MySQL 客戶端與MySQL server建立連接后，就可以執行SQL語句了。
如何查看一個連接上是否正在執行SQL語句，或者連接是否處於空閑呢？
下面我們做下測試。
1.查看連接的空閑時間
首先看下測試程序。
代碼中，每3s執行一條sql語句。
//conn_idle_time.go
package main
import (
"database/sql"
"log"
"time"
_ "github.com/go-sql-driver/mysql"
)
var DB *sql.DB
var dataBase = "root:Aa123456@tcp(127.0.0.1:3306)/?loc=Local&parseTime=true"
func mysqlInit() {
var err error
DB, err = sql.Open("mysql", dataBase)
if err != nil {
log.Fatalln("open db fail:", err)
}
DB.SetMaxOpenConns(1)
err = DB.Ping()
if err != nil {
log.Fatalln("ping db fail:", err)
}
}
func main() {
mysqlInit()
for {
execSql()
time.Sleep(3*time.Second)
}
}
func execSql() {
var connection_id int
err := DB.QueryRow("select CONNECTION_ID()").Scan(&connection_id)
if err != nil {
log.Println("query connection id failed:", err)
return
}
log.Println("connection id:", connection_id)
}
啟動程序，輸出結果如下：
2019/10/13 12:20:59 connection id: 5
2019/10/13 12:21:02 connection id: 5
2019/10/13 12:21:05 connection id: 5
2019/10/13 12:21:08 connection id: 5
2019/10/13 12:21:11 connection id: 5
2019/10/13 12:21:14 connection id: 5
2019/10/13 12:21:17 connection id: 5
2019/10/13 12:21:20 connection id: 5
2019/10/13 12:21:23 connection id: 5
2019/10/13 12:21:26 connection id: 5
2019/10/13 12:21:29 connection id: 5
可以看到，連接MySQL的connection id 為5。
接着，通過show processlist查看連接情況：
mysql> show processlist;
+----+------+-----------------+------+---------+------+----------+------------------+
| Id | User | Host | db | Command | Time | State | Info |
+----+------+-----------------+------+---------+------+----------+------------------+
| 3 | root | localhost | NULL | Query | 0 | starting | show processlist |
| 5 | root | localhost:51823 | NULL | Sleep | 0 | | NULL |
+----+------+-----------------+------+---------+------+----------+------------------+
2 rows in set (0.00 sec)
mysql> show processlist;
+----+------+-----------------+------+---------+------+----------+------------------+
| Id | User | Host | db | Command | Time | State | Info |
+----+------+-----------------+------+---------+------+----------+------------------+
| 3 | root | localhost | NULL | Query | 0 | starting | show processlist |
| 5 | root | localhost:51823 | NULL | Sleep | 3 | | NULL |
+----+------+-----------------+------+---------+------+----------+------------------+
2 rows in set (0.00 sec)
mysql> show processlist;
+----+------+-----------------+------+---------+------+----------+------------------+
| Id | User | Host | db | Command | Time | State | Info |
+----+------+-----------------+------+---------+------+----------+------------------+
| 3 | root | localhost | NULL | Query | 0 | starting | show processlist |
| 5 | root | localhost:51823 | NULL | Sleep | 1 | | NULL |
+----+------+-----------------+------+---------+------+----------+------------------+
2 rows in set (0.00 sec)
mysql> show processlist;
+----+------+-----------------+------+---------+------+----------+------------------+
| Id | User | Host | db | Command | Time | State | Info |
+----+------+-----------------+------+---------+------+----------+------------------+
| 3 | root | localhost | NULL | Query | 0 | starting | show processlist |
| 5 | root | localhost:51823 | NULL | Sleep | 3 | | NULL |
+----+------+-----------------+------+---------+------+----------+------------------+
2 rows in set (0.00 sec)
mysql> show processlist;
+----+------+-----------------+------+---------+------+----------+------------------+
| Id | User | Host | db | Command | Time | State | Info |
+----+------+-----------------+------+---------+------+----------+------------------+
| 3 | root | localhost | NULL | Query | 0 | starting | show processlist |
| 5 | root | localhost:51823 | NULL | Sleep | 2 | | NULL |
+----+------+-----------------+------+---------+------+----------+------------------+
2 rows in set (0.00 sec)
mysql> show processlist;
+----+------+-----------------+------+---------+------+----------+------------------+
| Id | User | Host | db | Command | Time | State | Info |
+----+------+-----------------+------+---------+------+----------+------------------+
| 3 | root | localhost | NULL | Query | 0 | starting | show processlist |
| 5 | root | localhost:51823 | NULL | Sleep | 1 | | NULL |
+----+------+-----------------+------+---------+------+----------+------------------+
2 rows in set (0.00 sec)
可以看到localhost:51823是連接MySQL server使用的端口，當Command列為Sleep時，表示當前連接是空閑的，Time列顯示了處於當前狀態的時間。
每執行一次SQL語句，Sleep狀態的Time都會被重置為0.
