DOC Changelog CMS search with elemental

en/04_Changelogs/5.1.0.md

@@ -9,6 +9,7 @@ title: 5.1.0 (unreleased)
 - [Features and enhancements](#features-and-enhancements)
   - [Eager loading](#eager-loading)
   - [GraphQL schema can be stored in `silverstripe-cache`](#gql-schema-is-cache)
+  - [Improvement to page search performance with Elemental](#cms-search-performance)
   - [Other new features](#other-features)
 - [API changes](#api-changes)
 - [Dependency changes](#dependency-changes)
@@ -48,6 +49,25 @@ Note that even if you store the schema in the cache directory, the schema still
 
 See [choosing where the cache is stored](/developer_guides/graphql/getting_started/building_the_schema/#cache-location) for more information about configuring the schema storage directory.
 
+### Improvement to page search performance with Elemental {#cms-search-performance}
+
+- The CMS search has been optimised to reduce the number of database queries made when searching for pages with elemental content blocks. This has resulted in a small performance improvement. In our test environment, with 1,000 pages each with 5 content blocks we observed a 9% performance improvement. Performance will vary with your environment.
+- A new opt-in behaviour is available that makes a very large difference to performance when using elemental content blocks. In testing, this behaviour more than halved the response time of the sitetree search request. The opt-in feature disables the default behaviour of rendering all content blocks for CMS search. Instead, it simply extracts the database contents of the elements from its text and html fields. There is a downside to consider which is that any related content not directly on the element will not be matched against the search query. Note this does not use the `$searchable_fields` config. To opt-in to this behaviour, use the following config:
+
+```yml
+DNADesign\Elemental\Controllers\ElementSiteTreeFilterSearch:
+  render_elements: false
+```
+
+If `render_elements` is set to `false` then individual fields on elements can be excluded from search by adding them to a config array:
+
+```yml
+App\MyElement:
+  fields_excluded_from_cms_search:
+    - MyFieldToExclude
+    - AnotherFieldToExclude
+```
+
 ### Other new features
 
 - You can now exclude specific `DataObject` models from the check and repair step of `dev/build` - see [ORM Performance](/developer_guides/performance/orm/#skip-check-and-repair) for more information.