4 files changed, 18 insertions, 8 deletions
diff --git a/app/services/merge_requests/close_service.rb b/app/services/merge_requests/close_service.rb
index c0ce01f7523..40213c99014 100644
--- a/app/services/merge_requests/close_service.rb
+++ b/app/services/merge_requests/close_service.rb
@@ -14,6 +14,7 @@ module MergeRequests
         todo_service.close_merge_request(merge_request, current_user)
         execute_hooks(merge_request, 'close')
         invalidate_cache_counts(merge_request, users: merge_request.assignees)
+        merge_request.update_project_counter_caches
       end
 
       merge_request
diff --git a/app/services/merge_requests/create_service.rb b/app/services/merge_requests/create_service.rb
index 3d53fe0646b..820709583fa 100644
--- a/app/services/merge_requests/create_service.rb
+++ b/app/services/merge_requests/create_service.rb
@@ -13,7 +13,10 @@ module MergeRequests
       merge_request.source_branch = params[:source_branch]
       merge_request.merge_params['force_remove_source_branch'] = params.delete(:force_remove_source_branch)
 
-      create(merge_request)
+      # n+1: https://gitlab.com/gitlab-org/gitlab-ce/issues/37439
+      Gitlab::GitalyClient.allow_n_plus_1_calls do
+        create(merge_request)
+      end
     end
 
     def before_create(merge_request)
diff --git a/app/services/merge_requests/merge_service.rb b/app/services/merge_requests/merge_service.rb
index 07cbd8f92a9..bf26859dd6d 100644
--- a/app/services/merge_requests/merge_service.rb
+++ b/app/services/merge_requests/merge_service.rb
@@ -14,13 +14,13 @@ module MergeRequests
       @merge_request = merge_request
 
       unless @merge_request.mergeable?
-        return log_merge_error('Merge request is not mergeable', save_message_on_model: true)
+        return handle_merge_error(log_message: 'Merge request is not mergeable', save_message_on_model: true)
       end
 
       @source = find_merge_source
 
       unless @source
-        return log_merge_error('No source for merge', save_message_on_model: true)
+        return handle_merge_error(log_message: 'No source for merge', save_message_on_model: true)
       end
 
       merge_request.in_locked_state do
@@ -31,8 +31,7 @@ module MergeRequests
         end
       end
     rescue MergeError => e
-      clean_merge_jid
-      log_merge_error(e.message, save_message_on_model: true)
+      handle_merge_error(log_message: e.message, save_message_on_model: true)
     end
 
     private
@@ -74,10 +73,16 @@ module MergeRequests
       @merge_request.force_remove_source_branch? ? @merge_request.author : current_user
     end
 
-    def log_merge_error(message, save_message_on_model: false)
-      Rails.logger.error("MergeService ERROR: #{merge_request_info} - #{message}")
+    # Logs merge error message and cleans `MergeRequest#merge_jid`.
+    #
+    def handle_merge_error(log_message:, save_message_on_model: false)
+      Rails.logger.error("MergeService ERROR: #{merge_request_info} - #{log_message}")
 
-      @merge_request.update(merge_error: message) if save_message_on_model
+      if save_message_on_model
+        @merge_request.update(merge_error: log_message, merge_jid: nil)
+      else
+        clean_merge_jid
+      end
     end
 
     def merge_request_info
diff --git a/app/services/merge_requests/post_merge_service.rb b/app/services/merge_requests/post_merge_service.rb
index 261a8bfa200..b1d6bac4d4a 100644
--- a/app/services/merge_requests/post_merge_service.rb
+++ b/app/services/merge_requests/post_merge_service.rb
@@ -14,6 +14,7 @@ module MergeRequests
       notification_service.merge_mr(merge_request, current_user)
       execute_hooks(merge_request, 'merge')
       invalidate_cache_counts(merge_request, users: merge_request.assignees)
+      merge_request.update_project_counter_caches
     end
 
     private