Whenever the random topic list backfill is executed page load time is dramatically hit.
In this example here an additional
301.9 ms for the single query.
If the “random topic” plays any part of a new users experience to a site…
…perhaps it would be best to not make the query immediately and only return / update the results via the message bus once available?
Executing action: show T+493.1 ms Reader 301.9 ms lib/freedom_patches/fast_pluck.rb:41:in `select_raw' lib/freedom_patches/fast_pluck.rb:79:in `pluck' lib/freedom_patches/fast_pluck.rb:71:in `pluck' app/services/random_topic_selector.rb:27:in `backfill' app/services/random_topic_selector.rb:57:in `next' lib/topic_query.rb:657:in `random_suggested' lib/topic_query.rb:111:in `list_suggested_for' lib/topic_view.rb:298:in `suggested_topics' app/serializers/topic_view_serializer.rb:90:in `details' app/controllers/application_controller.rb:262:in `render_json_dump' app/controllers/topics_controller.rb:580:in `block (2 levels) in perform_show_response' app/controllers/topics_controller.rb:572:in `perform_show_response' app/controllers/topics_controller.rb:89:in `show' lib/middleware/anonymous_cache.rb:129:in `call' config/initializers/100-quiet_logger.rb:10:in `call_with_quiet_assets' config/initializers/100-silence_logger.rb:26:in `call' lib/middleware/request_tracker.rb:73:in `call' lib/scheduler/defer.rb:85:in `process_client' lib/middleware/unicorn_oobgc.rb:95:in `process_client'
SELECT "topics"."id" FROM "topics" LEFT OUTER JOIN "categories" ON "categories"."id" = "topics"."category_id" LEFT OUTER JOIN topic_users AS tu ON (topics.id = tu.topic_id AND tu.user_id = -1) WHERE (categories.id = 114 OR (categories.parent_category_id = 114 AND categories.topic_id <> topics.id)) AND (topics.archetype <> 'private_message') AND (COALESCE(categories.topic_id, 0) <> topics.id) AND "topics"."visible" = 't' AND ("topics"."id" != 67459) AND (topics.deleted_at IS NULL) AND (COALESCE(tu.notification_level,1) > 0) AND ( NOT EXISTS ( SELECT 1 FROM category_users cu WHERE cu.user_id = -1 AND cu.category_id = topics.category_id AND cu.notification_level = 0 AND cu.category_id <> 114 AND (tu.notification_level IS NULL OR tu.notification_level < 2) )) AND "topics"."closed" = 'f' AND "topics"."archived" = 'f' ORDER BY RANDOM() LIMIT 3000
For information that is perhaps rarely seen on initial render (bottom of page), just may be this is a good optimisation?