[[doc-values]]
=== `doc_values`

Most fields are <<mapping-index,indexed>> by default, which makes them
searchable. The inverted index allows queries to look up the search term in
unique sorted list of terms, and from that immediately have access to the list
of documents that contain the term.

Sorting, aggregations, and access to field values in scripts requires a
different data access pattern. Instead of looking up the term and finding
documents, we need to be able to look up the document and find the terms that
it has in a field.

Doc values are the on-disk data structure, built at document index time, which
makes this data access pattern possible. They store the same values as the
`_source` but in a column-oriented fashion that is way more efficient for
sorting and aggregations. Doc values are supported on almost all field types,
with the __notable exception of `text` and `annotated_text` fields__.

[[doc-value-only-fields]]
==== Doc-value-only fields

<<number,Numeric types>>, <<date,date types>>, the <<boolean,boolean type>>,
<<ip,ip type>>, <<geo-point,geo_point type>> and the <<keyword,keyword type>>
can also be queried when they are not <<mapping-index,indexed>> but only
have doc values enabled.
Query performance on doc values is much slower than on index structures, but
offers an interesting tradeoff between disk usage and query performance for
fields that are only rarely queried and where query performance is not as
important. This makes doc-value-only fields a good fit for fields that are
not expected to be normally used for filtering, for example gauges or
counters on metric data.

Doc-value-only fields can be configured as follows:

[source,console]
--------------------------------------------------
PUT my-index-000001
{
  "mappings": {
    "properties": {
      "status_code": { <1>
        "type":  "long"
      },
      "session_id": { <2>
        "type":  "long",
        "index": false
      }
    }
  }
}
--------------------------------------------------

<1> The `status_code` field is a regular long field.
<2> The `session_id` field has `index` disabled, and is therefore a
    doc-value-only long field as doc values are enabled by default.

==== Disabling doc values

All fields which support doc values have them enabled by default. If you are
sure that you don't need to sort or aggregate on a field, or access the field
value from a script, you can disable doc values in order to save disk space:

[source,console]
--------------------------------------------------
PUT my-index-000001
{
  "mappings": {
    "properties": {
      "status_code": { <1>
        "type":       "keyword"
      },
      "session_id": { <2>
        "type":       "keyword",
        "doc_values": false
      }
    }
  }
}
--------------------------------------------------

<1> The `status_code` field has `doc_values` enabled by default.
<2> The `session_id` has `doc_values` disabled, but can still be queried.

NOTE: You cannot disable doc values for <<wildcard-field-type,`wildcard`>>
fields.
