Issue #2392235 by Berdir: ChainedFastBackend shouldn't write cache tags to the fast cache back-end

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

@@ -160,7 +160,9 @@ class ChainedFastBackend implements CacheBackendInterface {
     if ($cids) {
       foreach ($this->consistentBackend->getMultiple($cids, $allow_invalid) as $item) {
         $cache[$item->cid] = $item;
-        $this->fastBackend->set($item->cid, $item->data, $item->expire, $item->tags);
+        // 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);
       }
     }
 
@@ -173,7 +175,9 @@ class ChainedFastBackend implements CacheBackendInterface {
   public function set($cid, $data, $expire = Cache::PERMANENT, array $tags = array()) {
     $this->consistentBackend->set($cid, $data, $expire, $tags);
     $this->markAsOutdated();
-    $this->fastBackend->set($cid, $data, $expire, $tags);
+    // 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);
   }
 
   /**
@@ -182,6 +186,11 @@ class ChainedFastBackend implements CacheBackendInterface {
   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);
   }
 

core/modules/system/src/Tests/Cache/GenericCacheBackendUnitTestBase.php

@@ -411,7 +411,6 @@ abstract class GenericCacheBackendUnitTestBase extends KernelTestBase {
     $this->assertEqual($cached['cid_4']->expire, $future_expiration, 'Cache expiration has been correctly set.');
 
     $this->assertEqual($cached['cid_5']->data, $items['cid_5']['data'], 'New cache item set correctly.');
-    $this->assertEqual($cached['cid_5']->tags, array('test:a', 'test:b'));
 
     // Calling ::setMultiple() with invalid cache tags.
     try {

core/tests/Drupal/Tests/Core/Cache/ChainedFastBackendTest.php

@@ -103,7 +103,7 @@ class ChainedFastBackendTest extends UnitTestCase {
     // We should get a call to set the cache item on the fast backend.
     $fast_cache->expects($this->once())
       ->method('set')
-      ->with($cache_item->cid, $cache_item->data, $cache_item->expire, $cache_item->tags);
+      ->with($cache_item->cid, $cache_item->data, $cache_item->expire);
 
     $chained_fast_backend = new ChainedFastBackend(
       $consistent_cache,