elastic/elasticsearch · error · IllegalArgumentException

vector dimensions differ: {}!={}

Error message

vector dimensions differ: {}!={}

What it means

Thrown by ESVectorUtil.andBitCount when the two signed-byte vectors differ in length. andBitCount computes the bitwise AND population count, which requires identical byte arrays. The guard runs before invoking the method-handle kernel that assumes equal lengths.

Source

Thrown at libs/simdvec/src/main/java/org/elasticsearch/simdvec/ESVectorUtil.java:421

     * @return the inner product of the two vectors
     */
    public static float ipFloatByte(float[] q, byte[] d) {
        if (q.length != d.length) {
            throw new IllegalArgumentException("vector dimensions incompatible: " + q.length + "!= " + d.length);
        }
        return IMPL.ipFloatByte(q, d);
    }

    /**
     * AND bit count computed over signed bytes.
     * Copied from Lucene's XOR implementation
     * @param a bytes containing a vector
     * @param b bytes containing another vector, of the same dimension
     * @return the value of the AND bit count of the two vectors
     */
    public static int andBitCount(byte[] a, byte[] b) {
        if (a.length != b.length) {
            throw new IllegalArgumentException("vector dimensions differ: " + a.length + "!=" + b.length);
        }
        try {
            return (int) BIT_COUNT_MH.invokeExact(a, b);
        } catch (Throwable e) {
            if (e instanceof Error err) {
                throw err;
            } else if (e instanceof RuntimeException re) {
                throw re;
            } else {
                throw new RuntimeException(e);
            }
        }
    }

    /**
     * Hamming similarity between two equal-length bit vectors, matching Lucene's
     * {@code FlatBitVectorsScorer}: {@code (numBits - xorBitCount) / numBits}.
     */

View on GitHub (pinned to db6a809a66)

Solutions

1. Ensure both byte arrays have identical length before calling.
2. Validate that both vectors share the same logical dimension and element_type.
3. Pad the shorter vector with zeros or reject the mismatch upstream rather than at the scorer.

Example fix

// before
int andCount = ESVectorUtil.andBitCount(a, b);
// after
if (a.length != b.length) {
    throw new IllegalArgumentException("bit vectors differ: " + a.length + " vs " + b.length);
}
int andCount = ESVectorUtil.andBitCount(a, b);

if (a.length != b.length) {
    throw new IllegalArgumentException("bit vectors differ: " + a.length + " vs " + b.length);
}
int andCount = ESVectorUtil.andBitCount(a, b);

static boolean sameLength(byte[] a, byte[] b) {
    return a != null && b != null && a.length == b.length;
}

When it happens

Trigger: Calling ESVectorUtil.andBitCount(byte[] a, byte[] b) with a.length != b.length. Occurs in scoring paths that compare two bit-packed vectors (e.g., hamming/and-based similarity) where the query and document bit encodings disagree on packed length.

Common situations: Two bit vectors indexed with different dims; one vector was truncated or zero-padded during ingestion; quantization/encoding path produced inconsistent byte counts; query and document came from different element_type=bit mappings.

Related errors

• Pitch needs to be at least {}
• vector dimensions incompatible
• distances array must have length >= 4, but was: {}
• distancesOffset must be between 0 and distances.length - 4
• distances array must have length 4, but was: {}

AI-assisted analysis of elastic/elasticsearch@db6a809a66 (2026-08-12). Data as JSON: /api/errors/525989953bf67153. Report an issue: GitHub.