Reduce query for popular worker ExpireJobCacheWorker

This worker runs a million times per hour, so reducing 5 queries to 1
means we have 4 million queries per hour

app/models/commit_status.rb

@@ -55,6 +55,7 @@ class CommitStatus < ApplicationRecord
   scope :for_ref, -> (ref) { where(ref: ref) }
   scope :by_name, -> (name) { where(name: name) }
   scope :in_pipelines, ->(pipelines) { where(pipeline: pipelines) }
+  scope :eager_load_pipeline, -> { eager_load(:pipeline, project: { namespace: :route }) }
 
   scope :for_project_paths, -> (paths) do
     where(project: Project.where_full_path_in(Array(paths)))

app/workers/expire_job_cache_worker.rb

@@ -10,7 +10,7 @@ class ExpireJobCacheWorker
 
   # rubocop: disable CodeReuse/ActiveRecord
   def perform(job_id)
-    job = CommitStatus.joins(:pipeline, :project).find_by(id: job_id)
+    job = CommitStatus.eager_load_pipeline.find_by(id: job_id)
     return unless job
 
     pipeline = job.pipeline

changelogs/unreleased/query_count_expire_job_cache_worker.yml

+---
+title: Reduce query count for popular worker ExpireJobCacheWorker
+merge_request: 57773
+author:
+type: performance

spec/workers/expire_job_cache_worker_spec.rb

@@ -8,7 +8,8 @@ RSpec.describe ExpireJobCacheWorker do
 
   describe '#perform' do
     context 'with a job in the pipeline' do
-      let(:job) { create(:ci_build, pipeline: pipeline) }
+      let_it_be(:job) { create(:ci_build, pipeline: pipeline) }
+
       let(:job_args) { job.id }
 
       include_examples 'an idempotent worker' do
@@ -31,6 +32,24 @@ RSpec.describe ExpireJobCacheWorker do
           subject
         end
       end
+
+      it 'does not perform extra queries', :aggregate_failures do
+        worker = described_class.new
+        recorder = ActiveRecord::QueryRecorder.new { worker.perform(job.id) }
+
+        occurences = recorder.data.values.flat_map {|v| v[:occurrences]}
+        project_queries = occurences.select {|s| s.include?('FROM "projects"')}
+        namespace_queries = occurences.select {|s| s.include?('FROM "namespaces"')}
+        route_queries = occurences.select {|s| s.include?('FROM "routes"')}
+
+        # This worker is run 1 million times an hour, so we need to save as much
+        # queries as possible.
+        expect(recorder.count).to be <= 1
+
+        expect(project_queries.size).to eq(0)
+        expect(namespace_queries.size).to eq(0)
+        expect(route_queries.size).to eq(0)
+      end
     end
 
     context 'when there is no job in the pipeline' do