SigNoz/signoz · error

error while scanning metric name: %s

Error message

error while scanning metric name: %s

What it means

While iterating the result rows of the metric-name query, rows.Scan(&name) failed for at least one row. This happens when the result set's column layout does not match the single string destination — usually a schema change in the underlying view/table or a driver deserialization problem for the metric name column.

Source

Thrown at pkg/query-service/app/clickhouseReader/reader.go:2994

			signozMetricDBName, signozTSTableNameV41Day)
	}

	if req.Limit != 0 {
		query = query + fmt.Sprintf(" LIMIT %d;", req.Limit)
	}

	rows, err := r.db.Query(ctx, query, fmt.Sprintf("%%%s%%", req.SearchText))
	if err != nil {
		r.logger.Error("Error while querying metric names", errorsV2.Attr(err))
		return nil, fmt.Errorf("error while executing metric name query: %s", err.Error())
	}
	defer rows.Close()

	var metricNames []string
	for rows.Next() {
		var name string
		if err := rows.Scan(&name); err != nil {
			return nil, fmt.Errorf("error while scanning metric name: %s", err.Error())
		}
		if skipSignozMetrics && strings.HasPrefix(name, "signoz") {
			continue
		}
		metricNames = append(metricNames, name)
	}

	if len(metricNames) == 0 {
		return &response, nil
	}

	// Get all metadata in one shot
	metadataMap, apiError := r.GetUpdatedMetricsMetadata(ctx, orgID, metricNames...)
	if apiError != nil {
		return &response, fmt.Errorf("error getting updated metrics metadata: %s", apiError.Error())
	}

	seen := make(map[string]struct{})

View on GitHub (pinned to 5069bf80b0)

Solutions

1. Run the logged query manually in ClickHouse and inspect the result column types
2. Align query-service version with the schema (upgrade both or roll both back)
3. Scan into a []string-compatible type like sql.NullString if nulls appear
4. Check clickhouse-go driver version compatibility if errors started after a dependency bump

Example fix

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

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

// log and skip bad rows rather than aborting the whole listing
for rows.Next() {
  var name sql.NullString
  if err := rows.Scan(&name); err != nil {
    logger.Warn("skipping unscannable metric row", errorsV2.Attr(err))
    continue
  }
  if name.Valid { metricNames = append(metricNames, name.String) }
}

When it happens

Trigger: The metric names query returns columns that aren't a single string (e.g. after a table/view redefinition or a UNION with mismatched types), or the name column becomes Nullable(String)/LowCardinality the driver can't scan into plain string on some rows.

Common situations: Schema drift between query-service version and ClickHouse tables; partial upgrades; a view over time_series changed shape; driver version incompatibility.

Related errors

• error while scanning meter name: %s
• couldn't scan attrib value rows: %w
• error in reading data
• error while scanning rows: %s
• CodeLicenseUnavailable

AI-assisted analysis of SigNoz/signoz@5069bf80b0 (2026-08-28). Data as JSON: /api/errors/c02f20bcfbeb9df5. Report an issue: GitHub.