feat: implement parent pointer tree recovery (#3390)

Author: kolesnikovae

pkg/phlaredb/symdb/stacktrace_tree.go

@@ -186,6 +186,37 @@ func (t *parentPointerTree) Nodes() []Node {
 	return dst
 }
 
+func (t *parentPointerTree) toStacktraceTree() *stacktraceTree {
+	l := int32(len(t.nodes))
+	x := stacktraceTree{nodes: make([]node, l)}
+	x.nodes[0] = node{
+		p:  sentinel,
+		fc: sentinel,
+		ns: sentinel,
+	}
+	lc := make([]int32, len(t.nodes))
+	var s int32
+	for i := int32(1); i < l; i++ {
+		n := t.nodes[i]
+		x.nodes[i] = node{
+			p:  n.p,
+			r:  n.r,
+			fc: sentinel,
+			ns: sentinel,
+		}
+		// Swap the last child of the parent with self.
+		// If this is the first child, update the parent.
+		// Otherwise, update the sibling.
+		s, lc[n.p] = lc[n.p], i
+		if s == 0 {
+			x.nodes[n.p].fc = i
+		} else {
+			x.nodes[s].ns = i
+		}
+	}
+	return &x
+}
+
 // ReadFrom decodes parent pointer tree from the reader.
 // The tree must have enough nodes.
 func (t *parentPointerTree) ReadFrom(r io.Reader) (int64, error) {

pkg/phlaredb/symdb/stacktrace_tree_test.go

@@ -164,6 +164,44 @@ func Test_stacktrace_tree_pprof_locations(t *testing.T) {
 	}
 }
 
+// The test is helpful for debugging.
+func Test_parentPointerTree_toStacktraceTree(t *testing.T) {
+	x := newStacktraceTree(10)
+	for _, stack := range [][]uint64{
+		{5, 4, 3, 2, 1},
+		{6, 4, 3, 2, 1},
+		{4, 3, 2, 1},
+		{3, 2, 1},
+		{4, 2, 1},
+		{7, 2, 1},
+		{2, 1},
+		{1},
+	} {
+		x.insert(stack)
+	}
+	assertRestoredStacktraceTree(t, x)
+}
+
+func Test_parentPointerTree_toStacktraceTree_profile(t *testing.T) {
+	p, err := pprof.OpenFile("testdata/profile.pb.gz")
+	require.NoError(t, err)
+	x := newStacktraceTree(defaultStacktraceTreeSize)
+	for _, s := range p.Sample {
+		x.insert(s.LocationId)
+	}
+	assertRestoredStacktraceTree(t, x)
+}
+
+func assertRestoredStacktraceTree(t *testing.T, x *stacktraceTree) {
+	var b bytes.Buffer
+	_, _ = x.WriteTo(&b)
+	ppt := newParentPointerTree(x.len())
+	_, err := ppt.ReadFrom(bytes.NewBuffer(b.Bytes()))
+	require.NoError(t, err)
+	restored := ppt.toStacktraceTree()
+	assert.Equal(t, x.nodes, restored.nodes)
+}
+
 func Benchmark_stacktrace_tree_insert(b *testing.B) {
 	p, err := pprof.OpenFile("testdata/profile.pb.gz")
 	require.NoError(b, err)