今天论坛打开了这个会话功能，结果很荣幸踩坑里了，连接数直接给干到2000开外。
好了，直接上图说下：
show processlist，满屏显示这条SQL，情急之下，立即pt-kill，先让论坛活下来。顺便想问候下discuz开发，你们真的做了测试了吗，就直接发布了？
表结构：
|
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
|
mysql> desc pre_common_session;
+--------------+----------------------+------+-----+---------+-------+
| Field | Type |
Null
| Key | Default | Extra |
+--------------+----------------------+------+-----+---------+-------+
| sid | char(
6
) | NO | PRI | | |
| ip1 | tinyint(
3
) unsigned | NO | |
0
| |
| ip2 | tinyint(
3
) unsigned | NO | |
0
| |
| ip3 | tinyint(
3
) unsigned | NO | |
0
| |
| ip4 | tinyint(
3
) unsigned | NO | |
0
| |
| uid |
int
(
11
) unsigned | NO | MUL |
0
| |
| username | char(
50
) | NO | | | |
| groupid | smallint(
6
) unsigned | NO | |
0
| |
| invisible | tinyint(
1
) | NO | |
0
| |
| action | tinyint(
1
) unsigned | NO | |
0
| |
| lastactivity |
int
(
10
) unsigned | NO | |
0
| |
| lastolupdate |
int
(
10
) unsigned | NO | |
0
| |
| fid |
int
(
11
) unsigned | NO | |
0
| |
| tid |
int
(
11
) unsigned | NO | |
0
| |
+--------------+----------------------+------+-----+---------+-------+
14
rows
in
set
(
0.00
sec)
|
由于该SQL导致全表扫描，虽然表数据不多1万多行，但InnoDB引擎在没有使用到索引的情况下，会转为表级锁，并发一大，线程处理不完，连接不释放，连接数就会上升。
最终让开发在后台关闭该功能，解决之。
本文转自hcymysql51CTO博客，原文链接： http://blog.51cto.com/hcymysql/1381352，如需转载请自行联系原作者
