Expose wal_log_hints PostgreSQL setting

This setting needs to be enabled for pg_rewind to work during a Patroni
failover.

Relates to https://gitlab.com/gitlab-org/gitlab/-/issues/267144

changelogs/unreleased/sh-enable-wal-log-hints.yml

+---
+title: Expose wal_log_hints PostgreSQL setting
+merge_request: 4642
+author:
+type: added

files/gitlab-config-template/gitlab.rb.template

@@ -1036,6 +1036,7 @@ gitlab_rails['object_store']['objects']['terraform_state']['bucket'] = nil
 ### Replication settings
 ###! Note, some replication settings do not require a full restart. They are documented below.
 # postgresql['wal_level'] = "hot_standby"
+# postgresql['wal_log_hints'] = 'off'
 # postgresql['max_wal_senders'] = 5
 # postgresql['max_replication_slots'] = 0
 # postgresql['max_locks_per_transaction'] = 128

files/gitlab-cookbooks/gitlab-ee/attributes/default.rb

@@ -119,6 +119,7 @@ default['gitlab']['geo-postgresql']['default_statistics_target'] = 1000
 # Replication settings
 default['gitlab']['geo-postgresql']['wal_level'] = 'minimal'
+default['gitlab']['geo-postgresql']['wal_log_hints'] = 'off'
 default['gitlab']['geo-postgresql']['max_wal_senders'] = 0
 default['gitlab']['geo-postgresql']['wal_keep_segments'] = 10
 default['gitlab']['geo-postgresql']['hot_standby'] = 'off'

files/gitlab-cookbooks/postgresql/attributes/default.rb

@@ -104,6 +104,7 @@ default['postgresql']['log_rotation_size'] = nil
 # Replication settings
 default['postgresql']['sql_replication_user'] = "gitlab_replicator"
 default['postgresql']['wal_level'] = "minimal"
+default['postgresql']['wal_log_hints'] = "off"
 default['postgresql']['max_wal_senders'] = 0
 default['postgresql']['wal_keep_segments'] = 10
 default['postgresql']['hot_standby'] = "off"

files/gitlab-cookbooks/postgresql/templates/default/postgresql.conf.erb

@@ -171,6 +171,7 @@ shared_preload_libraries = '<%= @shared_preload_libraries %>'    # (change requi
 # - Settings -
 wal_level = <%= @wal_level %>
+wal_log_hints = <%= @wal_log_hints %>      # also do full page writes of non-critical updates
           # (change requires restart)
 #fsync = on       # turns forced synchronization on or off
 #wal_sync_method = fsync    # the default is the first option

spec/chef/gitlab-ee/recipes/geo_spec.rb

@@ -48,6 +48,10 @@ RSpec.describe 'gitlab-ee::geo' do
         expect(config_attrs['wal_level']).to eq('hot_standby')
       end
+      it 'defines wal_log_hints' do
+        expect(config_attrs['wal_log_hints']).to eq('off')
+      end
+
       it 'defines max_wal_senders' do
         expect(config_attrs['max_wal_senders']).to eq(10)
       end
@@ -95,6 +99,10 @@ RSpec.describe 'gitlab-ee::geo' do
         expect(config_attrs['wal_level']).to eq('hot_standby')
       end
+      it 'defines wal_log_hints' do
+        expect(config_attrs['wal_log_hints']).to eq('off')
+      end
+
       it 'defines max_wal_senders' do
         expect(config_attrs['max_wal_senders']).to eq(10)
       end

spec/chef/recipes/postgresql_spec.rb

@@ -377,6 +377,14 @@ RSpec.describe 'postgresql 9.6' do
         ).with_content(/synchronous_standby_names = ''/)
       end
+      it 'disables wal_log_hints setting' do
+        expect(chef_run.node['postgresql']['wal_log_hints']).to eq('off')
+
+        expect(chef_run).to render_file(
+          postgresql_conf
+        ).with_content(/wal_log_hints = off/)
+      end
+
       it 'does not set dynamic_shared_memory_type by default' do
         expect(chef_run).not_to render_file(
           postgresql_conf
@@ -467,6 +475,22 @@ RSpec.describe 'postgresql 9.6' do
           ).with_content(/^dynamic_shared_memory_type = none/)
         end
       end
+
+      context 'when wal_log_hints is on' do
+        before do
+          stub_gitlab_rb({
+                           postgresql: {
+                             wal_log_hints: 'on'
+                           }
+                         })
+        end
+
+        it 'enables wal_log_hints' do
+          expect(chef_run).to render_file(
+            postgresql_conf
+          ).with_content(/^wal_log_hints = on/)
+        end
+      end
     end
     context 'renders runtime.conf' do