使用ActiveRecord进行普通数据库查询时，我遇到了以下错误：
Mysql2 :: Error：在查询期间与MySQL服务器的连接中断
甚至是
ActiveRecord :: StatementInvalid（Mysql2 :: Error：MySQL客户端内存不足）
这些错误是不可恢复的（只有通过应用程序重启才能重新连接），并且不绑定到特定的数据库查询（它们突然在应用程序的各个地方出现）。
该应用程序负载不高。实际上，我是唯一的用户。
有时应用程序整夜运行而没有任何问题，有时在运行几个小时/几分钟后崩溃。有时，在MySQL错误之前，WEBrick / Puma突然退出某些退出代码。
我尝试将Rails从4.0.4升级到更高版本，尝试将MySQL从5.6降级到5.5，尝试更改mysql2 gem版本 - 但都没有起作用。
这不可能是网络连接故障，因为MySQL运行在同一台机器上，并通过localhost名称访问。
数据库不存储数百万行，并且没有查询返回重复的行。
我不确定初始连接是否因为我不知道Rails是否为几个查询重用现有连接还是为每个查询创建新连接。它不能是远程或缓慢的连接，因为它是localhost。
问题：
我怎么会遇到这种情况？
如何解决问题？
以下是一段日志：
Driver Load (0.0ms) SELECT `drivers`.* FROM `drivers` WHERE `drivers`.`ts_id` = 1
WorkShift Load (1.0ms) SELECT `work_shifts`.* FROM `work_shifts` WHERE `work_shifts`.`driver_id` = 1 AND `work_shifts`.`current_state` = 1 ORDER BY `work_shifts`.`scheduled_opened_at` DESC LIMIT 1
Trip Load (1.0ms) SELECT `trips`.* FROM `trips` WHERE `trips`.`work_shift_id` = 1 AND (current_state in (3,4,5,9)) ORDER BY `trips`.`id` ASC LIMIT 1
Mysql2::Error: Lost connection to MySQL server during query: SELECT `trips`.* FROM `trips` WHERE `trips`.`work_shift_id` = 1 AND (current_state in (3,4,5,9)) ORDER BY `trips`.`id` ASC LIMIT 1
2014-10-11 22:56:30 UpCloud(1).send_driver_statuses: Exception(ActiveRecord::StatementInvalid): Mysql2::Error: Lost connection to MySQL server during query: SELECT `trips`.* FROM `trips` WHERE `trips`.`work_shift_id` = 1 AND (current_state in (3,4,5,9)) ORDER BY `trips`.`id` ASC LIMIT 1
==== Stack trace: ====
C:/Ruby200/lib/ruby/gems/2.0.0/gems/activerecord-4.0.4/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:287:in `query'
C:/Ruby200/lib/ruby/gems/2.0.0/gems/activerecord-4.0.4/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:287:in `block in execute'
C:/Ruby200/lib/ruby/gems/2.0.0/gems/activerecord-4.0.4/lib/active_record/connection_adapters/abstract_adapter.rb:442:in `block in log'
C:/Ruby200/lib/ruby/gems/2.0.0/gems/activesupport-4.0.4/lib/active_support/notifications/instrumenter.rb:20:in `instrument'
C:/Ruby200/lib/ruby/gems/2.0.0/gems/activerecord-4.0.4/lib/active_record/connection_adapters/abstract_adapter.rb:437:in `log'
C:/Ruby200/lib/ruby/gems/2.0.0/gems/activerecord-4.0.4/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:287:in `execute'
C:/Ruby200/lib/ruby/gems/2.0.0/gems/activerecord-4.0.4/lib/active_record/connection_adapters/mysql2_adapter.rb:222:in `execute'
C:/Ruby200/lib/ruby/gems/2.0.0/gems/activerecord-4.0.4/lib/active_record/connection_adapters/mysql2_adapter.rb:226:in `exec_query'
C:/Ruby200/lib/ruby/gems/2.0.0/gems/activerecord-4.0.4/lib/active_record/connection_adapters/mysql2_adapter.rb:235:in `select'
