同时运行GraphQL Ruby的解析器

1 年 ago
清, 扬
5 minutes

这篇文章是GraphQL Advent Calendar 2020的第20天的文章。
昨天是@marin_a__的Apollo Client × codegen中使用LocalState的方法。

我们假设有以下类型的GraphQL模式。

type Query {
  articles: [Article!]
  users: [User!]
}

type Article {
  title: String!
}

type User {
  avatar: String!
}

假设文章、用户和头像分别成为独立的微服务。

image.png

另外，假设每个服务所提供的API如下所示。

    • Article サービスは articles を返す (ArticleServiceClient.get_articles)

 

    • User サービスは users (avatar はなく、id のみ) を返す (UserServiceClient.get_users)

 

    Avatar サービスは user id を受け取って avatar を返す (AvatarServiceClient.get_avatar(id))

让我们考虑解决以下这个查询的问题。

query {
  articles {
    title
  }
  users {
    avatar
  }
}

如果直译的话，可能会变成这样。

class ArticleType < GraphQL::Schema::Object
  field :title, String, null: false
end

class UserType < GraphQL::Schema::Object
  field :avatar, String, null: false

  def avatar
    AvatarServiceClient.get_avatar(object.id)
  end
end

class QueryType < GraphQL::Schema::Object
  field :users, [UserType], null: true
  field :articles, [ArticleType], null: true

  def users
    UserServiceClient.get_users
  end

  def articles
    ArticleServiceClient.get_articles
  end
end

class TestSchema < GraphQL::Schema
  query QueryType
end

假设返回 `users` 需要 2 秒，返回 `articles` 需要 3 秒，返回 `avatar` 需要 1 秒。再假设共有3个用户，则总共需要时间为 2 + 3 + 1 * 3，即 8 秒。

image.png

然而，由于文章和用户在数据库结构上是独立的，所以似乎可以并行地发送请求。在GraphQL Ruby中，有一种延迟评估的机制，通过与concurrent-ruby结合使用，可以实现并发处理。

通过使用Concurrent::Promises.future来封装到服务的请求部分，并通过设置lazy_resolve来实现。

class UserType < GraphQL::Schema::Object
  def avatar
    Concurrent::Promises.future do
      AvatarServiceClient.get_avatar(object.id)
    end
  end
end

class QueryType < GraphQL::Schema::Object
  def users
    Concurrent::Promises.future do
      UserServiceClient.get_users
    end
  end

  def articles
    Concurrent::Promises.future do
      ArticleServiceClient.get_articles
    end
  end
end

class TestSchema < GraphQL::Schema
  lazy_resolve Concurrent::Promises::Future, :value!
end

然而，GraphQL Ruby的lazy_resolve似乎需要等待所有相关的兄弟字段。
在这个例子中，users可以在1秒钟内先于articles返回，但是avatar会在等待articles后才会被评估。
换句话说，如果avatar可以在users之后立即运行，本来只需要3秒钟，但实际上需要4秒钟才能完成。

码.

将以下代码保存，通过输入命令”$ ARTICLE_SERVICE_SLEEP=3 USER_SERVICE_SLEEP=2 AVATAR_SERVICE_SLEEP=1 FUTURE=1 ruby a.rb”来进行验证。通过有无”FUTURE=1″来确认执行时间从大约8秒缩短到大约4秒。

require "bundler/inline"

gemfile do
  source "https://rubygems.org"

  gem "graphql"
  gem "concurrent-ruby"
end

query = <<~Q
  query {
    articles {
      title
    }
    users {
      avatar
    }
  }
Q

require 'logger'

$logger = Logger.new(STDOUT)

module ArticleServiceClient
  Article = Struct.new(:id, :title, keyword_init: true)

  ALL_ARTICLES = Array.new(3) do |i|
    Article.new(id: i, title: "title#{i}")
  end

  def self.get_articles
    $logger.debug("#{name}##{__method__} start")
    sleep ENV['ARTICLE_SERVICE_SLEEP'].to_i
    $logger.debug("#{name}##{__method__} end")

    ALL_ARTICLES
  end
end

module UserServiceClient
  User = Struct.new(:id, keyword_init: true)

  ALL_USERS = Array.new(3) do |i|
    User.new(id: i)
  end

  def self.get_users
    $logger.debug("#{name}##{__method__} start")
    sleep ENV['USER_SERVICE_SLEEP'].to_i
    $logger.debug("#{name}##{__method__} end")

    ALL_USERS
  end
end

module AvatarServiceClient
  def self.get_avatar(id)
    $logger.debug("#{name}##{__method__} start")
    sleep ENV['AVATAR_SERVICE_SLEEP'].to_i
    $logger.debug("#{name}##{__method__} end")

