risingwavelabs/risingwave · error

no vnodes to assign; assignment is meaningless

Error message

no vnodes to assign; assignment is meaningless

What it means

The final `ensure!` in the guard chain (assignment.rs:757) rejects an empty vnode list; like the worker/actor checks, assignment over zero vnodes is undefined, so the function fails fast with this message.

Source

Thrown at src/meta/src/stream/stream_graph/assignment.rs:757

        &self,
        workers: &BTreeMap<W, NonZeroUsize>,
        actors: &[A],
        vnodes: &[V],
    ) -> Result<BTreeMap<W, BTreeMap<A, Vec<V>>>>
    where
        W: Ord + Hash + Eq + Clone + Debug,
        A: Ord + Hash + Eq + Copy + Debug,
        V: Hash + Eq + Copy + Debug,
    {
        ensure!(
            !workers.is_empty(),
            "no workers to assign; assignment is meaningless"
        );
        ensure!(
            !actors.is_empty(),
            "no actors to assign; assignment is meaningless"
        );
        ensure!(
            !vnodes.is_empty(),
            "no vnodes to assign; assignment is meaningless"
        );
        ensure!(
            vnodes.len() >= actors.len(),
            "not enough vnodes ({}) for actors ({}); each actor needs at least one vnode",
            vnodes.len(),
            actors.len()
        );

        let chunk_size = match self.vnode_chunking_strategy {
            VnodeChunkingStrategy::NoChunking => {
                return assign_hierarchical(
                    workers,
                    actors,
                    vnodes,
                    self.salt,
                    self.actor_capacity,

View on GitHub (pinned to 6469eb736d)

Solutions

1. Generate the full vnode set (default 256) before assignment.
2. Handle unset/zero `maybe_vnode_count` upstream with an explicit error instead of an empty set.
3. Validate inputs at the API boundary before reaching the scheduler.

Example fix

// before
let plan = assign_hierarchical(&workers, &actors, &[], strategy)?;
// after
let vnodes: Vec<u32> = (0..DEFAULT_VNODE_COUNT).collect();
let plan = assign_hierarchical(&workers, &actors, &vnodes, strategy)?;

// Rust, before scheduling
if vnodes.is_empty() {
    anyhow::bail!("vnode set not generated");
}

fn vnodes_ready(v: &[VnodeId], actors: &[ActorId]) -> bool {
    !v.is_empty() && v.len() >= actors.len()
}

match assign_hierarchical(&workers, &actors, &vnodes, strategy) {
    Ok(m) => m,
    Err(e) if e.to_string().contains("no vnodes") => {
        Err(anyhow!("generate the vnode set (default 256) before scheduling: {e:#}"))
    }
    Err(e) => Err(e),
}

When it happens

Trigger: Calling the inner `assign_hierarchical` with `vnodes.is_empty()` — e.g. vnode set derived from a zero or unset vnode count.

Common situations: Zero/unknown vnode count in table properties; helper called in tests with empty slices; vnode computation skipped for some fragment type.

Understand the failure class

Background: "must not be empty", "cannot be empty" — required-field validation errors across open-source libraries — this error's family across 41 libraries.

Related errors

• no actors to assign
• no vnodes to assign
• actor count ({}) exceeds vnode count ({})
• no workers to assign; assignment is meaningless
• no actors to assign; assignment is meaningless

AI-assisted analysis of risingwavelabs/risingwave@6469eb736d (2026-09-11). Data as JSON: /api/errors/85343ff0ccccee5e. Report an issue: GitHub.