dashboard/app: update memcache with cron

Building the memcache object with bug stats takes
significant time and periodically slows down user requests.
Update it with cron ahead of time.

1 files changed, 38 insertions, 16 deletions

diff --git a/dashboard/app/cache.go b/dashboard/app/cache.go
index 574324518..7040f65e8 100644
--- a/dashboard/app/cache.go
+++ b/dashboard/app/cache.go
@@ -9,6 +9,8 @@ import (
 	"time"
 
 	"golang.org/x/net/context"
+	"google.golang.org/appengine"
+	"google.golang.org/appengine/log"
 	"google.golang.org/appengine/memcache"
 )
 
@@ -20,35 +22,43 @@ type Cached struct {
 
 func CacheGet(c context.Context, r *http.Request, ns string) (*Cached, error) {
 	accessLevel := accessLevel(c, r)
-	key := fmt.Sprintf("%v-%v", ns, accessLevel)
 	v := new(Cached)
-	_, err := memcache.Gob.Get(c, key, v)
+	_, err := memcache.Gob.Get(c, cacheKey(ns, accessLevel), v)
 	if err != nil && err != memcache.ErrCacheMiss {
 		return nil, err
 	}
 	if err == nil {
 		return v, nil
 	}
-	if v, err = buildCached(c, ns, accessLevel); err != nil {
+	bugs, _, err := loadNamespaceBugs(c, ns)
+	if err != nil {
 		return nil, err
 	}
-	item := &memcache.Item{
-		Key:        key,
-		Object:     v,
-		Expiration: time.Hour,
-	}
-	if err := memcache.Gob.Set(c, item); err != nil {
-		return nil, err
+	return buildAndStoreCached(c, bugs, ns, accessLevel)
+}
+
+// cacheUpdate updates memcache every hour (called by cron.yaml).
+// Cache update is slow and we don't want to slow down user requests.
+func cacheUpdate(w http.ResponseWriter, r *http.Request) {
+	c := appengine.NewContext(r)
+	for ns := range config.Namespaces {
+		bugs, _, err := loadNamespaceBugs(c, ns)
+		if err != nil {
+			log.Errorf(c, "failed load ns=%v bugs: %v", ns, err)
+			continue
+		}
+		for _, accessLevel := range []AccessLevel{AccessPublic, AccessUser, AccessAdmin} {
+			_, err := buildAndStoreCached(c, bugs, ns, accessLevel)
+			if err != nil {
+				log.Errorf(c, "failed to build cached for ns=%v access=%v: %v", ns, accessLevel, err)
+				continue
+			}
+		}
 	}
-	return v, nil
 }
 
-func buildCached(c context.Context, ns string, accessLevel AccessLevel) (*Cached, error) {
+func buildAndStoreCached(c context.Context, bugs []*Bug, ns string, accessLevel AccessLevel) (*Cached, error) {
 	v := &Cached{}
-	bugs, _, err := loadNamespaceBugs(c, ns)
-	if err != nil {
-		return nil, err
-	}
 	for _, bug := range bugs {
 		switch bug.Status {
 		case BugStatusOpen:
@@ -66,5 +76,17 @@ func buildCached(c context.Context, ns string, accessLevel AccessLevel) (*Cached
 			v.Invalid++
 		}
 	}
+	item := &memcache.Item{
+		Key:        cacheKey(ns, accessLevel),
+		Object:     v,
+		Expiration: 4 * time.Hour, // supposed to be updated by cron every hour
+	}
+	if err := memcache.Gob.Set(c, item); err != nil {
+		return nil, err
+	}
 	return v, nil
 }
+
+func cacheKey(ns string, accessLevel AccessLevel) string {
+	return fmt.Sprintf("%v-%v", ns, accessLevel)
+}