What causes "unable to retrieve column names: %w" in googleapis/mcp-toolbox?

Check the wrapped error and retry the query — this is often transient

unable to retrieve column names: %w

Error message

unable to retrieve column names: %w

What it means

Trino RunSQL wraps results.Columns() failures. Columns() asks the driver for the result-set column metadata and fails only if the rows handle is invalid or the driver hit a protocol error while fetching metadata. This is rare because the query already succeeded at submission.

Source

Thrown at internal/sources/trino/trino.go:125

func (s *Source) ToConfig() sources.SourceConfig {
	return s.Config
}

func (s *Source) TrinoDB() *sql.DB {
	return s.Pool
}

func (s *Source) RunSQL(ctx context.Context, statement string, params []any) (any, error) {
	results, err := s.TrinoDB().QueryContext(ctx, statement, params...)
	if err != nil {
		return nil, fmt.Errorf("unable to execute query: %w", err)
	}
	defer results.Close()

	cols, err := results.Columns()
	if err != nil {
		return nil, fmt.Errorf("unable to retrieve column names: %w", err)
	}

	// create an array of values for each column, which can be re-used to scan each row
	rawValues := make([]any, len(cols))
	values := make([]any, len(cols))
	for i := range rawValues {
		values[i] = &rawValues[i]
	}

	out := []any{}
	for results.Next() {
		err := results.Scan(values...)
		if err != nil {
			return nil, fmt.Errorf("unable to parse row: %w", err)
		}
		vMap := make(map[string]any)
		for i, name := range cols {
			val := rawValues[i]

View on GitHub (pinned to 8cc6e09de2)

Solutions

Check the wrapped error and retry the query — this is often transient
Upgrade the trino-go-client driver to the latest version
Avoid exotic result shapes (very wide rows, complex types) if reproducible
Verify coordinator stability and proxy timeouts between client and Trino

Example fix

// before
// no retry on metadata errors
// after
cols, err := results.Columns()
if err != nil && isTransient(err) {
    cols, err = retryQuery(ctx, statement, params)
}

Defensive patterns

Strategy: try-catch

Try / catch

out, err := src.RunSQL(ctx, stmt, params)
if err != nil && strings.Contains(err.Error(), "unable to retrieve column names") {
    // usually transient: retry once with a fresh query
    out, err = src.RunSQL(ctx, stmt, params)
}

Prevention

Keep trino-go-client up to date
Avoid SELECT * over tables with complex nested types when the consumer is the toolbox
Ensure coordinator and proxies don't kill connections between submit and metadata fetch
Add a bounded retry for metadata-stage failures

When it happens

Trigger: Source.RunSQL after a successful QueryContext where results.Columns() fails: result set already closed/corrupted, driver protocol error, or the underlying connection dropped between query submission and metadata fetch.

Common situations: Coordinator restart mid-query killing the HTTP session; driver bug with unusual column types (complex Trino types like map/row); extremely wide result sets causing metadata fetch issues.

Related errors

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/196e643b0e8238f3. Report an issue: GitHub.