Added fallback code to database load balancer to with Standby clusters

ee/lib/gitlab/database/load_balancing/load_balancer.rb

@@ -135,6 +135,8 @@ module Gitlab
         def primary_write_location
           location = read_write do |connection|
             ::Gitlab::Database.get_write_location(connection)
+          rescue ActiveRecord::StatementInvalid
+            ::Gitlab::Database.get_replay_write_location(connection)
           end
 
           return location if location

ee/spec/lib/gitlab/database/load_balancing/load_balancer_spec.rb

@@ -255,6 +255,15 @@ RSpec.describe Gitlab::Database::LoadBalancing::LoadBalancer, :request_store do
 
       expect { lb.primary_write_location }.to raise_error(RuntimeError)
     end
+
+    it 'fallbacks to #get_replay_write_location when #get_write_location raises error' do
+      connection = double(:connection)
+      allow(lb).to receive(:read_write).and_yield(connection)
+      allow(::Gitlab::Database).to receive(:get_write_location).and_raise(ActiveRecord::StatementInvalid)
+      expect(::Gitlab::Database).to receive(:get_replay_write_location).and_return('0/C73A0D88')
+
+      lb.primary_write_location
+    end
   end
 
   describe '#all_caught_up?' do

lib/gitlab/database.rb

@@ -256,6 +256,8 @@ module Gitlab
       row['system_identifier']
     end
 
+    # @param [ActiveRecord::Connection] ar_connection
+    # @return [String]
     def self.get_write_location(ar_connection)
       row = ar_connection
         .select_all("SELECT pg_current_wal_insert_lsn()::text AS location")
@@ -264,6 +266,16 @@ module Gitlab
       row['location'] if row
     end
 
+    # @param [ActiveRecord::Connection] ar_connection
+    # @return [String]
+    def self.get_replay_write_location(ar_connection)
+      row = ar_connection
+              .select_all("SELECT pg_last_wal_replay_lsn()::text AS location")
+              .first
+
+      row['location'] if row
+    end
+
     private_class_method :database_version
 
     def self.add_post_migrate_path_to_rails(force: false)