What causes "unable to create pool: %w" in googleapis/mcp-toolbox?

Inspect the wrapped cause for the exact failing step (DSN build vs sql.Open)

unable to create pool: %w

Error message

unable to create pool: %w

What it means

Trino Config.Initialize wraps any failure from initTrinoConnectionPool. Pool creation involves building the Trino DSN, sql.Open, and setting driver-level connector options, so failures here mean the pool could not be constructed at all (not a connectivity issue yet — that is the following PingContext error). The underlying cause is preserved via %w.

Source

Thrown at internal/sources/trino/trino.go:77

	Catalog                string `yaml:"catalog" validate:"required"`
	Schema                 string `yaml:"schema" validate:"required"`
	QueryTimeout           string `yaml:"queryTimeout"`
	AccessToken            string `yaml:"accessToken"`
	KerberosEnabled        bool   `yaml:"kerberosEnabled"`
	SSLEnabled             bool   `yaml:"sslEnabled"`
	SSLCertPath            string `yaml:"sslCertPath"`
	SSLCert                string `yaml:"sslCert"`
	DisableSslVerification bool   `yaml:"disableSslVerification"`
}

func (r Config) SourceConfigType() string {
	return SourceType
}

func (r Config) Initialize(ctx context.Context, tracer trace.Tracer) (sources.Source, error) {
	pool, err := initTrinoConnectionPool(ctx, tracer, r.Name, r.Host, r.Port, r.User, r.Password, r.Catalog, r.Schema, r.QueryTimeout, r.AccessToken, r.KerberosEnabled, r.SSLEnabled, r.SSLCertPath, r.SSLCert, r.DisableSslVerification)
	if err != nil {
		return nil, fmt.Errorf("unable to create pool: %w", err)
	}

	err = pool.PingContext(ctx)
	if err != nil {
		pool.Close()
		return nil, fmt.Errorf("unable to connect successfully: %w", err)
	}

	s := &Source{
		Config: r,
		Pool:   pool,
	}
	return s, nil
}

var _ sources.Source = &Source{}

type Source struct {

View on GitHub (pinned to 8cc6e09de2)

Solutions

Inspect the wrapped cause for the exact failing step (DSN build vs sql.Open)
Validate trino source config: host, port, user, catalog, schema, queryTimeout are well-formed
If SSL is enabled, verify the certificate file exists and is PEM-encoded at sslCertPath
Check for invalid auth combos (e.g. both accessToken and kerberos enabled)

Example fix

// before
sslCertPath: "./certs/trino.crt"  // file missing
// after
sslCertPath: "/etc/trino/tls/ca.pem" // verify: ls -l /etc/trino/tls/ca.pem

Defensive patterns

Strategy: validation

Validate before calling

func validateTrinoConfig(r trino.Config) error {
    if r.Host == "" || r.Port == "" || r.User == "" { return errors.New("trino: host, port and user are required") }
    if _, err := strconv.Atoi(r.Port); err != nil { return fmt.Errorf("trino: bad port %q", r.Port) }
    if r.SSLEnabled && r.SSLCertPath != "" {
        if _, err := os.ReadFile(r.SSLCertPath); err != nil { return fmt.Errorf("trino: cert unreadable: %w", err) }
    }
    if r.KerberosEnabled && r.AccessToken != "" { return errors.New("trino: kerberos and accessToken are mutually exclusive") }
    return nil
}

Try / catch

src, err := cfg.Initialize(ctx, tracer)
if err != nil && strings.Contains(err.Error(), "unable to create pool") {
    return fmt.Errorf("trino source misconfigured: %w", err)
}

Prevention

Validate all trino config fields (host, port, catalog, schema) before calling Initialize
Pre-check SSL cert files exist and are readable PEM
Avoid enabling both kerberos and access token auth
Keep queryTimeout a plain numeric string

When it happens

Trigger: Initialize on a Trino source where initTrinoConnectionPool returns an error: buildTrinoDSN failure, sql.Open failure, or errors configuring the connector (e.g. invalid SSL cert material).

Common situations: Invalid sslCertPath or inline sslCert content; malformed host/port values from config; unsupported combination of kerberosEnabled/accessToken/SSL flags passed to buildTrinoDSN.

Related errors

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/8ffc5e007582509d. Report an issue: GitHub.