for high post count tags use cosine similarity to calculate related tags

app/models/tag.rb

@@ -1,4 +1,5 @@
 class Tag < ActiveRecord::Base
+  COSINE_SIMILARITY_RELATED_TAG_THRESHOLD = 100_000
   METATAGS = "-user|user|-approver|approver|commenter|comm|noter|noteupdater|artcomm|-pool|pool|ordpool|-favgroup|favgroup|-fav|fav|ordfav|sub|md5|-rating|rating|-locked|locked|width|height|mpixels|ratio|score|favcount|filesize|source|-source|id|-id|date|age|order|limit|-status|status|tagcount|gentags|arttags|chartags|copytags|parent|-parent|child|pixiv_id|pixiv|search"
   SUBQUERY_METATAGS = "commenter|comm|noter|noteupdater|artcomm"
   attr_accessible :category, :as => [:moderator, :janitor, :gold, :member, :anonymous, :default, :builder, :admin]
@@ -621,8 +622,13 @@ class Tag < ActiveRecord::Base
     end
 
     def update_related_if_outdated
-      if should_update_related? && Delayed::Job.count < 200
-        delay(:queue => "default").update_related
+      if should_update_related?
+        if post_count < COSINE_SIMILARITY_RELATED_TAG_THRESHOLD && Delayed::Job.count < 200
+          delay(:queue => "default").update_related
+        elsif post_count >= COSINE_SIMILARITY_RELATED_TAG_THRESHOLD
+          sqs = SqsService.new(Danbooru.config.aws_sqs_queue_reltagcalc_url)
+          sqs.send_message("calculate #{name}")
+        end
       end
     end
 

config/danbooru_default_config.rb

@@ -431,6 +431,9 @@ module Danbooru
     def aws_sqs_queue_url
     end
 
+    def aws_sqs_queue_reltagcalc_url
+    end
+
     def aws_sqs_region
     end
   end