[root@test3 ~]# mysqldump
Usage: mysqldump [OPTIONS] database [tables]            #备份单个库
OR     mysqldump [OPTIONS] --databases [OPTIONS] DB1 [DB2 DB3...] #备份多个库
OR     mysqldump [OPTIONS] --all-databases [OPTIONS]              #备份所有的数据库

#可以使用mysqldump --help查看mysqldump的更多参数，会在下面使用的时候介绍到经常用的参数。

[root@test3 ~]# mysqldump -uroot -p123456 --single-transaction employees departments > dep.sql#备份INNODB存储引擎时建议加上参数--single-transaction【实际上是必须加】，这样会保证数据的一致性。查看一下备份出来的数据：[root@test3 ~]# cat dep.sql           #可以看到基本就是SQL语句-- MySQL dump 10.13  Distrib 5.7.22, for linux-glibc2.12 (x86_64)---- Host: localhost    Database: employees-- -------------------------------------------------------- Server version    5.7.22-log

/*!40101 SET @OLD_CHARACTER_SET_CLIENT=@@CHARACTER_SET_CLIENT */;/*!40101 SET @OLD_CHARACTER_SET_RESULTS=@@CHARACTER_SET_RESULTS */;/*!40101 SET @OLD_COLLATION_CONNECTION=@@COLLATION_CONNECTION */;/*!40101 SET NAMES utf8 */;/*!40103 SET @OLD_TIME_ZONE=@@TIME_ZONE */;/*!40103 SET TIME_ZONE='+00:00' */;/*!40014 SET @OLD_UNIQUE_CHECKS=@@UNIQUE_CHECKS, UNIQUE_CHECKS=0 */;/*!40014 SET @OLD_FOREIGN_KEY_CHECKS=@@FOREIGN_KEY_CHECKS, FOREIGN_KEY_CHECKS=0 */;/*!40101 SET @OLD_SQL_MODE=@@SQL_MODE, SQL_MODE='NO_AUTO_VALUE_ON_ZERO' */;/*!40111 SET @OLD_SQL_NOTES=@@SQL_NOTES, SQL_NOTES=0 */;

---- Table structure for table `departments`--

DROP TABLE IF EXISTS `departments`;        #看到这里发现了建表语句，也就是没有建库语句，因此若想把sql语句导入指定库，需要先创建库/*!40101 SET @saved_cs_client     = @@character_set_client */;/*!40101 SET character_set_client = utf8 */;CREATE TABLE `departments` (  `dept_no` char(4) NOT NULL,  `dept_name` varchar(40) NOT NULL,  PRIMARY KEY (`dept_no`),  UNIQUE KEY `dept_name` (`dept_name`)) ENGINE=InnoDB DEFAULT CHARSET=latin1;/*!40101 SET character_set_client = @saved_cs_client */;

---- Dumping data for table `departments`--

LOCK TABLES `departments` WRITE;/*!40000 ALTER TABLE `departments` DISABLE KEYS */;           #插入语句INSERT INTO `departments` VALUES ('d009','Customer Service'),('d005','Development'),('d002','Finance'),('d003','Human Resources'),('d001','Marketing'),('d004','Production'),('d006','Quality Management'),('d008','Research'),('d007','Sales');/*!40000 ALTER TABLE `departments` ENABLE KEYS */;UNLOCK TABLES;/*!40103 SET TIME_ZONE=@OLD_TIME_ZONE */;

/*!40101 SET SQL_MODE=@OLD_SQL_MODE */;/*!40014 SET FOREIGN_KEY_CHECKS=@OLD_FOREIGN_KEY_CHECKS */;/*!40014 SET UNIQUE_CHECKS=@OLD_UNIQUE_CHECKS */;/*!40101 SET CHARACTER_SET_CLIENT=@OLD_CHARACTER_SET_CLIENT */;/*!40101 SET CHARACTER_SET_RESULTS=@OLD_CHARACTER_SET_RESULTS */;/*!40101 SET COLLATION_CONNECTION=@OLD_COLLATION_CONNECTION */;/*!40111 SET SQL_NOTES=@OLD_SQL_NOTES */;

-- Dump completed on 2018-11-28  9:51:01

在备份文件中插入二进制日志的信息该选项将binlog的位置和文件名追加到输出文件中。如果为1，将会输出CHANGE MASTER 命令；如果为2，输出的CHANGE MASTER命令前添加注释信息。该选项将打开--lock-all-tables 选项，除非--single-transaction也被指定（在这种情况下，全局读锁在开始导出时获得很短的时间）。该选项自动关闭--lock-tables选项。[root@test3 mysql]# mysqldump -uroot -p123456 --single-transaction --master-data employees departments > dep.sqlmysqldump: [Warning] Using a password on the command line interface can be insecure.[root@test3 mysql]# cat dep.sql -- MySQL dump 10.13  Distrib 5.7.22, for linux-glibc2.12 (x86_64)---- Host: localhost    Database: employees-- -------------------------------------------------------- Server version    5.7.22-log

......

---- Position to start replication or point-in-time recovery from    #这里有个提示基于这个点开始复制或者PIT恢复--

CHANGE MASTER TO MASTER_LOG_FILE='test3-bin.000001', MASTER_LOG_POS=20182;.....

