mvcc/kvstore.go
func appendMarkTombstone(lg *zap.Logger, b []byte) []byte {
	if len(b) != revBytesLen {
		if lg != nil {
			lg.Panic(
				"cannot append tombstone mark to non-normal revision bytes",
				zap.Int("expected-revision-bytes-size", revBytesLen),
				zap.Int("given-revision-bytes-size", len(b)),
			)
		} else {
			plog.Panicf("cannot append mark to non normal revision bytes")
		}
	}
	return append(b, markTombstone)
}
func appendMarkTombstone(lg *zap.Logger, b []byte) []byte {
	if len(b) != revBytesLen {
		if lg != nil {
			lg.Panic(
				"cannot append tombstone mark to non-normal revision bytes",
				zap.Int("expected-revision-bytes-size", revBytesLen),
				zap.Int("given-revision-bytes-size", len(b)),
			)
		} else {
			plog.Panicf("cannot append mark to non normal revision bytes")
		}
	}
	return append(b, markTombstone)
}
// appendMarkTombstone appends tombstone mark to normal revision bytes.