Only load MySQL2Adapter connection fix is MySQL2 is available.

Useful for Sqlite or Postgres installations.

config/initializers/connection_fix.rb

-module ActiveRecord::ConnectionAdapters
+if defined?(ActiveRecord::ConnectionAdapters::Mysql2Adapter)
+  module ActiveRecord::ConnectionAdapters
     class Mysql2Adapter
       alias_method :execute_without_retry, :execute
 
@@ -14,4 +15,5 @@ module ActiveRecord::ConnectionAdapters
         end
       end
     end
+  end
 end
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