apache/beam · error

expected 1 option, got

Error message

expected 1 option, got %v: %v

What it means

Error returned by the element-wise sampler hook's Init function when the hook was configured with more than one option string. The sampler hook accepts exactly zero or one option (a duration like '500ms' controlling the sample period), so a longer option list is rejected before time.ParseDuration runs.

Solutions

1. Pass exactly one duration string, e.g. "10s".
2. Strip extra comma/space-separated values from the option.
3. Omit the option entirely to disable sampling (len==0 accepted).

Example fix

// before
--sampler_frequency="10s,60s"
// after
--sampler_frequency="10s"

opts := strings.Split(samplerOpt, ",")
if len(opts) > 1 { return fmt.Errorf("sampler hook takes at most 1 option, got %d", len(opts)) }
if len(opts) == 1 { if _, err := time.ParseDuration(opts[0]); err != nil { return err } }

if err := hook.Init(ctx); err != nil {
	log.Fatalf("sampler hook option error: %v", err)
}

When it happens

Trigger: Configuring the sampler hook (sampler_frequency style options) with multiple values, e.g. "10s,5s", or an option string with stray separators creating more than one opt.

Common situations: Copy-pasted flag values with extra arguments, or runners emitting deprecated multi-value formats no longer accepted by the SDK.

Understand the failure class

Background: "Must pass :limit option" / "Missing required option" — required option errors explained — this error's family across 41 libraries.

Related errors

• expected 1 option, got
• expected 2 options, got
• max time between dumps
• sample period should be greater than 1ms, got
• bad coder kind

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/3fccfeeb61b501f9. Report an issue: GitHub.

Appendix: source

Thrown at sdks/go/pkg/beam/core/runtime/harness/sampler_hook.go:38

	"fmt"
	"time"

	"github.com/apache/beam/sdks/v2/go/pkg/beam/core/util/hooks"
)

var (
	samplePeriod time.Duration = 200 * time.Millisecond
)

func init() {
	hf := func(opts []string) hooks.Hook {
		return hooks.Hook{
			Init: func(ctx context.Context) (context.Context, error) {
				if len(opts) == 0 {
					return ctx, nil
				}
				if len(opts) > 1 {
					return ctx, fmt.Errorf("expected 1 option, got %v: %v", len(opts), opts)
				}

				sampleTime, err := time.ParseDuration(opts[0])
				if err != nil {
					return nil, err
				}
				samplePeriod = sampleTime
				return ctx, nil
			},
		}
	}
	hooks.RegisterHook("beam:go:hook:dofnmetrics:sampletime", hf)
}

View on GitHub (pinned to 12126d8942)