Add migration for backfilling project namespaces

Adding capabilities to backfill project namespace for each
project. Starting with ability to backfill project namespaces
for a single root namespace first.

Changelog: added

app/models/namespace.rb

@@ -17,6 +17,9 @@ class Namespace < ApplicationRecord
   include EachBatch
 
   ignore_column :delayed_project_removal, remove_with: '14.1', remove_after: '2021-05-22'
+  # Temporary column used for back-filling project namespaces.
+  # Remove it once the back-filling of all project namespaces is done.
+  ignore_column :tmp_project_id, remove_with: '14.7', remove_after: '2022-01-22'
 
   # Tells ActiveRecord not to store the full class name, in order to save some space
   # https://gitlab.com/gitlab-org/gitlab/-/merge_requests/69794

db/migrate/20211018101034_add_tmp_project_id_column_to_namespaces.rb

+# frozen_string_literal: true
+
+class AddTmpProjectIdColumnToNamespaces < Gitlab::Database::Migration[1.0]
+  enable_lock_retries!
+
+  def change
+    # this is a temporary column to be able to batch insert records into namespaces table and then be able to link these
+    # to projects table.
+    add_column :namespaces, :tmp_project_id, :integer # rubocop: disable Migration/AddColumnsToWideTables
+  end
+end

db/post_migrate/20211018101552_add_index_to_tmp_project_id_column_on_namespaces_table.rb

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

db/post_migrate/20211018101852_add_fk_to_tmp_project_id_column_on_namespaces_table.rb

+# frozen_string_literal: true
+
+class AddFkToTmpProjectIdColumnOnNamespacesTable < Gitlab::Database::Migration[1.0]
+  disable_ddl_transaction!
+
+  def up
+    add_concurrent_foreign_key :namespaces, :projects, column: :tmp_project_id
+  end
+
+  def down
+    remove_foreign_key :namespaces, column: :tmp_project_id
+  end
+end

db/post_migrate/20211018102252_add_index_to_group_id_column_on_webhooks_table.rb

+# frozen_string_literal: true
+
+class AddIndexToGroupIdColumnOnWebhooksTable < Gitlab::Database::Migration[1.0]
+  disable_ddl_transaction!
+
+  INDEX_NAME = 'index_on_group_id_on_webhooks'
+
+  def up
+    add_concurrent_index :web_hooks, :group_id, name: INDEX_NAME
+  end
+
+  def down
+    remove_concurrent_index_by_name :web_hooks, INDEX_NAME
+  end
+end

db/schema_migrations/20211018101034

+1cadc3a932d5b62cfeafcd4090eddc37b44997dbbd0b34da1c7c87a5774bb683
\ No newline at end of file

db/schema_migrations/20211018101552

+9a62f0ec43ab295619d82494090c38539cb16408c8971bdde86bb8d02546f558
\ No newline at end of file

db/schema_migrations/20211018101852

+30e9632877d3ad33528be0f56962c0ab57f5eee3889183d9638cbaea903a3d82
\ No newline at end of file

db/schema_migrations/20211018102252

+14bb815cbdad2db56dafb7eaaff893de96116a1a9e8d6c5ed95f4bef9b9717fc
\ No newline at end of file

db/structure.sql

@@ -16375,7 +16375,8 @@ CREATE TABLE namespaces (
     push_rule_id bigint,
     shared_runners_enabled boolean DEFAULT true NOT NULL,
     allow_descendants_override_disabled_shared_runners boolean DEFAULT false NOT NULL,
-    traversal_ids integer[] DEFAULT '{}'::integer[] NOT NULL
+    traversal_ids integer[] DEFAULT '{}'::integer[] NOT NULL,
+    tmp_project_id integer
 );
 
 CREATE SEQUENCE namespaces_id_seq
@@ -26591,6 +26592,8 @@ CREATE INDEX index_oauth_openid_requests_on_access_grant_id ON oauth_openid_requ
 
 CREATE UNIQUE INDEX index_on_deploy_keys_id_and_type_and_public ON keys USING btree (id, type) WHERE (public = true);
 
+CREATE INDEX index_on_group_id_on_webhooks ON web_hooks USING btree (group_id);
+
 CREATE INDEX index_on_identities_lower_extern_uid_and_provider ON identities USING btree (lower((extern_uid)::text), provider);
 
 CREATE UNIQUE INDEX index_on_instance_statistics_recorded_at_and_identifier ON analytics_usage_trends_measurements USING btree (identifier, recorded_at);
@@ -27769,6 +27772,8 @@ CREATE INDEX tmp_index_namespaces_empty_traversal_ids_with_child_namespaces ON n
 
