Resolve labels with duplicate title and group ID

- Add uniqueness index to DB

changelogs/unreleased/30390-duplicate-group-label.yml

+---
+title: Deduplicate labels with identical title and group
+merge_request: 37148
+author:
+type: fixed

db/post_migrate/20200716234259_remove_duplicate_labels_from_group.rb

+# frozen_string_literal: true
+
+class RemoveDuplicateLabelsFromGroup < ActiveRecord::Migration[6.0]
+  DOWNTIME = false
+
+  CREATE = 1
+  RENAME = 2
+
+  disable_ddl_transaction!
+
+  class BackupLabel < ApplicationRecord
+    include EachBatch
+
+    self.table_name = 'backup_labels'
+  end
+
+  class Label < ApplicationRecord
+    self.table_name = 'labels'
+  end
+
+  class Group < ApplicationRecord
+    include EachBatch
+
+    self.table_name = 'namespaces'
+  end
+
+  BATCH_SIZE = 10_000
+
+  def up
+    # Split to smaller chunks
+    # Loop rather than background job, every 10,000
+    # there are ~1,800,000 groups in total (excluding personal namespaces, which can't have labels)
+    Group.where(type: 'Group').each_batch(of: BATCH_SIZE) do |batch|
+      range = batch.pluck('MIN(id)', 'MAX(id)').first
+
+      transaction do
+        remove_full_duplicates(*range)
+      end
+
+      transaction do
+        rename_partial_duplicates(*range)
+      end
+    end
+  end
+
+  DOWN_BATCH_SIZE = 1000
+
+  def down
+    BackupLabel.where('project_id IS NULL AND group_id IS NOT NULL').each_batch(of: DOWN_BATCH_SIZE) do |batch|
+      range = batch.pluck('MIN(id)', 'MAX(id)').first
+
+      restore_renamed_labels(*range)
+      restore_deleted_labels(*range)
+    end
+  end
+
+  def remove_full_duplicates(start_id, stop_id)
+    # Fields that are considered duplicate:
+    # group_id title template description type color
+
+    duplicate_labels = ApplicationRecord.connection.execute(<<-SQL.squish)
+WITH data AS (
+  SELECT labels.*,
+  row_number() OVER (PARTITION BY labels.group_id, labels.title, labels.template, labels.description, labels.type, labels.color ORDER BY labels.id) AS row_number,
+  #{CREATE} AS restore_action
+  FROM labels
+  WHERE labels.group_id BETWEEN #{start_id} AND #{stop_id}
+  AND NOT EXISTS (SELECT * FROM board_labels WHERE board_labels.label_id = labels.id)
+  AND NOT EXISTS (SELECT * FROM label_links WHERE label_links.label_id = labels.id)
+  AND NOT EXISTS (SELECT * FROM label_priorities WHERE label_priorities.label_id = labels.id)
+  AND NOT EXISTS (SELECT * FROM lists WHERE lists.label_id = labels.id)
+  AND NOT EXISTS (SELECT * FROM resource_label_events WHERE resource_label_events.label_id = labels.id)
+) SELECT * FROM data WHERE row_number > 1;
+    SQL
+
+    if duplicate_labels.any?
+      # create backup records
+      BackupLabel.insert_all!(duplicate_labels.map { |label| label.except("row_number") })
+
+      Label.unscoped.where(id: duplicate_labels.pluck("id")).delete_all
+    end
+  end
+
+  def rename_partial_duplicates(start_id, stop_id)
+    # We need to ensure that the new title (with `_duplicate#{ID}`) doesn't exceed the limit.
+    # Truncate the original title (if needed) to 245 characters minus the length of the ID
+    # then add `_duplicate#{ID}`
+
+    soft_duplicates = ApplicationRecord.connection.execute(<<-SQL.squish)
+WITH data AS (
+  SELECT
+     *,
+     substring(title from 1 for 245 - length(id::text)) || '_duplicate' || id::text as new_title,
+     #{RENAME} AS restore_action,
+     row_number() OVER (PARTITION BY group_id, title ORDER BY id) AS row_number
+  FROM labels
+  WHERE group_id BETWEEN #{start_id} AND #{stop_id}
+) SELECT * FROM data WHERE row_number > 1;
+    SQL
+
+    if soft_duplicates.any?
+      # create backup records
+      BackupLabel.insert_all!(soft_duplicates.map { |label| label.except("row_number") })
+
+      ApplicationRecord.connection.execute(<<-SQL.squish)
+UPDATE labels SET title = substring(title from 1 for 245 - length(id::text)) || '_duplicate' || id::text
+WHERE labels.id IN (#{soft_duplicates.map { |dup| dup["id"] }.join(", ")});
+      SQL
+    end
+  end
+
+  def restore_renamed_labels(start_id, stop_id)
+    # the backup label IDs are not incremental, they are copied directly from the Labels table
+    ApplicationRecord.connection.execute(<<-SQL.squish)
+WITH backups AS (
+  SELECT id, title
+  FROM backup_labels
+  WHERE id BETWEEN #{start_id} AND #{stop_id}
+  AND restore_action = #{RENAME}
+) UPDATE labels SET title = backups.title
+FROM backups
+WHERE labels.id = backups.id;
+    SQL
+  end
+
+  def restore_deleted_labels(start_id, stop_id)
+    ActiveRecord::Base.connection.execute(<<-SQL.squish)
+INSERT INTO labels
+SELECT id, title, color, group_id, created_at, updated_at, template, description, description_html, type, cached_markdown_version FROM backup_labels
+  WHERE backup_labels.id BETWEEN #{start_id} AND #{stop_id}
+  AND backup_labels.project_id IS NULL AND backup_labels.group_id IS NOT NULL
+  AND backup_labels.restore_action = #{CREATE}
+    SQL
+  end
+end

