func (st *Stream) produceRanges(ctx context.Context) {
	splits := st.db.KeySplits(st.Prefix)
	start := y.SafeCopy(nil, st.Prefix)
	for _, key := range splits {
		st.rangeCh <- keyRange{left: start, right: y.SafeCopy(nil, []byte(key))}
		start = y.SafeCopy(nil, []byte(key))
	}
	// Edge case: prefix is empty and no splits exist. In that case, we should have at least one
	// keyRange output.
	st.rangeCh <- keyRange{left: start}
	close(st.rangeCh)
}
func (st *Stream) produceRanges(ctx context.Context) {
	splits := st.db.KeySplits(st.Prefix)
	start := y.SafeCopy(nil, st.Prefix)
	for _, key := range splits {
		st.rangeCh <- keyRange{left: start, right: y.SafeCopy(nil, []byte(key))}
		start = y.SafeCopy(nil, []byte(key))
	}
	// Edge case: prefix is empty and no splits exist. In that case, we should have at least one
	// keyRange output.
	st.rangeCh <- keyRange{left: start}
	close(st.rangeCh)
}
// keyRange is [start, end), including start, excluding end. Do ensure that the start,
// end byte slices are owned by keyRange struct.