Switch ThreadMemoryCache to ProcessMemoryCache

Thread-local cache is ineffective when using Puma because unused threads
are reaped until it reaches the min threads setting.

We already tested this ProcessMemoryCache for feature flags so this
enables it for other classes where we're still using ThreadMemoryCache

app/controllers/admin/application_settings_controller.rb

@@ -5,7 +5,7 @@ class Admin::ApplicationSettingsController < Admin::ApplicationController
 
   # NOTE: Use @application_setting in this controller when you need to access
   # application_settings after it has been modified. This is because the
-  # ApplicationSetting model uses Gitlab::ThreadMemoryCache for caching and the
+  # ApplicationSetting model uses Gitlab::ProcessMemoryCache for caching and the
   # cache might be stale immediately after an update.
   # https://gitlab.com/gitlab-org/gitlab-foss/-/merge_requests/30233
   before_action :set_application_setting, except: :integrations

app/models/application_setting.rb

@@ -421,7 +421,7 @@ class ApplicationSetting < ApplicationRecord
   # can cause a significant amount of load on Redis, let's cache it in
   # memory.
   def self.cache_backend
-    Gitlab::ThreadMemoryCache.cache_backend
+    Gitlab::ProcessMemoryCache.cache_backend
   end
 
   def recaptcha_or_login_protection_enabled

changelogs/unreleased/switch-thread-to-process-memory-cache.yml

+---
+title: Use process-wide cache for application settings and performance bar
+merge_request: 31135
+author:
+type: performance

config/environments/test.rb

 require 'gitlab/testing/request_blocker_middleware'
 require 'gitlab/testing/request_inspector_middleware'
-require 'gitlab/testing/clear_thread_memory_cache_middleware'
+require 'gitlab/testing/clear_process_memory_cache_middleware'
 
 Rails.application.configure do
   # Make sure the middleware is inserted first in middleware chain
   config.middleware.insert_before(ActionDispatch::Static, Gitlab::Testing::RequestBlockerMiddleware)
   config.middleware.insert_before(ActionDispatch::Static, Gitlab::Testing::RequestInspectorMiddleware)
-  config.middleware.insert_before(ActionDispatch::Static, Gitlab::Testing::ClearThreadMemoryCacheMiddleware)
+  config.middleware.insert_before(ActionDispatch::Static, Gitlab::Testing::ClearProcessMemoryCacheMiddleware)
 
   # Settings specified here will take precedence over those in config/application.rb
 

config/initializers/0_thread_cache.rb

-# frozen_string_literal: true
-
-Gitlab::ThreadMemoryCache.cache_backend

ee/lib/gitlab/geo.rb

@@ -87,7 +87,7 @@ module Gitlab
 
     def self.l1_cache
       SafeRequestStore[:geo_l1_cache] ||=
-        Gitlab::JsonCache.new(namespace: :geo, backend: ::Gitlab::ThreadMemoryCache.cache_backend)
+        Gitlab::JsonCache.new(namespace: :geo, backend: ::Gitlab::ProcessMemoryCache.cache_backend)
     end
 
     def self.l2_cache

ee/spec/lib/gitlab/geo_spec.rb

@@ -13,7 +13,7 @@ describe Gitlab::Geo, :geo, :request_store do
     it 'includes GitLab version and Rails.version in the cache key' do
       expanded_key = "geo:#{key}:#{Gitlab::VERSION}:#{Rails.version}"
 
-      expect(Gitlab::ThreadMemoryCache.cache_backend).to receive(:write)
+      expect(Gitlab::ProcessMemoryCache.cache_backend).to receive(:write)
         .with(expanded_key, an_instance_of(String), expires_in: 1.minute).and_call_original
       expect(Rails.cache).to receive(:write)
         .with(expanded_key, an_instance_of(String), expires_in: 2.minutes)

ee/spec/requests/projects/audit_events_spec.rb

@@ -21,6 +21,8 @@ describe 'view audit events' do
     end
 
     it 'avoids N+1 DB queries', :request_store do
+      send_request
+
       control = ActiveRecord::QueryRecorder.new(skip_cached: false) { send_request }
 
       create_list(:project_audit_event, 2, entity_id: project.id)

