psql：致命：抱歉，已经有太多的客户了

Question

在尝试访问使用 postgresql 数据库的网站时，甚至在使用 psql 实用程序或 pgadmin3 时，我突然收到此错误。

我的数据库设置为处理 150 个最大连接数：

# SHOW max_connections;
 max_connections 
-----------------
 150
(1 row)

重新启动我的网站所在的 ubuntu 服务器（这实际上是唯一使用连接的东西）后，我看到当前的连接量为 140：

# select count(*) from pg_stat_activity;
 count 
-------
   140
(1 row)

我不明白在重新启动服务器后突然有这么多连接。所以我检查了 postgresql 活动：

# SELECT * FROM pg_stat_activity;

我看到 100 多列具有相同的精确查询，如下所示：

SELECT  "reports".* FROM "reports"  WHERE (("reports"."time" < '2014-06-28 13:30:42.000000' AND "reports"."unit_id" = 3192)) ORDER BY "reports"."id" DESC LIMIT 1

更重要的是它们都具有相同的客户端地址（我的 Web 服务器）。

该 Web 服务器使用 ruby​​ on rails，连接池为 50。即使连接池为 50，Passenger 进程/prefork apache 配置是单线程的，因此每个进程不能产生 50 个线程和 50 个数据库连接。更重要的是，这是在系统重新启动后发生的，这将所有用户都从我的 Web 服务器上删除了。可能是数据库服务器上的 postgresql 不知道 Web 服务器重新启动并且仍在尝试执行这些查询。

为了回答克雷格的评论，在等待栏下它显示了字母“f”。看起来查询仍在执行，并且锁尚未释放。正如我之前所说的，奇怪的是，在这种执行状态下，突然之间在几毫秒内突然出现了 100 多个彼此相同的查询。这就是我的奥秘：

mydb=# SELECT * FROM pg_stat_activity;

 datid  | datname  | procpid | usesysid | usename |                                                                           current_query                                                                           | waiting |          xact_start           |          query_start          |         backend_start         |  client_addr   | client_port
--------+----------+---------+----------+---------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------+---------+-------------------------------+-------------------------------+-------------------------------+----------------+-------------
 464875 | mydb     |    4992 |    16387 | myuser | SELECT  "reports".* FROM "reports"  WHERE (("reports"."time" < '2014-06-28 13:30:42.000000' AND "reports"."unit_id" = 3192)) ORDER BY "reports"."id" DESC LIMIT 1 | f       | 2014-06-28 22:46:48.437081-04 | 2014-06-28 22:46:48.437081-04 | 2014-06-28 22:46:44.089764-04 | 192.111.11.111 |       37166
 464875 | mydb     |    4993 |    16387 | myuser | SELECT  "reports".* FROM "reports"  WHERE (("reports"."time" < '2014-06-28 13:30:42.000000' AND "reports"."unit_id" = 3192)) ORDER BY "reports"."id" DESC LIMIT 1 | f       | 2014-06-28 22:46:48.497764-04 | 2014-06-28 22:46:48.497764-04 | 2014-06-28 22:46:44.277856-04 | 192.111.11.111 |       37167
 464875 | mydb     |    4994 |    16387 | myuser | SELECT  "reports".* FROM "reports"  WHERE (("reports"."time" < '2014-06-28 13:30:42.000000' AND "reports"."unit_id" = 3192)) ORDER BY "reports"."id" DESC LIMIT 1 | f       | 2014-06-28 22:46:48.504425-04 | 2014-06-28 22:46:48.504425-04 | 2014-06-28 22:46:44.485269-04 | 192.111.11.111 |       37168
 464875 | mydb     |    4996 |    16387 | myuser | SELECT  "reports".* FROM "reports"  WHERE (("reports"."time" < '2014-06-28 13:30:42.000000' AND "reports"."unit_id" = 3192)) ORDER BY "reports"."id" DESC LIMIT 1 | f       | 2014-06-28 22:46:48.482695-04 | 2014-06-28 22:46:48.482695-04 | 2014-06-28 22:46:44.688203-04 | 192.111.11.111 |       37169
 464875 | mydb     |    4998 |    16387 | myuser | SELECT  "reports".* FROM "reports"  WHERE (("reports"."time" < '2014-06-28 13:30:42.000000' AND "reports"."unit_id" = 3192)) ORDER BY "reports"."id" DESC LIMIT 1 | f       | 2014-06-28 22:46:48.432836-04 | 2014-06-28 22:46:48.432836-04 | 2014-06-28 22:46:44.703883-04 | 192.111.11.111 |       37170

