Enable FDW for Geo by default

If the database is set up for that.

config/database_geo.yml.postgresql

@@ -9,7 +9,7 @@ production:
   username: git
   password: "secure password"
   host: localhost
-  # fdw: false
+  fdw: true
 
 #
 # Development specific
@@ -22,7 +22,7 @@ development:
   username: postgres
   password: "secure password"
   host: localhost
-  # fdw: false
+  fdw: true
 
 #
 # Staging specific
@@ -35,7 +35,7 @@ staging:
   username: git
   password: "secure password"
   host: localhost
-  # fdw: false
+  fdw: true
 
 # Warning: The database defined as "test" will be erased and
 # re-generated from your development database when you run "rake".
@@ -48,4 +48,4 @@ test: &test
   username: postgres
   password:
   host: localhost
-  # fdw: false
+  fdw: true

doc/gitlab-geo/database.md

@@ -304,7 +304,7 @@ because we have not yet configured the secondary server. This is the next step.
     connections. The certificate can only be replicated by someone with access
     to the private key, which is **only** present on the primary node.
 
-1. Optional: Configure PostreSQL to enable FDW support
+1. Configure PostreSQL to enable FDW support
 
     This step is similar to how we configured the primary instance.
     We need to enable this, to enable FDW support, even if using a single node.

doc/gitlab-geo/database_source.md

@@ -263,7 +263,7 @@ node.
     bundle exec rake geo:db:migrate
     ```
 
-1. Optional: Configure the [PostgreSQL FDW][FDW] connection and credentials:
+1. Configure the [PostgreSQL FDW][FDW] connection and credentials:
 
     Save the script below in a file, ex. `/tmp/geo_fdw.sh` and modify the connection
     params to match your environment.

ee/lib/gitlab/geo.rb

@@ -76,9 +76,9 @@ module Gitlab
     def self.fdw?
       return false unless self.fdw_capable?
 
-      # FDW is disabled by default: https://gitlab.com/gitlab-org/gitlab-ee/issues/4558
-      # Enable it by setting `fdw: true` in config/database_geo.yml
-      Rails.configuration.geo_database.fetch('fdw', false)
+      # FDW is enabled by default, disable it by setting `fdw: false` in config/database_geo.yml
+      value = Rails.configuration.geo_database['fdw']
+      value.nil? ? true : value
     end
 
     def self.fdw_table(table_name)

spec/ee/spec/lib/gitlab/geo_spec.rb

@@ -46,15 +46,15 @@ describe Gitlab::Geo, :geo do
       expect(described_class.fdw?).to be_falsey
     end
 
-    context 'fdw capable' do
+    context 'with fdw capable' do
       before do
         allow(described_class).to receive(:fdw_capable?).and_return(true)
       end
 
-      it 'returns false by default' do
+      it 'returns true by default' do
         allow(Rails.configuration).to receive(:geo_database).and_return('fdw' => nil)
 
-        expect(described_class.fdw?).to be_falsey
+        expect(described_class.fdw?).to be_truthy
       end
 
       it 'returns false if configured in `config/database_geo.yml`' do