redis: got %d elements in the VSIM array, wanted a multiple

Error message

redis: got %d elements in the VSIM array, wanted a multiple of 3

What it means

VSIM replies parsed into VectorScoreAttrib values contain name/score/attribute triples, so the array length must be a multiple of 3. Any other count means the reply shape does not match the requested options and parsing fails immediately.

Source

Thrown at command.go:8923

			score, err := rd.ReadFloat()
			if err != nil {
				return err
			}
			attrib, err := readVectorAttribStringOrNil(rd)
			if err != nil {
				return err
			}
			cmd.val[i] = VectorScoreAttrib{Name: name, Score: score, Attribs: attrib}
		}
		return nil
	}

	n, err := rd.ReadArrayLen()
	if err != nil {
		return err
	}
	if n%3 != 0 {
		return fmt.Errorf("redis: got %d elements in the VSIM array, wanted a multiple of 3", n)
	}
	cmd.val = make([]VectorScoreAttrib, n/3)
	for i := range cmd.val {
		name, err := rd.ReadString()
		if err != nil {
			return err
		}
		score, err := rd.ReadFloat()
		if err != nil {
			return err
		}
		attrib, err := readVectorAttribStringOrNil(rd)
		if err != nil {
			return err
		}
		cmd.val[i] = VectorScoreAttrib{Name: name, Score: score, Attribs: attrib}
	}
	return nil

View on GitHub (pinned to c5cad058c7)

Solutions

Confirm the server supports attributes in VSIM replies and is not silently dropping them (redis-cli VSIM ... WITHSCORES WITHATTRIBS).
Use RESP3 (Protocol: 3) so the reply structure is explicit.
Upgrade go-redis and the Redis server to matching current versions.
If only scores are needed, switch to the score-only variant so a 2-field reply parses correctly.

Example fix

// before: server drops attribs -> 2 fields per element vs expected 3
res, err := rdb.VSimWithScoresAttrib(ctx, "pts", vector)
// redis: got 6 elements in the VSIM array, wanted a multiple of 3

// after: match the parser to the actual reply shape
res, err := rdb.VSimWithScores(ctx, "pts", vector)

Defensive patterns

Strategy: try-catch

Validate before calling

raw, _ := rdb.Do(ctx, "VSIM", "pts", vec, "WITHSCORES", "WITHATTRIBS").Result()
_ = raw // confirm 3 fields per element in the reply

Try / catch

cmd := rdb.VSimWithScoresAttrib(ctx, "pts", vec)
if err := cmd.Err(); err != nil {
    if strings.Contains(err.Error(), "wanted a multiple of 3") {
        // degrade to VSimWithScores (2 fields) or raw parsing
    }
    return err
}

Prevention

Confirm the server actually returns attributes for VSIM
Match the parser variant to the requested WITH* flags
Use RESP3 to make reply arity explicit
Version-gate vector-set usage in CI against REDIS_VERSION

When it happens

Trigger: Calling VSIM with both WITHSCORES and WITHATTRIBS (the tri-field parser at command.go:~8923) and receiving an array whose length is not divisible by 3.

Common situations: Server returning fewer fields per element (e.g. attribs dropped for large attributes) causing arity mismatch; version skew between client expectations and server vector-set implementation; proxies altering the reply.

Related errors

AI-assisted analysis of redis/go-redis@c5cad058c7 (2026-09-01). Data as JSON: /api/errors/9ab4dee9d2fe53f5. Report an issue: GitHub.