如何确定在Rails中随时打开哪些数据库连接？

Question

我正在通过“ rails控制台”运行单线程Rails 5.0应用程序，并在我的开发环境中使用config/database.yml的以下配置：

development:
  adapter: postgresql
  encoding: utf8
  database: sims 
  username: postgres
  password: password
  pool: 5
  timeout: 15000
  host: 127.0.0.1

始终，在下面运行我的代码最终将因“无法获取连接”错误而死亡：

  pool = Concurrent::FixedThreadPool.new(1) 
  promises = links.map do |link| 
    Concurrent::Promise.execute(executor: pool) do
      result = process_link(link) 
      if result
        if result.kind_of?(Array) 
          result.each do |my_obj|
            my_obj.update_attributes({ :a => a }) 
            records_processed = records_processed + my_obj.matches.count 
          end
        else
          records_processed = records_processed + result.matches.count 
          result.update_attributes({ :a => a }) 
        end
      end
    end
  end
  promises.map(&:wait).map(&:value!)

如何确定未关闭哪些连接，或者哪些查询仍在运行，这会导致这种情况发生？ 我感到困惑，因为并发查询不应在任何地方一次运行。

Error during processing: (ActiveRecord::ConnectionTimeoutError) could not obtain a connection from the pool within 5.000 seconds (waited 5.003 seconds); all pooled connections were in use
/Users/nataliab/.rvm/gems/ruby-2.4.0@global/gems/activerecord-5.0.1/lib/active_record/connection_adapters/abstract/connection_pool.rb:202:in `block in wait_poll'
/Users/nataliab/.rvm/gems/ruby-2.4.0@global/gems/activerecord-5.0.1/lib/active_record/connection_adapters/abstract/connection_pool.rb:193:in `loop'
/Users/nataliab/.rvm/gems/ruby-2.4.0@global/gems/activerecord-5.0.1/lib/active_record/connection_adapters/abstract/connection_pool.rb:193:in `wait_poll'
/Users/nataliab/.rvm/gems/ruby-2.4.0@global/gems/activerecord-5.0.1/lib/active_record/connection_adapters/abstract/connection_pool.rb:154:in `internal_poll'
/Users/nataliab/.rvm/gems/ruby-2.4.0@global/gems/activerecord-5.0.1/lib/active_record/connection_adapters/abstract/connection_pool.rb:278:in `internal_poll'
/Users/nataliab/.rvm/gems/ruby-2.4.0@global/gems/activerecord-5.0.1/lib/active_record/connection_adapters/abstract/connection_pool.rb:148:in `block in poll'
/Users/nataliab/.rvm/rubies/ruby-2.4.0/lib/ruby/2.4.0/monitor.rb:214:in `mon_synchronize'
/Users/nataliab/.rvm/gems/ruby-2.4.0@global/gems/activerecord-5.0.1/lib/active_record/connection_adapters/abstract/connection_pool.rb:158:in `synchronize'
/Users/nataliab/.rvm/gems/ruby-2.4.0@global/gems/activerecord-5.0.1/lib/active_record/connection_adapters/abstract/connection_pool.rb:148:in `poll'
/Users/nataliab/.rvm/gems/ruby-2.4.0@global/gems/activerecord-5.0.1/lib/active_record/connection_adapters/abstract/connection_pool.rb:717:in `acquire_connection'
/Users/nataliab/.rvm/gems/ruby-2.4.0@global/gems/activerecord-5.0.1/lib/active_record/connection_adapters/abstract/connection_pool.rb:490:in `checkout'
/Users/nataliab/.rvm/gems/ruby-2.4.0@global/gems/activerecord-5.0.1/lib/active_record/connection_adapters/abstract/connection_pool.rb:364:in `connection'

Answer 1

您可以使用以下方法从PostgreSQL获取此信息：

SELECT * from pg_stat_activity;

Answer 2

我正在运行一个单线程的Rails 5.0应用程序

一旦您的应用程序代码创建了另一个线程（通过Concurrent::FixedThreadPool.new(1) ），它就不再是“单线程应用程序”。

我如何确定哪些连接没有关闭或哪些查询仍在运行，这会导致这种情况发生。

要检查未关闭的连接，可以通过ActiveRecord::Base.connection_pool.connections访问当前连接池的连接列表，该列表将返回一个ActiveRecord::ConnectionAdapters::AbstractAdapter对象数组。 例如，要inspect连接池中当前每个连接的线程owner ，可以运行：

ActiveRecord::Base.connection_pool.connections.map(&:owner).map(&:inspect)

我感到困惑，因为并发查询不应在任何地方一次运行。

您认为由于连接池已耗尽而正在运行并发查询的假设是不正确的。 关于如何解决此问题，请参考我对另一个（非常相似）问题的回答： 即使线程池中只有一个线程 ， 并发也会发生吗？