 CREATE INDEX tmp_index_namespaces_empty_traversal_ids_with_root_namespaces ON namespaces USING btree (id) WHERE ((parent_id IS NULL) AND (traversal_ids = '{}'::integer[]));
 
+CREATE UNIQUE INDEX tmp_index_on_tmp_project_id_on_namespaces ON namespaces USING btree (tmp_project_id);
+
 CREATE INDEX tmp_index_on_vulnerabilities_non_dismissed ON vulnerabilities USING btree (id) WHERE (state <> 2);
 
 CREATE UNIQUE INDEX uniq_pkgs_deb_grp_architectures_on_distribution_id_and_name ON packages_debian_group_architectures USING btree (distribution_id, name);
@@ -29012,6 +29017,9 @@ ALTER TABLE ONLY application_settings
 ALTER TABLE ONLY merge_requests
     ADD CONSTRAINT fk_6a5165a692 FOREIGN KEY (milestone_id) REFERENCES milestones(id) ON DELETE SET NULL;
 
+ALTER TABLE ONLY namespaces
+    ADD CONSTRAINT fk_6a77f66919 FOREIGN KEY (tmp_project_id) REFERENCES projects(id) ON DELETE CASCADE;
+
 ALTER TABLE ONLY geo_event_log
     ADD CONSTRAINT fk_6ada82d42a FOREIGN KEY (container_repository_updated_event_id) REFERENCES geo_container_repository_updated_events(id) ON DELETE CASCADE;
 

lib/gitlab/background_migration/project_namespaces/backfill_project_namespaces.rb

