Add index on events using created_at and id

To suport Service Ping metrics performance dedicated index is required.
This is follow up commit to
https://gitlab.com/gitlab-org/gitlab/-/merge_requests/73273
which scheduled async index creation,
Changelog: other

db/post_migrate/20211103162025_add_index_on_events_using_btree_created_at_id.rb

@@ -0,0 +1,17 @@
+# frozen_string_literal: true
+
+class AddIndexOnEventsUsingBtreeCreatedAtId < Gitlab::Database::Migration[1.0]
+  INDEX_NAME = 'index_events_on_created_at_and_id'
+  TABLE = :events
+  COLUMNS = %i[created_at id]
+  CONSTRAINTS = "created_at > '2021-08-27 00:00:00+00'::timestamp with time zone"
+  disable_ddl_transaction!
+
+  def up
+    add_concurrent_index TABLE, COLUMNS, name: INDEX_NAME, where: CONSTRAINTS
+  end
+
+  def down
+    remove_concurrent_index TABLE, COLUMNS, name: INDEX_NAME, where: CONSTRAINTS
+  end
+end

db/schema_migrations/20211103162025

@@ -0,0 +1 @@
+2ed9198926eb0579fccd4a8b1866f10ba4f42683d676e0664db3fadefe0bed39

db/structure.sql

@@ -25853,6 +25853,8 @@ CREATE INDEX index_events_on_author_id_and_created_at_merge_requests ON events U
 
 CREATE INDEX index_events_on_author_id_and_project_id ON events USING btree (author_id, project_id);
 
+CREATE INDEX index_events_on_created_at_and_id ON events USING btree (created_at, id) WHERE (created_at > '2021-08-27 00:00:00+00'::timestamp with time zone);
+
 CREATE INDEX index_events_on_group_id_partial ON events USING btree (group_id) WHERE (group_id IS NOT NULL);
 
 CREATE INDEX index_events_on_project_id_and_created_at ON events USING btree (project_id, created_at);

ee/spec/lib/ee/gitlab/usage_data_non_sql_metrics_spec.rb

@@ -15,7 +15,7 @@
         described_class.uncached_data
       end
 
-      expect(recorder.count).to eq(57)
+      expect(recorder.count).to eq(59)
     end
   end
 end

lib/gitlab/usage_data.rb

@@ -723,7 +723,9 @@ def stage_manage_events(time_period)
         else
           # rubocop: disable CodeReuse/ActiveRecord
           # rubocop: disable UsageData/LargeTable
-          estimate_batch_distinct_count(::Event.where(time_period), :author_id)
+          start = ::Event.where(time_period).select(:id).order(created_at: :asc).first&.id
+          finish = ::Event.where(time_period).select(:id).order(created_at: :asc).first&.id
+          estimate_batch_distinct_count(::Event.where(time_period), :author_id, start: start, finish: finish)
           # rubocop: enable UsageData/LargeTable
           # rubocop: enable CodeReuse/ActiveRecord
         end