databendlabs/databend · error

Failed to load zipf_load_generator

Error message

Failed to load zipf_load_generator: {}

What it means

`setup_lua_environment` evaluates the embedded `ZIPF_LOAD_GENERATOR` Lua source with `lua.load(...).eval::<Table>()` to expose `metactl.ZipfGenerator`. This error wraps any failure to compile or evaluate that Lua chunk, or to convert its result into a `Table` (e.g. the chunk returned a non-table value).

Solutions

1. Read the inner error: if it is a syntax error, check recent changes to the ZIPF_LOAD_GENERATOR constant in this crate.
2. Confirm the chunk ends with `return` of the ZipfGenerator table so `.eval::<Table>()` succeeds.
3. Verify the mlua Lua version feature (lua54/lua51/vendored) supports the syntax used in the constant.
4. Reproduce by evaluating the constant standalone with the same Lua version to isolate the failing line.

Example fix

// before (chunk no longer returns a table)
local ZipfGenerator = {}
function ZipfGenerator:new(n, a) ... end
// after
local ZipfGenerator = {}
function ZipfGenerator:new(n, a) ... end
return ZipfGenerator

// sanity-check the embedded chunk in CI (Rust test)
let t: mlua::Table = lua.load(ZIPF_LOAD_GENERATOR).eval()?;
assert!(t.get::<_, mlua::Function>("new").is_ok());

match setup_lua_environment(&lua) {
    Err(e) if e.to_string().contains("Failed to load zipf_load_generator") => {
        // embedded Lua source broken: fail fast, surface inner syntax/runtime error
    }
    other => other?,
}

When it happens

Trigger: Evaluating the built-in ZIPF_LOAD_GENERATOR source fails during `setup_lua_environment` — a Lua syntax error in the embedded constant, a runtime error while the chunk executes, or the chunk evaluating to something that is not a table.

Common situations: An edited/truncated ZIPF_LOAD_GENERATOR constant after a code change, an mlua Lua-version incompatibility with Lua syntax used in the constant (e.g. Lua 5.1 vs 5.4 features), or the chunk's `return` statement being altered so it no longer yields a table.

Related errors

• Failed to load lua_util functions
• Failed to create now_ms function
• Failed to create sleep function
• Failed to create spawn function
• Failed to register metactl namespace

AI-assisted analysis of databendlabs/databend@288d84d76e (2026-09-11). Data as JSON: /api/errors/017bede0689b74d8. Report an issue: GitHub.

Appendix: source

Thrown at src/meta/control/src/lua_support.rs:482

    // Register a monotonic millisecond clock for timing and benchmarks. The
    // epoch is this environment's setup time; only differences between calls are
    // meaningful. `Instant` guarantees the value never goes backwards.
    let start = std::time::Instant::now();
    let now_ms_fn = lua
        .create_function(move |_lua, ()| Ok(start.elapsed().as_secs_f64() * 1000.0))
        .map_err(|e| anyhow::anyhow!("Failed to create now_ms function: {}", e))?;

    metactl_table
        .set("now_ms", now_ms_fn)
        .map_err(|e| anyhow::anyhow!("Failed to register now_ms function: {}", e))?;

    // Register the Zipf load generator. The module returns the `ZipfGenerator`
    // table, exposed as `metactl.ZipfGenerator` so any script can call
    // `metactl.ZipfGenerator:new(num_keys, alpha)` directly.
    let zipf_generator = lua
        .load(ZIPF_LOAD_GENERATOR)
        .eval::<Table>()
        .map_err(|e| anyhow::anyhow!("Failed to load zipf_load_generator: {}", e))?;

    metactl_table
        .set("ZipfGenerator", zipf_generator)
        .map_err(|e| anyhow::anyhow!("Failed to register ZipfGenerator: {}", e))?;

    // Set the metactl table as a global
    lua.globals()
        .set("metactl", metactl_table)
        .map_err(|e| anyhow::anyhow!("Failed to register metactl namespace: {}", e))?;

    // Load lua_util functions (which registers to_string in metactl namespace)
    lua.load(LUA_UTIL)
        .exec()
        .map_err(|e| anyhow::anyhow!("Failed to load lua_util functions: {}", e))?;

    Ok(())
}

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