Enhance trimming to avoid locking and lag

app/jobs/solid_cable/trim_job.rb

@@ -2,8 +2,17 @@
 
 module SolidCable
   class TrimJob < ActiveJob::Base
-    def perform
-      ::SolidCable::Message.trimmable.delete_all
+    def perform(id = ::SolidCable::Message.maximum(:id))
+      return unless (id % (trim_batch_size / 2)).zero?
+
+      ::SolidCable::Message.trimmable.
+        limit(trim_batch_size).non_blocking_lock.delete_all
+    end
+
+    private
+
+    def trim_batch_size
+      ::Solidcable.trim_batch_size
     end
   end
 end

app/models/solid_cable/record.rb

@@ -5,5 +5,13 @@ class Record < ActiveRecord::Base
     self.abstract_class = true
 
     connects_to(**SolidCable.connects_to) if SolidCable.connects_to.present?
+
+    def self.non_blocking_lock
+      if SolidCable.use_skip_locked
+        lock(Arel.sql("FOR UPDATE SKIP LOCKED"))
+      else
+        lock
+      end
+    end
   end
 end

lib/action_cable/subscription_adapter/solid_cable.rb

@@ -15,9 +15,9 @@ def initialize(*)
       end
 
       def broadcast(channel, payload)
-        ::SolidCable::Message.broadcast(channel, payload)
+        id = ::SolidCable::Message.broadcast(channel, payload).rows.flatten.max
 
-        ::SolidCable::TrimJob.perform_now if ::SolidCable.autotrim?
+        ::SolidCable::TrimJob.perform_now(id) if ::SolidCable.autotrim?
       end
 
       def subscribe(channel, callback, success_callback = nil)

lib/solid_cable.rb

@@ -26,6 +26,18 @@ def autotrim?
       cable_config.autotrim != false
     end
 
+    def trim_batch_size
+      if (size = cable_config.trim_batch_size.to_i).zero?
+        100
+      else
+        size
+      end
+    end
+
+    def use_skip_locked
+      cable_config.use_skip_locked != false
+    end
+
     private
 
     def cable_config

test/solid_cable_test.rb

@@ -26,4 +26,20 @@ class SolidCableTest < ActiveSupport::TestCase
       assert SolidCable.autotrim?
     end
   end
+
+  test "default trim_batch_size is 100" do
+    assert_equal 100, SolidCable.trim_batch_size
+  end
+
+  test "trim_batch_size when set badly" do
+    with_cable_config trim_batch_size: "weird" do
+      assert_equal 100, SolidCable.trim_batch_size
+    end
+  end
+
+  test "trim_batch_size when set" do
+    with_cable_config trim_batch_size: 42 do
+      assert_equal 42, SolidCable.trim_batch_size
+    end
+  end
 end