有关mysql死锁
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MySQL批量更新死锁案例分析:
直接上图
mysql提示 Lock wait timeout exceeded
原因:原因是你使用的InnoDB 表类型的时候,
默认参数:innodb_lock_wait_timeout设置锁等待的时间是50s,
因为有的锁等待超过了这个时间,所以抱错.
你可以把这个时间加长,或者优化存储过程,事务避免过长时间的等待.
解决的办法有两个:
第一:innodb_lock_wait_timeout 锁定等待时间改大
my.ini文件:
代码如下复制代码#innodb_lock_wait_timeout = 50
修改为
innodb_lock_wait_timeout = 500
A.应急方法:show processlist; kill掉出现问题的进程
B.根治方法:select * from innodb_trx 查看有是哪些事务占据了表资源
C.我的方法:设置MySQL锁等待超时 innodb_lock_wait_timeout=50 ,autocommit=on
DBA光从数据库无法着手找出源头是哪个SQL锁住了;
有时候看看show engine innodb status , 并结合 show full processlist; 能暂时解决问题;但一直不能精确定位;‘
下面是转载:
在5.5中,information_schema 库中增加了三个关于锁的表(MEMORY引擎);
SELECT * FROM information_schema.INNODB_LOCKS//当前出现的锁
SELECT * FROM information_schema.INNODB_LOCK_WAITS//锁等待的对应关系
SELECT * FROM information_schema.INNODB_TRX//当前运行的所有事务看到这个就非常激动 ; 这可是解决了一个大麻烦,先来看一下表结构
root@127.0.0.1 : information_schema 13:28:38> desc innodb_locks;
+-------------+---------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------------+---------------------+------+-----+---------+-------+
| lock_id | varchar(81) | NO | | | |#锁ID
| lock_trx_id | varchar(18) | NO | | | |#拥有锁的事务ID
| lock_mode | varchar(32) | NO | | | |#锁模式
| lock_type | varchar(32) | NO | | | |#锁类型
| lock_table | varchar(1024) | NO | | | |#被锁的表
| lock_index | varchar(1024) | YES | | NULL | |#被锁的索引
| lock_space | bigint(21) unsigned | YES | | NULL | |#被锁的表空间号
| lock_page | bigint(21) unsigned | YES | | NULL | |#被锁的页号
| lock_rec | bigint(21) unsigned | YES | | NULL | |#被锁的记录号
| lock_data | varchar(8192) | YES | | NULL | |#被锁的数据
+-------------+---------------------+------+-----+---------+-------+
10 rows in set (0.00 sec)
root@127.0.0.1 : information_schema 13:28:56> desc innodb_lock_waits;
+-------------------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------------------+-------------+------+-----+---------+-------+
| requesting_trx_id | varchar(18) | NO | | | |#请求锁的事务ID
| requested_lock_id | varchar(81) | NO | | | |#请求锁的锁ID
| blocking_trx_id | varchar(18) | NO | | | |#当前拥有锁的事务ID
| blocking_lock_id | varchar(81) | NO | | | |#当前拥有锁的锁ID
+-------------------+-------------+------+-----+---------+-------+
4 rows in set (0.00 sec)
root@127.0.0.1 : information_schema 13:29:05> desc innodb_trx ;
+----------------------------+---------------------+------+-----+---------------------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------------------------+---------------------+------+-----+---------------------+-------+
| trx_id | varchar(18) | NO | | | |#事务ID
| trx_state | varchar(13) | NO | | | |#事务状态:
| trx_started | datetime | NO | | 0000-00-00 00:00:00 | |#事务开始时间;
| trx_requested_lock_id | varchar(81) | YES | | NULL | |#innodb_locks.lock_id
| trx_wait_started | datetime | YES | | NULL | |#事务开始等待的时间
| trx_weight | bigint(21) unsigned | NO | | 0 | |#
| trx_mysql_thread_id | bigint(21) unsigned | NO | | 0 | |#事务线程ID
| trx_query | varchar(1024) | YES | | NULL | |#具体SQL语句
| trx_operation_state | varchar(64) | YES | | NULL | |#事务当前操作状态
| trx_tables_in_use | bigint(21) unsigned | NO | | 0 | |#事务中有多少个表被使用
| trx_tables_locked | bigint(21) unsigned | NO | | 0 | |#事务拥有多少个锁
| trx_lock_structs | bigint(21) unsigned | NO | | 0 | |#
| trx_lock_memory_bytes | bigint(21) unsigned | NO | | 0 | |#事务锁住的内存大小(B)
