Limit tables to 20 rows

report/table.go

@@ -7,31 +7,51 @@ import (
 	"github.com/weaveworks/scope/common/mtime"
 )
 
+// MaxTableRows sets the limit on the table size to render
+// TODO: this won't be needed once we send reports incrementally
+const MaxTableRows = 20
+
 // AddTable appends arbirary key-value pairs to the Node, returning a new node.
 func (node Node) AddTable(prefix string, labels map[string]string) Node {
+	count := 0
 	for key, value := range labels {
+		// It's enough to only include MaxTableRows+1
+		// since they won't be rendered anyhow
+		if count > MaxTableRows {
+			break
+		}
 		node = node.WithLatest(prefix+key, mtime.Now(), value)
+		count++
+
 	}
 	return node
 }
 
 // ExtractTable returns the key-value pairs with the given prefix from this Node,
-func (node Node) ExtractTable(prefix string) map[string]string {
-	result := map[string]string{}
+func (node Node) ExtractTable(prefix string) (rows map[string]string, truncated bool) {
+	rows = map[string]string{}
+	truncated = false
+	count := 0
 	node.Latest.ForEach(func(key, value string) {
 		if strings.HasPrefix(key, prefix) {
+			if count >= MaxTableRows {
+				truncated = true
+				return
+			}
 			label := key[len(prefix):]
-			result[label] = value
+			rows[label] = value
+			count++
 		}
 	})
-	return result
+	return rows, truncated
 }
 
 // Table is the type for a table in the UI.
 type Table struct {
-	ID    string        `json:"id"`
-	Label string        `json:"label"`
-	Rows  []MetadataRow `json:"rows"`
+	ID           string        `json:"id"`
+	Label        string        `json:"label"`
+	Rows         []MetadataRow `json:"rows"`
+	WasTruncated bool          `json:"was_truncated"`
 }
 
 type tablesByID []Table
@@ -90,12 +110,13 @@ type TableTemplates map[string]TableTemplate
 func (t TableTemplates) Tables(node Node) []Table {
 	var result []Table
 	for _, template := range t {
+		rows, truncated := node.ExtractTable(template.Prefix)
 		table := Table{
-			ID:    template.ID,
-			Label: template.Label,
-			Rows:  []MetadataRow{},
+			ID:           template.ID,
+			Label:        template.Label,
+			Rows:         []MetadataRow{},
+			WasTruncated: truncated,
 		}
-		rows := node.ExtractTable(template.Prefix)
 		keys := make([]string, 0, len(rows))
 		for k := range rows {
 			keys = append(keys, k)

report/table_test.go

@@ -16,7 +16,11 @@ func TestTables(t *testing.T) {
 	nmd := report.MakeNode("foo1")
 
 	nmd = nmd.AddTable("foo_", want)
-	have := nmd.ExtractTable("foo_")
+	have, truncated := nmd.ExtractTable("foo_")
+
+	if truncated {
+		t.Error("Table shouldn't had been truncated")
+	}
 
 	if !reflect.DeepEqual(want, have) {
 		t.Error(test.Diff(want, have))