSeqno();
    LOG.debug("Receiving one packet for block {} seqno:{} header:{} ", block,
        seqno, header);

    // Sanity check the header
    if (header.getOffsetInBlock() > replicaInfo.getNumBytes()) {
      throw new IOException("Received an out-of-sequence packet for " + block + 
          "from " + inAddr + " at offset " + header.getOffsetInBlock() +
          ". Expecting packet starting at " + replicaInfo.getNumBytes());
    }
    if (header.getDataLen() < 0) {
      throw new IOException("Got wrong length during writeBlock(" + block + 
                            ") from " + inAddr + " at offset " + 
                            header.getOffsetInBlock() + ": " +
                            header.getDataLen()); 
    }

    long offsetInBlock = header.getOffsetInBlock();
    boolean lastPacketInBlock = header.isLastPacketInBlock();
    final int len = header.getDataLen();
    boolean syncBlock = header.getSyncBlock();

    // avoid double sync'ing on close
    if (syncBlock && lastPacketInBlock) {
      this.syncOnClose = false;
      // sync directory for finalize irrespective of syncOnClose config since
      // sync is requested.
      this.dirSyncOnFinalize = true;
    }

View on GitHub (pinned to 2add963021)

Solutions

1. Verify client and DataNode versions are compatible; a malformed packet header length field usually indicates protocol mismatch or stream corruption.
2. Inspect the network path for truncation/corruption and check the client logs for earlier errors in the same block write.

When it happens

Trigger: The data length read from the stream during receiveBlock does not match the length advertised in the packet header at the current offset.

Common situations: The packet length field did not match the data actually received, typically from stream corruption or a truncated connection. Check network stability between client and DataNode.

AI-assisted analysis of apache/hadoop@2add963021 (2026-08-22). Data as JSON: /api/errors/299c35c7942a22d8. Report an issue: GitHub.