From 82b61e4811fc94650e7ef00e9afc318ac1e642de Mon Sep 17 00:00:00 2001
From: Rolf Schmidt <rolf.schmidt@zammad.com>
Date: Fri, 3 Dec 2021 11:13:40 +0100
Subject: [PATCH] Fixes #3877 - Missing ticket updates on high load in
 MariaDB/MySQL environments.

---
 config/initializers/db_preferences.rb | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/config/initializers/db_preferences.rb b/config/initializers/db_preferences.rb
index b4ade9b1a..265b0d552 100644
--- a/config/initializers/db_preferences.rb
+++ b/config/initializers/db_preferences.rb
@@ -6,6 +6,13 @@ when 'mysql2'
   Rails.application.config.db_case_sensitive = false
   Rails.application.config.db_like = 'LIKE'
   Rails.application.config.db_null_byte = true
+
+  # Because of missing ticket updates in high load environments
+  # we changed the transaction isolation level equally to postgres
+  # to READ COMMITTED which fixed the problem entirely #3877
+  ActiveRecord::ConnectionAdapters::Mysql2Adapter.set_callback :checkout, :before do |conn|
+    conn.execute('SET SESSION TRANSACTION ISOLATION LEVEL READ COMMITTED')
+  end
 when 'postgresql'
   Rails.application.config.db_4bytes_utf8 = true
   Rails.application.config.db_case_sensitive = true