Updating documentation around keyword fields (#5453)

* Updating documentation around keyword fields

Signed-off-by: Harsha Vamsi Kalluri <[email protected]>

* Rewording with additional info

Signed-off-by: Fanit Kolchina <[email protected]>

* Copyedits

Signed-off-by: Fanit Kolchina <[email protected]>

---------

Signed-off-by: Harsha Vamsi Kalluri <[email protected]>
Signed-off-by: Fanit Kolchina <[email protected]>
Signed-off-by: kolchfa-aws <[email protected]>
Co-authored-by: Fanit Kolchina <[email protected]>
Co-authored-by: kolchfa-aws <[email protected]>

_field-types/supported-field-types/keyword.md

@@ -14,20 +14,23 @@ redirect_from:
 
 A keyword field type contains a string that is not analyzed. It allows only exact, case-sensitive matches.
 
+By default, keyword fields are both indexed (because `index` is enabled) and stored on disk (because `doc_values` is enabled). To reduce disk space, you can specify not to index keyword fields by setting `index` to `false`.
+
 If you need to use a field for full-text search, map it as [`text`]({{site.url}}{{site.baseurl}}/opensearch/supported-field-types/text/) instead.
 {: .note }
 
 ## Example
 
-Create a mapping with a keyword field:
+The following query creates a mapping with a keyword field. Setting `index` to `false` specifies to store the `genre` field on disk and to retrieve it using `doc_values`:
 
 ```json
 PUT movies
 {
   "mappings" : {
     "properties" : {
       "genre" : {
-        "type" :  "keyword"
+        "type" :  "keyword",
+        "index" : false
       }
     }
   }
@@ -46,12 +49,13 @@ Parameter | Description
 `eager_global_ordinals` | Specifies whether global ordinals should be loaded eagerly on refresh. If the field is often used for aggregations, this parameter should be set to `true`. Default is `false`.
 `fields` | To index the same string in several ways (for example, as a keyword and text), provide the fields parameter. You can specify one version of the field to be used for search and another to be used for sorting and aggregations.
 `ignore_above` | Any string longer than this integer value should not be indexed. Default is 2147483647. Default dynamic mapping creates a keyword subfield for which `ignore_above` is set to 256.
-`index` | A Boolean value that specifies whether the field should be searchable. Default is `true`.
+`index` | A Boolean value that specifies whether the field should be searchable. Default is `true`. To reduce disk space, set `index` to `false`.
 `index_options` | Information to be stored in the index that will be considered when calculating relevance scores. Can be set to `freqs` for term frequency. Default is `docs`.
 `meta` | Accepts metadata for this field.
 `normalizer` | Specifies how to preprocess this field before indexing (for example, make it lowercase). Default is `null` (no preprocessing).
 `norms` | A Boolean value that specifies whether the field length should be used when calculating relevance scores. Default is `false`.
-[`null_value`]({{site.url}}{{site.baseurl}}/opensearch/supported-field-types/index#null-value) | A  value to be used in place of `null`. Must be of the same type as the field. If this parameter is not specified, the field is treated as missing when its value is `null`. Default is `null`.
+[`null_value`]({{site.url}}{{site.baseurl}}/opensearch/supported-field-types/index#null-value) | A value to be used in place of `null`. Must be of the same type as the field. If this parameter is not specified, the field is treated as missing when its value is `null`. Default is `null`.
 `similarity` | The ranking algorithm for calculating relevance scores. Default is `BM25`. 
 `split_queries_on_whitespace` | A Boolean value that specifies whether full-text queries should be split on white space. Default is `false`.
-`store` | A Boolean value that specifies whether the field value should be stored and can be retrieved separately from the _source field. Default is `false`. 
+`store` | A Boolean value that specifies whether the field value should be stored and can be retrieved separately from the `_source` field. Default is `false`. 
+