optimization: store just IDs of child nodes

IDs are a lot smaller, hence quicker to manage.
Any time we want to refer back to the full node we look it up in its topology.

(This relies on nobody trying to store a rendered node as a child).

report/id.go

@@ -262,6 +262,19 @@ func split2(s, sep string) (s1, s2 string, ok bool) {
 	return s[:pos], s[pos+1:], true
 }
 
+// NodeIDType returns the type of a node ID - e.g. process, pod, endpoint
+func NodeIDType(nodeID string) (string, bool) {
+	if _, tag, ok := ParseNodeID(nodeID); ok {
+		switch {
+		case len(tag) >= 2 && tag[0] == '<' && tag[len(tag)-1] == '>':
+			return tag[1 : len(tag)-1], true
+		case len(tag) >= 1 && tag[0] >= '0' && tag[0] <= '9':
+			return Endpoint, true
+		}
+	}
+	return "", false
+}
+
 // ParseNodeID produces the id and tag of a single-component node ID.
 func ParseNodeID(nodeID string) (id string, tag string, ok bool) {
 	return split2(nodeID, ScopeDelim)

report/id_test.go

@@ -3,6 +3,7 @@ package report_test
 import (
 	"testing"
 
+	"github.com/stretchr/testify/assert"
 	"github.com/weaveworks/scope/report"
 )
 
@@ -78,3 +79,18 @@ func TestECSServiceNodeIDCompat(t *testing.T) {
 		t.Errorf("Backwards-compatible id %q parsed name to %q, expected %q", testID, name, testName)
 	}
 }
+
+func TestNodeIDType(t *testing.T) {
+	ty, ok := report.NodeIDType("")
+	assert.False(t, ok)
+	ty, ok = report.NodeIDType(clientHostNodeID)
+	assert.True(t, ok)
+	assert.Equal(t, report.Host, ty)
+	ty, ok = report.NodeIDType(client54001EndpointNodeID)
+	assert.True(t, ok)
+	assert.Equal(t, report.Endpoint, ty)
+	rsetID := report.MakeReplicaSetNodeID("foo")
+	ty, ok = report.NodeIDType(rsetID)
+	assert.True(t, ok)
+	assert.Equal(t, report.ReplicaSet, ty)
+}

report/node.go

@@ -19,7 +19,7 @@ type Node struct {
 	Latest    StringLatestMap `json:"latest,omitempty"`
 	Metrics   Metrics         `json:"metrics,omitempty" deepequal:"nil==empty"`
 	Parents   Sets            `json:"parents,omitempty"`
-	Children  NodeSet         `json:"children,omitempty"`
+	ChildIDs  IDList          `json:"cs,omitempty"`
 }
 
 // MakeNode creates a new Node with no initial metadata.
@@ -162,14 +162,16 @@ func (n Node) PruneParents() Node {
 }
 
 // WithChildren returns a fresh copy of n, with children merged in.
-func (n Node) WithChildren(children NodeSet) Node {
-	n.Children = n.Children.Merge(children)
+func (n Node) WithChildren(children IDList) Node {
+	for _, childID := range children {
+		n.ChildIDs = n.ChildIDs.Add(childID)
+	}
 	return n
 }
 
-// WithChild returns a fresh copy of n, with one child merged in.
-func (n Node) WithChild(child Node) Node {
-	n.Children = n.Children.Merge(MakeNodeSet(child))
+// WithChildID returns a fresh copy of n, with one child merged in.
+func (n Node) WithChildID(childID string) Node {
+	n.ChildIDs = n.ChildIDs.Add(childID)
 	return n
 }
 
@@ -194,7 +196,7 @@ func (n Node) Merge(other Node) Node {
 		Latest:    n.Latest.Merge(other.Latest),
 		Metrics:   n.Metrics.Merge(other.Metrics),
 		Parents:   n.Parents.Merge(other.Parents),
-		Children:  n.Children.Merge(other.Children),
+		ChildIDs:  n.ChildIDs.Merge(other.ChildIDs),
 	}
 }