diff --git a/core/lib/Drupal/Core/Lock/PersistentDatabaseLockBackend.php b/core/lib/Drupal/Core/Lock/PersistentDatabaseLockBackend.php
index 514967b..f14f87a 100644
--- a/core/lib/Drupal/Core/Lock/PersistentDatabaseLockBackend.php
+++ b/core/lib/Drupal/Core/Lock/PersistentDatabaseLockBackend.php
@@ -24,11 +24,13 @@ class PersistentDatabaseLockBackend extends DatabaseLockBackend {
    *   The database connection.
    */
   public function __construct(Connection $database) {
-    // This simply overrides the parent constructor, to not have it register
-    // releaseAll() as a shutdown function.
+    // Do not call the parent constructor to avoid registering a shutdown
+    // function that releases all the locks at the end of a request.
     $this->database = $database;
     // Set the lockId to a fixed string to make the lock ID the same across
-    // multiple requests.
+    // multiple requests. The lock ID is use as a page token to relate all the
+    // locks set during a request to each other.
+    // @see \Drupal\Core\Lock\LockBackendInterface::getLockId()
     $this->lockId = 'persistent';
   }
 }