diff --git a/core/lib/Drupal/Core/Cache/DatabaseBackend.php b/core/lib/Drupal/Core/Cache/DatabaseBackend.php
index 48018b1..81e83bb 100644
--- a/core/lib/Drupal/Core/Cache/DatabaseBackend.php
+++ b/core/lib/Drupal/Core/Cache/DatabaseBackend.php
@@ -235,7 +235,9 @@ public function setMultiple(array $items) {
     }
 
     // Use a transaction so that the database can write the changes in a single
-    // commit.
+    // commit. The transaction is started after calculating the tag checksums
+    // since that can create a table and this causes an exception when using
+    // PostgreSQL.
     $transaction = $this->connection->startTransaction();
 
     try {
@@ -247,8 +249,9 @@ public function setMultiple(array $items) {
         ->insert($this->bin)
         ->fields(array('cid', 'expire', 'created', 'tags', 'checksum', 'data', 'serialized'));
       foreach ($values as $fields) {
-        // Only pass the values to values since the order of $fields matches the
-        // order of the insert fields.
+        // Only pass the values since the order of $fields matches the order of
+        // the insert fields. This is a performance optimization to avoid
+        // unnecessary loops within the method.
         $query->values(array_values($fields));
       }