今天就跟大家聊聊有关如何进行MySQLdump单表备份加--single-transaction --master-data=2参数执行过程的内部剖析，可能很多人都不太了解，为了让大家更加了解，小编给大家总结了以下内容，希望大家根据这篇文章可以有所收获。

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开启general_log:

mysql(mdba@localhost:(none) 01:08:55)>set global general_log=on;
Query OK, 0 rows affected (0.02 sec)

mysql(mdba@localhost:(none) 01:09:07)>show variables like '%general%';

| Variable_name    | Value                               |

| general_log      | ON                                  |
| general_log_file | /usr/local/mysql/data/localhost.log |

2 rows in set (0.00 sec)


mysql(mdba@localhost:(none) 01:31:43)>show databases;

| Database           |

| information_schema |
| bbb                |
| credit             |
| e_contract         |
| ixinnuo_sjcj       |
| ixinnuo_sjcj-_T    |
| mysql              |
| percona            |
| performance_schema |
| sys                |
| test               |
| whpmap             |

12 rows in set (0.05 sec)


mysql(mdba@localhost:(none) 01:31:46)>use credit
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(mdba@localhost:credit 01:32:02)>show tables;

| Tables_in_credit     |

| f_audit              |
| f_audit_bak_20170504 |

2 rows in set (0.00 sec)



例如备份credit库下面的f_audit表，使用--single-transaction --master-data=2参数:

[root@localhost tmp]# mysqldump -umdba -pdsf0723 --single-transaction --master-data=2 credit f_audit > /tmp/f_audit.sql



