_id field

Each document has an _id that uniquely identifies it, which is indexed so that documents can be looked up either with the GET API or the ids query.

The value of the _id field is accessible in certain queries (term, terms, match, query_string, simple_query_string).

  1. # Example documents
  2. PUT my-index-000001/_doc/1
  3. {
  4.   "text": "Document with ID 1"
  5. }
  7. PUT my-index-000001/_doc/2?refresh=true
  8. {
  9.   "text": "Document with ID 2"
  10. }
  12. GET my-index-000001/_search
  13. {
  14.   "query": {
  15.     "terms": {
  16.       "_id": [ "1", "2" ] 
  17.     }
  18.   }
  19. }

Querying on the _id field (also see the ids query)

The value of the _id field is also accessible in aggregations or for sorting, but doing so is discouraged as it requires to load a lot of data in memory. In case sorting or aggregating on the _id field is required, it is advised to duplicate the content of the _id field in another field that has doc_values enabled.

_id is limited to 512 bytes in size and larger values will be rejected.