New pg_last_xact_replay_timestamp DB helper

ee/lib/gitlab/geo/health_check.rb

@@ -42,7 +42,7 @@ module Gitlab
             WHEN #{Gitlab::Database.pg_last_wal_receive_lsn}() = #{Gitlab::Database.pg_last_wal_replay_lsn}()
               THEN 0
             ELSE
-              EXTRACT (EPOCH FROM now() - pg_last_xact_replay_timestamp())::INTEGER
+              EXTRACT (EPOCH FROM now() - #{Gitlab::Database.pg_last_xact_replay_timestamp}())::INTEGER
             END
             AS replication_lag
           SQL

lib/gitlab/database.rb

@@ -102,6 +102,10 @@ module Gitlab
       Gitlab::Database.postgresql_9_or_less? ? 'pg_last_xlog_replay_location' : 'pg_last_wal_replay_lsn'
     end
 
+    def self.pg_last_xact_replay_timestamp
+      'pg_last_xact_replay_timestamp'
+    end
+
     def self.nulls_last_order(field, direction = 'ASC')
       order = "#{field} #{direction}"
 

spec/lib/gitlab/database_spec.rb

@@ -195,6 +195,12 @@ describe Gitlab::Database do
     end
   end
 
+  describe '.pg_last_xact_replay_timestamp' do
+    it 'returns pg_last_xact_replay_timestamp' do
+      expect(described_class.pg_last_xact_replay_timestamp).to eq('pg_last_xact_replay_timestamp')
+    end
+  end
+
   describe '.nulls_last_order' do
     context 'when using PostgreSQL' do
       before do