Add markdown cache columns to the database, but don't use them yet

This commit adds a number of _html columns and, with the exception of Note,
starts updating them whenever the content of their partner fields changes.

Note has a collision with the note_html attr_accessor; that will be fixed later

A background worker for clearing these cache columns is also introduced - use
`rake cache:clear` to set it off. You can clear the database or Redis caches
separately by running `rake cache:clear:db` or `rake cache:clear:redis`,
respectively.

1 files changed, 23 insertions, 0 deletions

diff --git a/app/workers/clear_database_cache_worker.rb b/app/workers/clear_database_cache_worker.rb
new file mode 100644
index 00000000000..c541daba50e
--- /dev/null
+++ b/app/workers/clear_database_cache_worker.rb
@@ -0,0 +1,23 @@
+# This worker clears all cache fields in the database, working in batches.
+class ClearDatabaseCacheWorker
+  include Sidekiq::Worker
+
+  BATCH_SIZE = 1000
+
+  def perform
+    CacheMarkdownField.caching_classes.each do |kls|
+      fields = kls.cached_markdown_fields.html_fields
+      clear_cache_fields = fields.each_with_object({}) do |field, memo|
+        memo[field] = nil
+      end
+
+      Rails.logger.debug("Clearing Markdown cache for #{kls}: #{fields.inspect}")
+
+      kls.unscoped.in_batches(of: BATCH_SIZE) do |relation|
+        relation.update_all(clear_cache_fields)
+      end
+    end
+
+    nil
+  end
+end