Fix project destruction failing due to idle in transaction timeouts

When deleting associated records, Rails loads all associations into memory
(https://github.com/rails/rails/issues/22510) before destroying them. This
can cause a surge in memory and cause destruction of objects to fail
due to idle in transaction database timeouts. This fix is inspired from
https://github.com/thisismydesign to destroy `has_many` relationships
in batches.

Closes #44610

1 files changed, 28 insertions, 0 deletions

diff --git a/app/models/concerns/batch_destroy_dependent_associations.rb b/app/models/concerns/batch_destroy_dependent_associations.rb
new file mode 100644
index 00000000000..353ee2e73d0
--- /dev/null
+++ b/app/models/concerns/batch_destroy_dependent_associations.rb
@@ -0,0 +1,28 @@
+# Provides a way to work around Rails issue where dependent objects are all
+# loaded into memory before destroyed: https://github.com/rails/rails/issues/22510.
+#
+# This concern allows an ActiveRecord module to destroy all its dependent
+# associations in batches. The idea is borrowed from https://github.com/thisismydesign/batch_dependent_associations.
+#
+# The differences here with that gem:
+#
+# 1. We allow excluding certain associations.
+# 2. We don't need to support delete_all since we can use the EachBatch concern.
+module BatchDestroyDependentAssociations
+  extend ActiveSupport::Concern
+
+  DEPENDENT_ASSOCIATIONS_BATCH_SIZE = 1000
+
+  def dependent_associations_to_destroy
+    self.class.reflect_on_all_associations(:has_many).select { |assoc| assoc.options[:dependent] == :destroy }
+  end
+
+  def destroy_dependent_associations_in_batches(exclude: [])
+    dependent_associations_to_destroy.each do |association|
+      next if exclude.include?(association.name)
+
+      # rubocop:disable GitlabSecurity/PublicSend
+      public_send(association.name).find_each(batch_size: DEPENDENT_ASSOCIATIONS_BATCH_SIZE, &:destroy)
+    end
+  end
+end