Eliminate unnecessary and duplicate system hook fires

Previously `SystemHookPushWorker` would always be called after a push event,
and this would queue a Sidekiq job regardless of whether any system hooks
needed that event. Moreover, another call inside `Project#execute_hooks` would
also fire system hooks if they existed.

This change both removes the duplicate system hook calls. For installations
without system hooks for push events, this change also can save significant
amount of RAM used by Redis.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/50549

3 files changed, 12 insertions, 4 deletions

diff --git a/app/services/git_push_service.rb b/app/services/git_push_service.rb
index 637c1df4ad9..156b4b3c6ec 100644
--- a/app/services/git_push_service.rb
+++ b/app/services/git_push_service.rb
@@ -140,7 +140,6 @@ class GitPushService < BaseService
     EventCreateService.new.push(project, current_user, build_push_data)
     Ci::CreatePipelineService.new(project, current_user, build_push_data).execute(:push)
 
-    SystemHookPushWorker.perform_async(build_push_data.dup, :push_hooks)
     project.execute_hooks(build_push_data.dup, :push_hooks)
     project.execute_services(build_push_data.dup, :push_hooks)
 
diff --git a/changelogs/unreleased/sh-conditional-system-hook-push.yml b/changelogs/unreleased/sh-conditional-system-hook-push.yml
new file mode 100644
index 00000000000..3a1a1b3d36c
--- /dev/null
+++ b/changelogs/unreleased/sh-conditional-system-hook-push.yml
@@ -0,0 +1,5 @@
+---
+title: Eliminate unnecessary and duplicate system hook fires
+merge_request: 21337
+author:
+type: performance
diff --git a/spec/services/git_push_service_spec.rb b/spec/services/git_push_service_spec.rb
index a3c9a660c2f..ed0088a9500 100644
--- a/spec/services/git_push_service_spec.rb
+++ b/spec/services/git_push_service_spec.rb
@@ -223,9 +223,13 @@ describe GitPushService, services: true do
       end
     end
 
-    context "Sends System Push data" do
-      it "when pushing on a branch" do
-        expect(SystemHookPushWorker).to receive(:perform_async).with(push_data, :push_hooks)
+    describe 'system hooks' do
+      let(:system_hook_service) { double() }
+
+      it "sends a system hook after pushing a branch" do
+        expect(SystemHooksService).to receive(:new).and_return(system_hook_service)
+        expect(system_hook_service).to receive(:execute_hooks).with(push_data, :push_hooks)
+
         execute_service(project, user, oldrev, newrev, ref)
       end
     end