mysql的show status 中 thread 的含义？

Question

MySQL使用show status like '%Thread%'，得到如下显示：

+---------------------------+-------+
| Variable_name             | Value |
+---------------------------+-------+
| Delayed_insert_threads    | 0     |
| Slow_launch_threads       | 0     |
| Threads_cached            | 23    |
| Threads_connected         | 399   |
| Threads_connected_reserve | 91    |
| Threads_created           | 2173  |
| Threads_running           | 3     |
+---------------------------+-------+

关于这个显示，有一些疑问。我的问题如下：

1. Threads_connected是不是代表连接池中目前所创建的所有连接？
2. Threads_running是否代表所创建的所有连接中正在使用的连接？
3. 如果上述理解是正确的，Threads_running很小而Threads_connected很大，是不是说明有很多空闲的 connection？那为何在做并发测试的时候，Threads_connected便直线上升，而不是直接使用空闲的？

Answer 1

你的理解错了
Threads_cached：
The number of threads in the thread cache. This variable was added in MySQL 3.23.17.

Threads_connected：
The number of currently open connections.当前打开的连接数

Threads_created：
The number of threads created to handle connections. If Threads_created is big, you may want to increase the thread_cache_size value. The cache miss rate can be calculated as Threads_created divided by Connections. This variable was added in MySQL 3.23.31.

Threads_running：
The number of threads that are not sleeping.当前未挂起的连接数

MYSQL官方解释http://dev.mysql.com/doc/refman/4.1/en/server-status-variables.html#statvar_Threads_connected