OpenSearch/docs/reference/mapping/fields/field-names-field.asciidoc

[[mapping-field-names-field]]
=== `_field_names`

added[1.3.0]

The `_field_names` field indexes the field names of a document, which can later
be used to search for documents based on the fields that they contain typically
using the `exists` and `missing` filters.

`_field_names` is indexed by default for indices that have been created after
Elasticsearch 1.3.0.
Index field names of documents. The `exists` and `missing` filters need to merge postings lists of all existing terms, which can be very costly, especially on high-cardinality fields. This commit indexes the field names of a document under `_field_names` and reuses it to speed up the `exists` and `missing` filters. This is only enabled for indices that are created on or after Elasticsearch 1.3.0. Close #5659 2014-05-20 17:34:00 +02:00			`[[mapping-field-names-field]]`
			=== `_field_names`

[DOCS] move all coming tags to added in master 2014-07-23 16:36:53 +02:00			`added[1.3.0]`
Index field names of documents. The `exists` and `missing` filters need to merge postings lists of all existing terms, which can be very costly, especially on high-cardinality fields. This commit indexes the field names of a document under `_field_names` and reuses it to speed up the `exists` and `missing` filters. This is only enabled for indices that are created on or after Elasticsearch 1.3.0. Close #5659 2014-05-20 17:34:00 +02:00
			The `_field_names` field indexes the field names of a document, which can later
			`be used to search for documents based on the fields that they contain typically`
			using the `exists` and `missing` filters.

			`_field_names` is indexed by default for indices that have been created after
			`Elasticsearch 1.3.0.`