How does elasticsearch sort the document with the same score?

Question

I am using Elasticsearch6.8 and I get a list of document in the response. Some of the document have the same score but they appear on the same order in the response list consistently. I wonder what the algorithm ES uses to sort the document with the same score?

Answer 1

ES uses the index order when there is a tie when sorting on score.

The index order is defined by the _doc field.