Consider Random Topic backfill as background task?

Dev
1

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?

4 Likes
2

You only hit:

https://github.com/discourse/discourse/blob/master/app/services/random_topic_selector.rb#L61-L67

In very extreme cases.

In general the low watermark will hit and it will be deferred per:

https://github.com/discourse/discourse/blob/master/app/services/random_topic_selector.rb#L69-L73

1 Like