查看general_log:
[root@localhost tmp]# cat /usr/local/mysql/data/localhost.log
/opt/app/mysql/5.7.18/bin/mysqld, Version: 5.7.18-log (MySQL Community Server (GPL)). started with:
Tcp port: 3306  Unix socket: /tmp/mysql.sock
Time                 Id Command    Argument
2017-08-31T05:09:09.189375Z     19513 Query     show variables like '%gen%'
2017-08-31T05:09:24.603322Z     19513 Query     SELECT DATABASE()
2017-08-31T05:09:24.604041Z     19513 Init DB   credit
2017-08-31T05:09:24.605173Z     19513 Query     show databases
2017-08-31T05:09:24.605838Z     19513 Query     show tables
2017-08-31T05:09:24.605976Z     19513 Field List        f_audit
2017-08-31T05:09:24.606416Z     19513 Field List        f_audit_bak_20170504
2017-08-31T05:09:26.575331Z     19513 Query     show tables
2017-08-31T05:11:18.126829Z     19514 Connect   mdba@localhost on  using Socket
2017-08-31T05:11:18.126927Z     19514 Query     /*!40100 SET @@SQL_MODE='' */
2017-08-31T05:11:18.130352Z     19514 Query     /*!40103 SET TIME_ZONE='+00:00' */
2017-08-31T05:11:18.130450Z     19514 Query     FLUSH /*!40101 LOCAL */ TABLES
2017-08-31T05:11:18.140266Z     19514 Query     FLUSH TABLES WITH READ LOCK
2017-08-31T05:11:18.140318Z     19514 Query     SET SESSION TRANSACTION ISOLATION LEVEL REPEATABLE READ
2017-08-31T05:11:18.140355Z     19514 Query     START TRANSACTION /*!40100 WITH CONSISTENT SNAPSHOT */
2017-08-31T05:11:18.140417Z     19514 Query     SHOW VARIABLES LIKE 'gtid\_mode'
2017-08-31T05:11:18.150840Z     19514 Query     SHOW MASTER STATUS
2017-08-31T05:11:18.168898Z     19514 Query     UNLOCK TABLES
2017-08-31T05:11:18.181199Z     19514 Query     SELECT LOGFILE_GROUP_NAME, FILE_NAME, TOTAL_EXTENTS, INITIAL_SIZE, ENGINE, EXTRA FROM INFORMATION_SCHEMA.FILES WHERE FILE_TYPE = 'UNDO LOG' AND FILE_NAME IS NOT NULL AND LOGFILE_GROUP_NAME IS NOT NULL AND LOGFILE_GROUP_NAME IN (SELECT DISTINCT LOGFILE_GROUP_NAME FROM INFORMATION_SCHEMA.FILES WHERE FILE_TYPE = 'DATAFILE' AND TABLESPACE_NAME IN (SELECT DISTINCT TABLESPACE_NAME FROM INFORMATION_SCHEMA.PARTITIONS WHERE TABLE_SCHEMA='credit' AND TABLE_NAME IN ('f_audit'))) GROUP BY LOGFILE_GROUP_NAME, FILE_NAME, ENGINE, TOTAL_EXTENTS, INITIAL_SIZE ORDER BY LOGFILE_GROUP_NAME
2017-08-31T05:11:18.210240Z     19514 Query     SELECT DISTINCT TABLESPACE_NAME, FILE_NAME, LOGFILE_GROUP_NAME, EXTENT_SIZE, INITIAL_SIZE, ENGINE FROM INFORMATION_SCHEMA.FILES WHERE FILE_TYPE = 'DATAFILE' AND TABLESPACE_NAME IN (SELECT DISTINCT TABLESPACE_NAME FROM INFORMATION_SCHEMA.PARTITIONS WHERE TABLE_SCHEMA='credit' AND TABLE_NAME IN ('f_audit')) ORDER BY TABLESPACE_NAME, LOGFILE_GROUP_NAME
2017-08-31T05:11:18.220125Z     19514 Query     SHOW VARIABLES LIKE 'ndbinfo\_version'
2017-08-31T05:11:18.221667Z     19514 Init DB   credit
2017-08-31T05:11:18.221712Z     19514 Query     SHOW TABLES LIKE 'f\_audit'
2017-08-31T05:11:18.221834Z     19514 Query     SAVEPOINT sp
2017-08-31T05:11:18.221887Z     19514 Query     show table status like 'f\_audit'
2017-08-31T05:11:18.222054Z     19514 Query     SET SQL_QUOTE_SHOW_CREATE=1
2017-08-31T05:11:18.222100Z     19514 Query     SET SESSION character_set_results = 'binary'
2017-08-31T05:11:18.222142Z     19514 Query     show create table `f_audit`
2017-08-31T05:11:18.222231Z     19514 Query     SET SESSION character_set_results = 'utf8'
2017-08-31T05:11:18.222287Z     19514 Query     show fields from `f_audit`
2017-08-31T05:11:18.222614Z     19514 Query     show fields from `f_audit`
2017-08-31T05:11:18.222940Z     19514 Query     SELECT /*!40001 SQL_NO_CACHE */ * FROM `f_audit`
2017-08-31T05:11:18.223074Z     19514 Query     SET SESSION character_set_results = 'binary'
2017-08-31T05:11:18.223116Z     19514 Query     use `credit`
2017-08-31T05:11:18.223165Z     19514 Query     select @@collation_database
2017-08-31T05:11:18.223224Z     19514 Query     SHOW TRIGGERS LIKE 'f\_audit'
2017-08-31T05:11:18.223465Z     19514 Query     SET SESSION character_set_results = 'utf8'
2017-08-31T05:11:18.223509Z     19514 Query     ROLLBACK TO SAVEPOINT sp
2017-08-31T05:11:18.223547Z     19514 Query     RELEASE SAVEPOINT sp
2017-08-31T05:11:18.281441Z     19514 Quit


发现其执行了FLUSH TABLES WITH READ LOCK:
2017-08-31T05:11:18.130450Z     19514 Query     FLUSH /*!40101 LOCAL */ TABLES
2017-08-31T05:11:18.140266Z     19514 Query     FLUSH TABLES WITH READ LOCK


通过进一步测试发现mysqldump备份的时候只使用--single-transaction不使用--master-data=2参数是不会进行锁表的。
不加--master-data=2参数:
[root@localhost tmp]#mysqldump -umdba -pdsf0723 --single-transaction  credit f_audit > f_audit.sql


