PERF: Improve performance of DiscourseTagging.hidden_tag_names (stable backport) (#36638)

nullchristo · web-flow · commit 5b19143e6990 · 2025-12-11T13:57:31.000-06:00
This backports #36636 to stable. Improve performance of `DiscourseTagging.hidden_tag_names` by using its own query. Previously it added `where.not(id: ` to the query from `DiscourseTagging.visible_tags`. This simplifies the hidden_tag_names query by just directly running the inverse query, to find names of tags which have at least one TagGroupPermission but do not have any for permitted tag groups. This query gets run every time tags are displayed on a page, and the goal here is to improve performance in the case tracked in internal topic /t/168944. On that customer's site, this reduces the query time from ~11ms to ~5ms.
diff --git a/lib/discourse_tagging.rb b/lib/discourse_tagging.rb
@@ -644,7 +644,21 @@ def self.filter_visible(query, guardian = nil)
   end
 
   def self.hidden_tag_names(guardian = nil)
-    guardian&.is_staff? ? [] : Tag.where.not(id: visible_tags(guardian).select(:id)).pluck(:name)
+    if guardian&.is_staff?
+      []
+    else
+      # Hidden tags have at least one TagGroupPermission but must not have any for permitted groups
+      Tag
+        .where(id: TagGroupMembership.joins(tag_group: :tag_group_permissions).select(:tag_id))
+        .where.not(
+          id:
+            TagGroupPermission
+              .joins(tag_group: :tag_group_memberships)
+              .where(group_id: permitted_group_ids_query(guardian))
+              .select("tag_group_memberships.tag_id"),
+        )
+        .pluck(:name)
+    end
   end
 
   def self.permitted_group_ids_query(guardian = nil)
