Add performance measurements, trash test and documentation

internal/scan/mem_test.go

@@ -0,0 +1,35 @@
+package scan
+
+import (
+	"context"
+	"os"
+	"runtime"
+	"testing"
+	"time"
+)
+
+// TestMemoryPerNode reports heap use per inventory node for a real tree.
+// Set MAPSIZE_MEM_ROOT to a directory to run it.
+func TestMemoryPerNode(t *testing.T) {
+	root := os.Getenv("MAPSIZE_MEM_ROOT")
+	if root == "" {
+		t.Skip("set MAPSIZE_MEM_ROOT")
+	}
+	var before, after runtime.MemStats
+	runtime.GC()
+	runtime.ReadMemStats(&before)
+	start := time.Now()
+	s, err := Start(context.Background(), root, Options{})
+	if err != nil {
+		t.Fatal(err)
+	}
+	<-s.Done()
+	el := time.Since(start)
+	runtime.GC()
+	runtime.ReadMemStats(&after)
+	n := s.Tree.Len()
+	heap := after.HeapAlloc - before.HeapAlloc
+	t.Logf("nodes=%d scan=%s heap=%.1f MiB (%.0f bytes/node)", n, el.Round(time.Millisecond),
+		float64(heap)/(1<<20), float64(heap)/float64(n))
+	runtime.KeepAlive(s)
+}