add a note to update guide about re-creating ES index

doc/update/9.2-to-9.3.md

@@ -264,6 +264,22 @@ sudo -u git -H bundle exec rake gitlab:check RAILS_ENV=production
 
 If all items are green, then congratulations, the upgrade is complete!
 
+### 13. Elasticsearch index update (if you currently use Elasticsearch)
+
+In 9.3 release we changed the index mapping to improve partial word matching. Please re-create your index by using one of two ways listed below:
+
+1. Re-create the index. The following command is acceptable for not very big GitLab instances (storage size no more than few gigabytes).
+
+    ```
+    # Omnibus installations
+    sudo gitlab-rake gitlab:elastic:index
+
+    # Installations from source
+    bundle exec rake gitlab:elastic:index
+    ```
+
+1. For very big GitLab instances we recommend following [Add GitLab's data to the Elasticsearch index](../integration/elasticsearch.md#add-gitlabs-data-to-the-elasticsearch-index).
+
 ## Things went south? Revert to previous version (9.2)
 
 ### 1. Revert the code to the previous version

spec/lib/gitlab/elastic/search_results_spec.rb

@@ -379,7 +379,7 @@ describe Gitlab::Elastic::SearchResults, lib: true do
       blobs = results.objects('blobs')
 
       expect(blobs.first['_source']['blob']['content']).to include('def')
-      expect(results.blobs_count).to eq 5
+      expect(results.blobs_count).to eq 7
     end
 
     it 'finds blobs from public projects only' do
@@ -388,10 +388,11 @@ describe Gitlab::Elastic::SearchResults, lib: true do
       Gitlab::Elastic::Helper.refresh_index
 
       results = described_class.new(user, 'def', [project_1.id])
-      expect(results.blobs_count).to eq 5
+      expect(results.blobs_count).to eq 7
 
       results = described_class.new(user, 'def', [project_1.id, project_2.id])
-      expect(results.blobs_count).to eq 10
+
+      expect(results.blobs_count).to eq 14
     end
 
     it 'returns zero when blobs are not found' do