class RandomTopicSelector BACKFILL_SIZE = 3000 BACKFILL_LOW_WATER_MARK = 500 def self.backfill(category=nil) exclude = category.try(:topic_id) # don't leak private categories into the "everything" group user = category ? CategoryFeaturedTopic.fake_admin : nil options = { per_page: SiteSetting.category_featured_topics, visible: true, no_definitions: true } options[:except_topic_ids] = [category.topic_id] if exclude options[:category] = category.id if category query = TopicQuery.new(user, options) results = query.latest_results.order('RANDOM()') .where(closed: false, archived: false) .where("topics.created_at > ?", SiteSetting.suggested_topics_max_days_old.days.ago) .limit(BACKFILL_SIZE) .reorder('RANDOM()') .pluck(:id) key = cache_key(category) results.each do |id| $redis.rpush(key, id) end $redis.expire(key, 2.days) results end def self.next(count, category=nil) key = cache_key(category) results = [] return results if count < 1 results = $redis.multi do $redis.lrange(key, 0, count-1) $redis.ltrim(key, count, -1) end if !results.is_a?(Array) # Redis is in readonly mode results = $redis.lrange(key, 0, count-1) else results = results[0] end results.map!(&:to_i) left = count - results.length backfilled = false if left > 0 ids = backfill(category) backfilled = true results += ids[0...count] results.uniq! results = results[0...count] end if !backfilled && $redis.llen(key) < BACKFILL_LOW_WATER_MARK Scheduler::Defer.later("backfill") do backfill(category) end end results end def self.cache_key(category=nil) "random_topic_cache_#{category.try(:id)}" end end