Fix zero-downtime reindexing docs count issue

ee/app/services/elastic/cluster_reindexing_service.rb

@@ -62,7 +62,7 @@ module Elastic
       index_name = elastic_helper.create_empty_index(with_alias: false, options: { settings: INITIAL_INDEX_OPTIONS })
 
       # Record documents count
-      documents_count = elastic_helper.index_size.dig('docs', 'count')
+      documents_count = elastic_helper.documents_count
 
       # Trigger reindex
       task_id = elastic_helper.reindex(to: index_name)
@@ -81,7 +81,7 @@ module Elastic
     def save_documents_count!(refresh:)
       elastic_helper.refresh_index(index_name: current_task.index_name_to) if refresh
 
-      new_documents_count = elastic_helper.index_size(index_name: current_task.index_name_to).dig('docs', 'count')
+      new_documents_count = elastic_helper.documents_count(index_name: current_task.index_name_to)
       current_task.update!(documents_count_target: new_documents_count)
     end
 

ee/changelogs/unreleased/fix-es-reindexing-documents-count.yml

+---
+title: Fix zero-downtime reindexing docs count
+merge_request: 36173
+author:
+type: fixed

ee/lib/gitlab/elastic/helper.rb

@@ -105,6 +105,12 @@ module Gitlab
         client.indices.stats['indices'][index_name || target_index_name]['total']
       end
 
+      def documents_count(index_name: nil)
+        index = index_name || target_index_name
+
+        client.indices.stats.dig('indices', index, 'primaries', 'docs', 'count')
+      end
+
       def index_size_bytes
         index_size['store']['size_in_bytes']
       end

ee/spec/services/elastic/cluster_reindexing_service_spec.rb

@@ -57,7 +57,7 @@ RSpec.describe Elastic::ClusterReindexingService, :elastic do
 
     context 'errors are raised' do
       before do
-        allow(Gitlab::Elastic::Helper.default).to receive(:index_size).and_return('docs' => { 'count' => task.reload.documents_count * 2 })
+        allow(Gitlab::Elastic::Helper.default).to receive(:documents_count).with(index_name: task.index_name_to).and_return(task.reload.documents_count * 2)
       end
 
       it 'errors if documents count is different' do
@@ -75,7 +75,7 @@ RSpec.describe Elastic::ClusterReindexingService, :elastic do
 
     context 'task finishes correctly' do
       before do
-        allow(Gitlab::Elastic::Helper.default).to receive(:index_size).and_return('docs' => { 'count' => task.reload.documents_count })
+        allow(Gitlab::Elastic::Helper.default).to receive(:documents_count).with(index_name: task.index_name_to).and_return(task.reload.documents_count)
       end
 
       it 'launches all state steps' do