+# frozen_string_literal: true
+
+module Gitlab
+  module BackgroundMigration
+    module ProjectNamespaces
+      # Back-fill project namespaces for projects that do not yet have a namespace.
+      #
+      # TODO: remove this comment when an actuall backfill migration is added.
+      #
+      # This is first being added without an actual migration as we need to initially test
+      # if backfilling project namespaces affects performance in any significant way.
+      # rubocop: disable Metrics/ClassLength
+      class BackfillProjectNamespaces
+        BATCH_SIZE = 100
+        DELETE_BATCH_SIZE = 10
+        PROJECT_NAMESPACE_STI_NAME = 'Project'
+
+        IsolatedModels = ::Gitlab::BackgroundMigration::ProjectNamespaces::Models
+
+        def perform(start_id, end_id, namespace_id, migration_type = 'up')
+          load_project_ids(start_id, end_id, namespace_id)
+
+          case migration_type
+          when 'up'
+            backfill_project_namespaces(namespace_id)
+            mark_job_as_succeeded(start_id, end_id, namespace_id, 'up')
+          when 'down'
+            cleanup_backfilled_project_namespaces(namespace_id)
+            mark_job_as_succeeded(start_id, end_id, namespace_id, 'down')
+          else
+            raise "Unknown migration type"
+          end
+        end
+
+        private
+
+        attr_accessor :project_ids
+
+        def backfill_project_namespaces(namespace_id)
+          project_ids.each_slice(BATCH_SIZE) do |project_ids|
+            # We need to lock these project records for the period when we create project namespaces
+            # and link them to projects so that if a project is modified in the time between creating
+            # project namespaces `batch_insert_namespaces` and linking them to projects `batch_update_projects`
+            # we do not get them out of sync.
+            #
+            # see https://gitlab.com/gitlab-org/gitlab/-/merge_requests/72527#note_730679469
+            Project.transaction do
+              Project.where(id: project_ids).select(:id).lock!('FOR UPDATE')
+
+              batch_insert_namespaces(project_ids)
+              batch_update_projects(project_ids)
+            end
+
+            batch_update_project_namespaces_traversal_ids(project_ids)
+          end
+        end
+
+        def cleanup_backfilled_project_namespaces(namespace_id)
+          project_ids.each_slice(BATCH_SIZE) do |project_ids|
+            # IMPORTANT: first nullify project_namespace_id in projects table to avoid removing projects when records
+            # from namespaces are deleted due to FK/triggers
+            nullify_project_namespaces_in_projects(project_ids)
+            delete_project_namespace_records(project_ids)
+          end
+        end
+
+        def batch_insert_namespaces(project_ids)
+          projects = IsolatedModels::Project.where(id: project_ids)
+            .select("projects.id, projects.name, projects.path, projects.namespace_id, projects.visibility_level, shared_runners_enabled, '#{PROJECT_NAMESPACE_STI_NAME}', now(), now()")
+
+          ActiveRecord::Base.connection.execute <<~SQL
+            INSERT INTO namespaces (tmp_project_id, name, path, parent_id, visibility_level, shared_runners_enabled, type, created_at, updated_at)
+            #{projects.to_sql}
+            ON CONFLICT DO NOTHING;
+          SQL
+        end
+
+        def batch_update_projects(project_ids)
+          projects = IsolatedModels::Project.where(id: project_ids)
+                       .joins("INNER JOIN namespaces ON projects.id = namespaces.tmp_project_id")
+                       .select("namespaces.id, namespaces.tmp_project_id")
+
+          ActiveRecord::Base.connection.execute <<~SQL
+            WITH cte(project_namespace_id, project_id) AS #{::Gitlab::Database::AsWithMaterialized.materialized_if_supported} (
+              #{projects.to_sql}
+            )
+            UPDATE projects
+            SET project_namespace_id = cte.project_namespace_id
+            FROM cte
+            WHERE id = cte.project_id AND projects.project_namespace_id IS DISTINCT FROM cte.project_namespace_id
+          SQL
+        end
+
+        def batch_update_project_namespaces_traversal_ids(project_ids)
+          namespaces = Namespace.where(tmp_project_id: project_ids)
+                         .joins("INNER JOIN namespaces n2 ON namespaces.parent_id = n2.id")
+                         .select("namespaces.id as project_namespace_id, n2.traversal_ids")
+
+          ActiveRecord::Base.connection.execute <<~SQL
+            UPDATE namespaces
+            SET traversal_ids = array_append(project_namespaces.traversal_ids, project_namespaces.project_namespace_id)
+            FROM (#{namespaces.to_sql}) as project_namespaces(project_namespace_id, traversal_ids)
+            WHERE id = project_namespaces.project_namespace_id
+          SQL
+        end
+
+        def nullify_project_namespaces_in_projects(project_ids)
+          IsolatedModels::Project.where(id: project_ids).update_all(project_namespace_id: nil)
+        end
+
+        def delete_project_namespace_records(project_ids)
+          project_ids.each_slice(DELETE_BATCH_SIZE) do |p_ids|
+            IsolatedModels::Namespace.where(type: PROJECT_NAMESPACE_STI_NAME).where(tmp_project_id: p_ids).delete_all
+          end
+        end
+
+        def load_project_ids(start_id, end_id, namespace_id)
+          projects = IsolatedModels::Project.arel_table
+          relation = IsolatedModels::Project.where(projects[:id].between(start_id..end_id))
+          relation = relation.where(projects[:namespace_id].in(Arel::Nodes::SqlLiteral.new(hierarchy_cte(namespace_id)))) if namespace_id
+
+          @project_ids = relation.pluck(:id)
+        end
+
+        def mark_job_as_succeeded(*arguments)
+          ::Gitlab::Database::BackgroundMigrationJob.mark_all_as_succeeded('BackfillProjectNamespaces', arguments)
+        end
+
+        def hierarchy_cte(root_namespace_id)
+          <<-SQL
+              WITH RECURSIVE "base_and_descendants" AS (
+                  (
+                      SELECT "namespaces"."id"
+                      FROM "namespaces"
+                      WHERE "namespaces"."type" = 'Group' AND "namespaces"."id" = #{root_namespace_id.to_i}
+                  )
+                  UNION
+                  (
+                      SELECT "namespaces"."id"
+                      FROM "namespaces", "base_and_descendants"
+                      WHERE "namespaces"."type" = 'Group' AND "namespaces"."parent_id" = "base_and_descendants"."id"
+                  )
+              )
+              SELECT "id" FROM "base_and_descendants" AS "namespaces"
+          SQL
+        end
+      end
+      # rubocop: enable Metrics/ClassLength
+    end
+  end
+end

lib/gitlab/background_migration/project_namespaces/models/namespace.rb

+# frozen_string_literal: true
+
+module Gitlab
+  module BackgroundMigration
+    module ProjectNamespaces
+      module Models
+        # isolated Namespace model
+        class Namespace < ActiveRecord::Base
+          include EachBatch
+
+          self.table_name = 'namespaces'
+          self.inheritance_column = :_type_disabled
+        end
+      end
+    end
+  end
+end

lib/gitlab/background_migration/project_namespaces/models/project.rb

+# frozen_string_literal: true
+
+module Gitlab
+  module BackgroundMigration
+    module ProjectNamespaces
+      module Models
+        # isolated Project model
+        class Project < ActiveRecord::Base
+          include EachBatch
+
+          self.table_name = 'projects'
+        end
+      end
+    end
+  end
+end