Issue #3334489 by catch, Berdir, longwave, andypost: ChainedFastBackend...

Issue #3334489 by catch, Berdir, longwave, andypost: ChainedFastBackend invalidates all items when cache tags are invalidated

core/lib/Drupal/Core/Cache/ChainedFastBackend.php

@@ -12,7 +12,9 @@
  * item. The fast backend will also typically be inconsistent (will only see
  * changes from one web node). The slower backend will be something like Mysql,
  * Memcached or Redis, and will be used by all web nodes, thus making it
- * consistent, but also require a network round trip for each cache get.
+ * consistent, but also require a network round trip for each cache get. The
+ * fast backend must however also use a consistent cache tag invalidation, for
+ * example by using the cache tag checksum API.
  *
  * In addition to being useful for sites running on multiple web nodes, this
  * backend can also be useful for sites running on a single web node where the
@@ -164,9 +166,7 @@ public function getMultiple(&$cids, $allow_invalid = FALSE) {
     if ($cids) {
       foreach ($this->consistentBackend->getMultiple($cids, $allow_invalid) as $item) {
         $cache[$item->cid] = $item;
-        // Don't write the cache tags to the fast backend as any cache tag
-        // invalidation results in an invalidation of the whole fast backend.
-        $this->fastBackend->set($item->cid, $item->data, $item->expire);
+        $this->fastBackend->set($item->cid, $item->data, $item->expire, $item->tags);
       }
     }
 
@@ -179,9 +179,7 @@ public function getMultiple(&$cids, $allow_invalid = FALSE) {
   public function set($cid, $data, $expire = Cache::PERMANENT, array $tags = []) {
     $this->consistentBackend->set($cid, $data, $expire, $tags);
     $this->markAsOutdated();
-    // Don't write the cache tags to the fast backend as any cache tag
-    // invalidation results in an invalidation of the whole fast backend.
-    $this->fastBackend->set($cid, $data, $expire);
+    $this->fastBackend->set($cid, $data, $expire, $tags);
   }
 
   /**
@@ -190,11 +188,6 @@ public function set($cid, $data, $expire = Cache::PERMANENT, array $tags = []) {
   public function setMultiple(array $items) {
     $this->consistentBackend->setMultiple($items);
     $this->markAsOutdated();
-    // Don't write the cache tags to the fast backend as any cache tag
-    // invalidation results in an invalidation of the whole fast backend.
-    foreach ($items as &$item) {
-      unset($item['tags']);
-    }
     $this->fastBackend->setMultiple($items);
   }
 
@@ -244,7 +237,9 @@ public function invalidateTags(array $tags) {
     if ($this->consistentBackend instanceof CacheTagsInvalidatorInterface) {
       $this->consistentBackend->invalidateTags($tags);
     }
-    $this->markAsOutdated();
+    if ($this->fastBackend instanceof CacheTagsInvalidatorInterface) {
+      $this->fastBackend->invalidateTags($tags);
+    }
   }
 
   /**