This is according to doc_id. If there is a doc with different doc_id but same content, we allow that because he comparison between content is rather hard and time-consuming.
UI: "doc_id" alreay exists. are you sure you want to upload this doc?
corresponding to (1), if YES, it deletes the old one from both ES and database and load the new one. Otherwise abort the mission.
This is according to doc_id. If there is a doc with different doc_id but same content, we allow that because he comparison between content is rather hard and time-consuming.