MC-31089: [Escalation] [SAQ] - Customer migration is too slow

Author: dhorytskyi

app/code/Magento/CustomerImportExport/Model/ResourceModel/Import/Address/Storage.php

@@ -142,13 +142,7 @@ public function prepareAddresses(array $forCustomersIds): void
         }
 
         $forCustomersIds = array_unique($forCustomersIds);
-        $customerIdsToUse = [];
-        foreach ($forCustomersIds as $customerId) {
-            if (!array_key_exists($customerId, $this->addresses)) {
-                $customerIdsToUse[] = (int) $customerId;
-            }
-        }
-
+        $customerIdsToUse = array_diff($forCustomersIds, array_keys($this->addresses));
         $this->loadAddresses($customerIdsToUse);
     }
 }

app/code/Magento/CustomerImportExport/Model/ResourceModel/Import/Customer/Storage.php

@@ -179,6 +179,18 @@ public function getCustomerId(string $email, int $websiteId)
         return false;
     }
 
+    /**
+     * Get previously loaded customer id.
+     *
+     * @param string $email
+     * @param int $websiteId
+     * @return int|null
+     */
+    public function getLoadedCustomerId(string $email, int $websiteId): ?int
+    {
+        return $this->_customerIds[mb_strtolower($email)][$websiteId] ?? null;
+    }
+
     /**
      * Find customer store ID for unique pair of email and website ID.
      *