C:/Ruby200/lib/ruby/gems/2.0.0/gems/activerecord-4.0.4/lib/active_record/connection_adapters/abstract/database_statements.rb:32:in `select_all'
C:/Ruby200/lib/ruby/gems/2.0.0/gems/activerecord-4.0.4/lib/active_record/connection_adapters/abstract/query_cache.rb:63:in `select_all'
C:/Ruby200/lib/ruby/gems/2.0.0/gems/activerecord-4.0.4/lib/active_record/querying.rb:36:in `find_by_sql'
C:/Ruby200/lib/ruby/gems/2.0.0/gems/activerecord-4.0.4/lib/active_record/relation.rb:585:in `exec_queries'
C:/Ruby200/lib/ruby/gems/2.0.0/gems/activerecord-4.0.4/lib/active_record/association_relation.rb:15:in `exec_queries'
C:/Ruby200/lib/ruby/gems/2.0.0/gems/activerecord-4.0.4/lib/active_record/relation.rb:471:in `load'
C:/Ruby200/lib/ruby/gems/2.0.0/gems/activerecord-4.0.4/lib/active_record/relation.rb:220:in `to_a'
C:/Ruby200/lib/ruby/gems/2.0.0/gems/activerecord-4.0.4/lib/active_record/relation/finder_methods.rb:326:in `find_first'
C:/Ruby200/lib/ruby/gems/2.0.0/gems/activerecord-4.0.4/lib/active_record/relation/finder_methods.rb:91:in `first'
C:/Ruby200/lib/ruby/gems/2.0.0/gems/activerecord-deprecated_finders-1.0.3/lib/active_record/deprecated_finders/relation.rb:129:in `first'
D:/Work/disp/lib/ex/up_cloud.rb:365:in `up_driver_status'
D:/Work/disp/lib/ex/up_cloud.rb:416:in `block (4 levels) in send_driver_statuses'
C:in `each'
C:in `each'
D:/Work/disp/lib/ex/up_cloud.rb:415:in `block (3 levels) in send_driver_statuses'
C:/Ruby200/lib/ruby/gems/2.0.0/gems/nokogiri-1.6.3.1-x86-mingw32/lib/nokogiri/xml/builder.rb:391:in `call'
C:/Ruby200/lib/ruby/gems/2.0.0/gems/nokogiri-1.6.3.1-x86-mingw32/lib/nokogiri/xml/builder.rb:391:in `insert'
C:/Ruby200/lib/ruby/gems/2.0.0/gems/nokogiri-1.6.3.1-x86-mingw32/lib/nokogiri/xml/builder.rb:375:in `method_missing'
D:/Work/disp/lib/ex/up_cloud.rb:414:in `block (2 levels) in send_driver_statuses'
C:/Ruby200/lib/ruby/gems/2.0.0/gems/nokogiri-1.6.3.1-x86-mingw32/lib/nokogiri/xml/builder.rb:391:in `call'
C:/Ruby200/lib/ruby/gems/2.0.0/gems/nokogiri-1.6.3.1-x86-mingw32/lib/nokogiri/xml/builder.rb:391:in `insert'
C:/Ruby200/lib/ruby/gems/2.0.0/gems/nokogiri-1.6.3.1-x86-mingw32/lib/nokogiri/xml/builder.rb:375:in `method_missing'
D:/Work/disp/lib/ex/up_cloud.rb:413:in `block in send_driver_statuses'
C:/Ruby200/lib/ruby/gems/2.0.0/gems/nokogiri-1.6.3.1-x86-mingw32/lib/nokogiri/xml/builder.rb:293:in `initialize'
D:/Work/disp/lib/ex/up_cloud.rb:412:in `new'
D:/Work/disp/lib/ex/up_cloud.rb:412:in `send_driver_statuses'
D:/Work/disp/lib/ex/up_cloud.rb:73:in `block in initialize'
Driver Load (1.0ms) SELECT drivers.id, work_shifts.latitude, work_shifts.longitude, work_shifts.updated_at FROM `drivers` INNER JOIN `work_shifts` ON `work_shifts`.`driver_id` = `drivers`.`id` WHERE `drivers`.`ts_id` = 1 AND `work_shifts`.`current_state` = 1
