apache/iceberg · error · UnsupportedOperationException

Cannot serialize an eager input file

Error message

Cannot serialize an eager input file: <location>

What it means

EagerInputFile cannot serialize a Hadoop Configuration supplier because the eager wrapper does not preserve the delegate's configurable behavior. Calling serializeConfWith on the EagerInputFileConfigurable subclass throws UnsupportedOperationException to prevent broken serialization when shipping the input file to a remote task.

Solutions

1. Use the delegate (original HadoopInputFile) for serialization instead of the eager wrapper.
2. Avoid wrapping in EagerInputFile before the serializeConfWith step.
3. Extract needed configuration eagerly and pass a SerializableSupplier yourself.
4. If this is framework-internal, gate the call with instanceof checks.

Example fix

// before
file.serializeConfWith(conf -> () -> conf); // UnsupportedOperationException on eager file
// after
if (file instanceof EagerInputFile) {
  delegateInputFile.serializeConfWith(conf -> () -> conf);
} else {
  file.serializeConfWith(conf -> () -> conf);
}

boolean serializable = !(inputFile instanceof EagerInputFile);
if (!serializable) { unwrapAndUseDelegate(inputFile); }

static InputFile serializableInputFile(InputFile f) {
  if (f instanceof EagerInputFile) {
    throw new UnsupportedOperationException("Use the delegate for serialization");
  }
  return f;
}

try {
  file.serializeConfWith(supplier);
} catch (UnsupportedOperationException e) {
  delegateOf(file).serializeConfWith(supplier);
}

When it happens

Trigger: Calling serializeConfWith(Function<Configuration, SerializableSupplier<Configuration>>) on an eager input file instance, typically in code paths that prepare Hadoop-backed FileIO for serialization to executors.

Common situations: Distributing an eagerly-cached InputFile with Spark/Flink that was wrapped from a HadoopInputFile; framework code unconditionally calling serializeConfWith on all input files.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

• Cannot serialize a Hadoop input file: " + location()
• Cannot serialize FileIO
• Cannot serialize type: + typeId
• Cannot write unsupported term
• Configuration was not serialized on purpose but was not set…

AI-assisted analysis of apache/iceberg@86d9c8fc54 (2026-09-12). Data as JSON: /api/errors/a98ca866c5fec54a. Report an issue: GitHub.

Appendix: source

Thrown at core/src/main/java/org/apache/iceberg/io/EagerInputFile.java:116

    EagerInputFileConfigurable(InputFile delegate, long length) {
      super(delegate, length);
      Preconditions.checkArgument(
          delegate instanceof HadoopConfigurable,
          "Cannot create Hadoop Configurable Eager Input File because %s does not implement HadoopConfigurable",
          delegate.getClass().getName());
      this.delegate = (HadoopConfigurable) delegate;
    }

    @Override
    public Configuration getConf() {
      return delegate.getConf();
    }

    @Override
    public void serializeConfWith(
        Function<Configuration, SerializableSupplier<Configuration>> confSerializer) {
      throw new UnsupportedOperationException(
          "Cannot serialize an eager input file: " + location());
    }
  }
}

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