By default, when performing an import, existing records are updated if they are found in the repository. You can set the update flag to false if you do not want to update existing records as setting this flag to false can increase the speed of the import process if all of the records being imported are new records. For example:

{
   "fileName": "product.json",
    "id" : "Products",
    "mode" : "standalone",
    "format" : "json",
    "params" :{
       "update":"false"
    }
}