ruby-on-rails – Rails：在每个请求上切换连接,但保持连接池

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/地区不同的数据库).

现在我们正在做类似于this question中推荐的内容.也就是说,在每个请求中调用ActiveRecord :: Base.establish_connection.

但是,it seems ActiveRecord :: Base.establish_connection删除当前的连接池,并在每次调用时建立一个新的连接.

我做了这个快速的基准测试,看看每次调用建立连接和建立连接是否有明显的区别：

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

我用rails runner运行这个脚本,指向一个本地的mysql,在DB上有几千条记录,结果似乎表明这两种方法之间实际上有一个很大的差别(一个数量级)(BTW,我不知道基准是否有效或我搞砸了,因此结果是误导的)：

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,我想知道是否有一种方法来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一个新的连接.拥有每个子域的模型子类是不可行的,因为有很多模型;我只想改变所有模型的连接(在ActiveRecord :: Base中)

解决方法

嗯,我一直在挖掘这一点,并设法使一些工作.

在阅读了关于ActiveRecord中的连接管理的tenderlove’s post之后,这解释了类层次结构如何不必要地与连接管理相结合,我明白为什么要做我不想像预期那样简单的做法.

我最终做的是对ActiveRecord的ConnectionHandler进行子类化,并在我的模型层次结构的顶部使用新的连接处理程序(在ConnectionHandler code上有些虚拟化需要了解它在内部的工作原理;因此当然这个解决方案可能与Rails有很大关系版本我正在使用(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,但是我在本地Unicorn服务器上运行的初始测试表明存在.