KingbaseES V8R6 空闲事务会话超时自动终止机制

背景

如果会话在事务中停留的时间过长，则允许自动终止空闲会话。可以由配置参数idle_in_transaction_session_timeout 事务处于空闲状态的时长，它有助于防止被遗忘的交易事务，避免长期持有锁，防止vacuum清理时间很长。

而且对于长时间不释放的连接会话，它所占用的本地内存也不会释放。所以，如果这类会话很多就会对服务器内存造成耗尽的风险。

实验

idle_in_transaction_session_timeout = 10000，参数单位为毫秒，这里设置 idle in transaction 空闲事务超时时间为 10 秒。

开启会话一：

test=# begin;
BEGIN
test=# select 2;
 ?column?
----------
        2
(1 row)

开启会话二：

select * from pg_stat_activity where pid<>pg_backend_pid();

datid | 16052
datname | test
pid | 13447
usesysid | 10
usename | system
application_name | kingbase_*&+_
client_addr |
client_hostname |
client_port | -1
backend_start | 2022-10-18 11:04:31.894706+08
xact_start | 2022-10-18 11:06:48.877390+08
query_start | 2022-10-18 11:06:56.214833+08
state_change | 2022-10-18 11:06:56.214963+08
wait_event_type | Client
wait_event | ClientRead
state | idle in transaction
backend_xid |
backend_xmin |
query | select 2;
backend_type | client backend

过10秒钟以后，就查不到这个事务了，再回到会话1执行某个查询会看到：

FATAL: terminating connection due to idle-in-transaction timeout
server closed the connection unexpectedly
This probably means the server terminated abnormally
before or while processing the request.
You have mail in /var/spool/mail/kingbase

这就说明参数生效了，超过10S的空闲事务会话超时中断。

数据库日志可以查看到：

2022-10-18 11:17:28.940 CST,"system","test",13447,"[local]",634e1ab2.4b42,1,"idle in transaction",2022-10-18 11:17:06 CST,10/324,0,FATAL,25P03,"terminating connection due to idle-in-transaction timeout",,,,,,,,,"kingbase_*&+_"

13447进程连接超时被中断。

总结：

以上演示了参数idle_in_transaction_session_timeout参数的功能。由此引申出另外一个参数，client_idle_timeout，这两个参数的区别在于client_idle_timeout规定了空闲会话超时中断时间，它不存在于事务里，默认是0，表示关闭。两个参数应该根据实际应用情况配合使用。