further mqtt concurrency tweaks. Limit sidekiq retry queue to one wor…

…ker and use stronger transaction isolation guarantee

Gemfile

@@ -54,6 +54,7 @@ gem 'rufus-scheduler'
 gem 'sentry-ruby'
 gem 'sentry-rails'
 gem 'sentry-sidekiq'
+gem 'sidekiq-limit_fetch'
 gem 'sinatra'
 #gem 'skylight'
 gem 'stamp'

Gemfile.lock

@@ -465,6 +465,8 @@ GEM
       rack (~> 2.0)
       rack-protection (>= 2.0.0)
       redis (>= 4.1.0)
+    sidekiq-limit_fetch (4.4.1)
+      sidekiq (>= 6)
     simplecov (0.22.0)
       docile (~> 1.1)
       simplecov-html (~> 0.11)
@@ -601,6 +603,7 @@ DEPENDENCIES
   sentry-sidekiq
   shoulda-matchers
   sidekiq (~> 6)
+  sidekiq-limit_fetch
   simplecov
   sinatra
   spring
@@ -621,4 +624,4 @@ RUBY VERSION
    ruby 3.0.6p216
 
 BUNDLED WITH
-   2.5.10
+   2.5.11

app/lib/mqtt_messages_handler.rb

@@ -24,7 +24,7 @@ def handle_topic(topic, message, retry_on_nil_device=true)
       return true
     end
 
-    Device.transaction(isolation: :repeatable_read) do
+    Device.transaction(isolation: :serializable) do
       device = Device.lock.find_by(device_token: device_token(topic))
       if device.nil?
         handle_nil_device(topic, message, retry_on_nil_device)

config/sidekiq.yml

@@ -5,6 +5,8 @@
   - default
   - mailers
   - mqtt_retry
+:limits:
+  - mqtt_retry: 1
 
 production:
   :concurrency: 25