nats-io/nats-server · error

ErrSetNotEmpty

ErrSetNotEmpty

Error message

ss: set not empty

What it means

ErrSetNotEmpty is returned by SequenceSet.SetInitialMin when the set already contains values. SetInitialMin can only initialize a fresh, empty set with a starting minimum, so calling it on a populated set is rejected to avoid corrupting existing intervals.

Source

Thrown at server/avl/seqset.go:309

	i += 8
	ss.root.nodeIter(func(n *node) {
		le.PutUint64(buf[i:], n.base)
		i += 8
		for _, b := range n.bits {
			le.PutUint64(buf[i:], b)
			i += 8
		}
		le.PutUint16(buf[i:], uint16(n.h))
		i += 2
	})
	return buf[:i]
}

// ErrBadEncoding is returned when we can not decode properly.
var (
	ErrBadEncoding = errors.New("ss: bad encoding")
	ErrBadVersion  = errors.New("ss: bad version")
	ErrSetNotEmpty = errors.New("ss: set not empty")
)

// Decode returns the sequence set and number of bytes read from the buffer on success.
func Decode(buf []byte) (*SequenceSet, int, error) {
	if len(buf) < minLen || buf[0] != magic {
		return nil, -1, ErrBadEncoding
	}

	switch v := buf[1]; v {
	case 1:
		return decodev1(buf)
	case 2:
		return decodev2(buf)
	default:
		return nil, -1, ErrBadVersion
	}
}

View on GitHub (pinned to 3a66a489d2)

Solutions

1. Only call SetInitialMin right after creating the SequenceSet, before any adds or Decode
2. Check ss.IsEmpty() before calling SetInitialMin and skip if already populated
3. If you need to seed a minimum on a populated set, delete the set and rebuild it with the desired initial value

Example fix

// before
ss.SetInitialMin(min) // panics-free but errors if ss already restored
// after
if ss.IsEmpty() {
    ss.SetInitialMin(min)
}

if !ss.IsEmpty() {
    // already initialized; skip seeding
} else {
    ss.SetInitialMin(min)
}

err := ss.SetInitialMin(min)
if errors.Is(err, avl.ErrSetNotEmpty) {
    log.Debug("sequence set already populated; skipping initial min")
}

When it happens

Trigger: Calling SetInitialMin on a SequenceSet that already has entries (e.g. one loaded via Decode or previously added to).

Common situations: Reinitializing a consumer's pending/reserved sequence state that was already restored from disk, or double-initialization during setup code.

Related errors

• ErrBadEncoding
• fileStore requires file storage type in config
• filestore max block size is %s
• could not create storage directory - %v
• storage directory is not a directory

AI-assisted analysis of nats-io/nats-server@3a66a489d2 (2026-09-02). Data as JSON: /api/errors/a1d47d93480eb2e4. Report an issue: GitHub.