apache/hadoop · error · IOException

Encoded type {} converted to valid component type {} but no

Error message

Encoded type {} converted to valid component type {} but no encoding is implemented for this type.

What it means

The tail else of readFields()'s dispatch chain: the component type name resolved to a class in PRIMITIVE_NAMES (so getPrimitiveClass returned non-null) but none of the eight read branches matched. Since PRIMITIVE_NAMES contains exactly the eight handled primitives, this is a defensive, effectively unreachable internal-consistency check — it can only fire if a fork adds a name to the map without a corresponding readXxxArray branch, or state is mutated abnormally.

Source

Thrown at hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/ArrayPrimitiveWritable.java:247

    // do the inner loop.  Walk the decision tree only once.
    if (componentType == Boolean.TYPE) {             // boolean
      readBooleanArray(in);
    } else if (componentType == Character.TYPE) {    // char
      readCharArray(in);
    } else if (componentType == Byte.TYPE) {         // byte
      readByteArray(in);
    } else if (componentType == Short.TYPE) {        // short
      readShortArray(in);
    } else if (componentType == Integer.TYPE) {      // int
      readIntArray(in);
    } else if (componentType == Long.TYPE) {         // long
      readLongArray(in);
    } else if (componentType == Float.TYPE) {        // float
      readFloatArray(in);
    } else if (componentType == Double.TYPE) {       // double
      readDoubleArray(in);
    } else {
      throw new IOException("Encoded type " + className
          + " converted to valid component type " + componentType.toString()
          + " but no encoding is implemented for this type.");
    }
  }
  
  //For efficient implementation, there's no way around
  //the following massive code duplication.
  
  private void writeBooleanArray(DataOutput out) throws IOException {
    boolean[] v = (boolean[]) value;
    for (int i = 0; i < length; i++)
      out.writeBoolean(v[i]);
  }
  
  private void writeCharArray(DataOutput out) throws IOException {
    char[] v = (char[]) value;
    for (int i = 0; i < length; i++)
      out.writeChar(v[i]);

View on GitHub (pinned to 2add963021)

Solutions

1. If you maintain a fork that adds a primitive, add both the map entry and the matching readXxxArray branch.
2. Otherwise, treat this as evidence of tampered internals or a classpath mix of Hadoop versions — align hadoop-common jars across the cluster.

try {
  w.readFields(in);
} catch (IOException e) {
  LOG.error("Read dispatch failed for " + w.getComponentType(), e);
  throw e;
}

When it happens

Trigger: A modified/forked ArrayPrimitiveWritable where PRIMITIVE_NAMES and the read dispatch chain are out of sync; reflection-assigned componentType. Not reachable in stock Hadoop.

Common situations: Vendored or patched hadoop-common where someone extended the supported primitive set incompletely.

Related errors

• Component type {} is set as the output type, but no encoding
• No URI in deserialized Path
• encoded array component type {} is not a candidate primitive
• encoded array length is negative {}
• Cannot initialize the class: {clazz}

AI-assisted analysis of apache/hadoop@2add963021 (2026-08-22). Data as JSON: /api/errors/d51a7387ab19076f. Report an issue: GitHub.