Description
Using the following code,
package main
import (
"database/sql"
_ "github.com/go-sql-driver/mysql"
"log"
)
func main() {
db, err := sql.Open("mysql", "root:@tcp(:12830)/")
if err != nil {
log.Fatal(err)
}
defer db.Close()
var s string
err = db.QueryRow("SELECT SLEEP(300)").Scan(&s)
if err != nil {
log.Fatal(err)
}
log.Println(s)
}And running it, I can see in MySQL,
mysql> show full processlist;
+----+------+-----------------+------+---------+------+------------+-----------------------+
| Id | User | Host | db | Command | Time | State | Info |
+----+------+-----------------+------+---------+------+------------+-----------------------+
| 95 | root | ::1:62318 | NULL | Query | 0 | init | show full processlist |
| 96 | root | 127.0.0.1:62446 | NULL | Query | 7 | User sleep | SELECT SLEEP(300) |
+----+------+-----------------+------+---------+------+------------+-----------------------+
2 rows in set (0.00 sec)
mysql> kill query 96;
Query OK, 0 rows affected (0.00 sec)
mysql> show full processlist;
+----+------+-----------+------+---------+------+-------+-----------------------+
| Id | User | Host | db | Command | Time | State | Info |
+----+------+-----------+------+---------+------+-------+-----------------------+
| 95 | root | ::1:62318 | NULL | Query | 0 | init | show full processlist |
+----+------+-----------+------+---------+------+-------+-----------------------+
1 row in set (0.00 sec)
The program prints out this:
2014/12/17 16:32:34 1
Now, if instead I kill the connection,
mysql> show full processlist;
+----+------+-----------------+------+---------+------+------------+-----------------------+
| Id | User | Host | db | Command | Time | State | Info |
+----+------+-----------------+------+---------+------+------------+-----------------------+
| 95 | root | ::1:62318 | NULL | Query | 0 | init | show full processlist |
| 97 | root | 127.0.0.1:62452 | NULL | Query | 5 | User sleep | SELECT SLEEP(300) |
+----+------+-----------------+------+---------+------+------------+-----------------------+
2 rows in set (0.00 sec)
mysql> kill 97;
Query OK, 0 rows affected (0.00 sec)
mysql> show full processlist;
+----+------+-----------------+------+---------+------+------------+-----------------------+
| Id | User | Host | db | Command | Time | State | Info |
+----+------+-----------------+------+---------+------+------------+-----------------------+
| 95 | root | ::1:62318 | NULL | Query | 0 | init | show full processlist |
| 98 | root | 127.0.0.1:62454 | NULL | Query | 3 | User sleep | SELECT SLEEP(300) |
+----+------+-----------------+------+---------+------+------------+-----------------------+
2 rows in set (0.00 sec)
So the statement got retried. This is, of course, because the connection got killed and the driver returned the error ErrBadConn. The program prints out:
[MySQL] 2014/12/17 16:35:41 packets.go:32: unexpected EOF
From the docs,
To prevent duplicate operations, ErrBadConn should NOT be returned if there's a possibility that the database server might have performed the operation. Even if the server sends back an error, you shouldn't return ErrBadConn.
What's happening here is that the query is a little bit unkillable if you kill the connection. It'll retry up to 10 times.
Is there any way we can detect that there was a kill? Given #185 I think the answer is "no" but I thought I should ask here anyway. From the client's point of view I think a KILL does look just like the connection was closed for some reason.