Mysql数据库管理--数据库行锁分析与测试

1 表无索引 update任何行，不提交简直是灾难

1 在不通过索引条件查询时，Innodb会锁定表中所有记录。

session 1

set autocommit=0;

update ta set user='chenliguo' where user='rp1';

session 2

update ta set user='wangbaosong' where user='root';

对于索引的表，session2 会被session 1 锁住。

mysql> select * from data_lock_waits\G

*************************** 1. row ***************************

ENGINE: INNODB

REQUESTING_ENGINE_LOCK_ID: 282791232:0:43:2:242839520

REQUESTING_ENGINE_TRANSACTION_ID: 434473

REQUESTING_THREAD_ID: 48

REQUESTING_EVENT_ID: 31

REQUESTING_OBJECT_INSTANCE_BEGIN: 242839520

BLOCKING_ENGINE_LOCK_ID: 282792056:0:43:2:242842776

BLOCKING_ENGINE_TRANSACTION_ID: 434472

BLOCKING_THREAD_ID: 49

BLOCKING_EVENT_ID: 14

BLOCKING_OBJECT_INSTANCE_BEGIN: 242842776s

mysql> desc performance_schema.threads;

+---------------------+------------------+------+-----+---------+-------+

+---------------------+------------------+------+-----+---------+-------+

+---------------------+------------------+------+-----+---------+-------+

18 rows in set (0.00 sec)

mysql> desc performance_schema.processlist;

+---------+-----------------+------+-----+---------+-------+

+---------+-----------------+------+-----+---------+-------+

| ID | bigint unsigned | NO | PRI | NULL | |

| DB | varchar(64) | YES | | NULL | |

+---------+-----------------+------+-----+---------+-------+

8 rows in set (0.01 sec)

select c.processlist_user,c.processlist_host,c.processlist_command,c.processlist_state from performance_schema.data_lock_waits a,performance_schema.threads c

where a.REQUESTING_THREAD_ID=c.thread_id

union all

select c.processlist_user,c.processlist_host,c.processlist_command,c.processlist_state from performance_schema.data_lock_waits a,performance_schema.threads c

where a.BLOCKING_THREAD_ID=c.thread_id;

mysql> select c.processlist_user,c.processlist_host,c.processlist_command,c.processlist_state from per

formance_schema.data_lock_waits a,performance_schema.threads c

-> where a.REQUESTING_THREAD_ID=c.thread_id

-> union all

-> select c.processlist_user,c.processlist_host,c.processlist_command,c.processlist_state from per

formance_schema.data_lock_waits a,performance_schema.threads c

-> where a.BLOCKING_THREAD_ID=c.thread_id;

+------------------+------------------+---------------------+-------------------+

+------------------+------------------+---------------------+-------------------+

+------------------+------------------+---------------------+-------------------+

2 rows in set (0.00 sec)

mysql>

2 mysql行锁是针对索引加的锁，不是针对所有记录加的锁，索引虽然访问的是不同行的记录，但是如果使用相同的索引键，会出现锁冲突的。

表tab1（id int,name varchar（100）） id列有索引，name列无索引。

则update1

update tab1 set name='1' where id=1 and name='CHENLIGUO';

update tab1 set name='2' where id=1 and name='LIZONGYUAN'

会发生阻塞。