Issue #1150072 by catch: Review expires handling.

memcache.inc

@@ -138,11 +138,14 @@ class MemCacheDrupal implements DrupalCacheInterface {
       $cache->expire = $expire;
     }
 
-    // We manually track the expire time in $cache->expire.  When the object
-    // expires, we only allow one request to rebuild it to avoid cache
-    // stampedes. Other requests for the expired object while it is still being
-    // rebuilt get the expired object.
-    dmemcache_set($cid, $cache, 0, $this->bin, $this->memcache);
+    // Manually track the expire time in $cache->expire.  When the object
+    // expires, if stampede protection is enabled, it may be served while one
+    // process rebuilds it. The ttl sent to memcache is set to the expire twice
+    // as long into the future, this allows old items to be expired by memcache
+    // rather than evicted along with a sufficient period for stampede
+    // protection to continue to work.
+    $memcache_expire = $cache->expire + (($cache->expire - REQUEST_TIME) * 2);
+    dmemcache_set($cid, $cache, $memcache_expire, $this->bin, $this->memcache);
   }
 
   function clear($cid = NULL, $wildcard = FALSE) {