按标签倒排求交，缩小需要读取的时间序列

328func postingsForMatcher(ctx context.Context, ix IndexReader, m *labels.Matcher) (index.Postings, error) {329	// This method will not return postings for missing labels.330331	// Fast-path for equal matching.332	if m.Type == labels.MatchEqual {333		return ix.Postings(ctx, m.Name, m.Value)334	}335336	// Fast-path for set matching.337	if m.Type == labels.MatchRegexp {338		setMatches := m.SetMatches()339		if len(setMatches) > 0 {340			return ix.Postings(ctx, m.Name, setMatches...)341		}342	}343344	it := ix.PostingsForLabelMatching(ctx, m.Name, m.Matches)345	return it, it.Err()

319	it := index.Intersect(its...)320321	for _, n := range notIts {322		it = index.Without(it, n)323	}324325	return it, nil326}

535func (it *intersectPostings) doNext() bool {536Loop:537	for {538		for _, p := range it.arr {539			if !p.Seek(it.cur) {540				return false541			}542			if p.At() > it.cur {543				it.cur = p.At()544				continue Loop545			}546		}547		return true548	}549}

551func (it *intersectPostings) Next() bool {552	for _, p := range it.arr {553		if !p.Next() {554			return false555		}556		if p.At() > it.cur {557			it.cur = p.At()558		}559	}560	return it.doNext()561}562563func (it *intersectPostings) Seek(id storage.SeriesRef) bool {564	it.cur = id565	return it.doNext()

757func (it *ListPostings) Seek(x storage.SeriesRef) bool {758	// If the current value satisfies, then return.759	if it.cur >= x {760		return true761	}762	if len(it.list) == 0 {763		return false764	}765766	// Do binary search between current position and end.767	i, _ := slices.BinarySearch(it.list, x)768	if i < len(it.list) {769		it.cur = it.list[i]770		it.list = it.list[i+1:]771		return true772	}773	it.list = nil774	return false775}