Clean up pending builds on GitLab.com in batches

db/post_migrate/20210525075724_clean_up_pending_builds_table.rb

 # frozen_string_literal: true
 
 class CleanUpPendingBuildsTable < ActiveRecord::Migration[6.0]
+  BATCH_SIZE = 1000
+
+  disable_ddl_transaction!
+
   def up
-    execute <<~SQL
-      DELETE FROM ci_pending_builds
-        USING ci_builds
-        WHERE ci_builds.id = ci_pending_builds.build_id
-          AND ci_builds.status != 'pending'
-          AND ci_builds.type = 'Ci::Build'
-    SQL
+    return unless Gitlab.com?
+
+    each_batch('ci_pending_builds', of: BATCH_SIZE) do |min, max|
+      execute <<~SQL
+        DELETE FROM ci_pending_builds
+          USING ci_builds
+          WHERE ci_builds.id = ci_pending_builds.build_id
+            AND ci_builds.status != 'pending'
+            AND ci_builds.type = 'Ci::Build'
+            AND ci_pending_builds.id BETWEEN #{min} AND #{max}
+      SQL
+    end
   end
 
   def down
     # noop
   end
+
+  private
+
+  def each_batch(table_name, scope: ->(table) { table.all }, of: 1000)
+    table = Class.new(ActiveRecord::Base) do
+      include EachBatch
+
+      self.table_name = table_name
+      self.inheritance_column = :_type_disabled
+    end
+
+    scope.call(table).each_batch(of: of) do |batch|
+      yield batch.pluck('MIN(id), MAX(id)').first
+    end
+  end
 end

spec/migrations/clean_up_pending_builds_table_spec.rb

@@ -10,6 +10,8 @@ RSpec.describe CleanUpPendingBuildsTable do
   let(:builds) { table(:ci_builds) }
 
   before do
+    allow(Gitlab).to receive(:com?).and_return(true)
+
     namespaces.create!(id: 123, name: 'sample', path: 'sample')
     projects.create!(id: 123, name: 'sample', path: 'sample', namespace_id: 123)
 
@@ -32,4 +34,16 @@ RSpec.describe CleanUpPendingBuildsTable do
     expect(queue.first.id).to eq 1
     expect(builds.all.count).to eq 6
   end
+
+  context 'when there are multiple batches' do
+    before do
+      stub_const("#{described_class}::BATCH_SIZE", 1)
+    end
+
+    it 'iterates the data correctly' do
+      migrate!
+
+      expect(queue.all.count).to eq 1
+    end
+  end
 end