Reduce Gitaly calls in PostReceive

This commit reduces I/O load and memory utilization during PostReceive
for the common case when no project hooks or services are set up.

We saw a Gitaly N+1 issue in `CommitDelta` when many tags or branches
are pushed. We can reduce this overhead in the common case because we
observe that most new projects do not have any Web hooks or services,
especially when they are first created. Previously, `BaseHooksService`
unconditionally iterated through the last 20 commits of each ref to
build the `push_data` structure. The `push_data` structured was used in
numerous places:

1. Building the push payload in `EventCreateService`
2. Creating a CI pipeline
3. Executing project Web or system hooks
4. Executing project services
5. As the return value of `BaseHooksService#execute`
6. `BranchHooksService#invalidated_file_types`

We only need to generate the full `push_data` for items 3, 4, and 6.

Item 1: `EventCreateService` only needs the last commit and doesn't
actually need the commit deltas.

Item 2: In addition, `Ci::CreatePipelineService` only needed a subset of
the parameters.

Item 5: The return value of `BaseHooksService#execute` also wasn't being
used anywhere.

Item 6: This is only used when pushing to the default branch, so if
many tags are pushed we can save significant I/O here.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/65878

Fic

1 files changed, 72 insertions, 0 deletions

diff --git a/spec/services/git/base_hooks_service_spec.rb b/spec/services/git/base_hooks_service_spec.rb
index 4a2ec769116..874df9a68cd 100644
--- a/spec/services/git/base_hooks_service_spec.rb
+++ b/spec/services/git/base_hooks_service_spec.rb
@@ -14,6 +14,78 @@ describe Git::BaseHooksService do
   let(:newrev) { "8a2a6eb295bb170b34c24c76c49ed0e9b2eaf34b" } # gitlab-test: git rev-parse refs/tags/v1.1.0
   let(:ref) { 'refs/tags/v1.1.0' }
 
+  describe '#execute_project_hooks' do
+    class TestService < described_class
+      def hook_name
+        :push_hooks
+      end
+
+      def commits
+        []
+      end
+    end
+
+    let(:project) { create(:project, :repository) }
+
+    subject { TestService.new(project, user, oldrev: oldrev, newrev: newrev, ref: ref) }
+
+    context '#execute_hooks' do
+      before do
+        expect(project).to receive(:has_active_hooks?).and_return(active)
+      end
+
+      context 'active hooks' do
+        let(:active) { true }
+
+        it 'executes the hooks' do
+          expect(subject).to receive(:push_data).at_least(:once).and_call_original
+          expect(project).to receive(:execute_hooks)
+
+          subject.execute
+        end
+      end
+
+      context 'inactive hooks' do
+        let(:active) { false }
+
+        it 'does not execute the hooks' do
+          expect(subject).not_to receive(:push_data)
+          expect(project).not_to receive(:execute_hooks)
+
+          subject.execute
+        end
+      end
+    end
+
+    context '#execute_services' do
+      before do
+        expect(project).to receive(:has_active_services?).and_return(active)
+      end
+
+      context 'active services' do
+        let(:active) { true }
+
+        it 'executes the services' do
+          expect(subject).to receive(:push_data).at_least(:once).and_call_original
+          expect(project).to receive(:execute_services)
+
+          subject.execute
+        end
+      end
+
+      context 'inactive services' do
+        let(:active) { false }
+
+        it 'does not execute the services' do
+          expect(subject).not_to receive(:push_data)
+          expect(project).not_to receive(:execute_services)
+
+          subject.execute
+        end
+      end
+    end
+  end
+
   describe 'with remote mirrors' do
     class TestService < described_class
       def commits