Rails 4多线程和connection_pool问题

Question

我正在尝试对Rails应用程序进行多线程处理，但是遇到了connection_pool的一些问题。 我启动一个线程并执行数据库查询，但是似乎从来没有关闭该线程中创建的数据库连接。 这是我的代码：

class A
def self.foo
    Thread.new do
      nc1 = ActiveRecord::Base.connection_pool.connections.size
      nw = ""
      nc2 = ""

      ActiveRecord::Base.connection_pool.with_connection do |conns|
        nw = Person.count
        nc2 = ActiveRecord::Base.connection_pool.connections.size
      end

      nc3 = ActiveRecord::Base.connection_pool.connections.size
      puts "First there were #{nc1} connections, after things there were #{nc2} and now finally there are #{nc3} connections, there are #{nw} people in the db"  
    end
  end 
end

当我执行10次{A.foo}时，它给出了这个输出。

First there were 1 connections, after things there were 3 and now finally there are 5 connections, there are 5325 people in the db
First there were 1 connections, after things there were 4 and now finally there are 5 connections, there are 5325 people in the db
First there were 1 connections, after things there were 2 and now finally there are 5 connections, there are 5325 people in the db
First there were 1 connections, after things there were 5 and now finally there are 5 connections, there are 5325 people in the db
First there were 1 connections, after things there were 5 and now finally there are 5 connections, there are 5325 people in the db
First there were 1 connections, after things there were 5 and now finally there are 5 connections, there are 5325 people in the db
First there were 1 connections, after things there were 5 and now finally there are 5 connections, there are 5325 people in the db
First there were 1 connections, after things there were 5 and now finally there are 5 connections, there are 5325 people in the db
First there were 1 connections, after things there were 5 and now finally there are 5 connections, there are 5325 people in the db
First there were 1 connections, after things there were 5 and now finally there are 5 connections, there are 5325 people in the db

最后我跑了：

ActiveRecord::Base.connection_pool.connections.size
5

现在，根据文档， with_connection应该包含一个块并使用连接将其执行，然后关闭该连接，但是根据我的输出，它没有。 我真的不明白。

是否有人有任何解决方案或想法可能会发生这种情况？ 使用“ connection_pool.connections.size”是检查多少个连接的正确方法吗？

还有其他方法可以在Rails中实现多线程数据库查询吗？

Answer 1

好的，所以我只是不了解connection_pool的工作方式。 连接池保存自创建该池以来已打开的连接，无论是否正在使用它们。 因此，我的问题的答案是，您（无法通过今天实现的方式）无法通过connection_pool查看正在积极使用的连接。 相反，我修补了连接池本身以包括此功能。

如果有人感兴趣，这是我的补丁放在config / initializers / connection_pool_patch.rb中：

module ActiveRecord
  module ConnectionAdapters
    class ConnectionPool
      def num_available
        @available.size
      end
    end
  end
end

module ActiveRecord
  module ConnectionAdapters
    class ConnectionPool
      class Queue
        def size
          @queue.size
        end
      end
    end
  end
end

它公开了私有列表@available的大小，该私有列表在连接池中保存了可用（即，当前未使用但已打开）的连接。 用法= ActiveRecord :: Base.connection_pool.num_available