Remove Marginalia feature flag

We've had this enabled on GitLab.com for over 10 months and have no
intention of disabling it. Even if we did, it would need an application
restart, so the value of a feature flag is quite low.

config/feature_flags/ops/marginalia.yml

----
-name: marginalia
-introduced_by_url: 
-rollout_issue_url: 
-milestone: 
-type: ops
-group: 
-default_enabled: false

config/initializers/0_marginalia.rb

@@ -4,11 +4,6 @@ require 'marginalia'
 
 ::Marginalia::Comment.extend(::Gitlab::Marginalia::Comment)
 
-# Patch to modify 'Marginalia::ActiveRecordInstrumentation.annotate_sql' method with feature check.
-# Orignal Marginalia::ActiveRecordInstrumentation is included to ActiveRecord::ConnectionAdapters::PostgreSQLAdapter in the Marginalia Railtie.
-# Refer: https://github.com/basecamp/marginalia/blob/v1.8.0/lib/marginalia/railtie.rb#L67
-ActiveRecord::ConnectionAdapters::PostgreSQLAdapter.prepend(Gitlab::Marginalia::ActiveRecordInstrumentation)
-
 # By default, PostgreSQL only tracks the first 1024 bytes of a SQL
 # query. Prepending the comment allows us to trace the source of the
 # query without having to increase the `track_activity_query_size`
@@ -25,5 +20,3 @@ Marginalia::Comment.components << :line if Rails.env.development?
 Gitlab::Marginalia.set_application_name
 
 Gitlab::Marginalia.enable_sidekiq_instrumentation
-
-Gitlab::Marginalia.set_enabled_from_feature_flag

doc/development/database_query_comments.md

@@ -47,16 +47,3 @@ Examples of queries with comments as observed in `development.log`:
    ```sql
    SELECT "ci_pipelines".* FROM "ci_pipelines" WHERE "ci_pipelines"."id" = $1 LIMIT $2 [["id", 64], ["LIMIT", 1]] /*application:sidekiq,jid:e7d6668a39a991e323009833,job_class:ExpireJobCacheWorker,correlation_id:rYF4mey9CH3,line:/app/workers/expire_job_cache_worker.rb:14:in `perform'*/
    ```
-
-## Enable/Disable the feature
-
-Enabling or disabling the feature requires a **restart/SIGHUP** of the Web and
-Sidekiq workers, as the feature flag's state is memoized upon starting up.
-
-The `feature_flag` for this feature is **disabled** by default. You can enable
-or disable it with:
-
-```ruby
-Feature.enable(:marginalia)
-Feature.disable(:marginalia)
-```

lib/gitlab/marginalia.rb

@@ -2,8 +2,6 @@
 
 module Gitlab
   module Marginalia
-    cattr_accessor :enabled, default: false
-
     def self.set_application_name
       ::Marginalia.application_name = Gitlab.process_name
     end
@@ -13,12 +11,5 @@ module Gitlab
         ::Marginalia::SidekiqInstrumentation.enable!
       end
     end
-
-    def self.set_enabled_from_feature_flag
-      # During db:create and db:bootstrap skip feature query as DB is not available yet.
-      return false unless Gitlab::Database.cached_table_exists?('features')
-
-      self.enabled = Feature.enabled?(:marginalia, type: :ops)
-    end
   end
 end

lib/gitlab/marginalia/active_record_instrumentation.rb

-# frozen_string_literal: true
-
-# Patch to annotate sql only when the feature is enabled.
-module Gitlab
-  module Marginalia
-    module ActiveRecordInstrumentation
-      def annotate_sql(sql)
-        Gitlab::Marginalia.enabled ? super(sql) : sql
-      end
-    end
-  end
-end

spec/lib/marginalia_spec.rb

@@ -37,26 +37,9 @@ RSpec.describe 'Marginalia spec' do
       }
     end
 
-    context 'when the feature is enabled' do
-      before do
-        stub_feature(true)
-      end
-
-      it 'generates a query that includes the component and value' do
-        component_map.each do |component, value|
-          expect(recorded.log.last).to include("#{component}:#{value}")
-        end
-      end
-    end
-
-    context 'when the feature is disabled' do
-      before do
-        stub_feature(false)
-      end
-
-      it 'excludes annotations in generated queries' do
-        expect(recorded.log.last).not_to include("/*")
-        expect(recorded.log.last).not_to include("*/")
+    it 'generates a query that includes the component and value' do
+      component_map.each do |component, value|
+        expect(recorded.log.last).to include("#{component}:#{value}")
       end
     end
   end
@@ -90,59 +73,37 @@ RSpec.describe 'Marginalia spec' do
       }
     end
 
-    context 'when the feature is enabled' do
-      before do
-        stub_feature(true)
+    it 'generates a query that includes the component and value' do
+      component_map.each do |component, value|
+        expect(recorded.log.last).to include("#{component}:#{value}")
       end
+    end
 
-      it 'generates a query that includes the component and value' do
-        component_map.each do |component, value|
-          expect(recorded.log.last).to include("#{component}:#{value}")
-        end
-      end
-
-      describe 'for ActionMailer delivery jobs' do
-        let(:delivery_job) { MarginaliaTestMailer.first_user.deliver_later }
-
-        let(:recorded) do
-          ActiveRecord::QueryRecorder.new do
-            delivery_job.perform_now
-          end
-        end
-
-        let(:component_map) do
-          {
-            "application"  => "sidekiq",
-            "jid"          => delivery_job.job_id,
-            "job_class"    => delivery_job.arguments.first
-          }
-        end
+    describe 'for ActionMailer delivery jobs' do
+      let(:delivery_job) { MarginaliaTestMailer.first_user.deliver_later }
 
-        it 'generates a query that includes the component and value' do
-          component_map.each do |component, value|
-            expect(recorded.log.last).to include("#{component}:#{value}")
-          end
+      let(:recorded) do
+        ActiveRecord::QueryRecorder.new do
+          delivery_job.perform_now
         end
       end
-    end
 
-    context 'when the feature is disabled' do
-      before do
-        stub_feature(false)
+      let(:component_map) do
+        {
+          "application"  => "sidekiq",
+          "jid"          => delivery_job.job_id,
+          "job_class"    => delivery_job.arguments.first
+        }
       end
 
-      it 'excludes annotations in generated queries' do
-        expect(recorded.log.last).not_to include("/*")
-        expect(recorded.log.last).not_to include("*/")
+      it 'generates a query that includes the component and value' do
+        component_map.each do |component, value|
+          expect(recorded.log.last).to include("#{component}:#{value}")
+        end
       end
     end
   end
 
-  def stub_feature(value)
-    stub_feature_flags(marginalia: value)
-    Gitlab::Marginalia.set_enabled_from_feature_flag
-  end
-
   def make_request(correlation_id)
     request_env = Rack::MockRequest.env_for('/')
 

spec/spec_helper.rb

@@ -249,9 +249,6 @@ RSpec.configure do |config|
       unstub_all_feature_flags
     end
 
-    # Enable Marginalia feature for all specs in the test suite.
-    Gitlab::Marginalia.enabled = true
-
     # Stub these calls due to being expensive operations
     # It can be reenabled for specific tests via:
     #