| trx_rows_locked | bigint(21) unsigned | NO | | 0 | |#事务锁住的行数
| trx_rows_modified | bigint(21) unsigned | NO | | 0 | |#事务更改的行数
| trx_concurrency_tickets | bigint(21) unsigned | NO | | 0 | |#事务并发票数
| trx_isolation_level | varchar(16) | NO | | | |#事务隔离级别
| trx_unique_checks | int(1) | NO | | 0 | |#是否唯一性检查
| trx_foreign_key_checks | int(1) | NO | | 0 | |#是否外键检查
| trx_last_foreign_key_error | varchar(256) | YES | | NULL | |#最后的外键错误
| trx_adaptive_hash_latched | int(1) | NO | | 0 | |#
| trx_adaptive_hash_timeout | bigint(21) unsigned | NO | | 0 | |#
+----------------------------+---------------------+------+-----+---------------------+-------+
22 rows in set (0.01 sec)下面我们来动手看看数据吧:
##建立测试数据:
use test;
create table tx1
(id int primary key ,
c1 varchar(20),
c2 varchar(30))
engine=innodb default charset = utf8 ;insert into tx1 values
(1,'aaaa','aaaaa2'),
(2,'bbbb','bbbbb2'),
(3,'cccc','ccccc2');commit;
###产生事务;
### Session1
start transaction;
update tx1 set c1='heyf',c2='heyf' where id =3 ;## 产生事务,在innodb_trx就有数据 ;
root@127.0.0.1 : information_schema 13:38:21> select * from innodb_trx G
*************************** 1. row ***************************
trx_id: 3669D82
trx_state: RUNNING
trx_started: 2010-12-24 13:38:06
trx_requested_lock_id: NULL
trx_wait_started: NULL
trx_weight: 3
trx_mysql_thread_id: 2344
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: 1
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
1 row in set (0.00 sec)### 由于没有产生锁等待,下面两个表没有数据 ;
information_schema 13:38:31> select * from innodb_lock_waits G
Empty set (0.00 sec)information_schema 13:38:57> select * from innodb_locks G
Empty set (0.00 sec)#### 产生锁等待
#### session 2
start transaction;
update tx1 set c1='heyfffff',c2='heyffffff' where id =3 ;
root@127.0.0.1 : information_schema 13:39:01> select * from innodb_trx G
*************************** 1. row ***************************
trx_id: 3669D83 ##第2个事务
trx_state: LOCK WAIT ## 处于等待状态
trx_started: 2010-12-24 13:40:07
trx_requested_lock_id: 3669D83:49:3:4 ##请求的锁ID
trx_wait_started: 2010-12-24 13:40:07
trx_weight: 2
trx_mysql_thread_id: 2346 ##线程 ID
trx_query: update tx1 set c1='heyfffff',c2='heyffffff' where id =3
trx_operation_state: starting index read
trx_tables_in_use: 1 ##需要用到1个表
trx_tables_locked: 1 ##有1个表被锁
trx_lock_structs: 2
trx_lock_memory_bytes: 376
trx_rows_locked: 1
trx_rows_modified: 0
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
*************************** 2. row ***************************
trx_id: 3669D82 ##第1个事务
trx_state: RUNNING
trx_started: 2010-12-24 13:38:06
trx_requested_lock_id: NULL
trx_wait_started: NULL
trx_weight: 3
trx_mysql_thread_id: 2344
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: 1
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
2 rows in set (0.00 sec)root@127.0.0.1 : information_schema 13:40:12> select * from innodb_locks G
*************************** 1. row ***************************
lock_id: 3669D83:49:3:4 ## 第2个事务需要的锁
lock_trx_id: 3669D83
lock_mode: X
lock_type: RECORD
lock_table: `test`.`tx1`
lock_index: `PRIMARY`
lock_space: 49
lock_page: 3
lock_rec: 4
lock_data: 3
*************************** 2. row ***************************
lock_id: 3669D82:49:3:4 ## 第1个事务需要的锁
lock_trx_id: 3669D82
lock_mode: X
lock_type: RECORD
lock_table: `test`.`tx1`
