atomic file write fix

common/os.go

@@ -43,12 +43,14 @@ func AtomicWriteFile(filePath string, newBytes []byte) error {
 			return fmt.Errorf("Failed to write file %v. %v", filePath+".bak", err)
 		}
 	}
-	// Write newBytes to filePath.
+	// Write newBytes to filePath.new
-	err := ioutil.WriteFile(filePath, newBytes, 0600)
+	err := ioutil.WriteFile(filePath+".new", newBytes, 0600)
 	if err != nil {
-		return fmt.Errorf("Failed to write file %v. %v", filePath, err)
+		return fmt.Errorf("Failed to write file %v. %v", filePath+".new", err)
 	}
-	return nil
+	// Move filePath.new to filePath
+	err = os.Rename(filePath+".new", filePath)
+	return err
 }
 
 func EnsureDir(dir string) error {

merkle/iavl_test.go

@@ -241,6 +241,8 @@ func BenchmarkImmutableAvlTree(b *testing.B) {
 	b.StopTimer()
 
 	t := NewIAVLTree(binary.BasicCodec, binary.BasicCodec, 0, nil)
+	// 23000ns/op, 43000ops/s
+	// for i := 0; i < 10000000; i++ {
 	for i := 0; i < 1000000; i++ {
 		t.Set(RandUint64(), "")
 	}