Move Connection#default_pool_size back to Database

This moves the method Connection#default_pool_size back into
Gitlab::Database, allowing it to be used without having to create a
Connection object. This is needed as the database load balancer needs
access to this method, but doesn't (nor should) use a Connection object.

config/initializers/database_config.rb

@@ -24,7 +24,7 @@ ActiveRecord::Base.establish_connection(Gitlab::Database.main.db_config_with_def
 
 Gitlab.ee do
   if Gitlab::Runtime.sidekiq? && Gitlab::Geo.geo_database_configured?
-    Rails.configuration.geo_database['pool'] = Gitlab::Database.main.default_pool_size
+    Rails.configuration.geo_database['pool'] = Gitlab::Database.default_pool_size
     Geo::TrackingBase.establish_connection(Rails.configuration.geo_database)
   end
 end

lib/gitlab/database.rb

@@ -6,6 +6,7 @@ module Gitlab
 
     MAIN_DATABASE_NAME = 'main'
     CI_DATABASE_NAME = 'ci'
+    DEFAULT_POOL_HEADROOM = 10
 
     # This constant is used when renaming tables concurrently.
     # If you plan to rename a table using the `rename_table_safely` method, add your table here one milestone before the rename.
@@ -62,6 +63,20 @@ module Gitlab
       DATABASES[PRIMARY_DATABASE_NAME]
     end
 
+    # We configure the database connection pool size automatically based on the
+    # configured concurrency. We also add some headroom, to make sure we don't
+    # run out of connections when more threads besides the 'user-facing' ones
+    # are running.
+    #
+    # Read more about this in
+    # doc/development/database/client_side_connection_pool.md
+    def self.default_pool_size
+      headroom =
+        (ENV["DB_POOL_HEADROOM"].presence || DEFAULT_POOL_HEADROOM).to_i
+
+      Gitlab::Runtime.max_threads + headroom
+    end
+
     def self.has_config?(database_name)
       Gitlab::Application.config.database_configuration[Rails.env].include?(database_name.to_s)
     end

lib/gitlab/database/connection.rb

@@ -5,8 +5,6 @@ module Gitlab
     # Configuration settings and methods for interacting with a PostgreSQL
     # database, with support for multiple databases.
     class Connection
-      DEFAULT_POOL_HEADROOM = 10
-
       attr_reader :scope
 
       # Initializes a new `Database`.
@@ -20,20 +18,6 @@ module Gitlab
         @open_transactions_baseline = 0
       end
 
-      # We configure the database connection pool size automatically based on
-      # the configured concurrency. We also add some headroom, to make sure we
-      # don't run out of connections when more threads besides the 'user-facing'
-      # ones are running.
-      #
-      # Read more about this in
-      # doc/development/database/client_side_connection_pool.md
-      def default_pool_size
-        headroom =
-          (ENV["DB_POOL_HEADROOM"].presence || DEFAULT_POOL_HEADROOM).to_i
-
-        Gitlab::Runtime.max_threads + headroom
-      end
-
       def config
         # The result of this method must not be cached, as other methods may use
         # it after making configuration changes and expect those changes to be
@@ -48,7 +32,7 @@ module Gitlab
       end
 
       def pool_size
-        config[:pool] || default_pool_size
+        config[:pool] || Database.default_pool_size
       end
 
       def username
@@ -77,7 +61,9 @@ module Gitlab
 
       def db_config_with_default_pool_size
         db_config_object = scope.connection_db_config
-        config = db_config_object.configuration_hash.merge(pool: default_pool_size)
+        config = db_config_object
+          .configuration_hash
+          .merge(pool: Database.default_pool_size)
 
         ActiveRecord::DatabaseConfigurations::HashConfig.new(
           db_config_object.env_name,

spec/lib/gitlab/database/connection_spec.rb

@@ -5,29 +5,14 @@ require 'spec_helper'
 RSpec.describe Gitlab::Database::Connection do
   let(:connection) { described_class.new }
 
-  describe '#default_pool_size' do
-    before do
-      allow(Gitlab::Runtime).to receive(:max_threads).and_return(7)
-    end
-
-    it 'returns the max thread size plus a fixed headroom of 10' do
-      expect(connection.default_pool_size).to eq(17)
-    end
-
-    it 'returns the max thread size plus a DB_POOL_HEADROOM if this env var is present' do
-      stub_env('DB_POOL_HEADROOM', '7')
-
-      expect(connection.default_pool_size).to eq(14)
-    end
-  end
-
   describe '#config' do
     it 'returns a HashWithIndifferentAccess' do
       expect(connection.config).to be_an_instance_of(HashWithIndifferentAccess)
     end
 
     it 'returns a default pool size' do
-      expect(connection.config).to include(pool: connection.default_pool_size)
+      expect(connection.config)
+        .to include(pool: Gitlab::Database.default_pool_size)
     end
 
     it 'does not cache its results' do
@@ -43,7 +28,7 @@ RSpec.describe Gitlab::Database::Connection do
       it 'returns the default pool size' do
         expect(connection).to receive(:config).and_return({ pool: nil })
 
-        expect(connection.pool_size).to eq(connection.default_pool_size)
+        expect(connection.pool_size).to eq(Gitlab::Database.default_pool_size)
       end
     end
 
@@ -129,7 +114,7 @@ RSpec.describe Gitlab::Database::Connection do
 
   describe '#db_config_with_default_pool_size' do
     it 'returns db_config with our default pool size' do
-      allow(connection).to receive(:default_pool_size).and_return(9)
+      allow(Gitlab::Database).to receive(:default_pool_size).and_return(9)
 
       expect(connection.db_config_with_default_pool_size.pool).to eq(9)
     end

spec/lib/gitlab/database_spec.rb

@@ -15,6 +15,22 @@ RSpec.describe Gitlab::Database do
     end
   end
 
+  describe '.default_pool_size' do
+    before do
+      allow(Gitlab::Runtime).to receive(:max_threads).and_return(7)
+    end
+
+    it 'returns the max thread size plus a fixed headroom of 10' do
+      expect(described_class.default_pool_size).to eq(17)
+    end
+
+    it 'returns the max thread size plus a DB_POOL_HEADROOM if this env var is present' do
+      stub_env('DB_POOL_HEADROOM', '7')
+
+      expect(described_class.default_pool_size).to eq(14)
+    end
+  end
+
   describe '.has_config?' do
     context 'two tier database config' do
       before do