Stop $this-validColumnNames array from growing and growing as its value is recursively updated with its own data several times. Importing hundred of customers affect performance and even break due to memory limits

Author: jalogut

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

@@ -569,11 +569,11 @@ public function getEntityTable()
      */
     public function getValidColumnNames()
     {
-        $this->validColumnNames = array_merge(
-            $this->validColumnNames,
-            $this->customerFields
+        return array_unique(
+            array_merge(
+                $this->validColumnNames,
+                $this->customerFields
+            )
         );
-
-        return $this->validColumnNames;
     }
 }

app/code/Magento/CustomerImportExport/Model/Import/CustomerComposite.php

@@ -488,13 +488,13 @@ protected function _prepareRowForDb(array $rowData)
      */
     public function getValidColumnNames()
     {
-        $this->validColumnNames = array_merge(
-            $this->validColumnNames,
-            $this->_customerAttributes,
-            $this->_addressAttributes,
-            $this->_customerEntity->getValidColumnNames()
+        return array_unique(
+            array_merge(
+                $this->validColumnNames,
+                $this->_customerAttributes,
+                $this->_addressAttributes,
+                $this->_customerEntity->getValidColumnNames()
+            )
         );
-
-        return $this->validColumnNames;
     }
 }