Remove need to call gitaly in ProjectPipelineStatus

Calling commit (gitaly) is un-nessary just to obtain the sha, for the
cache key. In fact, the cache key does not need to have the sha as the
sha is part of the cache value. The new cache key should be unique
enough for each project.

This saves us 20 gitaly calls on the dashboard page (assuming we have
one full page of projects).

changelogs/unreleased/reduce_pipeline_status_gitaly_call.yml

+---
+title: Remove need to call commit (gitaly call) in ProjectPipelineStatus
+merge_request: 33712
+author:
+type: performance

lib/gitlab/cache/ci/project_pipeline_status.rb

@@ -49,7 +49,6 @@ module Gitlab
 
         def load_status
           return if loaded?
-          return unless commit
 
           if has_cache?
             load_from_cache
@@ -66,6 +65,8 @@ module Gitlab
         end
 
         def load_from_project
+          return unless commit
+
           self.sha, self.status, self.ref = commit.sha, commit.status, project.default_branch
         end
 
@@ -114,7 +115,7 @@ module Gitlab
         end
 
         def cache_key
-          "#{Gitlab::Redis::Cache::CACHE_NAMESPACE}:project:#{project.id}:pipeline_status:#{commit&.sha}"
+          "#{Gitlab::Redis::Cache::CACHE_NAMESPACE}:project:#{project.id}:pipeline_status"
         end
 
         def commit

spec/lib/gitlab/cache/ci/project_pipeline_status_spec.rb

@@ -3,7 +3,7 @@
 require 'spec_helper'
 
 RSpec.describe Gitlab::Cache::Ci::ProjectPipelineStatus, :clean_gitlab_redis_cache do
-  let!(:project) { create(:project, :repository) }
+  let_it_be(:project) { create(:project, :repository) }
   let(:pipeline_status) { described_class.new(project) }
   let(:cache_key) { pipeline_status.cache_key }
 
@@ -77,6 +77,30 @@ RSpec.describe Gitlab::Cache::Ci::ProjectPipelineStatus, :clean_gitlab_redis_cac
   end
 
   describe '#load_status' do
+    describe 'gitaly call counts', :request_store do
+      context 'not cached' do
+        before do
+          expect(pipeline_status).not_to be_has_cache
+        end
+
+        it 'makes a Gitaly call' do
+          expect { pipeline_status.load_status }.to change { Gitlab::GitalyClient.get_request_count }.by(1)
+        end
+      end
+
+      context 'cached' do
+        before do
+          described_class.load_in_batch_for_projects([project])
+
+          expect(pipeline_status).to be_has_cache
+        end
+
+        it 'makes no Gitaly calls' do
+          expect { pipeline_status.load_status }.to change { Gitlab::GitalyClient.get_request_count }.by(0)
+        end
+      end
+    end
+
     it 'loads the status from the cache when there is one' do
       expect(pipeline_status).to receive(:has_cache?).and_return(true)
       expect(pipeline_status).to receive(:load_from_cache)