[root@mysql57 data]# mysqldump --help
 --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.

该参数通过在一个事务中导出所有表从而创建一个一致性的快照，当前版本的MySQL只可以对innodb 引擎保证一致性，导出过程中不会锁表其他引擎，如MyISAM 在导出期间会锁表为保证有效的dump文件，即正确的表内容和二进制日志位置，在导出的过程中不能有如下操作
ALTER TABLE
DROP TABLE
RENAME TABLE
TRUNCATE TABLE
如指定了 —lock-tables参数则会自动将其关闭，推荐在mysqldump中使用该参数http://www.cndba.cn/hbhe0316/article/22701http://www.cndba.cn/hbhe0316/article/22701http://www.cndba.cn/hbhe0316/article/22701

使用—single-transaction备份数据库
1.备份全库

[root@mysql57 data]# mysqldump -h127.0.0.1 -uroot -pwwwwww --single-transaction --set-gtid-purged=OFF  --all-databases --master-data=2  --triggers --events --routines> /tmp/all_master.sqlmysqldump: [Warning] Using a password on the command line interface can be insecure.[root@mysql57 data]# du -sm /tmp/all_master.sql 
512     /tmp/all_master.sql

2.备份单库

[root@mysql57 data]# mysqldump -h127.0.0.1 -uroot -pwwwwww --single-transaction --set-gtid-purged=OFF  --databases testdb  --master-data=2   --triggers --events --routines> /tmp/testdb_all_master.sql
mysqldump: [Warning] Using a password on the command line interface can be insecure.

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MYSQL