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KILL命令的语法格式如下:KILL [CONNECTION | QUERY] thread_id
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步骤如下:
1、KILL允许自选的CONNECTION或QUERY修改符:KILL CONNECTION与不含修改符的KILL一样:它会终止与给定的thread_id有关的连接。
2、KILL QUERY会终止连接当前正在执行的语句,但是会保持连接的原状。
3、如果您拥有PROCESS权限,则您可以查看所有线程。
4、如果您拥有超级管理员权限,您可以终止所有线程和语句。否则,您只能查看和终止您自己的线程和语句。
5、您也可以使用mysqladmin processlist和mysqladmin kill命令来检查和终止线程。
首先登录mysql,然后使用: show processlist; 查看当前mysql中各个线程状态。
以上显示出当前正在执行的sql语句列表,找到消耗资源最大的那条语句对应的id.
然后运行kill命令,命令格式如下:
[sql] view plain copy
kill id;
- 示例:
kill 8358
杀掉即可。
数据库为了及时响应请求,一定会保持一定数目的
线程,哪怕暂时不用。
你在
client
端
调用
close
释放了连接,那么你工作就已经完成了。
想确定会不会有问题,那么可以这么做。
不停的重新运行你的这段代码,如果
mysql
的线程数
没有增多
就不是问题。
如果随运行次数
线性增加,再来考虑解决这个问题
就是这样的,线程的回收,mysql
有自己的机制。你写程序的时候,最好也这么做,资源的回收不是越快越好,因为初始化资源也是要消耗代价的。
如果遇到死锁了,怎么解决呢?找到原始的锁ID,然后KILL掉一直持有的那个线程就可以了, 但是众多线程,可怎么找到引起死锁的线程ID呢? MySQL 发展到现在,已经非常强大了,这个问题很好解决。 直接从数据字典连查找。
我们来演示下。
线程A,我们用来锁定某些记录,假设这个线程一直没提交,或者忘掉提交了。 那么就一直存在,但是数据里面显示的只是SLEEP状态。
mysql set @@autocommit=0;
Query OK, 0 rows affected (0.00 sec)
mysql use test;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A
Database changed
mysql show tables;
+----------------+
| Tables_in_test |
+----------------+
| demo_test |
| t3 |
+----------------+
2 rows in set (0.00 sec)
mysql select * from t3;
+----+--------+--------+------------+----+----+----+
| id | fname | lname | birthday | c1 | c2 | c3 |
+----+--------+--------+------------+----+----+----+
| 19 | lily19 | lucy19 | 2013-04-18 | 19 | 0 | 0 |
| 20 | lily20 | lucy20 | 2013-03-13 | 20 | 0 | 0 |
+----+--------+--------+------------+----+----+----+
2 rows in set (0.00 sec)
mysql update t3 set birthday = '2022-02-23' where id = 19;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0
mysql select connection_id();
+-----------------+
| connection_id() |
+-----------------+
| 16 |
+-----------------+
1 row in set (0.00 sec)
mysql
线程B, 我们用来进行普通的更新,但是遇到问题了,此时不知道是哪个线程把这行记录给锁定了?
mysql use test;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A
Database changed
mysql select @@autocommit;
+--------------+
| @@autocommit |
+--------------+
| 1 |
+--------------+
1 row in set (0.00 sec)
mysql update t3 set birthday='2018-01-03' where id = 19;
ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction
mysql select connection_id();
+-----------------+
| connection_id() |
+-----------------+
| 17 |
+-----------------+
1 row in set (0.00 sec)
mysql show processlist;
+----+------+-----------+------+---------+------+-------+------------------+
| Id | User | Host | db | Command | Time | State | Info |
+----+------+-----------+------+---------+------+-------+------------------+
| 10 | root | localhost | NULL | Sleep | 1540 | | NULL |
| 11 | root | localhost | NULL | Sleep | 722 | | NULL |
| 16 | root | localhost | test | Sleep | 424 | | NULL |
| 17 | root | localhost | test | Query | 0 | init | show processlist |
| 18 | root | localhost | NULL | Sleep | 5 | | NULL |
+----+------+-----------+------+---------+------+-------+------------------+
5 rows in set (0.00 sec)
mysql show engine innodb status\G
------------
TRANSACTIONS
------------
Trx id counter 189327
Purge done for trx's n:o 189323 undo n:o 0 state: running but idle
History list length 343
LIST OF TRANSACTIONS FOR EACH SESSION:
---TRANSACTION 0, not started
MySQL thread id 11, OS thread handle 0x7f70a0c98700, query id 994 localhost root init
show engine innodb status
---TRANSACTION 189326, ACTIVE 2 sec starting index read
mysql tables in use 1, locked 1
LOCK WAIT 2 lock struct(s), heap size 376, 1 row lock(s)
MySQL thread id 17, OS thread handle 0x7f70a0bd5700, query id 993 localhost root updating
update t3 set birthday='2018-01-03' where id = 19
------- TRX HAS BEEN WAITING 2 SEC FOR THIS LOCK TO BE GRANTED:
RECORD LOCKS space id 529 page no 3 n bits 72 index `PRIMARY` of table `test`.`t3` trx id 189326 lock_mode X waiting
Record lock, heap no 2 PHYSICAL RECORD: n_fields 9; compact format; info bits 0
0: len 2; hex 3139; asc 19;;
1: len 6; hex 00000002e38c; asc ;;
2: len 7; hex 7e00000d2827c9; asc ~ (' ;;
3: len 6; hex 6c696c793139; asc lily19;;
4: len 6; hex 6c7563793139; asc lucy19;;
5: len 3; hex 8fcc57; asc W;;
6: len 4; hex 80000013; asc ;;
7: len 4; hex 80000000; asc ;;
8: len 4; hex 80000000; asc ;;
------------------
---TRANSACTION 189324, ACTIVE 641 sec
2 lock struct(s), heap size 376, 3 row lock(s), undo log entries 1
MySQL thread id 16, OS thread handle 0x7f70a0b94700, query id 985 localhost root cleaning up
Trx read view will not see trx with id = 189325, sees 189325
上面的信息很繁多,也看不清楚到底哪里是哪里。
不过现在,我们只要从数据字典里面拿出来这部分信息就OK了。
mysql SELECT * FROM information_schema.INNODB_TRX\G
*************************** 1. row ***************************
trx_id: 189324
trx_state: RUNNING
trx_started: 2013-04-18 17:48:14
trx_requested_lock_id: NULL
trx_wait_started: NULL
trx_weight: 3
trx_mysql_thread_id: 16
trx_query: NULL
trx_operation_state: NULL
trx_tables_in_use: 0
trx_tables_locked: 0
trx_lock_structs: 2
trx_lock_memory_bytes: 376
trx_rows_locked: 3
trx_rows_modified: 1
trx_concurrency_tickets: 0
trx_isolation_level: REPEATABLE READ
trx_unique_checks: 1
trx_foreign_key_checks: 1
trx_last_foreign_key_error: NULL
trx_adaptive_hash_latched: 0
trx_adaptive_hash_timeout: 10000
trx_is_read_only: 0
trx_autocommit_non_locking: 0
1 row in set (0.01 sec)
mysql
原来是线程16忘掉COMMIT了。