查看general_log:
2017-08-31T05:24:05.890881Z     19516 Connect   mdba@localhost on  using Socket
2017-08-31T05:24:05.890984Z     19516 Query     /*!40100 SET @@SQL_MODE='' */
2017-08-31T05:24:05.891037Z     19516 Query     /*!40103 SET TIME_ZONE='+00:00' */
2017-08-31T05:24:05.891478Z     19516 Query     SET SESSION TRANSACTION ISOLATION LEVEL REPEATABLE READ
2017-08-31T05:24:05.891520Z     19516 Query     START TRANSACTION /*!40100 WITH CONSISTENT SNAPSHOT */
2017-08-31T05:24:05.891589Z     19516 Query     SHOW VARIABLES LIKE 'gtid\_mode'
2017-08-31T05:24:05.893983Z     19516 Query     UNLOCK TABLES
2017-08-31T05:24:05.894099Z     19516 Query     SELECT LOGFILE_GROUP_NAME, FILE_NAME, TOTAL_EXTENTS, INITIAL_SIZE, ENGINE, EXTRA FROM INFORMATION_SCHEMA.FILES WHERE FILE_TYPE = 'UNDO LOG' AND FILE_NAME IS NOT NULL AND LOGFILE_GROUP_NAME IS NOT NULL AND LOGFILE_GROUP_NAME IN (SELECT DISTINCT LOGFILE_GROUP_NAME FROM INFORMATION_SCHEMA.FILES WHERE FILE_TYPE = 'DATAFILE' AND TABLESPACE_NAME IN (SELECT DISTINCT TABLESPACE_NAME FROM INFORMATION_SCHEMA.PARTITIONS WHERE TABLE_SCHEMA='credit' AND TABLE_NAME IN ('f_audit'))) GROUP BY LOGFILE_GROUP_NAME, FILE_NAME, ENGINE, TOTAL_EXTENTS, INITIAL_SIZE ORDER BY LOGFILE_GROUP_NAME
2017-08-31T05:24:05.911788Z     19516 Query     SELECT DISTINCT TABLESPACE_NAME, FILE_NAME, LOGFILE_GROUP_NAME, EXTENT_SIZE, INITIAL_SIZE, ENGINE FROM INFORMATION_SCHEMA.FILES WHERE FILE_TYPE = 'DATAFILE' AND TABLESPACE_NAME IN (SELECT DISTINCT TABLESPACE_NAME FROM INFORMATION_SCHEMA.PARTITIONS WHERE TABLE_SCHEMA='credit' AND TABLE_NAME IN ('f_audit')) ORDER BY TABLESPACE_NAME, LOGFILE_GROUP_NAME
2017-08-31T05:24:05.916870Z     19516 Query     SHOW VARIABLES LIKE 'ndbinfo\_version'
2017-08-31T05:24:05.918150Z     19516 Init DB   credit
2017-08-31T05:24:05.918208Z     19516 Query     SHOW TABLES LIKE 'f\_audit'
2017-08-31T05:24:05.918336Z     19516 Query     SAVEPOINT sp
2017-08-31T05:24:05.918390Z     19516 Query     show table status like 'f\_audit'
2017-08-31T05:24:05.918558Z     19516 Query     SET SQL_QUOTE_SHOW_CREATE=1
2017-08-31T05:24:05.918603Z     19516 Query     SET SESSION character_set_results = 'binary'
2017-08-31T05:24:05.918648Z     19516 Query     show create table `f_audit`
2017-08-31T05:24:05.918730Z     19516 Query     SET SESSION character_set_results = 'utf8'
2017-08-31T05:24:05.918786Z     19516 Query     show fields from `f_audit`
2017-08-31T05:24:05.919114Z     19516 Query     show fields from `f_audit`
2017-08-31T05:24:05.919417Z     19516 Query     SELECT /*!40001 SQL_NO_CACHE */ * FROM `f_audit`
2017-08-31T05:24:05.919547Z     19516 Query     SET SESSION character_set_results = 'binary'
2017-08-31T05:24:05.919592Z     19516 Query     use `credit`
2017-08-31T05:24:05.919639Z     19516 Query     select @@collation_database
2017-08-31T05:24:05.919698Z     19516 Query     SHOW TRIGGERS LIKE 'f\_audit'
2017-08-31T05:24:05.919999Z     19516 Query     SET SESSION character_set_results = 'utf8'
2017-08-31T05:24:05.920064Z     19516 Query     ROLLBACK TO SAVEPOINT sp
2017-08-31T05:24:05.920107Z     19516 Query     RELEASE SAVEPOINT sp
2017-08-31T05:24:05.971293Z     19516 Quit


发现并没有执行FLUSH TABLES WITH READ LOCK.

只使用--master-data=2参数为了获取show master status，会执行FLUSH TABLES WITH READ LOCK的全局锁，在业务低峰期，mysql获取全局锁会很快,但在业务高峰期又有很多库表的情况下是不建议执行全局锁的，
因此mysqldump备份尽量放在业务低峰期做，或者备份时直接去掉--master-data=2参数.

看完上述内容，你们对如何进行mysqldump单表备份加--single-transaction --master-data=2参数执行过程的内部剖析有进一步的了解吗？如果还想了解更多知识或者相关内容，请关注创新互联行业资讯频道，感谢大家的支持。

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