diff --git a/dashboard/app/build/update.go b/dashboard/app/build/update.go
new file mode 100644
index 00000000..75390434
--- /dev/null
+++ b/dashboard/app/build/update.go
@@ -0,0 +1,116 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build appengine
+
+package build
+
+import (
+	"encoding/json"
+	"fmt"
+	"net/http"
+
+	"appengine"
+	"appengine/datastore"
+)
+
+func init() {
+	http.HandleFunc("/updatebenchmark", updateBenchmark)
+}
+
+func updateBenchmark(w http.ResponseWriter, r *http.Request) {
+	if !appengine.IsDevAppServer() {
+		fmt.Fprint(w, "Update must not run on real server.")
+		return
+	}
+
+	if r.Method != "POST" {
+		fmt.Fprintf(w, "bad request method")
+		return
+	}
+
+	c := contextForRequest(r)
+	if !validKey(c, r.FormValue("key"), r.FormValue("builder")) {
+		fmt.Fprintf(w, "bad builder/key")
+		return
+	}
+
+	defer r.Body.Close()
+	var hashes []string
+	if err := json.NewDecoder(r.Body).Decode(&hashes); err != nil {
+		fmt.Fprintf(w, "failed to decode request: %v", err)
+		return
+	}
+
+	ncommit := 0
+	nrun := 0
+	tx := func(c appengine.Context) error {
+		var cr *CommitRun
+		for _, hash := range hashes {
+			// Update Commit.
+			com := &Commit{Hash: hash}
+			err := datastore.Get(c, com.Key(c), com)
+			if err != nil && err != datastore.ErrNoSuchEntity {
+				return fmt.Errorf("fetching Commit: %v", err)
+			}
+			if err == datastore.ErrNoSuchEntity {
+				continue
+			}
+			com.NeedsBenchmarking = true
+			if _, err := datastore.Put(c, com.Key(c), com); err != nil {
+				return fmt.Errorf("putting Commit: %v", err)
+			}
+			ncommit++
+
+			// create PerfResult
+			res := &PerfResult{CommitHash: com.Hash, CommitNum: com.Num}
+			err = datastore.Get(c, res.Key(c), res)
+			if err != nil && err != datastore.ErrNoSuchEntity {
+				return fmt.Errorf("fetching PerfResult: %v", err)
+			}
+			if err == datastore.ErrNoSuchEntity {
+				if _, err := datastore.Put(c, res.Key(c), res); err != nil {
+					return fmt.Errorf("putting PerfResult: %v", err)
+				}
+			}
+
+			// Update CommitRun.
+			if cr != nil && cr.StartCommitNum != com.Num/PerfRunLength*PerfRunLength {
+				if _, err := datastore.Put(c, cr.Key(c), cr); err != nil {
+					return fmt.Errorf("putting CommitRun: %v", err)
+				}
+				nrun++
+				cr = nil
+			}
+			if cr == nil {
+				var err error
+				cr, err = GetCommitRun(c, com.Num)
+				if err != nil {
+					return fmt.Errorf("getting CommitRun: %v", err)
+				}
+			}
+			if com.Num < cr.StartCommitNum || com.Num >= cr.StartCommitNum+PerfRunLength {
+				return fmt.Errorf("commit num %v out of range [%v, %v)", com.Num, cr.StartCommitNum, cr.StartCommitNum+PerfRunLength)
+			}
+			idx := com.Num - cr.StartCommitNum
+			cr.Hash[idx] = com.Hash
+			cr.User[idx] = shortDesc(com.User)
+			cr.Desc[idx] = shortDesc(com.Desc)
+			cr.Time[idx] = com.Time
+			cr.NeedsBenchmarking[idx] = com.NeedsBenchmarking
+		}
+		if cr != nil {
+			if _, err := datastore.Put(c, cr.Key(c), cr); err != nil {
+				return fmt.Errorf("putting CommitRun: %v", err)
+			}
+			nrun++
+		}
+		return nil
+	}
+	if err := datastore.RunInTransaction(c, tx, nil); err != nil {
+		fmt.Fprintf(w, "failed to execute tx: %v", err)
+		return
+	}
+	fmt.Fprintf(w, "OK (updated %v commits and %v commit runs)", ncommit, nrun)
+}