更新到mysql 8安装后出现mysql gem故障

Question

I recently updated mysql through brew upgrade to the newest version:

$ mysql -V
mysql  Ver 8.0.11 for osx10.13 on x86_64 (Homebrew)

Now my Ruby on Rails mysql connection stopped working.

For compatibility with the production environment I have to use gem 'mysql', '2.8.1' and everything was working perfectly before updating. After updating mysql I get the following error message:

$ rails s
=> Booting WEBrick
=> Rails 3.2.5 application starting in development on http://0.0.0.0:3000
=> Call with -d to detach
=> Ctrl-C to shutdown server
    SECURITY WARNING: No secret option provided to Rack::Session::Cookie.
    This poses a security threat. It is strongly recommended that you
    provide a secret to prevent exploits that may be possible from crafted
    cookies. This will not be supported in future versions of Rack, and
    future versions will even invalidate your existing user cookies.

    Called from: /Users/MyAccount/.rvm/gems/ruby-version@webapp/gems/actionpack-3.2.5/lib/action_dispatch/middleware/session/abstract_store.rb:28:in `initialize'.

Exiting
/Users/MyAccount/.rvm/gems/ruby-version@webapp/gems/activerecord-3.2.5/lib/active_record/connection_adapters/mysql_adapter.rb:32:in `mysql_connection': undefined method `init' for Mysql:Class (NoMethodError)
from /Users/MyAccount/.rvm/gems/ruby-version@webapp/gems/activerecord-3.2.5/lib/active_record/connection_adapters/abstract/connection_pool.rb:309:in `send'
from /Users/MyAccount/.rvm/gems/ruby-version@webapp/gems/activerecord-3.2.5/lib/active_record/connection_adapters/abstract/connection_pool.rb:309:in `new_connection'
from /Users/MyAccount/.rvm/gems/ruby-version@webapp/gems/activerecord-3.2.5/lib/active_record/connection_adapters/abstract/connection_pool.rb:319:in `checkout_new_connection'
from /Users/MyAccount/.rvm/gems/ruby-version@webapp/gems/activerecord-3.2.5/lib/active_record/connection_adapters/abstract/connection_pool.rb:241:in `checkout'
from /Users/MyAccount/.rvm/gems/ruby-version@webapp/gems/activerecord-3.2.5/lib/active_record/connection_adapters/abstract/connection_pool.rb:236:in `loop'
from /Users/MyAccount/.rvm/gems/ruby-version@webapp/gems/activerecord-3.2.5/lib/active_record/connection_adapters/abstract/connection_pool.rb:236:in `checkout'
from /Users/MyAccount/.rvm/rubies/ruby-version/lib/ruby/1.8/monitor.rb:242:in `synchronize'
from /Users/MyAccount/.rvm/gems/ruby-version@webapp/gems/activerecord-3.2.5/lib/active_record/connection_adapters/abstract/connection_pool.rb:233:in `checkout'
from /Users/MyAccount/.rvm/gems/ruby-version@webapp/gems/activerecord-3.2.5/lib/active_record/connection_adapters/abstract/connection_pool.rb:96:in `connection'
from /Users/MyAccount/.rvm/rubies/ruby-version/lib/ruby/1.8/monitor.rb:242:in `synchronize'
from /Users/MyAccount/.rvm/gems/ruby-version@webapp/gems/activerecord-3.2.5/lib/active_record/connection_adapters/abstract/connection_pool.rb:95:in `connection'
from /Users/MyAccount/.rvm/gems/ruby-version@webapp/gems/activerecord-3.2.5/lib/active_record/connection_adapters/abstract/connection_pool.rb:404:in `retrieve_connection'
from /Users/MyAccount/.rvm/gems/ruby-version@webapp/gems/activerecord-3.2.5/lib/active_record/connection_adapters/abstract/connection_specification.rb:168:in `retrieve_connection'
from /Users/MyAccount/.rvm/gems/ruby-version@webapp/gems/activerecord-3.2.5/lib/active_record/connection_adapters/abstract/connection_specification.rb:142:in `connection'
from /Users/MyAccount/.rvm/gems/ruby-version@webapp/gems/activerecord-3.2.5/lib/active_record/model_schema.rb:308:in `clear_cache!'
from /Users/MyAccount/.rvm/gems/ruby-version@webapp/gems/activerecord-3.2.5/lib/active_record/railtie.rb:97:in `_callback_before_13'
from /Users/MyAccount/.rvm/gems/ruby-version@webapp/gems/activesupport-3.2.5/lib/active_support/callbacks.rb:418:in `_run__1580337521__prepare__4__callbacks'
from /Users/MyAccount/.rvm/gems/ruby-version@webapp/gems/activesupport-3.2.5/lib/active_support/callbacks.rb:405:in `send'
from /Users/MyAccount/.rvm/gems/ruby-version@webapp/gems/activesupport-3.2.5/lib/active_support/callbacks.rb:405:in `__run_callback'
from /Users/MyAccount/.rvm/gems/ruby-version@webapp/gems/activesupport-3.2.5/lib/active_support/callbacks.rb:385:in `_run_prepare_callbacks'
from /Users/MyAccount/.rvm/gems/ruby-version@webapp/gems/activesupport-3.2.5/lib/active_support/callbacks.rb:81:in `send'
from /Users/MyAccount/.rvm/gems/ruby-version@webapp/gems/activesupport-3.2.5/lib/active_support/callbacks.rb:81:in `run_callbacks'
from /Users/MyAccount/.rvm/gems/ruby-version@webapp/gems/actionpack-3.2.5/lib/action_dispatch/middleware/reloader.rb:74:in `prepare!'
from /Users/MyAccount/.rvm/gems/ruby-version@webapp/gems/actionpack-3.2.5/lib/action_dispatch/middleware/reloader.rb:48:in `prepare!'
from /Users/MyAccount/.rvm/gems/ruby-version@webapp/gems/railties-3.2.5/lib/rails/application/finisher.rb:47
from /Users/MyAccount/.rvm/gems/ruby-version@webapp/gems/railties-3.2.5/lib/rails/initializable.rb:30:in `instance_exec'
from /Users/MyAccount/.rvm/gems/ruby-version@webapp/gems/railties-3.2.5/lib/rails/initializable.rb:30:in `run'
from /Users/MyAccount/.rvm/gems/ruby-version@webapp/gems/railties-3.2.5/lib/rails/initializable.rb:55:in `run_initializers'
from /Users/MyAccount/.rvm/gems/ruby-version@webapp/gems/railties-3.2.5/lib/rails/initializable.rb:54:in `each'
from /Users/MyAccount/.rvm/gems/ruby-version@webapp/gems/railties-3.2.5/lib/rails/initializable.rb:54:in `run_initializers'
from /Users/MyAccount/.rvm/gems/ruby-version@webapp/gems/railties-3.2.5/lib/rails/application.rb:136:in `initialize!'
from /Users/MyAccount/.rvm/gems/ruby-version@webapp/gems/railties-3.2.5/lib/rails/railtie/configurable.rb:30:in `send'
from /Users/MyAccount/.rvm/gems/ruby-version@webapp/gems/railties-3.2.5/lib/rails/railtie/configurable.rb:30:in `method_missing'
from /Users/MyAccount/Development/REPRO/webapp/config/environment.rb:9
from /Users/MyAccount/.rvm/gems/ruby-version@webapp/gems/activesupport-3.2.5/lib/active_support/dependencies.rb:251:in `gem_original_require'
from /Users/MyAccount/.rvm/gems/ruby-version@webapp/gems/activesupport-3.2.5/lib/active_support/dependencies.rb:251:in `require'
from /Users/MyAccount/.rvm/gems/ruby-version@webapp/gems/activesupport-3.2.5/lib/active_support/dependencies.rb:251:in `require'
from /Users/MyAccount/.rvm/gems/ruby-version@webapp/gems/activesupport-3.2.5/lib/active_support/dependencies.rb:236:in `load_dependency'
from /Users/MyAccount/.rvm/gems/ruby-version@webapp/gems/activesupport-3.2.5/lib/active_support/dependencies.rb:251:in `require'
from /Users/MyAccount/Development/REPRO/webapp/config.ru:3
from /Users/MyAccount/.rvm/gems/ruby-version@webapp/gems/rack-1.4.7/lib/rack/builder.rb:51:in `instance_eval'
from /Users/MyAccount/.rvm/gems/ruby-version@webapp/gems/rack-1.4.7/lib/rack/builder.rb:51:in `initialize'
from /Users/MyAccount/Development/REPRO/webapp/config.ru:0:in `new'
from /Users/MyAccount/Development/REPRO/webapp/config.ru:0

