apache/hadoop · error · IOException

Version Mismatch (Expected: {}, Received: {} )

Error message

Version Mismatch (Expected: {}, Received: {} )

What it means

Every data-transfer connection (DFSClient to DataNode, DN to DN on the xfer port) starts each operation with a short protocol version, DATA_TRANSFER_VERSION. Receiver.readOp rejects any value that differs, throwing IOException with expected vs received before the op is even parsed.

Source

Thrown at hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/protocol/datatransfer/Receiver.java:74

@InterfaceStability.Evolving
public abstract class Receiver implements DataTransferProtocol {
  private final Tracer tracer;
  protected DataInputStream in;

  protected Receiver(Tracer tracer) {
    this.tracer = tracer;
  }

  /** Initialize a receiver for DataTransferProtocol with a socket. */
  protected void initialize(final DataInputStream in) {
    this.in = in;
  }

  /** Read an Op.  It also checks protocol version. */
  protected final Op readOp() throws IOException {
    final short version = in.readShort();
    if (version != DataTransferProtocol.DATA_TRANSFER_VERSION) {
      throw new IOException( "Version Mismatch (Expected: " +
          DataTransferProtocol.DATA_TRANSFER_VERSION  +
          ", Received: " +  version + " )");
    }
    return Op.read(in);
  }

  private TraceScope continueTraceSpan(ByteString spanContextBytes,
                                       String description) {
    TraceScope scope = null;
    SpanContext spanContext =
        TraceUtils.byteStringToSpanContext(spanContextBytes);
    if (spanContext != null) {
      scope = tracer.newScope(description, spanContext);
    }
    return scope;
  }

  private TraceScope continueTraceSpan(ClientOperationHeaderProto header,

View on GitHub (pinned to 2add963021)

Solutions

1. Align the HDFS client and DataNode versions (rolling upgrades must step only through mutually compatible versions)
2. Check DataNode logs for the peer address - if it is not an expected client/DN, find and stop whatever is connecting to the xfer port
3. For custom clients, send the DATA_TRANSFER_VERSION constant of the cluster being targeted

// Client-side preflight: refuse to run against a cluster whose version may differ
String dnVersion = someDn.getHdfsBlockReportsVersionHint(); // e.g. via DataNode JMX VersionInfo
// practical form: assert the client's Hadoop version equals the cluster's reported
// version (jmx `Hadoop:service=DataNode,name=DataNodeInfo` -> Version) before heavy IO

try {
  fs.open(path).read();
} catch (IOException e) {
  if (e.getMessage() != null && e.getMessage().contains("Version Mismatch")) {
    // data-transfer protocol skew: stop and align client/DN versions; do not retry
  } else {
    throw e;
  }
}

When it happens

Trigger: A client or peer DataNode running a Hadoop build whose DATA_TRANSFER_VERSION differs from the serving DataNode; or a non-HDFS program connecting to dfs.datanode.data.port (default 9866) so its bytes decode as a bogus version.

Common situations: Version skew during rolling upgrades that skipped incompatible versions; downgraded clients; stray services or port scanners hitting the dataxceiver port; custom native clients hardcoding the wrong version.

Related errors

• Unknown op {} in data stream
• Cannot create a secured connection if DataNode listens on un
• Received %x instead of %x from client.
• BUG: The stored LV = {} is newer than the supported LV = {}
• Unexpected blockChecksumType '%s', expecting COMPOSITE_CRC

AI-assisted analysis of apache/hadoop@2add963021 (2026-08-22). Data as JSON: /api/errors/8820e4cd47a4879f. Report an issue: GitHub.