Replace namespaces unique index on name and parent_id

This replaces the unique index on name and parent_id in
namespaces table with an unique index on name, parent_id
and type. We need this index change in order to cover name
uniqueness across namespaces of type Group and also allow
the possibility to have one namespace of type ProjectNamespace
with the same name as a Group to maintain current functionality
parity between namespaces and projects.

https://gitlab.com/gitlab-org/gitlab/-/issues/341814

Changelog: changed

db/migrate/20210922172056_add_unique_namespaces_index_on_name_parent_id_and_type.rb

+# frozen_string_literal: true
+
+class AddUniqueNamespacesIndexOnNameParentIdAndType < Gitlab::Database::Migration[1.0]
+  INDEX_NAME = 'index_namespaces_name_parent_id_type'
+
+  disable_ddl_transaction!
+
+  def up
+    add_concurrent_index :namespaces, [:name, :parent_id, :type], unique: true, name: INDEX_NAME
+  end
+
+  def down
+    remove_concurrent_index_by_name :namespaces, INDEX_NAME
+  end
+end

db/migrate/20210922172156_drop_unique_namespaces_index_on_name_and_parent_id.rb

+# frozen_string_literal: true
+
+class DropUniqueNamespacesIndexOnNameAndParentId < Gitlab::Database::Migration[1.0]
+  INDEX_NAME = 'index_namespaces_on_name_and_parent_id'
+
+  disable_ddl_transaction!
+
+  def up
+    remove_concurrent_index_by_name :namespaces, INDEX_NAME
+  end
+
+  def down
+    add_concurrent_index :namespaces, [:name, :parent_id], unique: true, name: INDEX_NAME
+  end
+end

db/schema_migrations/20210922172056

+c50ccd9986188356776c2d19c5544a6da6e31b5bb1b16ed259455604cb6fd862
\ No newline at end of file

db/schema_migrations/20210922172156

+083b18b8e687ae8ff9d93ee77c6d4fc2916a2f1b77acf44132f216236b0ff06c
\ No newline at end of file

db/structure.sql

@@ -25678,6 +25678,8 @@ CREATE INDEX index_namespaces_id_parent_id_is_not_null ON namespaces USING btree
 
 CREATE INDEX index_namespaces_id_parent_id_is_null ON namespaces USING btree (id) WHERE (parent_id IS NULL);
 
+CREATE UNIQUE INDEX index_namespaces_name_parent_id_type ON namespaces USING btree (name, parent_id, type);
+
 CREATE INDEX index_namespaces_on_created_at ON namespaces USING btree (created_at);
 
 CREATE INDEX index_namespaces_on_custom_project_templates_group_id_and_type ON namespaces USING btree (custom_project_templates_group_id, type) WHERE (custom_project_templates_group_id IS NOT NULL);
@@ -25688,8 +25690,6 @@ CREATE INDEX index_namespaces_on_ldap_sync_last_successful_update_at ON namespac
 
 CREATE INDEX index_namespaces_on_ldap_sync_last_update_at ON namespaces USING btree (ldap_sync_last_update_at);
 
-CREATE UNIQUE INDEX index_namespaces_on_name_and_parent_id ON namespaces USING btree (name, parent_id);
-
 CREATE INDEX index_namespaces_on_name_trigram ON namespaces USING gin (name gin_trgm_ops);
 
 CREATE INDEX index_namespaces_on_owner_id ON namespaces USING btree (owner_id);