googleapis/mcp-toolbox · error

unable to create pool: %w

Error message

unable to create pool: %w

What it means

clickhouse.Config.Initialize wraps any failure from initClickHouseConnectionPool (building the sqlx/database-sql connection pool) with this message. It means the pool object itself could not be created, typically due to invalid DSN or driver issues.

Source

Thrown at internal/sources/clickhouse/clickhouse.go:69

	Name     string `yaml:"name" validate:"required"`
	Type     string `yaml:"type" validate:"required"`
	Host     string `yaml:"host" validate:"required"`
	Port     string `yaml:"port" validate:"required"`
	Database string `yaml:"database" validate:"required"`
	User     string `yaml:"user" validate:"required"`
	Password string `yaml:"password"`
	Protocol string `yaml:"protocol"`
	Secure   bool   `yaml:"secure"`
}

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

func (r Config) Initialize(ctx context.Context, tracer trace.Tracer) (sources.Source, error) {
	pool, err := initClickHouseConnectionPool(ctx, tracer, r.Name, r.Host, r.Port, r.User, r.Password, r.Database, r.Protocol, r.Secure)
	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

1. Verify host, port, protocol values are valid and correctly formatted.
2. Check special characters in user/password are URL-escaped in the DSN.
3. Confirm the ClickHouse server accepts connections on the configured port (8123 http / 9000 native).
4. Read the wrapped error (%w) for the driver's root cause.

Example fix

// before
r := clickhouse.Config{Host: "ch host", Port: "notaport"}
// after
r := clickhouse.Config{Host: "127.0.0.1", Port: "8123", Protocol: "http"}

if r.Host == "" || r.Port == "" { return errors.New("clickhouse host/port required") }
if _, err := strconv.Atoi(r.Port); err != nil { return fmt.Errorf("invalid port: %w", err) }

src, err := cfg.Initialize(ctx, tracer)
if err != nil {
    if strings.Contains(err.Error(), "unable to create pool") { return err } // config-level, no retry
    return err
}

When it happens

Trigger: Calling Initialize on a clickhouse Config when the driver cannot construct a pool from host/port/user/password/database/protocol/secure parameters.

Common situations: Invalid host or port format, unsupported protocol (http/native), bad DSN characters in credentials, missing driver registration.

Related errors

• unable to create pool: %w
• unable to create pool: %w
• failed to initialize resources: %w
• toolbox failed to initialize: %w
• failed to initialize resources: %w

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/4d7825d0c474ccbd. Report an issue: GitHub.