针对联合表的查询失去连接？

Debian 9 上的 Mysql 5.6：我在服务器 serverA 上有一个非常大的表，我已经使用 定义了从 serverB 上的数据库到 serverA 上的数据库的连接，create server connA ...并且我在 serverB 上定义了一个表，该表通过 connA 连接到非常大的桌子。

当我在 serverB 上查询联合表时，如果查询在 serverA 上快速处理，它可以正常工作：

# on serverB:
mysql> select * from game_action where game_action_id=4;
+----------------+---------+---------+------------------+-------+--------+----------+---------------------+
| game_action_id | game_id | user_id | game_instance_id | type  | amount | currency | created_timestamp   |
+----------------+---------+---------+------------------+-------+--------+----------+---------------------+
|              4 |    1096 |       1 |                4 | WAGER |   1.00 | GBP      | 2017-09-06 14:37:15 |
+----------------+---------+---------+------------------+-------+--------+----------+---------------------+
1 row in set (0.40 sec)

但是（仍在服务器B上）：

mysql> select count(*) from game_action;
ERROR 2013 (HY000): Lost connection to MySQL server during query

表很大，所以处理需要很长时间并不奇怪，但我需要能够做需要很长时间的事情。过去我们遇到过由于超时而导致连接断开的问题，并且很难解决；在 my.cnf 中更改不同的超时没有帮助。

解决此特定问题的最佳做法是什么？

编辑

我觉得非常奇怪的是，似乎没有任何超时变量与我看到的相匹配——我设置了一个 mysql 实例只是为了测试它：

$ # On serverB:
$ time mysql -u root -pAtauseq01 gameiom -e "select count(*) from game_action;"
mysql: [Warning] Using a password on the command line interface can be insecure.
ERROR 2013 (HY000) at line 1: Lost connection to MySQL server during query

real    9m23.275s
user    0m0.014s
sys     0m0.004s

所以，如果是超时，大约 9 分钟超时。但是在远程服务器（serverA）上：

mysql> show variables like "%timeout%";
+-------------------------------------+----------+
| Variable_name                       | Value    |
+-------------------------------------+----------+
| connect_timeout                     | 10       |
| delayed_insert_timeout              | 300      |
| have_statement_timeout              | YES      |
| innodb_flush_log_at_timeout         | 1        |
| innodb_lock_wait_timeout            | 50       |
| innodb_print_lock_wait_timeout_info | OFF      |
| innodb_rollback_on_timeout          | OFF      |
| interactive_timeout                 | 28800    |
| lock_wait_timeout                   | 31536000 |
| net_read_timeout                    | 30       |
| net_write_timeout                   | 60       |
| rpl_stop_slave_timeout              | 31536000 |
| slave_net_timeout                   | 3600     |
| thread_pool_idle_timeout            | 60       |
| wait_timeout                        | 28800    |
+-------------------------------------+----------+
15 rows in set (0.00 sec)

编辑 2

服务器A：

mysql> show variables like "flush%";
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| flush         | OFF   |
| flush_time    | 0     |
+---------------+-------+
2 rows in set (0.00 sec)

服务器B：

mysql> show variables like "flush%";
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| flush         | OFF   |
| flush_time    | 0     |
+---------------+-------+
2 rows in set (0.01 sec)

编辑 3

在服务器 A 上：

mysql> pager grep -v PARTITION
PAGER set to 'grep -v PARTITION'
mysql> show create table game_action\G
*************************** 1. row ***************************
       Table: game_action
Create Table: CREATE TABLE `game_action` (
  `game_action_id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
  `game_id` int(11) NOT NULL,
  `user_id` int(11) NOT NULL,
  `game_instance_id` bigint(20) unsigned DEFAULT NULL,
  `type` varchar(15) NOT NULL,
  `amount` decimal(18,2) NOT NULL,
  `currency` varchar(15) NOT NULL,
  `created_timestamp` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
  PRIMARY KEY (`game_action_id`,`created_timestamp`),
  KEY `GA_IX01` (`game_id`),
  KEY `GA_IX02` (`user_id`),
  KEY `GA_IX03` (`game_instance_id`),
  KEY `game_action_created_timestamp` (`created_timestamp`),
  KEY `ga_id_cur_tstmp` (`game_id`,`currency`,`created_timestamp`)
) ENGINE=InnoDB AUTO_INCREMENT=1064199804 DEFAULT CHARSET=utf8
1 row in set (0.00 sec)

在服务器 B 上：

mysql> show create table game_action\G
*************************** 1. row ***************************
       Table: game_action
Create Table: CREATE TABLE `game_action` (
  `game_action_id` bigint unsigned NOT NULL AUTO_INCREMENT,
  `game_id` int NOT NULL,
  `user_id` int NOT NULL,
  `game_instance_id` bigint unsigned DEFAULT NULL,
  `type` varchar(15) NOT NULL,
  `amount` decimal(18,2) NOT NULL,
  `currency` varchar(15) NOT NULL,
  `created_timestamp` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
  PRIMARY KEY (`game_action_id`,`created_timestamp`),
  KEY `GA_IX01` (`game_id`),
  KEY `GA_IX02` (`user_id`),
  KEY `GA_IX03` (`game_instance_id`),
  KEY `game_action_created_timestamp` (`created_timestamp`),
  KEY `ga_id_cur_tstmp` (`game_id`,`currency`,`created_timestamp`)
) ENGINE=FEDERATED DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_general_ci CONNECTION='gameiom'
1 row in set (0.00 sec)