cannot claim a position lower than the previously claimed po

Error message

cannot claim a position lower than the previously claimed position

What it means

offsetrange.Tracker.TryClaim enforces monotonic progress: each claimed position must be strictly greater than the last successfully claimed position. Attempting to claim an equal or lower position records this error and permanently stops the tracker, since Beam requires that claimed work never regresses.

Source

Thrown at sdks/go/pkg/beam/io/rtrackers/offsetrange/offsetrange.go:173

// The tracker stops with an error if a claim is attempted after the tracker has signalled to stop,
// if a position is claimed before the start of the restriction, or if a position is claimed before
// the latest successfully claimed.
func (tracker *Tracker) TryClaim(rawPos any) bool {
	if tracker.stopped {
		tracker.err = errors.New("cannot claim work after restriction tracker returns false")
		return false
	}

	pos := rawPos.(int64)
	tracker.attempted = pos
	if pos < tracker.rest.Start {
		tracker.stopped = true
		tracker.err = errors.New("position claimed is out of bounds of the restriction")
		return false
	}
	if pos <= tracker.claimed {
		tracker.stopped = true
		tracker.err = errors.New("cannot claim a position lower than the previously claimed position")
		return false
	}

	tracker.claimed = pos
	if pos >= tracker.rest.End {
		tracker.stopped = true
		return false
	}
	return true
}

// GetError returns the error that caused the tracker to stop, if there is one.
func (tracker *Tracker) GetError() error {
	return tracker.err
}

// TrySplit splits at the nearest integer greater than the given fraction of the remainder. If the
// fraction given is outside of the [0, 1] range, it is clamped to 0 or 1.

View on GitHub (pinned to 12126d8942)

Solutions

Ensure each TryClaim uses a strictly increasing position; advance the loop counter unconditionally.
Never retry a failed claim at the same position — return the tracker error and let the framework retry the whole element instead.
Restart iteration from tracker.claimed+1 (or the restriction start on a fresh tracker), not from a cached stale position.

Example fix

// before
for pos := start; pos < end; pos++ {
    if err := process(pos); err != nil {
        continue // re-claims same pos next iteration pattern
    }
}
// after
for pos := start; pos < end; pos++ {
    if !tracker.TryClaim(pos) {
        return tracker.GetError()
    }
    if err := process(pos); err != nil {
        return err // framework retries whole element, new tracker
    }
}

Defensive patterns

Strategy: validation

Validate before calling

if pos <= lastClaimed {
    return fmt.Errorf("pos %d must be greater than last claimed %d", pos, lastClaimed)
}

Try / catch

if !tracker.TryClaim(pos) {
    return tracker.GetError() // monotonicity violation stops the tracker
}

Prevention

Advance the position counter unconditionally in claim loops.
On processing failure, return the error instead of retrying the same claim.
Resume iteration from tracker's current claim state, never a cached position.
Write a test asserting each claimed position strictly increases.

When it happens

Trigger: Calling TryClaim(pos) where pos <= tracker.claimed — e.g. retrying the same offset after a processing error, restarting iteration from the start, or advancing by 0 due to an increment bug.

Common situations: Retry logic inside ProcessElement that re-claims the same position on transient failure; loops with a non-advancing counter (increment outside the loop or conditional increments); reprocessing an element whose claimed position was already recorded.

Understand the failure class

Background: "Invalid state transition" errors: "status must be X, actually Y", "already rejected/charging/uninstalled", "cannot ... while running" — what they mean when a library rejects your call — this error's family across 31 libraries.

Related errors

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/4aeb57d928ec9c89. Report an issue: GitHub.