apache/pulsar · error · RuntimeException

Unsupported schema type${type}

Error message

Unsupported schema type${type}

What it means

TopicSchema.newSchemaInstance maps a SchemaType to a concrete Schema implementation for function input/output topics. Thrown when the configured schema type has no supported instantiation path in this switch (default branch), typically a schema type the function runtime doesn't know how to build.

Source

Thrown at pulsar-functions/instance/src/main/java/org/apache/pulsar/functions/source/TopicSchema.java:190

                    .withPojo(clazz).build());

        case JSON:
            return JSONSchema.of(SchemaDefinition.<T>builder().withPojo(clazz).build());

        case KEY_VALUE:
            return (Schema<T>) Schema.KV_BYTES();

        case PROTOBUF:
            return ProtobufSchema.ofGenericClass(clazz, new HashMap<>());

        case PROTOBUF_NATIVE:
            return ProtobufNativeSchema.ofGenericClass(clazz, new HashMap<>());

        case AUTO_PUBLISH:
            return (Schema<T>) Schema.AUTO_PRODUCE_BYTES();

        default:
            throw new RuntimeException("Unsupported schema type" + type);
        }
    }

    private static boolean isProtobufClass(Class<?> pojoClazz) {
        try {
            Class<?> protobufBaseClass = Class.forName("com.google.protobuf.Message");
            return protobufBaseClass.isAssignableFrom(pojoClazz);
        } catch (ClassNotFoundException | NoClassDefFoundError e) {
            // If function does not have protobuf in classpath then it cannot be protobuf
            return false;
        }
    }

    @SuppressWarnings("unchecked")
    private <T> Schema<T> newSchemaInstance(String topic, Class<T> clazz, String schemaTypeOrClassName, boolean input,
                                            ClassLoader classLoader) {
        return newSchemaInstance(topic, clazz, new ConsumerConfig(schemaTypeOrClassName), input, classLoader);
    }

View on GitHub (pinned to 820761864e)

Solutions

1. Set an explicitly supported schemaType in the function config (STRING, JSON, AVRO, PROTOBUF, AUTO_CONSUME/AUTO_PUBLISH as supported by your version).
2. Use the Java class name (serdeClassname) with a built-in type instead of an exotic schema type.
3. Upgrade the function instance runtime if the schema type is from a newer Pulsar release.

Example fix

// before (functions.yml)
schemaType: KEY_VALUE
// after
schemaType: JSON
// or use class-based config
className: com.google.protobuf.Message

Set<String> supported = Set.of("STRING","JSON","AVRO","PROTOBUF","PROTOBUF_NATIVE","AUTO_CONSUME","AUTO_PUBLISH");
String t = fnConfig.getOutputSchemaType();
if (!supported.contains(t)) {
  throw new IllegalArgumentException("schemaType " + t + " not supported by this runtime");
}

try {
  Schema<T> s = topicSchema.getSchema(topic, clazz, conf, type, ...);
} catch (RuntimeException e) {
  if (e.getMessage().startsWith("Unsupported schema type")) {
    // fall back to a supported type or upgrade the runtime
  }
}

When it happens

Trigger: Function config declares a schema type (schemaType / serialization class resolution) that reaches the default case, e.g. KEY_VALUE, AVRO variants, or AUTO_CONSUME used where unsupported, instead of the handled types (STRING, JSON, AVRO, PROTOBUF, PROTOBUF_NATIVE, AUTO_PUBLISH, etc.).

Common situations: Misconfigured function YAML (wrong schemaType string); using a newer schema type with an older function instance; letting the runtime infer a type that maps to an unhandled enum constant.

Related errors

• Schema should not be null.
• Config class not found: %s
• Unsupported schema type%s
• Unknown component type: ${componentType}
• Batch Configs cannot be found

AI-assisted analysis of apache/pulsar@820761864e (2026-09-06). Data as JSON: /api/errors/a094f130efa59051. Report an issue: GitHub.