Fix: an application freezes when a slave is down

[palexvs]

I get a freeze application (Rails 5.1.4, ActiveRecord 5.1.4) when slave is down with infinitive count of requests like:

SET NAMES utf8mb4 COLLATE utf8mb4_unicode_ci,  @@SESSION.sql_mode = 'TRADITIONAL',  @@SESSION.sql_auto_is_null = 0, @@SESSION.wait_timeout = 2147483

config:

  makara:
    sticky: false
    master_strategy: failover
    slave_strategy: failover

    connections:
      - role: master
        host: <%= SENV['MYSQL_HOST_MASTER'] %>
        disable_blacklist: true
      - role: slave
        host: <%= SENV['MYSQL_HOST_SLAVE'] %>
        blacklist_duration: 60
      - role: slave
        host: <%= SENV['MYSQL_HOST_MASTER'] %>
        disable_blacklist: true

It happens when line con.send(method, *args) raises an error Can't connect to MySQL server but nothing handles it

[bleonard]

Thanks!