googleapis/mcp-toolbox · error

errors encountered during row iteration: %w

Error message

errors encountered during row iteration: %w

What it means

database/sql Rows.Err() reports any error that occurred during iteration over the result set (e.g. the connection dropped mid-scan). RunSQL surfaces it with this message after processing all rows.

Source

Thrown at internal/sources/oceanbase/oceanbase.go:154

		vMap := make(map[string]any)
		for i, name := range cols {
			val := rawValues[i]
			if val == nil {
				vMap[name] = nil
				continue
			}

			// oceanbase uses mysql driver
			vMap[name], err = mysqlcommon.ConvertToType(colTypes[i], val)
			if err != nil {
				return nil, fmt.Errorf("errors encountered when converting values: %w", err)
			}
		}
		out = append(out, vMap)
	}

	if err := results.Err(); err != nil {
		return nil, fmt.Errorf("errors encountered during row iteration: %w", err)
	}

	return out, nil
}

func initOceanBaseConnectionPool(ctx context.Context, tracer trace.Tracer, name, host, port, user, pass, dbname, queryTimeout string) (*sql.DB, error) {
	_, span := sources.InitConnectionSpan(ctx, tracer, SourceType, name)
	defer span.End()

	dsn := fmt.Sprintf("%s:%s@tcp(%s:%s)/%s?parseTime=true", user, pass, host, port, dbname)

	if queryTimeout != "" {
		timeout, err := time.ParseDuration(queryTimeout)
		if err != nil {
			return nil, fmt.Errorf("invalid queryTimeout %q: %w", queryTimeout, err)
		}
		dsn += "&readTimeout=" + timeout.String()
	}

View on GitHub (pinned to 8cc6e09de2)

Solutions

1. Check the wrapped error for 'connection lost'/'invalid connection' and retry the query
2. Increase the queryTimeout/readTimeout configuration
3. Reduce result size (LIMIT, pagination) to shorten streaming time
4. Verify network stability and server wait_timeout settings

Example fix

// before
toolbox --tools oceanbase_run_sql --query-timeout 30s
// after
toolbox --tools oceanbase_run_sql --query-timeout 5m

// bound result size before streaming
sql := baseSQL + " LIMIT 10000"

out, err := src.RunSQL(ctx, sql)
if err != nil && strings.Contains(err.Error(), "row iteration") {
    // backoff then retry once
    time.Sleep(time.Second)
    out, err = src.RunSQL(ctx, sql)
}

When it happens

Trigger: RunSQL iterates results.Next(); the underlying MySQL/OceanBase connection errors, times out, or is closed while rows are still being streamed.

Common situations: Long-running queries exceeding the readTimeout; server-side kill of the connection; network interruption during large result streaming.

Related errors

• error iterating rows: %w
• unable to parse row: %w
• errors encountered when converting values: %w
• sql.Open: %w
• unable to connect to Oracle successfully: %w

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/2869d240742184aa. Report an issue: GitHub.