diff --git a/.github/workflows/coverage.yml b/.github/workflows/coverage.yml
index 85a977f..a6361ac 100644
--- a/.github/workflows/coverage.yml
+++ b/.github/workflows/coverage.yml
@@ -33,6 +33,7 @@ jobs:
       POSTGRES_USERNAME: postgres
       POSTGRES_PASSWORD: postgres
       SCHEMA: structure.sql
+      PERFORMANCE_TESTS_DISABLED: 1
     steps:
       - name: Checkout repository
         uses: actions/checkout@v3
diff --git a/.github/workflows/pull_request.yml b/.github/workflows/pull_request.yml
index f522fae..6712f67 100644
--- a/.github/workflows/pull_request.yml
+++ b/.github/workflows/pull_request.yml
@@ -58,6 +58,7 @@ jobs:
       POSTGRES_PASSWORD: postgres
       BUNDLE_GEMFILE: ${{ matrix.gemfile }}
       SPEC_DISABLE_DROP_DATABASE: 1
+      PERFORMANCE_TESTS_DISABLED: 1
       SCHEMA: structure.sql
     steps:
       - name: Checkout repository
diff --git a/README.md b/README.md
index 07819c3..1f44b14 100644
--- a/README.md
+++ b/README.md
@@ -163,7 +163,7 @@ photo.destroy()
 Photo.profile.ordered.pluck(:label, :position) # => [["A", 0], ["B", 1],  ["C", 2]]
 Photo.cover.ordered.pluck(:label, :position) # => [["D", 0], ["E", 1]]
 ```
-#### Default push front
+#### Auto set
 
 ```ruby
 class Image < ActiveRecord::Base
@@ -216,7 +216,7 @@ Image.create(label: "B")
 Image.ordered.pluck(:label, :position) # => [["A", 10], ["B", 11]]
 ```
 
-### Decremental sequence
+#### Decremental sequence
 