-- many more

 464875 | mydb     |    5052 |    16387 | myuser | SELECT  "reports".* FROM "reports"  WHERE (("reports"."time" < '2014-06-28 13:30:42.000000' AND "reports"."unit_id" = 3192)) ORDER BY "reports"."id" DESC LIMIT 1 | f       | 2014-06-28 22:46:59.584386-04 | 2014-06-28 22:46:59.584386-04 | 2014-06-28 22:46:51.85682-04  | 192.111.11.111 |       37360
 464875 | mydb     |    5053 |    16387 | myuser | SELECT  "reports".* FROM "reports"  WHERE (("reports"."time" < '2014-06-28 13:30:42.000000' AND "reports"."unit_id" = 3192)) ORDER BY "reports"."id" DESC LIMIT 1 | f       | 2014-06-28 22:46:59.506483-04 | 2014-06-28 22:46:59.506483-04 | 2014-06-28 22:46:52.083316-04 | 192.111.11.111 |       37367
 464875 | mydb     |    8958 |    16387 | myuser | <IDLE>                                                                                                                                                            | f       |                               | 2014-06-29 00:05:06.735249-04 | 2014-06-27 16:34:39.307312-04 | 192.111.11.111 |       52759
 464875 | mydb     |    5054 |    16387 | myuser | SELECT  "reports".* FROM "reports"  WHERE (("reports"."time" < '2014-06-28 13:30:42.000000' AND "reports"."unit_id" = 3192)) ORDER BY "reports"."id" DESC LIMIT 1 | f       | 2014-06-28 22:46:59.52573-04  | 2014-06-28 22:46:59.52573-04  | 2014-06-28 22:46:52.285867-04 | 192.111.11.111 |       37371
 464875 | mydb     |    5055 |    16387 | myuser | SELECT  "reports".* FROM "reports"  WHERE (("reports"."time" < '2014-06-28 13:30:42.000000' AND "reports"."unit_id" = 3192)) ORDER BY "reports"."id" DESC LIMIT 1 | f       | 2014-06-28 22:46:59.530804-04 | 2014-06-28 22:46:59.530804-04 | 2014-06-28 22:46:52.303562-04 | 192.111.11.111 |       37372
 464875 | mydb     |    5056 |    16387 | myuser | SELECT  "reports".* FROM "reports"  WHERE (("reports"."time" < '2014-06-28 13:30:42.000000' AND "reports"."unit_id" = 3192)) ORDER BY "reports"."id" DESC LIMIT 1 | f       | 2014-06-28 22:46:59.572198-04 | 2014-06-28 22:46:59.572198-04 | 2014-06-28 22:46:52.31447-04  | 192.111.11.111 |       37373
 464875 | mydb     |    5057 |    16387 | myuser | SELECT  "reports".* FROM "reports"  WHERE (("reports"."time" < '2014-06-28 13:30:42.000000' AND "reports"."unit_id" = 3192)) ORDER BY "reports"."id" DESC LIMIT 1 | f       | 2014-06-28 22:46:59.872037-04 | 2014-06-28 22:46:59.872037-04 | 2014-06-28 22:46:52.323721-04 | 192.111.11.111 |       37374
 464875 | mydb     |    5058 |    16387 | myuser | SELECT  "reports".* FROM "reports"  WHERE (("reports"."time" < '2014-06-28 13:30:42.000000' AND "reports"."unit_id" = 3192)) ORDER BY "reports"."id" DESC LIMIT 1 | f       | 2014-06-28 22:46:59.961803-04 | 2014-06-28 22:46:59.961803-04 | 2014-06-28 22:46:52.334238-04 | 192.111.11.111 |       37375
 464875 | mydb     |    5059 |    16387 | myuser | SELECT  "reports".* FROM "reports"  WHERE (("reports"."time" < '2014-06-28 13:30:42.000000' AND "reports"."unit_id" = 3192)) ORDER BY "reports"."id" DESC LIMIT 1 | f       | 2014-06-28 22:46:59.53713-04  | 2014-06-28 22:46:59.53713-04  | 2014-06-28 22:46:52.347227-04 | 192.111.11.111 |       37376
 464875 | mydb     |    5060 |    16387 | myuser | SELECT  "reports".* FROM "reports"  WHERE (("reports"."time" < '2014-06-28 13:30:42.000000' AND "reports"."unit_id" = 3192)) ORDER BY "reports"."id" DESC LIMIT 1 | f       | 2014-06-28 22:47:00.208948-04 | 2014-06-28 22:47:00.208948-04 | 2014-06-28 22:46:52.360008-04 | 192.111.11.111 |       37377
 464875 | mydb     |    5061 |    16387 | myuser | SELECT  "reports".* FROM "reports"  WHERE (("reports"."time" < '2014-06-28 13:30:42.000000' AND "reports"."unit_id" = 3192)) ORDER BY "reports"."id" DESC LIMIT 1 | f       | 2014-06-28 22:46:59.938983-04 | 2014-06-28 22:46:59.938983-04 | 2014-06-28 22:46:52.369496-04 | 192.111.11.111 |       37378

Answer 1

这似乎是客户端编程的特定问题。您将无法通过例如提高“max_connections”参数来解决此问题。

我发现了一个可能的相关问题： Ruby 数据库连接池

尽管您还可以进行更多的服务器端调试：

启用“log_connections”和“log_disconnections”。还将“log_line_prefix”与“%m %a %p”一起使用。

用于调试 PostgreSQL 服务器的非常有用的应用程序是powa或更像：pg_activity

对于实时服务器调试，我更喜欢pg_activity - 特别是它具有显示阻止程序和终止会话的功能。

Answer 2

这是解决问题的最佳方法......它有效

使用SSH putty登录服务器，

sudo /etc/init.d/postgresql 停止

这会杀死数据库中的死日志进程，

sudo /etc/init.d/postgresql 启动