How can I solve this problem? Is there a way to solve the mysql connection?

Unfortunately mysql2 is not an option for the production environment.

Update mysql versions:

$ brew info mysql
mysql: stable 8.0.11 (bottled)
Open source relational database management system
https://dev.mysql.com/doc/refman/8.0/en/
Conflicts with:
  mariadb (because mysql, mariadb, and percona install the same binaries.)
  mariadb-connector-c (because both install plugins)
  mysql-cluster (because mysql, mariadb, and percona install the same binaries.)
  mysql-connector-c (because both install MySQL client libraries)
  percona-server (because mysql, mariadb, and percona install the same binaries.)
/usr/local/Cellar/mysql/5.7.21 (323 files, 233.9MB)
  Poured from bottle on 2018-02-21 at 14:26:22
/usr/local/Cellar/mysql/8.0.11 (254 files, 232.6MB) *
  Poured from bottle on 2018-06-22 at 06:21:48
From: https://github.com/Homebrew/homebrew-core/blob/master/Formula/mysql.rb
==> Dependencies
Build: cmake ✔
Required: openssl ✔
==> Requirements
Required: macOS >= 10.10 ✔
==> Options
--with-debug
    Build with debug support
--with-embedded
    Build the embedded server
--with-local-infile
    Build with local infile loading support
--with-memcached
    Build with InnoDB Memcached plugin
--with-test
    Build with unit tests
==> Caveats
We've installed your MySQL database without a root password. To secure it run:
    mysql_secure_installation

MySQL is configured to only allow connections from localhost by default

To connect run:
    mysql -uroot

To have launchd start mysql now and restart at login:
  brew services start mysql
Or, if you don't want/need a background service you can just run:
  mysql.server start

With 5.7.21 everything was working.

Answer 1

After a lot of work I was able to find the culprit. MySQL 8.0.11 is not stable enough and breaks several of my gems.

In the end it was enough to:

$ brew info mysql (to get info about the installed versions)

$ brew switch mysql 5.7.21 (to switch to a stable version)

Now the server, the mysql gems as well as DB connections are working again…

There was no need to uninstall mysql 8 in my case.