TSDB: Move merge of head postings into index

This enables it to take advantage of a more compact data structure
since all postings are known to be `*ListPostings`.

Remove the `Get` member which was not used for anything else, and fix up
tests.

Signed-off-by: Bryan Boreham <bjboreham@gmail.com>

tsdb/head_read.go

@@ -103,20 +103,7 @@ func (h *headIndexReader) LabelNames(ctx context.Context, matchers ...*labels.Ma
 
 // Postings returns the postings list iterator for the label pairs.
 func (h *headIndexReader) Postings(ctx context.Context, name string, values ...string) (index.Postings, error) {
-	switch len(values) {
-	case 0:
-		return index.EmptyPostings(), nil
-	case 1:
-		return h.head.postings.Get(name, values[0]), nil
-	default:
-		res := make([]index.Postings, 0, len(values))
-		for _, value := range values {
-			if p := h.head.postings.Get(name, value); !index.IsEmptyPostingsType(p) {
-				res = append(res, p)
-			}
-		}
-		return index.Merge(ctx, res...), nil
-	}
+	return h.head.postings.Postings(ctx, name, values...), nil
 }
 
 func (h *headIndexReader) PostingsForLabelMatching(ctx context.Context, name string, match func(string) bool) index.Postings {

tsdb/head_test.go

@@ -962,12 +962,12 @@ func TestHead_Truncate(t *testing.T) {
 	require.Nil(t, h.series.getByID(s3.ref))
 	require.Nil(t, h.series.getByID(s4.ref))
 
-	postingsA1, _ := index.ExpandPostings(h.postings.Get("a", "1"))
-	postingsA2, _ := index.ExpandPostings(h.postings.Get("a", "2"))
-	postingsB1, _ := index.ExpandPostings(h.postings.Get("b", "1"))
-	postingsB2, _ := index.ExpandPostings(h.postings.Get("b", "2"))
-	postingsC1, _ := index.ExpandPostings(h.postings.Get("c", "1"))
-	postingsAll, _ := index.ExpandPostings(h.postings.Get("", ""))
+	postingsA1, _ := index.ExpandPostings(h.postings.Postings(ctx, "a", "1"))
+	postingsA2, _ := index.ExpandPostings(h.postings.Postings(ctx, "a", "2"))
+	postingsB1, _ := index.ExpandPostings(h.postings.Postings(ctx, "b", "1"))
+	postingsB2, _ := index.ExpandPostings(h.postings.Postings(ctx, "b", "2"))
+	postingsC1, _ := index.ExpandPostings(h.postings.Postings(ctx, "c", "1"))
+	postingsAll, _ := index.ExpandPostings(h.postings.Postings(ctx, "", ""))
 
 	require.Equal(t, []storage.SeriesRef{storage.SeriesRef(s1.ref)}, postingsA1)
 	require.Equal(t, []storage.SeriesRef{storage.SeriesRef(s2.ref)}, postingsA2)

tsdb/index/postings.go

@@ -235,25 +235,9 @@ func (p *MemPostings) Stats(label string, limit int, labelSizeFunc func(string,
 	}
 }
 
-// Get returns a postings list for the given label pair.
-func (p *MemPostings) Get(name, value string) Postings {
-	var lp []storage.SeriesRef
-	p.mtx.RLock()
-	l := p.m[name]
-	if l != nil {
-		lp = l[value]
-	}
-	p.mtx.RUnlock()
-
-	if lp == nil {
-		return EmptyPostings()
-	}
-	return newListPostings(lp...)
-}
-
 // All returns a postings list over all documents ever added.
 func (p *MemPostings) All() Postings {
-	return p.Get(AllPostingsKey())
+	return p.Postings(context.Background(), allPostingsKey.Name, allPostingsKey.Value)
 }
 
 // EnsureOrder ensures that all postings lists are sorted. After it returns all further
@@ -490,7 +474,7 @@ func (p *MemPostings) PostingsForLabelMatching(ctx context.Context, name string,
 	}
 
 	// Now `vals` only contains the values that matched, get their postings.
-	its := make([]Postings, 0, len(vals))
+	its := make([]*ListPostings, 0, len(vals))
 	lps := make([]ListPostings, len(vals))
 	p.mtx.RLock()
 	e := p.m[name]
@@ -510,11 +494,27 @@ func (p *MemPostings) PostingsForLabelMatching(ctx context.Context, name string,
 	return Merge(ctx, its...)
 }
 
+// Postings returns a postings iterator for the given label values.
+func (p *MemPostings) Postings(ctx context.Context, name string, values ...string) Postings {
+	res := make([]*ListPostings, 0, len(values))
+	lps := make([]ListPostings, len(values))
+	p.mtx.RLock()
+	postingsMapForName := p.m[name]
+	for i, value := range values {
+		if lp := postingsMapForName[value]; lp != nil {
+			lps[i] = ListPostings{list: lp}
+			res = append(res, &lps[i])
+		}
+	}
+	p.mtx.RUnlock()
+	return Merge(ctx, res...)
+}
+
 func (p *MemPostings) PostingsForAllLabelValues(ctx context.Context, name string) Postings {
 	p.mtx.RLock()
 
 	e := p.m[name]
-	its := make([]Postings, 0, len(e))
+	its := make([]*ListPostings, 0, len(e))
 	lps := make([]ListPostings, len(e))
 	i := 0
 	for _, refs := range e {

tsdb/index/postings_test.go

@@ -979,7 +979,7 @@ func TestMemPostings_Delete(t *testing.T) {
 	p.Add(2, labels.FromStrings("lbl1", "b"))
 	p.Add(3, labels.FromStrings("lbl2", "a"))
 
-	before := p.Get(allPostingsKey.Name, allPostingsKey.Value)
+	before := p.Postings(context.Background(), allPostingsKey.Name, allPostingsKey.Value)
 	deletedRefs := map[storage.SeriesRef]struct{}{
 		2: {},
 	}
@@ -987,7 +987,7 @@ func TestMemPostings_Delete(t *testing.T) {
 		{Name: "lbl1", Value: "b"}: {},
 	}
 	p.Delete(deletedRefs, affectedLabels)
-	after := p.Get(allPostingsKey.Name, allPostingsKey.Value)
+	after := p.Postings(context.Background(), allPostingsKey.Name, allPostingsKey.Value)
 
 	// Make sure postings gotten before the delete have the old data when
 	// iterated over.
@@ -1001,7 +1001,7 @@ func TestMemPostings_Delete(t *testing.T) {
 	require.NoError(t, err)
 	require.Equal(t, []storage.SeriesRef{1, 3}, expanded)
 
-	deleted := p.Get("lbl1", "b")
+	deleted := p.Postings(context.Background(), "lbl1", "b")
 	expanded, err = ExpandPostings(deleted)
 	require.NoError(t, err)
 	require.Empty(t, expanded, "expected empty postings, got %v", expanded)
@@ -1073,7 +1073,7 @@ func BenchmarkMemPostings_Delete(b *testing.B) {
 									return
 								default:
 									// Get a random value of this label.
-									p.Get(lbl, itoa(rand.Intn(10000))).Next()
+									p.Postings(context.Background(), lbl, itoa(rand.Intn(10000))).Next()
 								}
 							}
 						}(i)