Disable Marginalia line backtrace in production

As mentioned in https://github.com/basecamp/marginalia/pull/93/files,
adding `:line` to the output of the Marginalia incurs some overhead
because a regexp on the backtrace has to be run on every SQL query. Only
enable this in development because we've seen it slow things down.

Identified in https://gitlab.com/gitlab-org/gitlab/issues/198694

changelogs/unreleased/sh-disable-line-in-marginalia.yml

+---
+title: Disable Marginalia line backtrace in production
+merge_request: 26199
+author:
+type: performance

config/initializers/0_marginalia.rb

@@ -9,7 +9,13 @@ require 'marginalia'
 # Refer: https://github.com/basecamp/marginalia/blob/v1.8.0/lib/marginalia/railtie.rb#L67
 ActiveRecord::ConnectionAdapters::PostgreSQLAdapter.prepend(Gitlab::Marginalia::ActiveRecordInstrumentation)
 
-Marginalia::Comment.components = [:application, :controller, :action, :correlation_id, :jid, :job_class, :line]
+Marginalia::Comment.components = [:application, :controller, :action, :correlation_id, :jid, :job_class]
+
+# As mentioned in https://github.com/basecamp/marginalia/pull/93/files,
+# adding :line has some overhead because a regexp on the backtrace has
+# to be run on every SQL query. Only enable this in development because
+# we've seen it slow things down.
+Marginalia::Comment.components << :line if Rails.env.development?
 
 Gitlab::Marginalia.set_application_name
 

spec/lib/marginalia_spec.rb

@@ -59,7 +59,6 @@ describe 'Marginalia spec' do
         "application"       => "test",
         "controller"        => "marginalia_test",
         "action"            => "first_user",
-        "line"              => "/spec/support/helpers/query_recorder.rb",
         "correlation_id"    => correlation_id
       }
     end
@@ -116,7 +115,6 @@ describe 'Marginalia spec' do
       {
         "application"       => "sidekiq",
         "job_class"         => "MarginaliaTestJob",
-        "line"              => "/spec/support/sidekiq_middleware.rb",
         "correlation_id"    => sidekiq_job['correlation_id'],
         "jid"               => sidekiq_job['jid']
       }
@@ -145,7 +143,6 @@ describe 'Marginalia spec' do
         let(:component_map) do
           {
             "application"  => "sidekiq",
-            "line"         => "/lib/gitlab/i18n.rb",
             "jid"          => delivery_job.job_id,
             "job_class"    => delivery_job.arguments.first
           }

spec/support_specs/helpers/active_record/query_recorder_spec.rb

@@ -14,9 +14,6 @@ describe ActiveRecord::QueryRecorder do
         TestQueries.first
       end
 
-      # Test first_only flag works as expected
-      expect(control.find_query(/.*query_recorder_spec.rb.*/, 0, first_only: true))
-        .to eq(control.find_query(/.*query_recorder_spec.rb.*/, 0).first)
       # Check #find_query
       expect(control.find_query(/.*/, 0).size)
         .to eq(control.data.keys.size)
@@ -32,9 +29,7 @@ describe ActiveRecord::QueryRecorder do
       # Ensure memoization value match the raw value above
       expect(control.count).to eq(control.log.size)
       # Ensure we have only two sources of queries
-      expect(control.data.keys.size).to eq(2)
-      # Ensure we detect only queries from this file
-      expect(control.data.keys.find_all { |i| i.match(/query_recorder_spec.rb/) }.count).to eq(2)
+      expect(control.data.keys.size).to eq(1)
     end
   end
 end