Rails:在每个请求上切换连接但保留连接池

Question

在我们的Rails应用程序中,我们需要使用不同的数据库,具体取决于请求的子域(每个国家/地区的DB不同).

现在我们正在做类似于这个问题的建议.也就是说,呼叫ActiveRecord::Base.establish_connection每个请求.

但它似乎 ActiveRecord::Base.establish_connection丢弃了当前的连接池,并在每次调用时建立新的连接.

我做了这个快速基准测试,看看establish_connection每次调用和建立连接之间是否有任何显着差异:

require 'benchmark/ips'

$config = Rails.configuration.database_configuration[Rails.env]
$db1_config = $config.dup.update('database' => 'db1')
$db2_config = $config.dup.update('database' => 'db2')

# Method 1: call establish_connection on each "request".
Benchmark.ips do |r|
  r.report('establish_connection:') do
    # Simulate two requests, one for each DB.
    ActiveRecord::Base.establish_connection($db1_config)
    MyModel.count # A little query to force the DB connection to establish.
    ActiveRecord::Base.establish_connection($db2_config)
    MyModel.count
  end
end

# Method 2: Have different subclasses of my models, one for each DB, and 
# call establish_connection only once
class MyModelDb1 < MyModel
  establish_connection($db1_config)
end

class MyModelDb2 < MyModel
  establish_connection($db2_config)
end

Benchmark.ips do |r|
  r.report('different models:') do
    MyModelDb1.count
    MyModelDb2.count
  end
end

我运行这个脚本rails runner并指向一个本地mysql,在DB上有几千条记录,结果似乎表明这两种方法之间存在相当大的差异(一个数量级)(BTW,i'我不确定基准是否有效或我搞砸了,结果是误导的):

Calculating -------------------------------------
establish_connection: 8 i/100ms
-------------------------------------------------
establish_connection: 117.9 (±26.3%) i/s -        544 in   5.001575s
Calculating -------------------------------------
    different models:  119 i/100ms
-------------------------------------------------
    different models:  1299.4 (±22.1%) i/s -       6188 in   5.039483s

所以,基本上,我想知道是否有办法维护每个子域的连接池,然后重新使用这些连接,而不是在每个请求上建立新的连接.为每个子域建立我的模型的子类是不可行的,因为有许多模型; 我只是想改变所有模型的连接(in ActiveRecord::Base)

Answer 1

好吧,我一直在深入研究这一点,并设法让一些工作.

看完后tenderlove的帖子有关连接管理ActiveRecord的,这也解释了类层次结构如何被不必要地加上连接管理,我明白了为什么在做什么,我想在没有直接的做正如人们所期望的那样.

我最终做的是继承ActiveRecord的ConnectionHandler并在模型层次结构的顶部使用新的连接处理程序(需要一些摆弄ConnectionHandler 代码才能理解它在内部的工作方式;所以当然这个解决方案可能与Rails非常相关版我正在使用(3.2)).就像是:

# A model class that connects to a different DB depending on the subdomain 
# we're in
class ModelBase < ActiveRecord::Base
  self.abstract_class = true
  self.connection_handler = CustomConnectionHandler.new
end

# ...

class CustomConnectionHandler < ActiveRecord::ConnectionAdapters::ConnectionHandler
  def initialize
    super
    @pools_by_subdomain = {}
  end

  # Override the behaviour of ActiveRecord's ConnectionHandler to return a
  # connection pool for the current domain.
  def retrieve_connection_pool(klass)
    # Get current subdomain somehow (Maybe store it in a class variable on 
    # each request or whatever)
    subdomain = @@subdomain
    @pools_by_subdomain[subdomain] ||= create_pool(subdomain)
  end

  private
  def create_pool(subdomain)
    conf = Rails.configuration.database_configuration[Rails.env].dup
    # The name of the DB for that subdomain...
    conf.update!('database' => "db_#{subdomain}")
    resolver = ActiveRecord::Base::ConnectionSpecification::Resolver.new(conf, nil)
    # Call ConnectionHandler#establish_connection, which receives a key 
    # (in this case the subdomain) for the new connection pool
    establish_connection(subdomain, resolver.spec)
  end
end

这仍然需要一些测试来检查实际上是否有性能提升,但我在本地Unicorn服务器上运行的初始测试表明存在.