databendlabs/databend · error

not implemented

Error message

not implemented

What it means

`create_udaf_script_function` builds the runtime for a script-based aggregate UDF. Only JavaScript (and Python behind a feature flag) are wired up; the WebAssembly branch panics with `unimplemented!`, so any attempt to register a WASM UDAF aborts the process.

Solutions

  1. Rewrite the aggregate function as a JavaScript script UDAF (LANGUAGE JAVASCRIPT) instead of WebAssembly
  2. If Python is available in your edition, deploy with the python-udf feature enabled and use LANGUAGE PYTHON
  3. File/track a Databend feature request for WebAssembly UDAF support

Example fix

// before
CREATE AGGREGATE FUNCTION my_agg AS (x) LANGUAGE WEBASSEMBLY ...;
// after
CREATE AGGREGATE FUNCTION my_agg AS (x DOUBLE) RETURNS DOUBLE LANGUAGE JAVASCRIPT $$ ... $$;
Defensive patterns

Strategy: validation

Validate before calling

if (udafDef.language.toUpperCase() === "WEBASSEMBLY") {
  throw new Error("WebAssembly UDAF is not implemented; use JAVASCRIPT or PYTHON");
}

Type guard

function hasSupportedUdafLanguage(def) {
  return ["JAVASCRIPT", "PYTHON"].includes((def.language || "").toUpperCase());
}

Try / catch

try {
  await createAggregateFunction(udafDef);
} catch (e) {
  if (isNotImplementedPanic(e)) {
    console.error(`Language ${udafDef.language} unsupported for UDAF; falling back to JAVASCRIPT`);
    return createAggregateFunction({ ...udafDef, language: "JAVASCRIPT" });
  }
  throw e;
}

Prevention

When it happens

Trigger: Creating a script UDAF with `LANGUAGE WEBASSEMBLY` (e.g. CREATE AGGREGATE FUNCTION ... LANGUAGE WEBASSEMBLY), which routes into the UDFLanguage::WebAssembly arm of the builder in udaf_script.rs.

Common situations: Following old or aspirational docs/examples that mention WebAssembly UDFs; migrating a UDF definition written for an engine that supports WASM UDAFs to Databend.

Related errors

AI-assisted analysis of databendlabs/databend@288d84d76e (2026-09-11). Data as JSON: /api/errors/53b64db34802c0fe. Report an issue: GitHub.

Appendix: source

Thrown at src/query/script_udf_support/src/udaf_script.rs:327

) -> Result<Arc<dyn AggregateFunction>> {
    let UDFScriptCode { language, code, .. } = code;
    let runtime = match language {
        UDFLanguage::JavaScript => {
            let builder = JsRuntimeBuilder {
                name,
                code: String::from_utf8(code.to_vec())?,
                state_type: ArrowType::Struct(
                    state_fields
                        .iter()
                        .map(|f| f.into())
                        .collect::<Vec<arrow_schema::Field>>()
                        .into(),
                ),
                output_type,
            };
            UDAFRuntime::JavaScript(JsRuntimePool::new(builder))
        }
        UDFLanguage::WebAssembly => unimplemented!(),
        #[cfg(not(feature = "python-udf"))]
        UDFLanguage::Python => {
            return Err(ErrorCode::EnterpriseFeatureNotEnable(
                "Failed to create python script udf",
            ));
        }
        #[cfg(feature = "python-udf")]
        UDFLanguage::Python => {
            let builder = python_pool::PyRuntimeBuilder {
                name,
                code: String::from_utf8(code.to_vec())?,
                state_type: ArrowType::Struct(
                    state_fields
                        .iter()
                        .map(|f| f.into())
                        .collect::<Vec<arrow_schema::Field>>()
                        .into(),
                ),

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