Rails 6 Multi-DB導入時のはまりどころについて話します。 こちらのイベントで発表した内容です。 Rails Developers Beer Bash 〜Railsのトレンドとこれから〜 https://techplay.jp/event/749901

1. Rails 6
Multi-DB

2. • (0x26)
• Rails (native)
• kiyot
• Falcon

3. •
• https://wap.nikkei.co.jp/
• Rails 6
• Multi-DB

4. •
• https://wap.nikkei.co.jp/
• Rails 6
• Multi-DB

5. Rails 6 Multi-DB
•
!
Rails 6 Multi-DB
•

6. Rails 6 Multi-DB
Rails 6 Multi-DB

7. Rails
• primary 1
replica
•
• HTTP verb primary replica
•
Rails

8. Rails
• DB (replica )
• DB
• DB DB
• DB Rails DB

9. Rails
•
!
DB (replica )
• DB
• DB DB
• DB Rails DB

10. DB
production:
primary:
database: my_primary_database
user: root
adapter: mysql2
primary_replica:
database: my_primary_database
user: root_readonly
adapter: mysql2
replica: true
animals:
database: my_animals_database
user: animals_root
adapter: mysql2
migrations_paths: db/animals_migrate
animals_replica:
database: my_animals_database
user: animals_readonly
adapter: mysql2
replica: true

11. Rails
• DB (replica )
•
!
DB
• DB DB
• DB Rails DB

12. DB (1)
DB
animals DB
class AnimalsBase < ApplicationRecord
self.abstract_class = true
connects_to database: { writing: :animals, reading: :animals_replica }
end
primary DB
class ApplicationRecord < ActiveRecord::Base
self.abstract_class = true
connects_to database: { writing: :primary, reading: :primary_replica }
end

14. DB (2)
transaction connection
# animals
# primary DB Monkey
ApplicationRecord.transaction do
Monkey.create!
raise ActiveRecord::Rollback
end
# animal DB
ApplicationRecord.connection.execute 'INSERT INTO monkeys ...'

15. DB (3)
ActiveRecord::Base.connected_to(database: { reading_slow: :animals_slow_replica }) do
# replica
end

16. Rails
• DB (replica )
• DB
•
!
DB DB
• DB Rails DB

17. middleware (1)
2
1. HTTP …
• GET/HEAD DB
• DB
2. DB GET/HEAD
DB

18. middleware (2)
application.rb
config.active_record.database_selector = { delay: 2.seconds }
config.active_record.database_resolver = ActiveRecord::Middleware::DatabaseSelector::Resolver
config.active_record.database_resolver_context = ActiveRecord::Middleware::DatabaseSelector::Resolver::Session

19. middleware (3)
•
•

20. Rails
• DB (replica )
• DB
• DB DB
•
!
DB Rails DB

21. DB Rails
$ rails -T
rails db:create
rails db:create:animals
rails db:create:primary
rails db:drop
rails db:drop:animals
rails db:drop:primary
rails db:migrate
rails db:migrate:animals
rails db:migrate:primary
rails db:migrate:status
rails db:migrate:status:animals
rails db:migrate:status:primary

22. Rails 6 Multi-DB
• Rails 6 Multi-DB
•
!

23. Multi-DB
• / DB
• middleware …

24. middleware

25. middleware
• HTTP read/write

26. middleware
• HTTP read/write
•
• DB
•

27. middleware
• HTTP read/write
•
• DB
•
• ActiveRecord::Base.connected_to
DB

28. • gem Rails

29. • gem Rails
• mountable engine
• middleware

30. •
• /

31. • middleware
• middleware around_action
• ApplicationController
•
• rails
around_action

32. mountable engine

33. mountable engine
…

34. Rails 6.0.0

35. Rails 6.0.0 Multi-DB
• middleware
• 6.0.1
• https://github.com/rails/rails/pull/37065

36. Middleware ( )
middleware
• DB GET/HEAD
DB
•

37. Middleware ( )
middleware
• DB GET/HEAD
DB
• ↑ DB

38. Middleware ( )
middleware
• DB GET/HEAD
DB
• ↑ DB
•

39. 1. DB
2. connected_to GET/HEAD
3.
!

40. 6.0.0
connected_to(role: :writing)
while_preventing_writes(false)
ActiveRecord::Base.connected_to(role: :writing) do
# ↓
ActiveRecord::Base.connection_handler.while_preventing_writes(false) do
# code that writes to the primary DB
end
end
※ Rails 6.0.1

41. Middleware
1. Middleware mountable engine
• Middleware around_action
2. 6.0.0 Multi-DB
• 6.0.1

42. Multi-DB