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 disables the default behaviour of rendering all content blocks for CMS search. Instead, it simply extracts the database contents of the elements. 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.