Efficient way to retrieve all _ids in ElasticSearch

Question

What is the fastest way to get all _ids of a certain index from ElasticSearch? Is it possible by using a simple query? One of my index has around 20,000 documents.

Answer 1

Inspired by @Aleck-Landgraf answer, for me it worked by using directly scan function in standard elasticsearch python API:

from elasticsearch import Elasticsearch
from elasticsearch.helpers import scan
es = Elasticsearch()
for dobj in scan(es, 
                 query={"query": {"match_all": {}}, "fields" : []},  
                 index="your-index-name", doc_type="your-doc-type"): 
        print dobj["_id"],