eskipfile: optimize Watch.LoadUpdates

eskipfile/watch.go

@@ -1,6 +1,7 @@
 package eskipfile
 
 import (
+	"bytes"
 	"os"
 	"reflect"
 	"sync"
@@ -17,12 +18,13 @@ type watchResponse struct {
 // WatchClient implements a route configuration client with file watching. Use the Watch function to initialize
 // instances of it.
 type WatchClient struct {
-	fileName   string
-	routes     map[string]*eskip.Route
-	getAll     chan (chan<- watchResponse)
-	getUpdates chan (chan<- watchResponse)
-	quit       chan struct{}
-	once       sync.Once
+	fileName    string
+	lastContent []byte
+	routes      map[string]*eskip.Route
+	getAll      chan (chan<- watchResponse)
+	getUpdates  chan (chan<- watchResponse)
+	quit        chan struct{}
+	once        sync.Once
 }
 
 // Watch creates a route configuration client with file watching. Watch doesn't follow file system nodes, it
@@ -97,35 +99,44 @@ func cloneRoutes(r []*eskip.Route) []*eskip.Route {
 func (c *WatchClient) loadAll() watchResponse {
 	content, err := os.ReadFile(c.fileName)
 	if err != nil {
+		c.lastContent = nil
 		return watchResponse{err: err}
 	}
 
 	r, err := eskip.Parse(string(content))
 	if err != nil {
+		c.lastContent = nil
 		return watchResponse{err: err}
 	}
 
 	c.storeRoutes(r)
+	c.lastContent = content
 	return watchResponse{routes: cloneRoutes(r)}
 }
 
 func (c *WatchClient) loadUpdates() watchResponse {
 	content, err := os.ReadFile(c.fileName)
 	if err != nil {
+		c.lastContent = nil
 		if os.IsNotExist(err) {
 			deletedIDs := c.deleteAllListIDs()
 			return watchResponse{deletedIDs: deletedIDs}
 		}
-
 		return watchResponse{err: err}
 	}
 
+	if bytes.Equal(content, c.lastContent) {
+		return watchResponse{}
+	}
+
 	r, err := eskip.Parse(string(content))
 	if err != nil {
+		c.lastContent = nil
 		return watchResponse{err: err}
 	}
 
 	upsert, del := c.diffStoreRoutes(r)
+	c.lastContent = content
 	return watchResponse{routes: cloneRoutes(upsert), deletedIDs: del}
 }
 

eskipfile/watch_test.go

@@ -1,12 +1,14 @@
 package eskipfile
 
 import (
+	"fmt"
 	"net/http"
 	"net/url"
 	"os"
 	"testing"
 	"time"
 
+	"github.com/stretchr/testify/require"
 	"github.com/zalando/skipper/filters/builtin"
 	"github.com/zalando/skipper/logging/loggingtest"
 	"github.com/zalando/skipper/routing"
@@ -236,3 +238,34 @@ func TestWatchUpdate(t *testing.T) {
 	updateFile(t)
 	test.waitAndSucceedUpdated()
 }
+
+func BenchmarkWatchLoadUpdate(b *testing.B) {
+	f, err := os.CreateTemp(b.TempDir(), "routes*.eskip")
+	require.NoError(b, err)
+	b.Cleanup(func() { require.NoError(b, os.Remove(f.Name())) })
+
+	const nRoutes = 10_000
+	for i := range nRoutes {
+		_, err := f.WriteString(fmt.Sprintf(`r%d: Path("/%d") -> "https://foo%d.example.org";`, i, i, i))
+		require.NoError(b, err)
+	}
+	require.NoError(b, f.Close())
+
+	w := Watch(f.Name())
+	b.Cleanup(w.Close)
+
+	r, err := w.LoadAll()
+	require.Len(b, r, nRoutes)
+	require.NoError(b, err)
+
+	r, deletedIds, err := w.LoadUpdate()
+	require.Nil(b, r)
+	require.Empty(b, deletedIds)
+	require.NoError(b, err)
+
+	b.ReportAllocs()
+	b.ResetTimer()
+	for range b.N {
+		w.LoadUpdate()
+	}
+}