[[mapping-field-names-field]] === `_field_names` field The `_field_names` field used to index the names of every field in a document that contains any value other than `null`. This field was used by the <<query-dsl-exists-query,`exists`>> query to find documents that either have or don't have any non-+null+ value for a particular field. Now the `_field_names` field only indexes the names of fields that have `doc_values` and `norms` disabled. For fields which have either `doc_values` or `norm` enabled the <<query-dsl-exists-query,`exists`>> query will still be available but will not use the `_field_names` field. [[disable-field-names]] ==== Disabling `_field_names` Disabling `_field_names` is often not necessary because it no longer carries the index overhead it once did. If you have a lot of fields which have `doc_values` and `norms` disabled and you do not need to execute `exists` queries using those fields you might want to disable `_field_names` be adding the following to the mappings: [source,js] -------------------------------------------------- PUT tweets { "mappings": { "_field_names": { "enabled": false } } } -------------------------------------------------- // CONSOLE