Banzai - avoid redis if attr is in DB cachebanzai-avoid-redis-if-db-cache

When cache_collection_render runs we end up reading and writing
things to redis even if we already have the rendered field cached
in the DB. This commit avoids using redis at all whenever we have
the field already rendered in the DB cache.

1 files changed, 13 insertions, 2 deletions

diff --git a/app/models/concerns/cache_markdown_field.rb b/app/models/concerns/cache_markdown_field.rb
index 42203a5f214..9713e79f525 100644
--- a/app/models/concerns/cache_markdown_field.rb
+++ b/app/models/concerns/cache_markdown_field.rb
@@ -87,6 +87,16 @@ module CacheMarkdownField
     __send__(cached_markdown_fields.html_field(markdown_field)) # rubocop:disable GitlabSecurity/PublicSend
   end
 
+  # Updates the markdown cache if necessary, then returns the field
+  # Unlike `cached_html_for` it returns `nil` if the field does not exist
+  def updated_cached_html_for(markdown_field)
+    return unless cached_markdown_fields.markdown_fields.include?(markdown_field)
+
+    refresh_markdown_cache if attribute_invalidated?(cached_markdown_fields.html_field(markdown_field))
+
+    cached_html_for(markdown_field)
+  end
+
   def latest_cached_markdown_version
     @latest_cached_markdown_version ||= (Gitlab::MarkdownCache::CACHE_COMMONMARK_VERSION << 16) | local_version
   end
@@ -139,8 +149,9 @@ module CacheMarkdownField
       # The HTML becomes invalid if any dependent fields change. For now, assume
       # author and project invalidate the cache in all circumstances.
       define_method(invalidation_method) do
-        invalidations = changed_markdown_fields & [markdown_field.to_s, *INVALIDATED_BY]
-        invalidations.delete(markdown_field.to_s) if changed_markdown_fields.include?("#{markdown_field}_html")
+        changed_fields = changed_attributes.keys
+        invalidations  = changed_fields & [markdown_field.to_s, *INVALIDATED_BY]
+        invalidations.delete(markdown_field.to_s) if changed_fields.include?("#{markdown_field}_html")
         !invalidations.empty? || !cached_html_up_to_date?(markdown_field)
       end
     end