正文
之前的博文当中提到备份工具mydumper的使用，而软件包中还包含了与之对应的恢复工具myloader，本文就总结下myloader的用法。关于mydumper的安装与使用可以参考之前的博文：mysql backup mydumper。
查看myloader的版本信息：
# myloader -v myloader 0.9.5, built against mysql 5.7.21-21
# myloader --help usage: myloader [option?] multi-threaded mysql loader help options: -?, --help show help options application options: -d, --directory directory of the dump to import -q, --queries-per-transaction number of queries per transaction, default 1000 -o, --overwrite-tables drop tables if they already exist -b, --database an alternative database to restore into -s, --source-db database to restore -e, --enable-binlog enable binary logging of the restore data -h, --host the host to connect to -u, --user username with the necessary privileges -p, --password user password -a, --ask-password prompt for user password -p, --port tcp/ip port to connect to -s, --socket unix domain socket file to use for connection -t, --threads number of threads to use, default 4 -c, --compress-protocol use compression on the mysql connection -v, --version show the program version and exit -v, --verbose verbosity of output, 0 = silent, 1 = errors, 2 = warnings, 3 = info, default 2 --defaults-file use a specific defaults file
-d, --directory
要import的备份文件所在目录
-q, --queries-per-transaction
每个事务的查询数, 默认为1000
-o, --overwrite-tables
如果表存在则删除表
-b, --database
指定需要还原成的数据库名
-s, --source-db
指定还原的源数据库
-e, --enable-binlog
还原数据时记录binlog日志
-h, --host
指定连接host
-u, --user
指定连接用户，需有相应的权限
-p, --password
指定用户密码
-a, --ask-password
指定用户密码提示输入
-p, --port
指定连接port
-s, --socket
指定本地socket文件连接
-t, --threads
指定dump线程数, 默认是4
-c, --compress-protocol
在mysql连接时使用压缩协议
-v, --version
显示程序版本并退出
-v, --verbose
显示更详细的输出, 0 = silent, 1 = errors, 2 = warnings, 3 = info, 默认是2
--defaults-file
指定默认参数文件
前期准备工作与mydumper一致，可参考mydumper备份流程mysql backup mydumper 备份流程。
# mydumper -h 192.168.58.3 -u admin -a -p 3306 -t 8 -e -o /data/test/
(root@localhost) [(none)] > use test2; database changed (root@localhost) [test2] > show tables; +-----------------+ | tables_in_test2 | +-----------------+ | t1 | +-----------------+ 1 row in set (0.00 sec) (root@localhost) [test2] > select * from t1; +----+----------+ | id | title | +----+----------+ | 1 | mydumper | | 2 | myloader | +----+----------+ 2 rows in set (0.00 sec)
(root@localhost) [(none)] > show databases; +--------------------+ | database | +--------------------+ | information_schema | | mysql | | performance_schema | | sys | | test1 | | test2 | +--------------------+ 6 rows in set (0.01 sec) (root@localhost) [(none)] > drop database test2; query ok, 4 rows affected (0.16 sec) (root@localhost) [(none)] > show databases; +--------------------+ | database | +--------------------+ | information_schema | | mysql | | performance_schema | | sys | | test1 | +--------------------+ 5 rows in set (0.01 sec)
# myloader -h 192.168.58.3 -u admin -a -p 3306 -s test2 -b test3 -d /data/test/
-- 主线程连接数据库，设置临时session级别参数，默认导入数据时不记录binlog 264 connect admin@dbabd on using tcp/ip 264 query set session wait_timeout = 2147483 264 query set sql_log_bin=0 264 query /*!40014 set foreign_key_checks=0*/ -- 产生了4个子进程，设置会话级参数，默认不记录binlog，关闭自动提交 265 connect admin@dbabd on using tcp/ip 265 query set session wait_timeout = 2147483 265 query set sql_log_bin=0 265 query /*!40101 set names binary*/ 265 query /*!40101 set sql_mode='no_auto_value_on_zero' */ 265 query /*!40014 set unique_checks=0 */ 265 query set autocommit=0 266 