SigNoz/signoz · error

error while scanning rows: %s

Error message

error while scanning rows: %s

What it means

Iterating the metric attribute-key query results, rows.Scan(&attributeKey) failed because a row could not be deserialized into a single string. Indicates the result column is not a plain string for that row (Nullable, wrong column count due to schema drift, or driver type mapping change).

Source

Thrown at pkg/query-service/app/clickhouseReader/reader.go:3128

	if reductionEnabled {
		query = fmt.Sprintf("SELECT arrayJoin(tagKeys) AS distinctTagKey FROM (SELECT JSONExtractKeys(labels) AS tagKeys FROM %s.%s WHERE metric_name=$1 AND unix_milli >= $2 GROUP BY tagKeys UNION ALL SELECT JSONExtractKeys(labels) AS tagKeys FROM %s.%s WHERE metric_name=$1 AND unix_milli >= $2 GROUP BY tagKeys) WHERE distinctTagKey ILIKE $3 AND distinctTagKey NOT LIKE '\\_\\_%%' GROUP BY distinctTagKey", signozMetricDBName, signozTSTableNameV41Day, signozMetricDBName, signozTSTableNameV4Reduced)
	} else {
		query = fmt.Sprintf("SELECT arrayJoin(tagKeys) AS distinctTagKey FROM (SELECT JSONExtractKeys(labels) AS tagKeys FROM %s.%s WHERE metric_name=$1 AND unix_milli >= $2 GROUP BY tagKeys) WHERE distinctTagKey ILIKE $3 AND distinctTagKey NOT LIKE '\\_\\_%%' GROUP BY distinctTagKey", signozMetricDBName, signozTSTableNameV41Day)
	}
	if req.Limit != 0 {
		query = query + fmt.Sprintf(" LIMIT %d;", req.Limit)
	}
	rows, err = r.db.Query(ctx, query, req.AggregateAttribute, common.PastDayRoundOff(), fmt.Sprintf("%%%s%%", req.SearchText))
	if err != nil {
		r.logger.Error("Error while executing query", errorsV2.Attr(err))
		return nil, fmt.Errorf("error while executing query: %s", err.Error())
	}
	defer rows.Close()

	var attributeKey string
	for rows.Next() {
		if err := rows.Scan(&attributeKey); err != nil {
			return nil, fmt.Errorf("error while scanning rows: %s", err.Error())
		}
		key := v3.AttributeKey{
			Key:      attributeKey,
			DataType: v3.AttributeKeyDataTypeString, // https://github.com/OpenObservability/OpenMetrics/blob/main/proto/openmetrics_data_model.proto#L64-L72.
			Type:     v3.AttributeKeyTypeTag,
			IsColumn: false,
		}
		response.AttributeKeys = append(response.AttributeKeys, key)
	}

	return &response, nil
}

func (r *ClickHouseReader) GetMeterAttributeKeys(ctx context.Context, req *v3.FilterAttributeKeyRequest) (*v3.FilterAttributeKeyResponse, error) {
	ctx = ctxtypes.NewContextWithCommentVals(ctx, map[string]string{
		instrumentationtypes.TelemetrySignal:  telemetrytypes.SignalMetrics.StringValue(),
		instrumentationtypes.CodeNamespace:    "clickhouse-reader",
		instrumentationtypes.CodeFunctionName: "GetMeterAttributeKeys",

View on GitHub (pinned to 5069bf80b0)

Solutions

1. Run the logged query manually and inspect result column types/NULLs
2. Align query-service and schema versions
3. Scan into sql.NullString and skip invalid rows
4. Report/check driver compatibility if it began after a dependency upgrade

Example fix

// before
var attributeKey string
if err := rows.Scan(&attributeKey); err != nil { ... }

// after
var attributeKey sql.NullString
if err := rows.Scan(&attributeKey); err != nil { ... }
if !attributeKey.Valid { continue }

for rows.Next() {
  var key sql.NullString
  if err := rows.Scan(&key); err != nil { logger.Warn(...); continue }
  if !key.Valid { continue }
  ...
}

When it happens

Trigger: The attribute-key SELECT runs but its result column type doesn't match string: e.g. Nullable(String) rows with NULLs, or a redefined view returning extra columns.

Common situations: Schema drift after partial upgrades; NULL tag keys in noisy data; clickhouse-go version changes affecting LowCardinality(String) scanning.

Related errors

• error while scanning metric name: %s
• error while scanning meter name: %s
• error while executing query: %s
• CodeLicenseUnavailable
• CodeForbidden

AI-assisted analysis of SigNoz/signoz@5069bf80b0 (2026-08-28). Data as JSON: /api/errors/e129e989777c3197. Report an issue: GitHub.