MC-34522: Two near-simultaneous product imports interfere with each other

- Change default value of user_id column to NULL for backward compatibility

Author: bubasuma

app/code/Magento/ImportExport/Model/ResourceModel/Import/Data.php

@@ -200,7 +200,8 @@ public function saveBunch($entity, $behavior, array $data)
      */
     private function prepareSelect(Select $select): Select
     {
-        $select->where('user_id=?', $this->getCurrentUserId() ?? self::DEFAULT_USER_ID);
+        // user_id is NULL part is for backward compatibility
+        $select->where('user_id=? OR user_id is NULL', $this->getCurrentUserId() ?? self::DEFAULT_USER_ID);
 
         return $select;
     }
@@ -226,7 +227,8 @@ private function prepareInsert(array $data): array
      */
     private function prepareDelete(array $where): array
     {
-        $where['user_id=?'] = $this->getCurrentUserId() ?? self::DEFAULT_USER_ID;
+        // user_id is NULL part is for backward compatibility
+        $where['user_id=? OR user_id is NULL'] = $this->getCurrentUserId() ?? self::DEFAULT_USER_ID;
 
         return $where;
     }

app/code/Magento/ImportExport/etc/db_schema.xml

@@ -12,8 +12,7 @@
         <column xsi:type="varchar" name="entity" nullable="false" length="50" comment="Entity"/>
         <column xsi:type="varchar" name="behavior" nullable="false" length="10" default="append" comment="Behavior"/>
         <column xsi:type="longtext" name="data" nullable="true" comment="Data"/>
-        <column xsi:type="int" name="user_id" unsigned="true" nullable="false" identity="false" default="0"
-                comment="User ID"/>
+        <column xsi:type="int" name="user_id" unsigned="true" nullable="true" identity="false" comment="User ID"/>
         <constraint xsi:type="primary" referenceId="PRIMARY">
             <column name="id"/>
         </constraint>