如果當前連接一直沒有執行SQL語句，那么Sleep狀態的Time會一直增加，直到達到連接最大時間(由參數wait_timeout控制)，最后連接斷開。
再來看下，如何查看正在執行的SQL語句。
2.查看連接正在執行的SQL
將上面示例程序執行的SQL語句改為:
select SLEEP(10)
查看連接情況:
mysql> show processlist;
+----+------+-----------------+------+---------+------+------------+------------------+
| Id | User | Host | db | Command | Time | State | Info |
+----+------+-----------------+------+---------+------+------------+------------------+
| 3 | root | localhost | NULL | Query | 0 | starting | show processlist |
| 6 | root | localhost:52186 | NULL | Query | 1 | User sleep | select SLEEP(10) |
+----+------+-----------------+------+---------+------+------------+------------------+
2 rows in set (0.00 sec)
mysql> show processlist;
+----+------+-----------------+------+---------+------+------------+------------------+
| Id | User | Host | db | Command | Time | State | Info |
+----+------+-----------------+------+---------+------+------------+------------------+
| 3 | root | localhost | NULL | Query | 0 | starting | show processlist |
| 7 | root | localhost:52200 | NULL | Query | 3 | User sleep | select SLEEP(10) |
+----+------+-----------------+------+---------+------+------------+------------------+
2 rows in set (0.00 sec)
mysql> show processlist;
+----+------+-----------------+------+---------+------+------------+------------------+
| Id | User | Host | db | Command | Time | State | Info |
+----+------+-----------------+------+---------+------+------------+------------------+
| 3 | root | localhost | NULL | Query | 0 | starting | show processlist |
| 7 | root | localhost:52200 | NULL | Query | 7 | User sleep | select SLEEP(10) |
+----+------+-----------------+------+---------+------+------------+------------------+
2 rows in set (0.00 sec)
mysql> show processlist;
+----+------+-----------------+------+---------+------+------------+------------------+
| Id | User | Host | db | Command | Time | State | Info |
+----+------+-----------------+------+---------+------+------------+------------------+
| 3 | root | localhost | NULL | Query | 0 | starting | show processlist |
| 7 | root | localhost:52200 | NULL | Query | 8 | User sleep | select SLEEP(10) |
+----+------+-----------------+------+---------+------+------------+------------------+
2 rows in set (0.00 sec)
mysql> show processlist;
+----+------+-----------------+------+---------+------+------------+------------------+
| Id | User | Host | db | Command | Time | State | Info |
+----+------+-----------------+------+---------+------+------------+------------------+
| 3 | root | localhost | NULL | Query | 0 | starting | show processlist |
| 7 | root | localhost:52200 | NULL | Query | 10 | User sleep | select SLEEP(10) |
+----+------+-----------------+------+---------+------+------------+------------------+
2 rows in set (0.00 sec)
mysql> show processlist;
+----+------+-----------------+------+---------+------+----------+------------------+
| Id | User | Host | db | Command | Time | State | Info |
+----+------+-----------------+------+---------+------+----------+------------------+
| 3 | root | localhost | NULL | Query | 0 | starting | show processlist |
| 7 | root | localhost:52200 | NULL | Sleep | 12 | | NULL |
+----+------+-----------------+------+---------+------+----------+------------------+
2 rows in set (0.00 sec)
從輸出可以看到，Command為Query表示正在執行語句，Info列顯示了正在執行的具體SQL語句。