嘮嘮mysql的連接數

1.查看mysql的當前連接數

[root@localhost ~]# mysqladmin -uroot -p123456 status
Uptime: 34070  Threads: 1  Questions: 8678  Slow queries: 0  Opens: 910  Flush tables: 43  Open tables: 4  Queries per second avg: 0.254
Therads 打開的連接數

mysql> show status like ‘%Thread%‘;
+------------------------------------------+-------+
 
| Variable_name                            | Value |
+------------------------------------------+-------+
| Delayed_insert_threads                   | 0     |
| Performance_schema_thread_classes_lost   | 0     |
| Performance_schema_thread_instances_lost | 0     |
| Slow_launch_threads                      | 0     |
 
| Threads_cached                           | 0     |
| Threads_connected                        | 1     |
| Threads_created                          | 4     |#創建的連接數
| Threads_running                          | 1     |#打開的連接數
+------------------------------------------+-------+
8 rows in set (0.00 sec

2.查看mysql允許的最大連接數

mysql> show variables like ‘%max_connections%‘；
+-----------------+-------+
| Variable_name   | Value |
+-----------------+-------+
| max_connections | 151   |
+-----------------+-------+
1 row in set (0.00 sec)

3.mysql連接數太多解決方案

http://www.cnblogs.com/lazyball/p/7424243.html

說說mysql的慢查詢

慢查詢產生的原因一般是因為select設計的條件比較多，比如子查詢之類的，數據庫一直在插卡在哪裏，別的語句也無法運行造成阻塞。開發也不是萬能的，也會寫一些 吊炸天的sql語句，一眼望去看不到結尾。

1. 查看mysql裏有哪些進程在運行

mysql> show processlist; #默認一般顯示100行  加上full顯示的多
+----+------+-----------+------+---------+------+-------+------------------+
| Id | User | Host      | db   | Command | Time | State | Info             |
+----+------+-----------+------+---------+------+-------+------------------+
|  4 | root | localhost | NULL | Sleep   |  882 |       | NULL             |
|  6 | root | localhost | NULL | Query   |    0 | NULL  | show processlist |
+----+------+-----------+------+---------+------+-------+------------------+
2 rows in set (0.00 sec)

mysql> show full processlist;
+----+------+-----------+------+---------+------+-------+-----------------------+
| Id | User | Host      | db   | Command | Time | State | Info                  |
+----+------+-----------+------+---------+------+-------+-----------------------+
|  4 | root | localhost | NULL | Sleep   |  894 |       | NULL                  |
|  6 | root | localhost | NULL | Query   |    0 | NULL  | show full processlist |
+----+------+-----------+------+---------+------+-------+-----------------------+
2 rows in set (0.00 sec)

[root@localhost ~]# mysqladmin -uroot -p processlist
Enter password: 
+----+------+-----------+----+---------+------+-------+------------------+
| Id | User | Host      | db | Command | Time | State | Info             |
+----+------+-----------+----+---------+------+-------+------------------+
| 4  | root | localhost |    | Sleep   | 1238 |       |                  |
| 7  | root | localhost |    | Query   | 0    |       | show processlist |
+----+------+-----------+----+---------+------+-------+------------------+

參數解釋：
id       #ID標識，要kill一個語句的時候很有用
use      #當前連接用戶
host     #顯示這個連接從哪個ip的哪個端口上發出
db       #數據庫名
command  #連接狀態，一般是休眠（sleep），查詢（query），連接（connect）
time     #連接持續時間，單位是秒
state    #顯示當前sql語句的狀態 
info     #顯示這個sql語句

##慢查詢發生的時候，state狀態一般是 watting for table level lock 觀察time 看是否運行的時間很久，緊急就殺死，不緊急找開發去，寫的什麽玩意（自己知道咋優化
的話，找開發炫耀去）

2. 緊急批量殺死mysql慢查詢的腳本

先說自己寫的吧

#!/bin/bash
for id in `mysqladmin  -uxxx -h 192.168.1.1 -p‘xxxx‘ processlist | grep Query | grep ‘paigoushop‘ | grep ‘Sending data‘  |  awk ‘{print $2}‘` 
        do 
                        mysqladmin  -uxxx -h 192.168.1.1 -p‘xxx‘  kill ${id} 
        done
#grep有點多  為了準確定位到自己想殺死的sql

下邊這個是網上找的，我也沒試過 放這裏 萬一以後自己用呢

#!/bin/bash
for i in `mysql -Bse ‘show full processlist;‘ | grep -i select |grep -i "Waiting for table level lock" | awk  ‘{print $1}‘`
do
        mysql -Bse "kill  $i"
done

3. 開啟慢查詢日誌記錄

總覺得上邊的方法不太好，比較被動，對於一些不懂的人，又要罵運維了，我來學一下：“不，什麽情況呀，小楊，你這數據庫也太慢了吧，怎麽搞得，趕緊給我查。”

說起來都是淚呀，那就不說了。用事實說話，把sql語句拿出來，讓開發好好看看寫的什麽玩意。

mysql生產環境常用命令