 ```ruby
 class Image < ActiveRecord::Base
diff --git a/spec/performance/index_spec.rb b/spec/performance/index_spec.rb
new file mode 100644
index 0000000..e730c0d
--- /dev/null
+++ b/spec/performance/index_spec.rb
@@ -0,0 +1,111 @@
+# frozen_string_literal: true
+
+RSpec.describe "Performance with index" do
+  before(:all) do
+    attrs = (0...100_000).map do |position|
+      "('#{SecureRandom.alphanumeric(8)}', #{position})"
+    end
+
+    BasicModel.connection.execute(<<-SQL)
+      INSERT INTO basic_models (name, position)
+      VALUES
+        #{attrs.join(', ')};
+    SQL
+  end
+
+  after(:all) { BasicModel.delete_all }
+
+  describe "model without scope" do
+    context "on #update" do
+      subject { create(:basic_model).update!(position: position) }
+
+      context "with position set as first value" do
+        let(:position) { 0 }
+
+        it "takes less than 1.25s" do
+          expect(elapsed_time { subject }).to be < 1.25
+        end
+      end
+
+      context "with position set as middle value" do
+        let(:position) { 50_000 }
+
+        it "takes less than 0.75s" do
+          expect(elapsed_time { subject }).to be < 0.75
+        end
+      end
+
+      context "with position set as last value" do
+        let(:position) { 99_999 }
+
+        it "takes less than 0.15s" do
+          expect(elapsed_time { subject }).to be < 0.15
+        end
+      end
+    end
+
+    context "on #create" do
+      subject { create(:basic_model, **attrs) }
+      let(:attrs) { {} }
+
+      context "without position specified" do
+        it "takes less than 0.07s" do
+          expect(elapsed_time { subject }).to be < 0.07
+        end
+      end
+
+      context "with postion set as 3/4 of total count" do
+        let(:attrs) { { position: 75_000 } }
+
+        it "takes less than 0.35s" do
+          expect(elapsed_time { subject }).to be < 0.35
+        end
+      end
+
+      context "with position set as the middle value" do
+        let(:attrs) { { position: 50_000 } }
+
+        it "takes less than 0.8s" do
+          expect(elapsed_time { subject }).to be < 0.8
+        end
+      end
+
+      context "with position set as first value" do
+        let(:attrs) { { position: 0 } }
+
+        it "takes less than 1.5s" do
+          expect(elapsed_time { subject }).to be < 1.5
+        end
+      end
+    end
+
+    context "on #destroy" do
+      subject { record.destroy! }
+      let!(:record) { create(:basic_model, **attrs) }
+
+      context "with position set as last value" do
+        let(:attrs) { { position: 100_000 } }
+
+        it "takes less than 0.01s" do
+          expect(elapsed_time { subject }).to be < 0.01
+        end
+      end
+
+      context "with position set as middle value" do
+        let(:attrs) { { position: 50_000 } }
+
+        it "takes less than 0.85s" do
+          expect(elapsed_time { subject }).to be < 0.85
+        end
+      end
+
+      context "with position set as first value" do
+        let(:attrs) { { position: 0 } }
+
+        it "takes less than 1.5s" do
+          expect(elapsed_time { subject }).to be < 1.5
+        end
+      end
+    end
+  end
+end
diff --git a/spec/performance/no_index_spec.rb b/spec/performance/no_index_spec.rb
new file mode 100644
index 0000000..c7c777f
--- /dev/null
+++ b/spec/performance/no_index_spec.rb
@@ -0,0 +1,120 @@
+# frozen_string_literal: true
+
+RSpec.describe "Performance no index" do
+  before(:all) do
+    attrs = (0...100_000).map do |position|
+      "('#{SecureRandom.alphanumeric(8)}', #{position})"
+    end
+
+    BasicModel.connection.execute(<<-SQL)
+      ALTER TABLE basic_models
+      DROP CONSTRAINT basic_models_position_key;
+
+      INSERT INTO basic_models (name, position)
+      VALUES
+        #{attrs.join(', ')};
+    SQL
+  end
+
+  after(:all) do
+    BasicModel.delete_all
+    BasicModel.connection.execute(<<-SQL)
+      ALTER TABLE basic_models
+      ADD UNIQUE(position) DEFERRABLE INITIALLY DEFERRED;
+    SQL
+  end
+
+  describe "model without scope" do
+    context "on #update" do
+      subject { create(:basic_model).update!(position: position) }
+
+      context "with position set as first value" do
+        let(:position) { 0 }
+
+        it "takes less than 0.9s" do
+          expect(elapsed_time { subject }).to be < 0.9
+        end
+      end
+
+      context "with position set as middle value" do
+        let(:position) { 50_000 }
+
+        it "takes less than 0.5s" do
+          expect(elapsed_time { subject }).to be < 0.5
+        end
+      end
+
+      context "with position set as last value" do
+        let(:position) { 99_999 }
+
+        it "takes less than 0.09s" do
+          expect(elapsed_time { subject }).to be < 0.09
+        end
+      end
+    end
+
+    context "on #create" do
+      subject { create(:basic_model, **attrs) }
+      let(:attrs) { {} }
+
+      context "without position specified" do
+        it "takes less than 0.04s" do
+          expect(elapsed_time { subject }).to be < 0.04
+        end
+      end
+
+      context "with postion set as 3/4 of total count" do
+        let(:attrs) { { position: 75_000 } }
+
+        it "takes less than 0.25s" do
+          expect(elapsed_time { subject }).to be < 0.25
+        end
+      end
+
+      context "with position set as the middle value" do
+        let(:attrs) { { position: 50_000 } }
+
+        it "takes less than 0.5s" do
+          expect(elapsed_time { subject }).to be < 0.5
+        end
+      end
+
+      context "with position set as first value" do
+        let(:attrs) { { position: 0 } }
+
+        it "takes less than 0.9s" do
+          expect(elapsed_time { subject }).to be < 0.9
+        end
+      end
+    end
+
+    context "on #destroy" do
+      subject { record.destroy! }
+      let!(:record) { create(:basic_model, **attrs) }
+
+      context "with position set as last value" do
+        let(:attrs) { { position: 100_000 } }
+
+        it "takes less than 0.025s" do
+          expect(elapsed_time { subject }).to be < 0.025
+        end
+      end
+
+      context "with position set as middle value" do
+        let(:attrs) { { position: 50_000 } }
+
+        it "takes less than 0.6s" do
+          expect(elapsed_time { subject }).to be < 0.6
+        end
+      end
+
+      context "with position set as first value" do
+        let(:attrs) { { position: 0 } }
+
+        it "takes less than 1.15s" do
+          expect(elapsed_time { subject }).to be < 1.15
+        end
+      end
+    end
+  end
+end
diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
index f0b5112..9c38a0d 100644
--- a/spec/spec_helper.rb
+++ b/spec/spec_helper.rb
@@ -36,6 +36,8 @@
     end
   end
 
+  config.exclude_pattern = "spec/performance/*.rb" if ENV["PERFORMANCE_TESTS_DISABLED"] == "1"
+
   config.before(:suite) do
     Rake::Task["db:create"].invoke
     Rake::Task["db:migrate"].invoke
@@ -62,3 +64,9 @@
     with.library :active_model
   end
 end
+
+def elapsed_time(&block)
+  Benchmark.measure do
+    block.call
+  end.real
+end