Rails sharding

application_record.rb

class ApplicationRecord < ActiveRecord::Base
  primary_abstract_class

  connects_to database: { writing: :primary }
end

database.yml

# SQLite. Versions 3.8.0 and up are supported.
#   gem install sqlite3
#
#   Ensure the SQLite 3 gem is defined in your Gemfile
#   gem "sqlite3"
#
default: &default
  adapter: sqlite3
  pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>
  timeout: 5000

development:
  primary:
    <<: *default
    database: storage/development_primary.sqlite3

  <% 0.upto(10).map do |i| %>
  "primary_shard_<%= i %>":
    <<: *default
    database: storage/development_primary_shard_<%= i %>.sqlite3
    migrations_paths: db/migrate_shard
  <% end %>

play.rb

ActiveSupport::IsolatedExecutionState.isolation_level = :fiber

# per fiber
ActiveRecord::Base.connected_to(role: :writing, shard: :shard_0) do
  Post.with_connection do |conn|
    conn.execute("select * from posts")
  end
end

sharded_record.rb

class ShardedRecord < ApplicationRecord
  self.abstract_class = true

  connects_to shards: {
    shard_0: { writing: :primary_shard_0 },
    shard_1: { writing: :primary_shard_1 }
  }
end