optimize: avoid redundant blob fetching

registry/proxy/proxyblobstore.go

@@ -79,35 +79,6 @@ func (pbs *proxyBlobStore) serveLocal(ctx context.Context, w http.ResponseWriter
 	return true, pbs.localStore.ServeBlob(ctx, w, r, dgst)
 }
 
-func (pbs *proxyBlobStore) storeLocal(ctx context.Context, dgst digest.Digest) error {
-	defer func() {
-		mu.Lock()
-		delete(inflight, dgst)
-		mu.Unlock()
-	}()
-
-	var desc distribution.Descriptor
-	var err error
-	var bw distribution.BlobWriter
-
-	bw, err = pbs.localStore.Create(ctx)
-	if err != nil {
-		return err
-	}
-
-	desc, err = pbs.copyContent(ctx, dgst, bw)
-	if err != nil {
-		return err
-	}
-
-	_, err = bw.Commit(ctx, desc)
-	if err != nil {
-		return err
-	}
-
-	return nil
-}
-
 func (pbs *proxyBlobStore) ServeBlob(ctx context.Context, w http.ResponseWriter, r *http.Request, dgst digest.Digest) error {
 	served, err := pbs.serveLocal(ctx, w, r, dgst)
 	if err != nil {
@@ -126,40 +97,50 @@ func (pbs *proxyBlobStore) ServeBlob(ctx context.Context, w http.ResponseWriter,
 	mu.Lock()
 	_, ok := inflight[dgst]
 	if ok {
+		// If the blob has been serving in other requests.
+		// Will return the blob from the remote store directly.
+		// TODO Maybe we could reuse the these blobs are serving remotely and caching locally.
 		mu.Unlock()
 		_, err := pbs.copyContent(ctx, dgst, w)
 		return err
 	}
 	inflight[dgst] = struct{}{}
 	mu.Unlock()
 
-	// storeLocalCtx will be independent with ctx, because ctx it used to fetch remote image.
-	// There would be a situation, that is pulling remote bytes ends before pbs.storeLocal( 'Copy', 'Commit' ...)
-	// Then the registry fails to cache the layer, even though the layer had been served to client.
-	storeLocalCtx, cancel := context.WithCancel(context.Background())
-	go func(dgst digest.Digest) {
-		defer cancel()
-		if err := pbs.storeLocal(storeLocalCtx, dgst); err != nil {
-			dcontext.GetLogger(storeLocalCtx).Errorf("Error committing to storage: %s", err.Error())
-		}
-
-		blobRef, err := reference.WithDigest(pbs.repositoryName, dgst)
-		if err != nil {
-			dcontext.GetLogger(storeLocalCtx).Errorf("Error creating reference: %s", err)
-			return
-		}
-
-		if pbs.scheduler != nil && pbs.ttl != nil {
-			pbs.scheduler.AddBlob(blobRef, *pbs.ttl)
-		}
-
-	}(dgst)
-
-	_, err = pbs.copyContent(ctx, dgst, w)
+	defer func() {
+		mu.Lock()
+		delete(inflight, dgst)
+		mu.Unlock()
+	}()
+
+	bw, err := pbs.localStore.Create(ctx)
+	if err != nil {
+		return err
+	}
+
+	// Serving client and storing locally over same fetching request.
+	// This can prevent a redundant blob fetching.
+	multiWriter := io.MultiWriter(w, bw)
+	desc, err := pbs.copyContent(ctx, dgst, multiWriter)
+	if err != nil {
+		return err
+	}
+
+	_, err = bw.Commit(ctx, desc)
 	if err != nil {
-		cancel()
 		return err
 	}
+
+	blobRef, err := reference.WithDigest(pbs.repositoryName, dgst)
+	if err != nil {
+		dcontext.GetLogger(ctx).Errorf("Error creating reference: %s", err)
+		return err
+	}
+
+	if pbs.scheduler != nil && pbs.ttl != nil {
+		pbs.scheduler.AddBlob(blobRef, *pbs.ttl)
+	}
+
 	return nil
 }
 

registry/proxy/proxyblobstore_test.go

@@ -336,6 +336,12 @@ func testProxyStoreServe(t *testing.T, te *testEnv, numClients int) {
 	remoteStats := te.RemoteStats()
 
 	var wg sync.WaitGroup
+	var descHitMap = map[digest.Digest]bool{}
+	var hitLock sync.Mutex
+
+	for _, remoteBlob := range te.inRemote {
+		descHitMap[remoteBlob.Digest] = true
+	}
 
 	for i := 0; i < numClients; i++ {
 		// Serveblob - pulls through blobs
@@ -362,6 +368,15 @@ func testProxyStoreServe(t *testing.T, te *testEnv, numClients int) {
 					t.Errorf("Mismatching blob fetch from proxy")
 					return
 				}
+
+				desc, err := te.store.localStore.Stat(te.ctx, remoteBlob.Digest)
+				if err != nil {
+					continue
+				}
+
+				hitLock.Lock()
+				delete(descHitMap, desc.Digest)
+				hitLock.Unlock()
 			}
 		}()
 	}
@@ -371,11 +386,16 @@ func testProxyStoreServe(t *testing.T, te *testEnv, numClients int) {
 		t.FailNow()
 	}
 
+	if len(descHitMap) > 0 {
+		t.Errorf("Expected hit cache at least once, but it turns out that no caches was hit")
+		t.FailNow()
+	}
+
 	remoteBlobCount := len(te.inRemote)
 	sbsMu.Lock()
-	if (*localStats)["stat"] != remoteBlobCount*numClients && (*localStats)["create"] != te.numUnique {
+	if (*localStats)["stat"] != remoteBlobCount*numClients*2 && (*localStats)["create"] != te.numUnique {
 		sbsMu.Unlock()
-		t.Fatal("Expected: stat:", remoteBlobCount*numClients, "create:", remoteBlobCount)
+		t.Fatal("Expected: stat:", remoteBlobCount*numClients, "create:", remoteBlobCount, "Got: stat:", (*localStats)["stat"], "create:", (*localStats)["create"])
 	}
 	sbsMu.Unlock()