Add a changelog entry

changelogs/unreleased/323163-restore-gitlab_database_transaction_seconds_sum-for-sidekiq.yml

+---
+title: Port essential database metrics to Sidekiq
+merge_request: 56005
+author:
+type: changed

lib/gitlab/metrics/subscribers/active_record.rb

@@ -13,8 +13,9 @@ module Gitlab
 
         DURATION_BUCKET = [0.05, 0.1, 0.25].freeze
 
-        # observe_transaction_duration is called from ActiveRecordBaseTransactionMetrics.transaction and used to
-        # record transaction durations.
+        # This event is published from ActiveRecordBaseTransactionMetrics and
+        # used to record a database transaction duration when calling
+        # ActiveRecord::Base.transaction {} block.
         def transaction(event)
           observe(:gitlab_database_transaction_seconds, event)
         end

spec/lib/gitlab/metrics/subscribers/active_record_spec.rb

@@ -6,7 +6,7 @@ RSpec.describe Gitlab::Metrics::Subscribers::ActiveRecord do
   using RSpec::Parameterized::TableSyntax
 
   let(:env) { {} }
-  let(:subscriber)  { described_class.new }
+  let(:subscriber) { described_class.new }
   let(:connection) { double(:connection) }
   let(:payload) { { sql: 'SELECT * FROM users WHERE id = 10', connection: connection } }