1 files changed, 73 insertions, 0 deletions
diff --git a/spec/initializers/database_config_spec.rb b/spec/initializers/database_config_spec.rb
new file mode 100644
index 00000000000..a5a074f5884
--- /dev/null
+++ b/spec/initializers/database_config_spec.rb
@@ -0,0 +1,73 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe 'Database config initializer' do
+  subject do
+    load Rails.root.join('config/initializers/database_config.rb')
+  end
+
+  before do
+    allow(ActiveRecord::Base).to receive(:establish_connection)
+  end
+
+  context "when using Puma" do
+    let(:puma) { double('puma') }
+    let(:puma_options) { { max_threads: 8 } }
+
+    before do
+      stub_const("Puma", puma)
+      allow(puma).to receive_message_chain(:cli_config, :options).and_return(puma_options)
+    end
+
+    context "and no existing pool size is set" do
+      before do
+        stub_database_config(pool_size: nil)
+      end
+
+      it "sets it to the max number of worker threads" do
+        expect { subject }.to change { Gitlab::Database.config['pool'] }.from(nil).to(8)
+      end
+    end
+
+    context "and the existing pool size is smaller than the max number of worker threads" do
+      before do
+        stub_database_config(pool_size: 7)
+      end
+
+      it "sets it to the max number of worker threads" do
+        expect { subject }.to change { Gitlab::Database.config['pool'] }.from(7).to(8)
+      end
+    end
+
+    context "and the existing pool size is larger than the max number of worker threads" do
+      before do
+        stub_database_config(pool_size: 9)
+      end
+
+      it "keeps the configured pool size" do
+        expect { subject }.not_to change { Gitlab::Database.config['pool'] }
+      end
+    end
+  end
+
+  context "when not using Puma" do
+    before do
+      stub_database_config(pool_size: 7)
+    end
+
+    it "does nothing" do
+      expect { subject }.not_to change { Gitlab::Database.config['pool'] }
+    end
+  end
+
+  def stub_database_config(pool_size:)
+    config = {
+      'adapter' => 'postgresql',
+      'host' => 'db.host.com',
+      'pool' => pool_size
+    }.compact
+
+    allow(Gitlab::Database).to receive(:config).and_return(config)
+  end
+end