lib/feature.rb

@@ -134,11 +134,7 @@ class Feature
     end
 
     def l1_cache_backend
-      if Gitlab::Utils.to_boolean(ENV['USE_THREAD_MEMORY_CACHE'])
-        Gitlab::ThreadMemoryCache.cache_backend
-      else
-        Gitlab::ProcessMemoryCache.cache_backend
-      end
+      Gitlab::ProcessMemoryCache.cache_backend
     end
 
     def l2_cache_backend

lib/gitlab/performance_bar.rb

@@ -44,7 +44,7 @@ module Gitlab
     end
 
     def self.l1_cache_backend
-      Gitlab::ThreadMemoryCache.cache_backend
+      Gitlab::ProcessMemoryCache.cache_backend
     end
 
     def self.l2_cache_backend

lib/gitlab/testing/clear_thread_memory_cache_middleware.rb → lib/gitlab/testing/clear_process_memory_cache_middleware.rb

@@ -2,13 +2,13 @@
 
 module Gitlab
   module Testing
-    class ClearThreadMemoryCacheMiddleware
+    class ClearProcessMemoryCacheMiddleware
       def initialize(app)
         @app = app
       end
 
       def call(env)
-        Gitlab::ThreadMemoryCache.cache_backend.clear
+        Gitlab::ProcessMemoryCache.cache_backend.clear
 
         @app.call(env)
       end

lib/gitlab/thread_memory_cache.rb

-# frozen_string_literal: true
-
-module Gitlab
-  class ThreadMemoryCache
-    THREAD_KEY = :thread_memory_cache
-
-    def self.cache_backend
-      # Note ActiveSupport::Cache::MemoryStore is thread-safe.  Since
-      # each backend is local per thread we probably don't need to worry
-      # about synchronizing access, but this is a drop-in replacement
-      # for ActiveSupport::Cache::RedisStore.
-      Thread.current[THREAD_KEY] ||= ActiveSupport::Cache::MemoryStore.new
-    end
-  end
-end

spec/lib/feature_spec.rb

@@ -146,14 +146,6 @@ describe Feature do
       expect(described_class.enabled?(:enabled_feature_flag)).to be_truthy
     end
 
-    context 'with USE_THREAD_MEMORY_CACHE defined' do
-      before do
-        stub_env('USE_THREAD_MEMORY_CACHE', '1')
-      end
-
-      it { expect(described_class.l1_cache_backend).to eq(Gitlab::ThreadMemoryCache.cache_backend) }
-    end
-
     it { expect(described_class.l1_cache_backend).to eq(Gitlab::ProcessMemoryCache.cache_backend) }
     it { expect(described_class.l2_cache_backend).to eq(Rails.cache) }
 

spec/lib/gitlab/performance_bar_spec.rb

@@ -38,7 +38,7 @@ describe Gitlab::PerformanceBar do
     end
   end
 
-  it { expect(described_class.l1_cache_backend).to eq(Gitlab::ThreadMemoryCache.cache_backend) }
+  it { expect(described_class.l1_cache_backend).to eq(Gitlab::ProcessMemoryCache.cache_backend) }
   it { expect(described_class.l2_cache_backend).to eq(Rails.cache) }
 
   describe '.enabled_for_user?' do

spec/models/concerns/cacheable_attributes_spec.rb

@@ -205,11 +205,11 @@ describe CacheableAttributes do
       end
     end
 
-    it 'uses RequestStore in addition to Thread memory cache', :request_store do
+    it 'uses RequestStore in addition to process memory cache', :request_store do
       # Warm up the cache
       create(:application_setting).cache!
 
-      expect(ApplicationSetting.cache_backend).to eq(Gitlab::ThreadMemoryCache.cache_backend)
+      expect(ApplicationSetting.cache_backend).to eq(Gitlab::ProcessMemoryCache.cache_backend)
       expect(ApplicationSetting.cache_backend).to receive(:read).with(ApplicationSetting.cache_key).once.and_call_original
 
       2.times { ApplicationSetting.current }

spec/spec_helper.rb

@@ -209,9 +209,7 @@ RSpec.configure do |config|
     # expect(Gitlab::Git::KeepAround).to receive(:execute).and_call_original
     allow(Gitlab::Git::KeepAround).to receive(:execute)
 
-    [Gitlab::ThreadMemoryCache, Gitlab::ProcessMemoryCache].each do |cache|
-      cache.cache_backend.clear
-    end
+    Gitlab::ProcessMemoryCache.cache_backend.clear
 
     Sidekiq::Worker.clear_all