    "#{id}.jpg"
  end
end

class ArticleType < GraphQL::Schema::Object
  field :title, String, null: false

  def title
    $logger.debug("#{self.class}##{__method__}")
    object.title
  end
end

class UserType < GraphQL::Schema::Object
  field :avatar, String, null: false

  def avatar
    if ENV['FUTURE']
      Concurrent::Promises.future do
        AvatarServiceClient.get_avatar(object.id)
      end
    else
      AvatarServiceClient.get_avatar(object.id)
    end
  end
end

class QueryType < GraphQL::Schema::Object
  field :articles, [ArticleType], null: true
  field :users, [UserType], null: true

  def articles
    if ENV['FUTURE']
      Concurrent::Promises.future do
        ArticleServiceClient.get_articles
      end
    else
      ArticleServiceClient.get_articles
    end
  end

  def users
    if ENV['FUTURE']
      Concurrent::Promises.future do
        UserServiceClient.get_users
      end
    else
      UserServiceClient.get_users
    end
  end
end

class TestSchema < GraphQL::Schema
  query QueryType
  lazy_resolve Concurrent::Promises::Future, :value!
end

pp TestSchema.execute(query).to_h

__END__
$ time ARTICLE_SERVICE_SLEEP=3 USER_SERVICE_SLEEP=2 AVATAR_SERVICE_SLEEP=1 ruby a.rb 
D, [2020-12-20T12:11:14.873364 #23151] DEBUG -- : ArticleServiceClient#get_articles start
D, [2020-12-20T12:11:17.876517 #23151] DEBUG -- : ArticleServiceClient#get_articles end
D, [2020-12-20T12:11:17.876831 #23151] DEBUG -- : ArticleType#title
D, [2020-12-20T12:11:17.876937 #23151] DEBUG -- : ArticleType#title
D, [2020-12-20T12:11:17.877046 #23151] DEBUG -- : ArticleType#title
D, [2020-12-20T12:11:17.877143 #23151] DEBUG -- : UserServiceClient#get_users start
D, [2020-12-20T12:11:19.879268 #23151] DEBUG -- : UserServiceClient#get_users end
D, [2020-12-20T12:11:19.879546 #23151] DEBUG -- : AvatarServiceClient#get_avatar start
D, [2020-12-20T12:11:20.880675 #23151] DEBUG -- : AvatarServiceClient#get_avatar end
D, [2020-12-20T12:11:20.880875 #23151] DEBUG -- : AvatarServiceClient#get_avatar start
D, [2020-12-20T12:11:21.882006 #23151] DEBUG -- : AvatarServiceClient#get_avatar end
D, [2020-12-20T12:11:21.882193 #23151] DEBUG -- : AvatarServiceClient#get_avatar start
D, [2020-12-20T12:11:22.883306 #23151] DEBUG -- : AvatarServiceClient#get_avatar end
{"data"=>
  {"articles"=>[{"title"=>"title0"}, {"title"=>"title1"}, {"title"=>"title2"}],
   "users"=>[{"avatar"=>"0.jpg"}, {"avatar"=>"1.jpg"}, {"avatar"=>"2.jpg"}]}}
ARTICLE_SERVICE_SLEEP=3 USER_SERVICE_SLEEP=2 AVATAR_SERVICE_SLEEP=1 ruby a.rb  0.26s user 0.02s system 3% cpu 8.286 total

$ time ARTICLE_SERVICE_SLEEP=3 USER_SERVICE_SLEEP=2 AVATAR_SERVICE_SLEEP=1 FUTURE=1 ruby a.rb
D, [2020-12-20T12:11:37.120206 #23200] DEBUG -- : ArticleServiceClient#get_articles start
D, [2020-12-20T12:11:37.120294 #23200] DEBUG -- : UserServiceClient#get_users start
D, [2020-12-20T12:11:39.120599 #23200] DEBUG -- : UserServiceClient#get_users end
D, [2020-12-20T12:11:40.120562 #23200] DEBUG -- : ArticleServiceClient#get_articles end
D, [2020-12-20T12:11:40.120985 #23200] DEBUG -- : ArticleType#title
D, [2020-12-20T12:11:40.121188 #23200] DEBUG -- : ArticleType#title
D, [2020-12-20T12:11:40.121261 #23200] DEBUG -- : ArticleType#title
D, [2020-12-20T12:11:40.121934 #23200] DEBUG -- : AvatarServiceClient#get_avatar start
D, [2020-12-20T12:11:40.121994 #23200] DEBUG -- : AvatarServiceClient#get_avatar start
D, [2020-12-20T12:11:40.122088 #23200] DEBUG -- : AvatarServiceClient#get_avatar start
D, [2020-12-20T12:11:41.122276 #23200] DEBUG -- : AvatarServiceClient#get_avatar end
D, [2020-12-20T12:11:41.122413 #23200] DEBUG -- : AvatarServiceClient#get_avatar end
D, [2020-12-20T12:11:41.122499 #23200] DEBUG -- : AvatarServiceClient#get_avatar end
{"data"=>
  {"articles"=>[{"title"=>"title0"}, {"title"=>"title1"}, {"title"=>"title2"}],
   "users"=>[{"avatar"=>"0.jpg"}, {"avatar"=>"1.jpg"}, {"avatar"=>"2.jpg"}]}}
ARTICLE_SERVICE_SLEEP=3 USER_SERVICE_SLEEP=2 AVATAR_SERVICE_SLEEP=1 FUTURE=1   0.22s user 0.07s system 6% cpu 4.285 total
由于 GVL 的关系，Ruby 在语言级别上是并发而不是并行的，为了使用 Ruby 的线程。然而，在等待 I/O 的情况下，GVL 会被释放，因此在像本例中的服务间通信中，它将以并行方式执行。
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