databendlabs/databend · error

internal error: entered unreachable code

Error message

internal error: entered unreachable code

What it means

`unreachable!()` in `ScriptRuntime::try_create` (transform_udf_script.rs): the function destructures `func.udf_type` expecting the `UDFType::Script` variant and panics if a script UDF runtime is requested for a non-script (e.g. UDF/UDAF lambda) descriptor. It means `try_create` was called with a UDF description whose type is not `Script` — an internal dispatch bug rather than a user-configurable error.

Solutions

1. Verify the UDF definition (`SHOW FUNCTIONS` / catalog entry) actually declares a script language (JavaScript) and re-create it if not.
2. Drop and re-create the UDF so its descriptor is written with the current `UDFType` format.
3. Upgrade/restart the cluster so query nodes and meta store agree on the UDF type enum.
4. If reproducible, file an issue with the `CREATE FUNCTION` statement and server version.

Example fix

// before
let UDFType::Script(box UDFScriptCode { language, code, .. }) = &func.udf_type else {
    unreachable!()
};
// after
let UDFType::Script(box UDFScriptCode { language, code, .. }) = &func.udf_type else {
    return Err(ErrorCode::BadArguments(format!(
        "script runtime requested for non-script UDF: {}", func.name
    )));
};

-- confirm the UDF is actually a script UDF before invoking
SELECT func_name, language FROM system.functions WHERE name = 'my_udf'; -- expect language = 'JavaScript'

// catch internal panic errors from UDF calls and fall back to re-creating the function
if err.to_string().contains("entered unreachable code") { drop_and_recreate_udf(name); }

When it happens

Trigger: Registering or invoking a script UDF where the descriptor's `udf_type` is not `UDFType::Script` — e.g. the catalog resolved a UDF whose type is the default/other variant but routed it to the script runtime factory, or a corrupted/malformed UDF entry in the meta store.

Common situations: Mixed UDF deployments after a version upgrade changed `UDFType` variants, calling a server-defined UDF that was mistakenly classified as script, or meta store entries written by an older Databend version.

Understand the failure class

Background: "This is a bug, please report it": internal invariant violations, unreachable panics, and SNH errors explained — this error's family across 47 libraries.

Related errors

• not implemented
• {}
• Temp table id used up
• Invalid temp table desc
• expect tuple type

AI-assisted analysis of databendlabs/databend@288d84d76e (2026-09-11). Data as JSON: /api/errors/abd391bab44fd9c9. Report an issue: GitHub.

Appendix: source

Thrown at src/query/script_udf_support/src/transform_udf_script.rs:73

use self::venv::TempDir;
use super::runtime_pool::Pool;
use super::runtime_pool::RuntimeBuilder;
use crate::ScriptUdfFunctionDesc;

pub enum ScriptRuntime {
    JavaScript(JsRuntimePool),
    WebAssembly(arrow_udf_runtime::wasm::Runtime),
    #[cfg(feature = "python-udf")]
    Python(python_pool::PyRuntimePool),
}

static PY_VERSION: LazyLock<String> =
    LazyLock::new(|| venv::detect_python_version().unwrap_or("3.12".to_string()));

impl ScriptRuntime {
    pub fn try_create(func: &ScriptUdfFunctionDesc, _temp_dir: Option<TempDir>) -> Result<Self> {
        let UDFType::Script(box UDFScriptCode { language, code, .. }) = &func.udf_type else {
            unreachable!()
        };
        match language {
            UDFLanguage::JavaScript => {
                let builder = JsRuntimeBuilder {
                    name: func.name.clone(),
                    handler: func.func_name.clone(),
                    code: String::from_utf8(code.to_vec())?,
                    output_type: func.data_type.as_ref().clone(),
                    counter: Default::default(),
                };
                Ok(Self::JavaScript(JsRuntimePool::new(builder)))
            }
            UDFLanguage::WebAssembly => {
                let start = std::time::Instant::now();
                let runtime = arrow_udf_runtime::wasm::Runtime::new(code).map_err(|err| {
                    ErrorCode::UDFRuntimeError(format!(
                        "Failed to create WASM runtime for module: {err}"
                    ))

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