Mysql2::Error: MySQL client ran out of memory: SELECT `orders`.* FROM `orders` WHERE `orders`.`current_state` = 2
2014-10-11 22:56:32 Postman.postman thread: Exception(ActiveRecord::StatementInvalid): Mysql2::Error: MySQL client ran out of memory: SELECT `orders`.* FROM `orders` WHERE `orders`.`current_state` = 2
==== Stack trace: ====
C:/Ruby200/lib/ruby/gems/2.0.0/gems/activerecord-4.0.4/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:287:in `query'
C:/Ruby200/lib/ruby/gems/2.0.0/gems/activerecord-4.0.4/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:287:in `block in execute'
C:/Ruby200/lib/ruby/gems/2.0.0/gems/activerecord-4.0.4/lib/active_record/connection_adapters/abstract_adapter.rb:442:in `block in log'
C:/Ruby200/lib/ruby/gems/2.0.0/gems/activesupport-4.0.4/lib/active_support/notifications/instrumenter.rb:20:in `instrument'
C:/Ruby200/lib/ruby/gems/2.0.0/gems/activerecord-4.0.4/lib/active_record/connection_adapters/abstract_adapter.rb:437:in `log'
C:/Ruby200/lib/ruby/gems/2.0.0/gems/activerecord-4.0.4/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:287:in `execute'
C:/Ruby200/lib/ruby/gems/2.0.0/gems/activerecord-4.0.4/lib/active_record/connection_adapters/mysql2_adapter.rb:222:in `execute'
C:/Ruby200/lib/ruby/gems/2.0.0/gems/activerecord-4.0.4/lib/active_record/connection_adapters/mysql2_adapter.rb:226:in `exec_query'
C:/Ruby200/lib/ruby/gems/2.0.0/gems/activerecord-4.0.4/lib/active_record/connection_adapters/mysql2_adapter.rb:235:in `select'
C:/Ruby200/lib/ruby/gems/2.0.0/gems/activerecord-4.0.4/lib/active_record/connection_adapters/abstract/database_statements.rb:32:in `select_all'
C:/Ruby200/lib/ruby/gems/2.0.0/gems/activerecord-4.0.4/lib/active_record/connection_adapters/abstract/query_cache.rb:63:in `select_all'
C:/Ruby200/lib/ruby/gems/2.0.0/gems/activerecord-4.0.4/lib/active_record/querying.rb:36:in `find_by_sql'
C:/Ruby200/lib/ruby/gems/2.0.0/gems/activerecord-4.0.4/lib/active_record/relation.rb:585:in `exec_queries'
C:/Ruby200/lib/ruby/gems/2.0.0/gems/activerecord-4.0.4/lib/active_record/relation.rb:471:in `load'
C:/Ruby200/lib/ruby/gems/2.0.0/gems/activerecord-4.0.4/lib/active_record/relation.rb:220:in `to_a'
C:/Ruby200/lib/ruby/gems/2.0.0/gems/activerecord-4.0.4/lib/active_record/relation.rb:565:in `blank?'
D:/Work/disp/lib/postman.rb:31:in `do_posting'
D:/Work/disp/lib/postman.rb:16:in `block (2 levels) in initialize'
D:/Work/disp/lib/advanced_logging.rb:8:in `with_level'
D:/Work/disp/lib/postman.rb:15:in `block in initialize'
find_each或类似方法来解决。 - D-side