FEATURE: push post rebake regular task to low priority queue

This allows us to run regular rebakes without starving the normal queue.

It additionally adds the ability to specify queue with `Jobs.enqueue` so
we can specifically queue a job with lower priority using the `queue` arg.

app/jobs/base.rb

@@ -197,14 +197,28 @@ module Jobs
 
     # If we are able to queue a job, do it
     if SiteSetting.queue_jobs?
-      if opts[:delay_for].present?
-        klass.perform_in(opts.delete(:delay_for), opts)
-      else
-        Sidekiq::Client.enqueue(klass, opts)
+      hash = {
+        'class' => klass,
+        'args' => [opts]
+      }
+
+      if delay = opts.delete(:delay_for)
+        if delay.to_f > 0
+          hash['at'] = Time.now.to_f + delay.to_f
+        end
       end
+
+      if queue = opts.delete(:queue)
+        hash['queue'] = queue
+      end
+
+      klass.client_push(hash)
+
     else
       # Otherwise execute the job right away
       opts.delete(:delay_for)
+      opts.delete(:queue)
+
       opts[:sync_exec] = true
       if Rails.env == "development"
         Scheduler::Defer.later("job") do

app/jobs/scheduled/periodical_updates.rb

@@ -15,7 +15,7 @@ module Jobs
       (@call_count % 24) == 1
     end
 
-    def execute(args)
+    def execute(args = nil)
       # Feature topics in categories
       CategoryFeaturedTopic.feature_topics(batched: true)
 
@@ -29,7 +29,7 @@ module Jobs
 
       # Forces rebake of old posts where needed, as long as no system avatars need updating
       if !SiteSetting.automatically_download_gravatars || !UserAvatar.where("last_gravatar_download_attempt IS NULL").limit(1).first
-        problems = Post.rebake_old(SiteSetting.rebake_old_posts_count)
+        problems = Post.rebake_old(SiteSetting.rebake_old_posts_count, priority: :low)
         problems.each do |hash|
           post_id = hash[:post].id
           Discourse.handle_job_exception(hash[:ex], error_context(args, "Rebaking post id #{post_id}", post_id: post_id))

app/models/post.rb

@@ -515,7 +515,7 @@ class Post < ActiveRecord::Base
     PostRevisor.new(self).revise!(updated_by, changes, opts)
   end
 
-  def self.rebake_old(limit)
+  def self.rebake_old(limit, priority: :normal)
 
     limiter = RateLimiter.new(
       nil,
@@ -534,7 +534,7 @@ class Post < ActiveRecord::Base
         break if !limiter.can_perform?
 
         post = Post.find(id)
-        post.rebake!
+        post.rebake!(priority: priority)
 
         begin
           limiter.performed!
@@ -560,15 +560,13 @@ class Post < ActiveRecord::Base
     problems
   end
 
-  def rebake!(opts = nil)
-    opts ||= {}
-
-    new_cooked = cook(raw, topic_id: topic_id, invalidate_oneboxes: opts.fetch(:invalidate_oneboxes, false))
+  def rebake!(invalidate_broken_images: false, invalidate_oneboxes: false, priority: nil)
+    new_cooked = cook(raw, topic_id: topic_id, invalidate_oneboxes: invalidate_oneboxes)
     old_cooked = cooked
 
     update_columns(cooked: new_cooked, baked_at: Time.new, baked_version: BAKED_VERSION)
 
-    if opts.fetch(:invalidate_broken_images, false)
+    if invalidate_broken_images
       custom_fields.delete(BROKEN_IMAGES)
       save_custom_fields
     end
@@ -578,7 +576,7 @@ class Post < ActiveRecord::Base
     QuotedPost.extract_from(self)
 
     # make sure we trigger the post process
-    trigger_post_process(bypass_bump: true)
+    trigger_post_process(bypass_bump: true, priority: priority)
 
     publish_change_to_clients!(:rebaked)
 
@@ -692,7 +690,7 @@ class Post < ActiveRecord::Base
   end
 
   # Enqueue post processing for this post
-  def trigger_post_process(bypass_bump: false)
+  def trigger_post_process(bypass_bump: false, priority: :normal)
     args = {
       post_id: id,
       bypass_bump: bypass_bump,
@@ -700,6 +698,11 @@ class Post < ActiveRecord::Base
     args[:image_sizes] = image_sizes if image_sizes.present?
     args[:invalidate_oneboxes] = true if invalidate_oneboxes.present?
     args[:cooking_options] = self.cooking_options
+
+    if priority == :low
+      args[:queue] = 'low'
+    end
+
     Jobs.enqueue(:process_post, args)
     DiscourseEvent.trigger(:after_trigger_post_process, self)
   end

spec/jobs/periodical_updates_spec.rb

@@ -13,13 +13,24 @@ describe Jobs::PeriodicalUpdates do
     SiteSetting.automatically_download_gravatars = false
     post = create_post
     post.update_columns(baked_at: Time.new(2000, 1, 1), baked_version: -1)
-    described_class.new.execute({})
+
+    Sidekiq::Testing.fake! do
+      Jobs::ProcessPost.jobs.clear
+
+      Jobs::PeriodicalUpdates.new.execute
+
+      jobs = Jobs::ProcessPost.jobs
+      expect(jobs.length).to eq(1)
+
+      expect(jobs[0]["queue"]).to eq("low")
+    end
 
     post.reload
     expect(post.baked_at).to be > 1.day.ago
-
     baked = post.baked_at
-    described_class.new.execute({})
+
+    # does not rebake
+    Jobs::PeriodicalUpdates.new.execute
     post.reload
     expect(post.baked_at).to eq(baked)
   end