googleapis/mcp-toolbox · critical

unable to create pool: %w

Error message

unable to create pool: %w

What it means

CockroachDB source Config.Initialize wraps failures from initCockroachDBConnectionPoolWithRetry as 'unable to create pool'. This means pgx could not establish a working connection pool to the CockroachDB instance after retry attempts — usually unreachable host, bad credentials, TLS problems, or invalid query parameters.

Source

Thrown at internal/sources/cockroachdb/cockroachdb.go:108

	// Observability
	EnableTelemetry  bool   `yaml:"enableTelemetry"`  // Default: true
	TelemetryVerbose bool   `yaml:"telemetryVerbose"` // Default: false
	ClusterID        string `yaml:"clusterID"`        // Optional cluster identifier for telemetry
}

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

func (r Config) Initialize(ctx context.Context, tracer trace.Tracer) (sources.Source, error) {
	retryBaseDelay, err := time.ParseDuration(r.RetryBaseDelay)
	if err != nil {
		return nil, fmt.Errorf("invalid retryBaseDelay: %w", err)
	}

	pool, err := initCockroachDBConnectionPoolWithRetry(ctx, tracer, r.Name, r.Host, r.Port, r.User, r.Password, r.Database, r.QueryParams, r.MaxRetries, retryBaseDelay)
	if err != nil {
		return nil, fmt.Errorf("unable to create pool: %w", err)
	}

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

var _ sources.Source = &Source{}

type Source struct {
	Config
	Pool *pgxpool.Pool
}

func (s *Source) IsReadOnly() bool {
	return false

View on GitHub (pinned to 8cc6e09de2)

Solutions

1. Verify connectivity: cockroach sql --url 'postgres://user:pass@host:26257/db' or nc -vz host 26257
2. Check host, port, user, password, and database values in the source config for typos or stale secrets
3. Confirm TLS settings/query params match the cluster's requirements (e.g. sslmode, root cert)
4. Ensure the CockroachDB instance is running and reachable from the toolbox's network
5. Increase MaxRetries / RetryBaseDelay if the failure is transient startup ordering

Example fix

// before (yaml)
host: crdb-internal
port: 26257
// after  # verified reachable + correct creds
host: crdb-internal.example.svc
port: 26257
queryParams: sslmode=require

// Preflight: raw TCP check before initializing the source
func crdbReachable(host string, port int) error {
    conn, err := net.DialTimeout("tcp", fmt.Sprintf("%s:%d", host, port), 3*time.Second)
    if err != nil { return err }
    return conn.Close()
}

src, err := cfg.Initialize(ctx, tracer)
if err != nil {
    if strings.Contains(err.Error(), "unable to create pool") {
        // check host/port reachability, creds, TLS params, then retry with backoff
        time.Sleep(2 * time.Second)
        return cfg.Initialize(ctx, tracer)
    }
    return err
}

When it happens

Trigger: Initialize calls initCockroachDBConnectionPoolWithRetry with host/port/user/password/database/queryParams and maxRetries/baseDelay; the pool creation fails after exhausting retries: wrong host/port, database or user does not exist, password rejected, TLS/mode mismatch, or malformed query params in the connection string.

Common situations: CockroachDB cluster not yet running or cloud instance paused, firewall/VPC blocking the SQL port (26257), expired/rotated password in config, connecting with sslmode requirements the client config doesn't satisfy, DNS failures in containers.

Related errors

• failed to connect to CockroachDB after %d retries: %w
• sql.Open: %w
• unable to connect successfully: %w
• unable to connect successfully: %w
• unable to initialize source %q: %w

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/b0b8e1ef2f1e7922. Report an issue: GitHub.