Backport various EE changes to Gitlab::Database

These changes are useful for CE as well. For example, the MR
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/20720 can make
use of some of the backported methods.

lib/gitlab/database.rb

@@ -61,6 +61,10 @@ module Gitlab
       @version ||= database_version.match(/\A(?:PostgreSQL |)([^\s]+).*\z/)[1]
     end
 
+    def self.postgresql_9_or_less?
+      postgresql? && version.to_f < 10
+    end
+
     def self.join_lateral_supported?
       postgresql? && version.to_f >= 9.3
     end
@@ -69,6 +73,28 @@ module Gitlab
       postgresql? && version.to_f >= 9.4
     end
 
+    def self.pg_stat_wal_receiver_supported?
+      postgresql? && version.to_f >= 9.6
+    end
+
+    # map some of the function names that changed between PostgreSQL 9 and 10
+    # https://wiki.postgresql.org/wiki/New_in_postgres_10
+    def self.pg_wal_lsn_diff
+      Gitlab::Database.postgresql_9_or_less? ? 'pg_xlog_location_diff' : 'pg_wal_lsn_diff'
+    end
+
+    def self.pg_current_wal_insert_lsn
+      Gitlab::Database.postgresql_9_or_less? ? 'pg_current_xlog_insert_location' : 'pg_current_wal_insert_lsn'
+    end
+
+    def self.pg_last_wal_receive_lsn
+      Gitlab::Database.postgresql_9_or_less? ? 'pg_last_xlog_receive_location' : 'pg_last_wal_receive_lsn'
+    end
+
+    def self.pg_last_wal_replay_lsn
+      Gitlab::Database.postgresql_9_or_less? ? 'pg_last_xlog_replay_location' : 'pg_last_wal_replay_lsn'
+    end
+
     def self.nulls_last_order(field, direction = 'ASC')
       order = "#{field} #{direction}"
 

spec/lib/gitlab/database_spec.rb

@@ -65,6 +65,28 @@ describe Gitlab::Database do
     end
   end
 
+  describe '.postgresql_9_or_less?' do
+    it 'returns false when using MySQL' do
+      allow(described_class).to receive(:postgresql?).and_return(false)
+
+      expect(described_class.postgresql_9_or_less?).to eq(false)
+    end
+
+    it 'returns true when using PostgreSQL 9.6' do
+      allow(described_class).to receive(:postgresql?).and_return(true)
+      allow(described_class).to receive(:version).and_return('9.6')
+
+      expect(described_class.postgresql_9_or_less?).to eq(true)
+    end
+
+    it 'returns false when using PostgreSQL 10 or newer' do
+      allow(described_class).to receive(:postgresql?).and_return(true)
+      allow(described_class).to receive(:version).and_return('10')
+
+      expect(described_class.postgresql_9_or_less?).to eq(false)
+    end
+  end
+
   describe '.join_lateral_supported?' do
     it 'returns false when using MySQL' do
       allow(described_class).to receive(:postgresql?).and_return(false)
@@ -109,6 +131,70 @@ describe Gitlab::Database do
     end
   end
 
+  describe '.pg_wal_lsn_diff' do
+    it 'returns old name when using PostgreSQL 9.6' do
+      allow(described_class).to receive(:postgresql?).and_return(true)
+      allow(described_class).to receive(:version).and_return('9.6')
+
+      expect(described_class.pg_wal_lsn_diff).to eq('pg_xlog_location_diff')
+    end
+
+    it 'returns new name when using PostgreSQL 10 or newer' do
+      allow(described_class).to receive(:postgresql?).and_return(true)
+      allow(described_class).to receive(:version).and_return('10')
+
+      expect(described_class.pg_wal_lsn_diff).to eq('pg_wal_lsn_diff')
+    end
+  end
+
+  describe '.pg_current_wal_insert_lsn' do
+    it 'returns old name when using PostgreSQL 9.6' do
+      allow(described_class).to receive(:postgresql?).and_return(true)
+      allow(described_class).to receive(:version).and_return('9.6')
+
+      expect(described_class.pg_current_wal_insert_lsn).to eq('pg_current_xlog_insert_location')
+    end
+
+    it 'returns new name when using PostgreSQL 10 or newer' do
+      allow(described_class).to receive(:postgresql?).and_return(true)
+      allow(described_class).to receive(:version).and_return('10')
+
+      expect(described_class.pg_current_wal_insert_lsn).to eq('pg_current_wal_insert_lsn')
+    end
+  end
+
+  describe '.pg_last_wal_receive_lsn' do
+    it 'returns old name when using PostgreSQL 9.6' do
+      allow(described_class).to receive(:postgresql?).and_return(true)
+      allow(described_class).to receive(:version).and_return('9.6')
+
+      expect(described_class.pg_last_wal_receive_lsn).to eq('pg_last_xlog_receive_location')
+    end
+
+    it 'returns new name when using PostgreSQL 10 or newer' do
+      allow(described_class).to receive(:postgresql?).and_return(true)
+      allow(described_class).to receive(:version).and_return('10')
+
+      expect(described_class.pg_last_wal_receive_lsn).to eq('pg_last_wal_receive_lsn')
+    end
+  end
+
+  describe '.pg_last_wal_replay_lsn' do
+    it 'returns old name when using PostgreSQL 9.6' do
+      allow(described_class).to receive(:postgresql?).and_return(true)
+      allow(described_class).to receive(:version).and_return('9.6')
+
+      expect(described_class.pg_last_wal_replay_lsn).to eq('pg_last_xlog_replay_location')
+    end
+
+    it 'returns new name when using PostgreSQL 10 or newer' do
+      allow(described_class).to receive(:postgresql?).and_return(true)
+      allow(described_class).to receive(:version).and_return('10')
+
+      expect(described_class.pg_last_wal_replay_lsn).to eq('pg_last_wal_replay_lsn')
+    end
+  end
+
   describe '.nulls_last_order' do
     context 'when using PostgreSQL' do
       before do