apache/flink · error · RuntimeException

Failed to delegate to ProtoSchemaConverter

Error message

Failed to delegate to ProtoSchemaConverter

What it means

PatchedProtoSchemaConverter.convert reflectively loads org.apache.parquet.proto.ProtoSchemaConverter and delegates schema conversion. If the class is missing, not constructed with a ParquetConfiguration, or invocation fails, it wraps the cause in RuntimeException('Failed to delegate to ProtoSchemaConverter').

Source

Thrown at flink-formats/flink-parquet/src/main/java/org/apache/flink/formats/parquet/protobuf/PatchedProtoWriteSupport.java:878

 * if present; else implement minimal mapping. To minimize risk, we reflectively invoke the original
 * ProtoSchemaConverter if available.
 */
class PatchedProtoSchemaConverter {
    private final ParquetConfiguration configuration;

    PatchedProtoSchemaConverter(ParquetConfiguration configuration) {
        this.configuration = configuration;
    }

    MessageType convert(Descriptor descriptor) {
        try {
            Class<?> clazz = Class.forName("org.apache.parquet.proto.ProtoSchemaConverter");
            Object inst =
                    clazz.getConstructor(ParquetConfiguration.class).newInstance(configuration);
            return (MessageType)
                    clazz.getMethod("convert", Descriptor.class).invoke(inst, descriptor);
        } catch (Exception e) {
            throw new RuntimeException("Failed to delegate to ProtoSchemaConverter", e);
        }
    }
}

View on GitHub (pinned to 2f3c205e92)

Solutions

1. Ensure flink-parquet's parquet-proto dependency (and its correct version) is on the runtime classpath
2. Check the wrapped cause in the stack trace - it names the exact reflective failure (ClassNotFoundException vs NoSuchMethodException)
3. Avoid repackaging/shading org.apache.parquet.proto classes away from this code path

try { Class.forName("org.apache.parquet.proto.ProtoSchemaConverter"); } catch (ClassNotFoundException e) { throw new IllegalStateException("parquet-proto missing on classpath", e); }

try { schema = converter.convert(descriptor); } catch (RuntimeException e) { // inspect e.getCause(): ClassNotFoundException -> classpath; NoSuchMethodException -> parquet-proto version mismatch }

When it happens

Trigger: Running the patched write support without parquet-proto's ProtoSchemaConverter on the classpath, or with a parquet-proto version whose ProtoSchemaConverter lacks the ParquetConfiguration constructor or convert(Descriptor) method.

Common situations: Shaded/slimer jars that exclude parquet-proto, a parquet-proto version mismatch after a dependency upgrade, or classloader isolation (e.g. SQL connectors, OSGi) hiding the class.

Related errors

• get %s descriptors error!
• The program's entry point class '{className}' could not be l
• Could not instantiate org.apache.flink.formats.avro.utils.Av
• Protocol buffer class or descriptor not specified. Please us
• Expected two fields for the map (key/value), but got: {}

AI-assisted analysis of apache/flink@2f3c205e92 (2026-08-14). Data as JSON: /api/errors/ba419b8ccd8c7e24. Report an issue: GitHub.