mysqldump :
--single-transaction
Creates a consistent snapshot by dumping all tables in a
single transaction. Works ONLY for tables stored in
storage engines which support multiversioning (currently
only InnoDB does); the dump is NOT guaranteed to be
consistent for other storage engines. While a
--single-transaction dump is in process, to ensure a
valid dump file (correct table contents and binary log
position), no other connection should use the following
statements: ALTER TABLE, DROP TABLE, RENAME TABLE,
TRUNCATE TABLE, as consistent snapshot is not isolated
from them. Option automatically turns off --lock-tables.
创建一个一致性的快照通过dump 所有的表到一个单独的transaction.
只能用于支持多版本的(目前只有InnoDB)
对其他的存储引擎 dump 是不能保证一直的。 当带上了 --single-transaction参数,
确保一个正确的dump 文件(正确的表内容和binary log 位置)
没有其他的连接来使用下面的语句；ALTER TABLE,DROP TABLE,RENAME TABLE ,TRUNCATE TABLE
[mysql@master ~]$ mysqldump test t3 >t3.sql
mysql> insert into t3 values(25255,'a','a','20110101')
-> ; --HANG
默认锁表:
[mysql@master ~]$ mysqldump --single-transaction test t3 >t3.sql
mysql> insert into t3 values(25255,'a','a','20110101');
Query OK, 1 row affected (0.10 sec)
mysql> commit;
Query OK, 0 rows affected (0.00 sec)
---可以看到加了 --single-transaction 参数后就可以进行insert 操作
表是可以 update, insert, delete, select 表中的数据的，
只是不能 ALTER TABLE, DROP TABLE, RENAME TABLE, TRUNCATE TABLE, 就是说锁是在表级别的，不能修改数据库表
的结构而已
[mysql@master ~]$ mysqldump --single-transaction test t3 >t3.sql
alter table t3 modify column name varchar(50); --此时HANG。