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

Edit: Please also read the answer from Aleck Landgraf

You just want the elasticsearch-internal _id field? Or an id field from within your documents?

For the former, try

curl http://localhost:9200/index/type/_search?pretty=true -d '
{ 
    "query" : { 
        "match_all" : {} 
    },
    "stored_fields": []
}
'

If you are using Elastic dev tools, use this instead:

GET <your-index-name>/_search
{ 
    "query" : { 
        "match_all" : {} 
    },
    "stored_fields": []
}

Note 2017 Update: The post originally included "fields": [] but since then the name has changed and stored_fields is the new value.

The result will contain only the "metadata" of your documents

{
  "took" : 7,
  "timed_out" : false,
  "_shards" : {
    "total" : 5,
    "successful" : 5,
    "failed" : 0
  },
  "hits" : {
    "total" : 4,
    "max_score" : 1.0,
    "hits" : [ {
      "_index" : "index",
      "_type" : "type",
      "_id" : "36",
      "_score" : 1.0
    }, {
      "_index" : "index",
      "_type" : "type",
      "_id" : "38",
      "_score" : 1.0
    }, {
      "_index" : "index",
      "_type" : "type",
      "_id" : "39",
      "_score" : 1.0
    }, {
      "_index" : "index",
      "_type" : "type",
      "_id" : "34",
      "_score" : 1.0
    } ]
  }
}

For the latter, if you want to include a field from your document, simply add it to the fields array

curl http://localhost:9200/index/type/_search?pretty=true -d '
{ 
    "query" : { 
        "match_all" : {} 
    },
    "fields": ["document_field_to_be_returned"]
}
'