Merge pull request #503 from grafana/fixup-labels-usage3

labels: add stringlabels version of StableHash

.github/workflows/test.yml

@@ -28,3 +28,27 @@ jobs:
 
       - name: Run Tests
         run: GO=/usr/local/go/bin/go make common-test
+
+  test-stringlabels:
+    runs-on: ubuntu-20.04
+    steps:
+      - name: Upgrade golang
+        run: |
+          cd /tmp
+          wget https://dl.google.com/go/go1.20.3.linux-amd64.tar.gz
+          tar -zxvf go1.20.3.linux-amd64.tar.gz
+          sudo rm -fr /usr/local/go
+          sudo mv /tmp/go /usr/local/go
+          cd -
+          ls -l /usr/bin/go
+
+      - name: Checkout Repo
+        uses: actions/checkout@v2
+
+      # This file would normally be created by `make assets`, here we just
+      #  mock it because the file is required for the tests to pass.
+      - name: Mock building of necessary react file
+        run: mkdir web/ui/static/react && touch web/ui/static/react/index.html
+
+      - name: Run Tests -tags=stringlabels
+        run: GO=/usr/local/go/bin/go GOOPTS=-tags=stringlabels make common-test

model/labels/sharding.go

@@ -1,3 +1,5 @@
+//go:build !stringlabels
+
 package labels
 
 import (

model/labels/sharding_stringlabels.go

@@ -0,0 +1,41 @@
+//go:build stringlabels
+
+package labels
+
+import (
+	"github.com/cespare/xxhash/v2"
+)
+
+// StableHash is a labels hashing implementation which is guaranteed to not change over time.
+// This function should be used whenever labels hashing backward compatibility must be guaranteed.
+func StableHash(ls Labels) uint64 {
+	// Use xxhash.Sum64(b) for fast path as it's faster.
+	b := make([]byte, 0, 1024)
+	var h *xxhash.Digest
+	for i := 0; i < len(ls.data); {
+		var v Label
+		v.Name, i = decodeString(ls.data, i)
+		v.Value, i = decodeString(ls.data, i)
+		if h == nil && len(b)+len(v.Name)+len(v.Value)+2 >= cap(b) {
+			// If labels entry is 1KB+, switch to Write API. Copy in the values up to this point.
+			h = xxhash.New()
+			_, _ = h.Write(b)
+		}
+		if h != nil {
+			_, _ = h.WriteString(v.Name)
+			_, _ = h.Write(seps)
+			_, _ = h.WriteString(v.Value)
+			_, _ = h.Write(seps)
+			continue
+		}
+
+		b = append(b, v.Name...)
+		b = append(b, seps[0])
+		b = append(b, v.Value...)
+		b = append(b, seps[0])
+	}
+	if h != nil {
+		return h.Sum64()
+	}
+	return xxhash.Sum64(b)
+}

model/labels/sharding_test.go

@@ -0,0 +1,19 @@
+package labels
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+// TestStableHash tests that StableHash is stable.
+// The hashes this test asserts should not be changed.
+func TestStableHash(t *testing.T) {
+	for expectedHash, lbls := range map[uint64]Labels{
+		0xef46db3751d8e999: EmptyLabels(),
+		0x347c8ee7a9e29708: FromStrings("hello", "world"),
+		0xcbab40540f26097d: FromStrings(MetricName, "metric", "label", "value"),
+	} {
+		require.Equal(t, expectedHash, StableHash(lbls))
+	}
+}