@startuml{seq.png}

actor Client
participant Rails
participant "Connection pool" as cp
participant "<size:10>active_recode_mysql_xverify</size>" as armx
participant MySQL

Client -> Rails : Request
activate Rails
Rails -> MySQL : Query
activate MySQL
group neg
  Rails <-- MySQL : <font color=red>"read-only" error happen!</font>
  deactivate MySQL
  Client <-- Rails : <font color=red>Error</font>
  deactivate Rails
end

Client -> Rails : Request
activate Rails
Rails -> cp : checkout
activate cp
cp -> armx : active?
activate armx
armx -> MySQL : Fetch "innodb_read_only"
activate MySQL
armx <-- MySQL : "ON"
deactivate MySQL
cp <-- armx : false
deactivate armx
cp --> MySQL : reconnect!
activate MySQL
deactivate MySQL
Rails <-- cp : Connection
deactivate cp

@enduml