db/post_migrate/20200716234518_add_uniqueness_index_to_label_title_and_group.rb

+# frozen_string_literal: true
+
+class AddUniquenessIndexToLabelTitleAndGroup < ActiveRecord::Migration[6.0]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  GROUP_AND_TITLE = [:group_id, :title]
+
+  def up
+    add_concurrent_index :labels, GROUP_AND_TITLE, where: "labels.project_id IS NULL", unique: true, name: "index_labels_on_group_id_and_title_unique"
+    remove_concurrent_index :labels, GROUP_AND_TITLE, name: "index_labels_on_group_id_and_title"
+  end
+
+  def down
+    add_concurrent_index :labels, GROUP_AND_TITLE, where: "labels.project_id IS NULL", unique: false, name: "index_labels_on_group_id_and_title"
+    remove_concurrent_index :labels, GROUP_AND_TITLE, name: "index_labels_on_group_id_and_title_unique"
+  end
+end

db/schema_migrations/20200716234259

+9683f55a327b9579b9b0b9484dd11a07b7ea4244b126c46e0144662cb25da6bb
\ No newline at end of file

db/schema_migrations/20200716234518

+71cd12e553b3acbb665770fe7478365f1f082e2d278c67b166f41461f689aa5e
\ No newline at end of file

db/structure.sql

@@ -21801,7 +21801,7 @@ CREATE UNIQUE INDEX index_label_priorities_on_project_id_and_label_id ON label_p
 
 CREATE UNIQUE INDEX index_labels_on_group_id_and_project_id_and_title ON labels USING btree (group_id, project_id, title);
 
-CREATE INDEX index_labels_on_group_id_and_title_with_null_project_id ON labels USING btree (group_id, title) WHERE (project_id IS NULL);
+CREATE UNIQUE INDEX index_labels_on_group_id_and_title_unique ON labels USING btree (group_id, title) WHERE (project_id IS NULL);
 
 CREATE INDEX index_labels_on_project_id ON labels USING btree (project_id);
 

spec/requests/api/labels_spec.rb

@@ -520,14 +520,29 @@ RSpec.describe API::Labels do
       expect(json_response['color']).to eq(label1.color)
     end
 
-    it 'returns 200 if group label already exists' do
-      create(:group_label, title: label1.name, group: group)
+    context 'if group label already exists' do
+      let!(:group_label) { create(:group_label, title: label1.name, group: group) }
 
-      expect { put api("/projects/#{project.id}/labels/promote", user), params: { name: label1.name } }
-        .to change(project.labels, :count).by(-1)
-        .and change(group.labels, :count).by(0)
+      it 'returns a status of 200' do
+        put api("/projects/#{project.id}/labels/promote", user), params: { name: label1.name }
 
-      expect(response).to have_gitlab_http_status(:ok)
+        expect(response).to have_gitlab_http_status(:ok)
+      end
+
+      it 'does not change the group label count' do
+        expect { put api("/projects/#{project.id}/labels/promote", user), params: { name: label1.name } }
+            .not_to change(group.labels, :count)
+      end
+
+      it 'does not change the group label max (reuses the same ID)' do
+        expect { put api("/projects/#{project.id}/labels/promote", user), params: { name: label1.name } }
+            .not_to change(group.labels, :max)
+      end
+
+      it 'changes the project label count' do
+        expect { put api("/projects/#{project.id}/labels/promote", user), params: { name: label1.name } }
+            .to change(project.labels, :count).by(-1)
+      end
     end
 
     it 'returns 403 if guest promotes label' do