1 files changed, 57 insertions, 0 deletions
diff --git a/rubocop/cop/migration/update_large_table.rb b/rubocop/cop/migration/update_large_table.rb
new file mode 100644
index 00000000000..3ae3fb1b68e
--- /dev/null
+++ b/rubocop/cop/migration/update_large_table.rb
@@ -0,0 +1,57 @@
+require_relative '../../migration_helpers'
+
+module RuboCop
+  module Cop
+    module Migration
+      # This cop checks for `add_column_with_default` on a table that's been
+      # explicitly blacklisted because of its size.
+      #
+      # Even though this helper performs the update in batches to avoid
+      # downtime, using it with tables with millions of rows still causes a
+      # significant delay in the deploy process and is best avoided.
+      #
+      # See https://gitlab.com/gitlab-com/infrastructure/issues/1602 for more
+      # information.
+      class UpdateLargeTable < RuboCop::Cop::Cop
+        include MigrationHelpers
+
+        MSG = 'Using `%s` on the `%s` table will take a long time to ' \
+              'complete, and should be avoided unless absolutely ' \
+              'necessary'.freeze
+
+        LARGE_TABLES = %i[
+          ci_pipelines
+          ci_builds
+          events
+          issues
+          merge_request_diff_files
+          merge_request_diffs
+          merge_requests
+          namespaces
+          notes
+          projects
+          routes
+          users
+        ].freeze
+
+        def_node_matcher :batch_update?, <<~PATTERN
+          (send nil ${:add_column_with_default :update_column_in_batches} $(sym ...) ...)
+        PATTERN
+
+        def on_send(node)
+          return unless in_migration?(node)
+
+          matches = batch_update?(node)
+          return unless matches
+
+          update_method = matches.first
+          table = matches.last.to_a.first
+
+          return unless LARGE_TABLES.include?(table)
+
+          add_offense(node, :expression, format(MSG, update_method, table))
+        end
+      end
+    end
+  end
+end