viewfeed: rate limit ccache_update

backend.php

@@ -273,8 +273,11 @@
 			/* Updating a label ccache means recalculating all of the caches
 			 * so for performance reasons we don't do that here */
 
-			if ($feed >= 0) {
+			if (time() - $_SESSION["viewfeed:ccache_update_stamp"] > 120) {
-				ccache_update($link, $feed, $_SESSION["uid"], $cat_view);
+				if ($feed >= 0) {
+					ccache_update($link, $feed, $_SESSION["uid"], $cat_view);
+				}
+				$_SESSION["viewfeed:ccache_update_stamp"] = time();
 			}
 
 			set_pref($link, "_DEFAULT_VIEW_MODE", $view_mode);