quickwit-oss/tantivy · error

Key length mismatch

Error message

Key length mismatch

What it means

ArrayHeapMap is a fixed-size-key map where every key is [K; S]; get_or_insert_with converts the incoming &[K] slice to &[K; S] with try_into().expect(...). If the caller passes a key slice whose length differs from the const generic S, the conversion fails and the process panics with "Key length mismatch". The doc comment explicitly states this panic condition.

Solutions

1. Ensure the composite collector's key length always equals S: assert/derive S from the source field count and size the map with that constant.
2. Validate key.len() == S at the API boundary and return an error instead of reaching try_into.
3. Avoid hardcoded S; make it a computed const from the number of group-by fields so it can never diverge.
4. Add a debug_assert!(key.len() == S) in tests covering all field-count configurations.

Example fix

// before
let key: &[K] = &dynamic_key; // length 3
map.get_or_insert_with(&key, default) // S == 2, panics
// after
assert_eq!(dynamic_key.len(), S, "composite key arity must match map width");
map.get_or_insert_with(&dynamic_key, default)

// Validate key length against map width before insert
if key.len() != S {
    return Err(TantivyError::InvalidArgument(format!(
        "composite key length {} != expected {}", key.len(), S)));
}
map.get_or_insert_with(key, default);

fn key_len_ok<K>(key: &[K], s: usize) -> bool { key.len() == s }

When it happens

Trigger: Calling get_or_insert_with with a key slice of length != S — e.g. building composite bucket keys from a number of source fields different from the ArrayHeapMap's declared width S, or pushing an extra/missing key element.

Common situations: Composite aggregation over a variable number of fields while the heap map was sized for a fixed arity; field list built dynamically (empty field or extra field added) changing key length at runtime.

Related errors

• could not convert to String
• dictionary missing for str accessor
• could not convert to String
• interval not precomputed for date histogram source
• non-zero packed bits fit in u64

AI-assisted analysis of quickwit-oss/tantivy@b5d8deb80c (2026-09-05). Data as JSON: /api/errors/746e54e9b0c4e9a8. Report an issue: GitHub.

Appendix: source

Thrown at src/aggregation/bucket/composite/map.rs:30

#[derive(Clone, Debug)]
struct ArrayHeapMap<K: Ord, V, const S: usize> {
    pub(crate) buckets: FxHashMap<[K; S], V>,
    pub(crate) heap: BinaryHeap<[K; S]>,
}

impl<K: Ord, V, const S: usize> Default for ArrayHeapMap<K, V, S> {
    fn default() -> Self {
        ArrayHeapMap {
            buckets: FxHashMap::default(),
            heap: BinaryHeap::default(),
        }
    }
}

impl<K: Eq + Hash + Clone + Ord, V, const S: usize> ArrayHeapMap<K, V, S> {
    /// Panics if the length of `key` is not S.
    fn get_or_insert_with<F: FnOnce() -> V>(&mut self, key: &[K], f: F) -> &mut V {
        let key_array: &[K; S] = key.try_into().expect("Key length mismatch");
        self.buckets.entry(key_array.clone()).or_insert_with(|| {
            self.heap.push(key_array.clone());
            f()
        })
    }

    /// Panics if the length of `key` is not S.
    fn get_mut(&mut self, key: &[K]) -> Option<&mut V> {
        let key_array: &[K; S] = key.try_into().expect("Key length mismatch");
        self.buckets.get_mut(key_array)
    }

    fn peek_highest(&self) -> Option<&[K]> {
        self.heap.peek().map(|k_array| k_array.as_slice())
    }

    fn evict_highest(&mut self) {
        if let Some(highest) = self.heap.pop() {

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