2014-05-20 23:34:00 +08:00
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[[mapping-field-names-field]]
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2015-07-20 07:24:29 +08:00
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=== `_field_names` field
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2018-06-04 16:17:11 +08:00
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The `_field_names` field used to index the names of every field in a document that
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contains any value other than `null`. This field was used by the
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2015-12-12 03:07:57 +08:00
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<<query-dsl-exists-query,`exists`>> query to find documents that
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either have or don't have any non-+null+ value for a particular field.
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2015-07-20 07:24:29 +08:00
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2018-06-04 16:17:11 +08:00
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Now the `_field_names` field only indexes the names of fields that have
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`doc_values` and `norms` disabled. For fields which have either `doc_values`
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or `norm` enabled the <<query-dsl-exists-query,`exists`>> query will still
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be available but will not use the `_field_names` field.
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2017-10-06 22:49:15 +08:00
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2019-04-30 22:19:09 +08:00
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[[disable-field-names]]
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2017-10-06 22:49:15 +08:00
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==== Disabling `_field_names`
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2019-09-23 20:13:44 +08:00
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Disabling `_field_names` is no longer possible. It is now enabled by default
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because it no longer carries the index overhead it once did.
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2019-09-11 20:55:30 +08:00
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2019-09-23 20:13:44 +08:00
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NOTE: Support for disabling `_field_names` has been removed. Using it on new
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indices will throw an error. Using it in pre-8.0 indices is still allowed but
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issues a deprecation warning.
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