the process of xadmin export plugin is as display all items online:
st=>start: initial request
op_checkall=>operation: check if export all
op_get_result_list=>operation: get result list
op_get_item=>operation: get each item for list
e=>end: generate file
st->op_checkall->op_get_result_list->op_get_item->e
Get item takes most of time to process. Therefore in order to optimize export process, we need to item override result_item in export.py or use import export app to write our own method