lock_index: `PRIMARY`
lock_space: 49
lock_page: 3
lock_rec: 4
lock_data: 3
2 rows in set (0.00 sec)root@127.0.0.1 : information_schema 13:40:15> select * from innodb_lock_waits G
*************************** 1. row ***************************
requesting_trx_id: 3669D83 ## 请求锁的事务
requested_lock_id: 3669D83:49:3:4 ## 请求锁的锁ID
blocking_trx_id: 3669D82 ## 拥有锁的事务
blocking_lock_id: 3669D82:49:3:4 ## 拥有锁的锁ID
1 row in set (0.00 sec)
其实解决的步骤如下:
1,查看数据库的隔离级别:
mysql> select @@tx_isolation;
+-----------------+
| @@tx_isolation |
+-----------------+
| REPEATABLE-READ |
+-----------------+
1 row in set (0.00 sec)
mysql>
2,去查看先当前库的线程情况:
mysql> show full processlist;
+----------+-----------------+-------------------+-----------------+-------------+---------+-------------------------+-----------------------+
| Id | User | Host | db | Command | Time | State | Info |
+----------+-----------------+-------------------+-----------------+-------------+---------+-------------------------+-----------------------+
| 1 | event_scheduler | localhost | NULL | Daemon | 9635385 | Waiting on empty queue | NULL |
| 9930577 | business_web | 192.168.1.21:45503 | business_db | Sleep | 153 | | NULL |
| 9945825 | business_web | 192.168.1.25:49518 | business_db | Sleep | 43 | | NULL |
| 9946322 | business_web | 192.168.1.23:44721 | business_db | Sleep | 153 | | NULL |
| 9960167 | business_web | 192.168.3.28:2409 | business_db | Sleep | 93 | | NULL |
| 9964484 | business_web | 192.168.1.21:24280 | business_db | Sleep | 7 | | NULL |
| 9972499 | business_web | 192.168.3.28:35752 | business_db | Sleep | 13 | | NULL |
| 10000117 | business_web | 192.168.3.28:9149 | business_db | Sleep | 6 | | NULL |
| 10002523 | business_web | 192.168.3.29:42872 | business_db | Sleep | 6 | | NULL |
| 10007545 | business_web | 192.168.1.21:51379 | business_db | Sleep | 155 | | NULL |
......
+----------+-----------------+-------------------+-----------------+-------------+---------+-------------------------+-----------------------+
没有看到正在执行的慢SQL记录线程,再去查看innodb的事务表INNODB_TRX,看下里面是否有正在锁定的事务线程,看看ID是否在show full processlist里面的sleep线程中,如果是,就证明这个sleep的线程事务一直没有commit或者rollback而是卡住了,我们需要手动kill掉。
mysql> SELECT * FROM information_schema.INNODB_TRX G;
*************************** 1. row ***************************
trx_id: 20866
trx_state: LOCK WAIT
trx_started: 2014-07-31 10:42:35
trx_requested_lock_id: 20866:617:3:3
trx_wait_started: 2014-07-30 10:42:35
trx_weight: 2
trx_mysql_thread_id: 9930577
trx_query: delete from dltask where id=1
trx_operation_state: starting index read
trx_tables_in_use: 1
trx_tables_locked: 1
trx_lock_structs: 2
trx_lock_memory_bytes: 376
trx_rows_locked: 1
trx_rows_modified: 0
trx_concurrency_tickets: 0
trx_isolation_level: READ COMMITTED
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
3,看到有这条9930577的sql,kill掉,执行kill 9930577;
mysql> kill 9930577;
Query OK, 0 rows affected (0.00 sec)
mysql>
然后再去查询INNODB_TRX表,就没有阻塞的事务sleep线程存在了,如下所示:
mysql> SELECT * FROM INNODB_TRX G;
Empty set (0.00 sec)
ERROR:
No query specified
mysql>
再去执行update语句,就能正常执行了,如下所示:
mysql> update order_info set province_id=15 ,city_id= 1667 where order_from=10 and order_out_sn='1407261241xxxx';
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0
mysql>
4,总结分析
表数据量也不大,按照普通的情况来说,简单的update应该不会造成阻塞的,mysql都是autocommit,不会出现update卡住的情况,去查看下autocommit的值。
