Work in progress

db/post_migrate/20210930211936_backfill_user_namespace.rb

@@ -3,7 +3,8 @@
 class BackfillUserNamespace < Gitlab::Database::Migration[1.0]
   MIGRATION = 'BackfillUserNamespace'
   INTERVAL = 2.minutes
-  BATCH_SIZE = 10_000
+  BATCH_SIZE = 1_000
+  SUB_BATCH_SIZE = 200
   DOWNTIME = false
 
   def up
@@ -12,7 +13,8 @@ class BackfillUserNamespace < Gitlab::Database::Migration[1.0]
       :namespaces,
       :id,
       job_interval: INTERVAL,
-      batch_size: BATCH_SIZE
+      batch_size: BATCH_SIZE,
+      sub_batch_size: SUB_BATCH_SIZE
     )
   end
 

lib/gitlab/background_migration/backfill_user_namespace.rb

@@ -5,12 +5,41 @@ module Gitlab
     # Backfills the `namespaces.type` column, replacing any
     # instances of `NULL` with `User`
     class BackfillUserNamespace
-      def perform(start_id, stop_id, *args)
-        ActiveRecord::Base.connection.execute(<<~SQL)
-          UPDATE namespaces SET type = 'User'
-          WHERE id BETWEEN #{start_id} AND #{stop_id}
-            AND type IS NULL
-        SQL
+      include Gitlab::Database::DynamicModelHelpers
+
+      def perform(start_id, end_id, batch_table, batch_column, sub_batch_size)
+        parent_batch_relation = relation_scoped_to_range(batch_table, batch_column, start_id, end_id)
+
+        parent_batch_relation.each_batch(column: batch_column, of: sub_batch_size) do |sub_batch|
+          batch_metrics.time_operation(:update_all) do
+            sub_batch.update_all(type: 'User')
+          end
+
+          pause_ms = 0 if pause_ms < 0
+          sleep(pause_ms * 0.001)
+        end
+
+        # ActiveRecord::Base.connection.execute(<<~SQL)
+        #   UPDATE namespaces SET type = 'User'
+        #   WHERE id BETWEEN #{start_id} AND #{end_id}
+        #     AND type IS NULL
+        # SQL
+      end
+
+      def batch_metrics
+        @batch_metrics ||= Gitlab::Database::BackgroundMigration::BatchMetrics.new
+      end
+
+      private
+
+      def connection
+        ActiveRecord::Base.connection
+      end
+
+      def relation_scoped_to_range(source_table, source_key_column, start_id, stop_id)
+        define_batchable_model(source_table)
+          .where(source_key_column => start_id..stop_id)
+          .where(type: nil)
       end
     end
   end