[15 min fix] Document data update scripts best practices (#13432)

* Add data update scripts best practices

* Remove leftover counter

docs/backend/data-update-scripts.md

@@ -79,3 +79,25 @@ DataUpdateScripts are also run automatically when a production deploy goes out.
 However, to ensure the new code they need to use has been deployed we use a
 [`DataUpdateWorker`](https://github.com/forem/forem/blob/main/app/workers/data_update_worker.rb)
 via Sidekiq and set it to run 10 minutes after the deploy script has completed.
+
+## Best practices
+
+### Working with large collections of rows
+
+From time to time, scripts need to operate on a large amount of rows; in those
+cases we encourage:
+
+- adding explicit logging to the script
+- reversing the order, to start processing the most recent records first
+
+For example:
+
+```ruby
+def run
+  Article.find_each(order: :desc).with_index do |article, index|
+    Rails.logging.info("...") if index % 1000 == 0 # this will log every 1000 articles
+
+    article.save
+  end
+end
+```