connect admin@dbabd on using tcp/ip 266 query set session wait_timeout = 2147483 266 query set sql_log_bin=0 266 query /*!40101 set names binary*/ 266 query /*!40101 set sql_mode='no_auto_value_on_zero' */ 266 query /*!40014 set unique_checks=0 */ 266 query set autocommit=0 267 connect admin@dbabd on using tcp/ip 267 query set session wait_timeout = 2147483 267 query set sql_log_bin=0 267 query /*!40101 set names binary*/ 267 query /*!40101 set sql_mode='no_auto_value_on_zero' */ 267 query /*!40014 set unique_checks=0 */ 267 query set autocommit=0 268 connect admin@dbabd on using tcp/ip 268 query set session wait_timeout = 2147483 268 query set sql_log_bin=0 268 query /*!40101 set names binary*/ 268 query /*!40101 set sql_mode='no_auto_value_on_zero' */ 268 query /*!40014 set unique_checks=0 */ 268 query set autocommit=0 -- 主线程创建还原数据库和表 264 query show create database `test3` 264 query create database `test3` 264 query use `test3` 264 query /*!40101 set names binary*/ 264 query /*!40014 set foreign_key_checks=0*/ 264 query /*!40103 set time_zone='+00:00' */ 264 query create table `t1` ( `id` int(11) not null auto_increment, `title` varchar(10) default null, primary key (`id`) ) engine=innodb auto_increment=3 default charset=utf8 -- 子线程插入表数据 265 query use `test3` 266 quit 265 query start transaction 267 quit 265 query /*!40101 set names binary*/ 265 query /*!40014 set foreign_key_checks=0*/ 265 query /*!40103 set time_zone='+00:00' */ 268 quit 265 query insert into `t1` values (1,"mydumper"), (2,"myloader") 265 query commit 265 quit 264 quit
总结下myloader的工作流程：
# myloader -h 192.168.58.3 -u admin -a -p 3306 -s test1 -o -v 3 -d /data/test/
# myloader -h 192.168.58.3 -u admin -a -p 3306 -s test1 -b test1_bak -o -v 3 -d /data/test/
# myloader -h 192.168.58.3 -u admin -a -p 3306 -s test1 -o -v 3 -t 8 -d /data/test/
很遗憾myloader没有针对单表或都多表的还原操作命令，有一种方法是通过mydumper将个别大表进行指定chunk大小切割备份，并将每张表单独目录存放备份数据，必须是每张表的数据单独放在一个目录中，目录中只包含一张表的信息代表着还原时只须还原这一张表，避免影响相同库下其他的表数据，因为myloader只能指定库级别的参数选项，这样就可以间接使用到myloader多线程还原功能，加快还原单表速度。
以下做个测试：
-- test1.t3表有100万行 (root@localhost) [test1] > select count(*) from t3; +----------+ | count(*) | +----------+ | 1000000 | +----------+ 1 row in set (0.00 sec) -- mydumper备份test1.t3，指定chunk大小为3m # mydumper -h 192.168.58.3 -u admin -a -p 3306 -b test1 -t t3 -f 2 -e -o /data/test/ -- 删除test1.t3表 (root@localhost) [test1] > drop table t3; query ok, 0 rows affected (0.04 sec) (root@localhost) [test1] > select * from t3; empty set (0.00 sec) -- myloader还原test1.t3 # myloader -h 192.168.58.3 -u admin -a -p 3306 -s test1 -o -v 3 -d /data/test/ ** message: 4 threads created ** message: dropping table or view (if exists) `test1`.`t3` ** message: creating table `test1`.`t3` ** message: thread 1 restoring `test1`.`t3` part 1 ** message: thread 4 restoring `test1`.`t3` part 3 ** message: thread 2 restoring `test1`.`t3` part 4 ** message: thread 3 restoring `test1`.`t3` part 2 ** message: thread 2 restoring `test1`.`t3` part 5 ** message: thread 3 restoring `test1`.`t3` part 6 ** message: thread 4 restoring `test1`.`t3` part 7 ** message: thread 1 shutting down ** message: thread 4 shutting down ** message: thread 2 shutting down ** message: thread 3 shutting down (root@localhost) [test1] > select count(*) from t3; +----------+ | count(*) | +----------+ | 1000000 | +----------+ 1 row in set (0.00 sec)
由以上结果可见，还原使用到了多线程，提高了还原的效率。
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