apache/beam · error

invalid input pcollection

Error message

invalid input pcollection

What it means

beam.TryWindowInto checks that the main input PCollection is valid before inserting the WindowInto transform. This error means col is the zero PCollection — usually the result of a previously failed (and ignored) Try-transform call or an unassigned variable — so there is no graph node to window.

Source

Thrown at sdks/go/pkg/beam/windowing.go:85

func (m allowedLateness) windowIntoOption() {}

// AllowedLateness configures for how long data may arrive after the end of a window.
func AllowedLateness(delay time.Duration) WindowIntoOption {
	return allowedLateness{delay: delay}
}

// WindowInto applies the windowing strategy to each element.
func WindowInto(s Scope, ws *window.Fn, col PCollection, opts ...WindowIntoOption) PCollection {
	return Must(TryWindowInto(s, ws, col, opts...))
}

// TryWindowInto attempts to insert a WindowInto transform.
func TryWindowInto(s Scope, wfn *window.Fn, col PCollection, opts ...WindowIntoOption) (PCollection, error) {
	if !s.IsValid() {
		return PCollection{}, errors.New("invalid scope")
	}
	if !col.IsValid() {
		return PCollection{}, errors.New("invalid input pcollection")
	}
	ws := window.WindowingStrategy{Fn: wfn, Trigger: trigger.DefaultTrigger{}}
	for _, opt := range opts {
		switch opt := opt.(type) {
		case windowTrigger:
			// TODO(BEAM-3304): call validation on trigger construction here
			// so local errors can be returned to the user in their pipeline
			// context instead of at pipeline translation time.
			ws.Trigger = opt.trigger
		case accumulationMode:
			ws.AccumulationMode = opt.mode
		case allowedLateness:
			ws.AllowedLateness = int(opt.delay / time.Millisecond)
		default:
			panic(fmt.Sprintf("Unknown WindowInto option type: %T: %v", opt, opt))
		}
	}

View on GitHub (pinned to 12126d8942)

Solutions

1. Propagate errors from every upstream Try* call so a zero PCollection never reaches WindowInto.
2. Verify the variable passed as col is the actual output of a successful transform.
3. Use Must-style constructors (impulse/ParDo) while debugging so the first failure panics at the source.
4. Add `if !col.IsValid() { return PCollection{}, errors.New("input not initialized") }` guards in helper functions wrapping windowing.

Example fix

// before
out, _ := beam.TryParDo(s, fn, input)
out, _ = beam.TryWindowInto(s, window.SlidingWindows(d, p), out)

// after
out, err := beam.TryParDo(s, fn, input)
if err != nil {
    return err
}
out, err = beam.TryWindowInto(s, window.SlidingWindows(d, p), out)
if err != nil {
    return err
}

if !col.IsValid() {
    return PCollection{}, errors.New("WindowInto input is a zero PCollection; check upstream Try* errors")
}

When it happens

Trigger: beam.TryWindowInto(s, wfn, col) with col == beam.PCollection{}; typical chain: `col, _ := beam.TryParDo(...)`, then WindowInto on the zero result.

Common situations: Swallowed errors from earlier Try* transforms feeding the windowing step; conditional logic that leaves a PCollection unassigned; passing a PCollection built in a pipeline other than the current scope's pipeline.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

• invalid scope
• Except when using GlobalWindows, calling .triggering() to sp
• Calling .triggering() to specify a trigger or calling .withA
• empty pipeline
• create has no values

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/a35680e193fefc91. Report an issue: GitHub.