ES Reindex should restore current refresh_interval setting

ee/app/services/elastic/cluster_reindexing_service.rb

@@ -35,9 +35,9 @@ module Elastic
       [elastic_helper.target_name] + elastic_helper.standalone_indices_proxies.map(&:index_name)
     end
 
-    def default_index_options
+    def default_index_options(index_name)
       {
-        refresh_interval: nil, # Change it back to the default
+        refresh_interval: elastic_helper.get_settings(index_name: index_name).dig('refresh_interval'), # Use existing setting or nil for default
         number_of_replicas: Gitlab::CurrentSettings.elasticsearch_replicas,
         translog: { durability: 'request' }
       }
@@ -142,7 +142,7 @@ module Elastic
 
     def apply_default_index_options
       current_task.subtasks.each do |subtask|
-        elastic_helper.update_settings(index_name: subtask.index_name_to, settings: default_index_options)
+        elastic_helper.update_settings(index_name: subtask.index_name_to, settings: default_index_options(subtask.index_name_from))
       end
     end
 

ee/changelogs/unreleased/249123-elasticsearch-reindexing-should-restore-the-original-refresh_in.yml

+---
+title: Restore refresh_interval from settings after reindex
+merge_request: 51147
+author:
+type: changed

ee/spec/services/elastic/cluster_reindexing_service_spec.rb

@@ -69,9 +69,10 @@ RSpec.describe Elastic::ClusterReindexingService, :elastic do
   context 'state: reindexing' do
     let(:task) { create(:elastic_reindexing_task, state: :reindexing) }
     let(:subtask) { create(:elastic_reindexing_subtask, elastic_reindexing_task: task, documents_count: 10)}
+    let(:refresh_interval) { nil }
     let(:expected_default_settings) do
       {
-        refresh_interval: nil,
+        refresh_interval: refresh_interval,
         number_of_replicas: Gitlab::CurrentSettings.elasticsearch_replicas,
         translog: { durability: 'request' }
       }
@@ -108,17 +109,27 @@ RSpec.describe Elastic::ClusterReindexingService, :elastic do
     end
 
     context 'task finishes correctly' do
-      before do
-        allow(helper).to receive(:documents_count).with(index_name: subtask.index_name_to).and_return(subtask.reload.documents_count)
+      using RSpec::Parameterized::TableSyntax
+
+      where(:refresh_interval, :current_settings) do
+        nil | {}
+        '60s' | { refresh_interval: '60s' }
       end
 
-      it 'launches all state steps' do
-        expect(helper).to receive(:update_settings).with(index_name: subtask.index_name_to, settings: expected_default_settings)
-        expect(helper).to receive(:switch_alias).with(to: subtask.index_name_to, from: subtask.index_name_from, alias_name: subtask.alias_name)
-        expect(Gitlab::CurrentSettings).to receive(:update!).with(elasticsearch_pause_indexing: false)
+      with_them do
+        before do
+          allow(helper).to receive(:documents_count).with(index_name: subtask.index_name_to).and_return(subtask.reload.documents_count)
+          allow(helper).to receive(:get_settings).with(index_name: subtask.index_name_from).and_return(current_settings.with_indifferent_access)
+        end
+
+        it 'launches all state steps' do
+          expect(helper).to receive(:update_settings).with(index_name: subtask.index_name_to, settings: expected_default_settings)
+          expect(helper).to receive(:switch_alias).with(to: subtask.index_name_to, from: subtask.index_name_from, alias_name: subtask.alias_name)
+          expect(Gitlab::CurrentSettings).to receive(:update!).with(elasticsearch_pause_indexing: false)
 
-        expect { subject.execute }.to change { task.reload.state }.from('reindexing').to('success')
-        expect(task.reload.delete_original_index_at).to be_within(1.minute).of(described_class::DELETE_ORIGINAL_INDEX_AFTER.from_now)
+          expect { subject.execute }.to change { task.reload.state }.from('reindexing').to('success')
+          expect(task.reload.delete_original_index_at).to be_within(1.minute).of(described_class::DELETE_ORIGINAL_INDEX_AFTER.from_now)
+        end
       end
     end
   end