databendlabs/databend · error

invalid engine

Error message

invalid engine: {}

What it means

This `unreachable!("invalid engine: {}", s)` fires in the `FromStr`-style parser for the `Engine` enum in table.rs. Any engine string outside the recognized list (materialized_view, view, random, iceberg, delta, paimon, and the other matched arms) causes an unrecoverable panic instead of returning a parse error.

Solutions

1. Use a supported engine name exactly as listed in the match arms (e.g. `MergeTree`, `View`, `Iceberg`)
2. Check engine-name spelling and normalization (lowercasing is applied upstream; verify the value reaching this code)
3. Upgrade Databend if the engine exists only in a newer release
4. Change the parser to return an `Err` with `invalid engine: {}` instead of panicking, so users get a proper error

Example fix

// before
_ => unreachable!("invalid engine: {}", s),
// after
_ => Err(ErrorCode::TableEngineNotSupported(format!(
    "invalid engine: {}",
    s
))),

SUPPORTED_ENGINES = {"merge_tree", "view", "materialized_view", "random", "iceberg", "delta", "paimon", "null", "memory"}
if engine_name.lower() not in SUPPORTED_ENGINES:
    raise ValueError(f"unsupported engine: {engine_name}")

fn is_supported_engine(s: &str) -> bool {
    matches!(s.to_ascii_lowercase().as_str(),
        "merge_tree" | "view" | "materialized_view" | "random"
        | "iceberg" | "delta" | "paimon")
}

// prefer the parser returning Err over panicking
let engine = Engine::from_str(s)
    .map_err(|e| format!("invalid engine '{}': {}", s, e))?;

When it happens

Trigger: Passing an unrecognized engine name string into the engine parser, e.g. when deserializing or validating a `CREATE TABLE ... ENGINE = <name>` where `<name>` is not one of the supported engines.

Common situations: Typo'd engine names in SQL or config (e.g. `merge_tree` casing/spacing mistakes), engines added in newer Databend versions used against older code, or programmatic construction of table options with an invalid engine value.

Understand the failure class

Background: Invalid enum value errors: "Unknown type", "Invalid scope", "must be one of" — when a string is not on the library's allowed list — this error's family across 23 libraries.

Related errors

• Token does not belong to this ContextVar
• MEMORY_EXCEEDS_LIMIT
• verifier did not complete within the timeout.
• {}
• Temp table id used up

AI-assisted analysis of databendlabs/databend@288d84d76e (2026-09-11). Data as JSON: /api/errors/2cf4c47750c50d9b. Report an issue: GitHub.

Appendix: source

Thrown at src/query/ast/src/ast/statements/table.rs:958

            Engine::Delta => write!(f, "DELTA"),
            Engine::Paimon => write!(f, "PAIMON"),
        }
    }
}

impl From<&str> for Engine {
    fn from(s: &str) -> Self {
        match s.to_lowercase().as_str() {
            "null" => Engine::Null,
            "memory" => Engine::Memory,
            "fuse" => Engine::Fuse,
            "materialized_view" => Engine::MaterializedView,
            "view" => Engine::View,
            "random" => Engine::Random,
            "iceberg" => Engine::Iceberg,
            "delta" => Engine::Delta,
            "paimon" => Engine::Paimon,
            _ => unreachable!("invalid engine: {}", s),
        }
    }
}

#[derive(Debug, Clone, PartialEq, Eq, Drive, DriveMut, Walk, WalkMut)]
pub enum CompactTarget {
    Block,
    Segment,
}

#[derive(Debug, Clone, PartialEq, Drive, DriveMut, Walk, WalkMut)]
pub enum OptimizeTableAction {
    Compact { target: CompactTarget },
}

impl Display for OptimizeTableAction {
    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        match self {

View on GitHub (pinned to 288d84d76e)