mysql> select @@autocommit;
+--------------+
| @@autocommit |
+--------------+
| 0 |
+--------------+
1 row in set (0.00 sec)
mysql>
看到亮闪闪的0,这个设置导致原来的update语句如果没有commit的话,你再重新执行update语句,就会等待锁定,当等待时间过长的时候,就会报ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction的错误。
所以赶紧commit刚才执行的update语句,之后 set global autocommit=1;
MySQL批量更新死锁案例分析
问题描述
在做项目的过程中,由于写SQL太过随意,一不小心就抛了一个死锁异常,如下:
- com.mysql.jdbc.exceptions.jdbc4.MySQLTransactionRollbackException: Deadlock found when trying to get lock; try restarting transaction
- at sun.reflect.GeneratedConstructorAccessor247.newInstance(Unknown Source)
- at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
- at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
- at com.mysql.jdbc.Util.handleNewInstance(Util.java:406)
- at com.mysql.jdbc.Util.getInstance(Util.java:381)
- at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1045)
- at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:956)
- at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3491)
- at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3423)
- at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1936)
- at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2060)
- at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2542)
- at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:1734)
- at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:2019)
- at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:1937)
- at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:1922)
表结构如下:
- CREATE TABLE `user_item` (
- `id` BIGINT(20) NOT NULL,
- `user_id` BIGINT(20) NOT NULL,
- `item_id` BIGINT(20) NOT NULL,
- `status` TINYINT(4) NOT NULL,
- PRIMARY KEY (`id`),
- KEY `idx_1` (`user_id`,`item_id`,`status`)
- ) ENGINE=INNODB DEFAULT CHARSET=utf-8
- update user_item set status=1 where user_id=? and item_id=? 【这里用到的上面的索引idx_1,所以肯定会加上行级锁】
原因分析
mysql的事务支持与存储引擎有关,---
1.MyISAM:不支持事务,
2.INNODB支持事务,更新时采用的是行级锁【行级锁必须建立在索引的基础】。
这里采用的是INNODB做存储引擎,意味着会将update语句做为一个事务来处理。
行级锁并不是直接锁记录,而是锁索引,
如果一条SQL语句用到了主键索引,mysql会锁住主键索引;
如果一条语句操作了非主键索引,mysql会先锁住非主键索引,再锁定主键索引。
这个update语句会执行以下步骤:
step1、由于用到了非主键索引,首先需要获取idx_1上的行级锁
step2、紧接着根据主键进行更新,所以需要获取主键上的行级锁;
step3、更新完毕后,提交,并释放所有锁。
如果在步骤1和2之间突然插入一条语句:
update user_item .....where id=? and user_id=?,这条语句会先锁住主键索引,然后锁住idx_1。
蛋疼的情况出现了,一条语句获取了idx_1上的锁,等待主键索引上的锁;另一条语句获取了主键上的锁,等待idx_1上的锁,这样就出现了死锁
解决方案
1、先获取需要更新的记录的主键
- select id from user_item where user_id=? and item_id=?
- for (Long id : idList) {
- userItemDAO.updateStatus(id, userId, 1);
- }
- update user_item set status=? where id=? and user_id=?
不过这个解决方案与先前的更新语句不一样,
先前的更新语句对所有记录的更新在一个事务中,
新的更新语句采用循环更新后并不在同一个事务中,
所以在for循环外面还得开一个事务。
- Exception e = (Exception)getDbfeelTransactionTemplate().execute(new TransactionCallback() {
- public Object doInTransaction(TransactionStatus status) {
- try {
- for(Long id:idList) {
- userItemDAO.updateStatus(id,userId,1)
- }
- return null;
- }catch(DAOException e) {
- status.setRollbackOnly();
- return e;
- }
- catch (Exception e) {
- status.setRollbackOnly();
- return e;
- }
- }
- });
更新操作默认会加行级锁,行级锁是基于索引的,
在分析死锁之前需要查询一下mysql的执行计划,看看是否用到了索引,用到了哪个索引,
对于没有用索引的操作会采用表级锁。
如果操作用到了主键索引会先在主键索引上加锁,然后在其他索引上加锁,否则加锁顺序相反。
在并发度高的应用中,批量更新一定要带上记录的主键,优先获取主键上的锁,
这样可以减少死锁的发生。
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