Reduce query count for extremely frequent worker

Consolide 4x queries into one using eager_load, which saves us 3N query
count for a worker which runs 1 million times an hour at peak.

app/models/ci/pipeline.rb

@@ -309,6 +309,7 @@ module Ci
     scope :created_after, -> (time) { where('ci_pipelines.created_at > ?', time) }
     scope :created_before_id, -> (id) { where('ci_pipelines.id < ?', id) }
     scope :before_pipeline, -> (pipeline) { created_before_id(pipeline.id).outside_pipeline_family(pipeline) }
+    scope :eager_load_project, -> { eager_load(project: [:route, { namespace: :route }]) }
 
     scope :outside_pipeline_family, ->(pipeline) do
       where.not(id: pipeline.same_family_pipeline_ids)

app/workers/expire_pipeline_cache_worker.rb

@@ -12,7 +12,7 @@ class ExpirePipelineCacheWorker
 
   # rubocop: disable CodeReuse/ActiveRecord
   def perform(pipeline_id)
-    pipeline = Ci::Pipeline.find_by(id: pipeline_id)
+    pipeline = Ci::Pipeline.eager_load_project.find_by(id: pipeline_id)
     return unless pipeline
 
     Ci::ExpirePipelineCacheService.new.execute(pipeline)

changelogs/unreleased/reduce_expire_pipeline_cache_worker_queries.yml

+---
+title: Reduce query count for ExpirePipelineCacheWorker
+merge_request: 57304
+author:
+type: performance

spec/workers/expire_pipeline_cache_worker_spec.rb

@@ -18,6 +18,23 @@ RSpec.describe ExpirePipelineCacheWorker do
       subject.perform(pipeline.id)
     end
 
+    it 'does not perform extra queries', :aggregate_failures do
+      recorder = ActiveRecord::QueryRecorder.new { subject.perform(pipeline.id) }
+
+      project_queries = recorder.data.values.flat_map {|v| v[:occurrences]}.select {|s| s.include?('FROM "projects"')}
+      namespace_queries = recorder.data.values.flat_map {|v| v[:occurrences]}.select {|s| s.include?('FROM "namespaces"')}
+      route_queries = recorder.data.values.flat_map {|v| v[:occurrences]}.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 <= 6
+
+      # These arises from #update_etag_cache
+      expect(project_queries.size).to eq(1)
+      expect(namespace_queries.size).to eq(1)
+      expect(route_queries.size).to eq(1)
+    end
+
     it "doesn't do anything if the pipeline not exist" do
       expect_any_instance_of(Ci::ExpirePipelineCacheService).not_to receive(:execute)
       expect_any_instance_of(Gitlab::EtagCaching::Store).not_to receive(:touch)