#mysqldump备份时常用的两个选项

--single-transaction Creates a consistent snapshot by dumping all tables in asingle transaction. Works ONLY for tables stored instorage engines which support multiversioning (currentlyonly InnoDB does); the dump is NOT guaranteed to beconsistent for other storage engines. While a--single-transaction dump is in process, to ensure avalid dump file (correct table contents and binary logposition), no other connection should use the followingstatements: ALTER TABLE, DROP TABLE, RENAME TABLE,TRUNCATE TABLE, as consistent snapshot is not isolatedfrom them. Option automatically turns off --lock-tables.
在备份INNODB数据库时，事实上必须加上--single-transaction参数，这个参数会保证备份出的数据是一致的，也就是备份的数据是当前执行此命令时刻点的数据。
--single-transaction利用INNODB的MVCC特性，在备份数据会根据undo和redo得到一份快照数据。INNODB的MVCC特性在RR和RC的隔离级别下，得到的快照数据是不同，在RR
得到的是当前事务开始时的快照数据，在RC时得到的最新的事务数据。因为数据库的正式环境一般是RC模式，因此这条命令在备份开始时，会设置当前会话的隔离级别为RR模式！

--single-transaction 参数说明

[root@test3 mysql]# mysqldump -uroot -p123456 --single-transaction --master-data --databases cmdb hostinfo  > dep.sql
mysqldump: [Warning] Using a password on the command line interface can be insecure.
[root@test3 mysql]# mysqldump -uroot -p123456 --single-transaction --master-data --all-databases  > all.sql
mysqldump: [Warning] Using a password on the command line interface can be insecure.
#查看数据
[root@test3 mysql]# cat dep.sql       #查看其中的一个数据
-- MySQL dump 10.13  Distrib 5.7.22, for linux-glibc2.12 (x86_64)
--
-- Host: localhost    Database: cmdb
-- ------------------------------------------------------
-- Server version    5.7.22-log
......--
-- Position to start replication or point-in-time recovery from
--CHANGE MASTER TO MASTER_LOG_FILE='test3-bin.000001', MASTER_LOG_POS=20182;--
-- Current Database: `cmdb`          #这里有了创建数据库的语句
--CREATE DATABASE /*!32312 IF NOT EXISTS*/ `cmdb` /*!40100 DEFAULT CHARACTER SET utf8 */;USE `cmdb`;

#因此在使用指定库备份文件恢复数据时，不需要再创建库，直接恢复即可

mysql -uroot -p123456 < all.sql

mysql> set global general_log=on;
Query OK, 0 rows affected (0.00 sec)
mysql> set global log_output="file";
Query OK, 0 rows affected (0.00 sec)
mysql> show variables like "%general%";
+------------------+-----------------------+
| Variable_name    | Value                 |
+------------------+-----------------------+
| general_log      | ON                    |
| general_log_file | /data/mysql/test3.log |
+------------------+-----------------------+
2 rows in set (0.00 sec)

[root@test3 ~]# mysqldump -uroot -p123456 --single-transaction --master-data --databases tpcc_test > dep.sql
mysqldump: [Warning] Using a password on the command line interface can be insecure.
[root@test3 ~]#

[root@test3 mysql]# cat test3.log 2018-11-28T05:20:31.014426Z       29 Connect    root@localhost on  using Socket
2018-11-28T05:20:31.014662Z       29 Query    /*!40100 SET @@SQL_MODE='' */
2018-11-28T05:20:31.014792Z       29 Query    /*!40103 SET TIME_ZONE='+00:00' */
2018-11-28T05:20:31.014915Z       29 Query    FLUSH /*!40101 LOCAL */ TABLES
2018-11-28T05:20:31.015141Z       29 Query    FLUSH TABLES WITH READ LOCK        #这里有个锁表
2018-11-28T05:20:31.015213Z       29 Query    SET SESSION TRANSACTION ISOLATION LEVEL REPEATABLE READ  #设置当前会话的隔离级别
2018-11-28T05:20:31.015271Z       29 Query    START TRANSACTION /*!40100 WITH CONSISTENT SNAPSHOT */   #开始事务
2018-11-28T05:20:31.015463Z       29 Query    SHOW VARIABLES LIKE 'gtid\_mode'                         #备份gtid信息
2018-11-28T05:20:31.018393Z       29 Query    SHOW MASTER STATUS                                       #在备份时指定master-data，这里备份日志点信息
2018-11-28T05:20:31.018467Z       29 Query    UNLOCK TABLES                                            #释放表
2018-11-28T05:20:31.018618Z       29 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 IN ('tpcc_test'))) GROUP BY LOGFILE_GROUP_NAME, FILE_NAME, ENGINE, TOTAL_EXTENTS, INITIAL_SIZE ORDER BY LOGFILE_GROUP_NAME
2018-11-28T05:20:31.021966Z       29 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 IN ('tpcc_test')) ORDER BY TABLESPACE_NAME, LOGFILE_GROUP_NAME
2018-11-28T05:20:31.022750Z       29 Query    SHOW VARIABLES LIKE 'ndbinfo\_version'
2018-11-28T05:20:31.023915Z       29 Init DB    tpcc_test
2018-11-28T05:20:31.023977Z       29 Query    SHOW CREATE DATABASE IF NOT EXISTS `tpcc_test`
2018-11-28T05:20:31.024045Z       29 Query    SAVEPOINT sp                                            #备份每张表之前会设置保存点
2018-11-28T05:20:31.024100Z       29 Query    show tables
2018-11-28T05:20:31.024253Z       29 Query    show table status like 'customer'
2018-11-28T05:20:31.024475Z       29 Query    SET SQL_QUOTE_SHOW_CREATE=1
2018-11-28T05:20:31.024541Z       29 Query    SET SESSION character_set_results = 'binary'
2018-11-28T05:20:31.024607Z       29 Query    show create table `customer`
2018-11-28T05:20:31.024737Z       29 Query    SET SESSION character_set_results = 'utf8'
2018-11-28T05:20:31.024806Z       29 Query    show fields from `customer`
2018-11-28T05:20:31.025199Z       29 Query    show fields from `customer`
2018-11-28T05:20:31.025582Z       29 Query    SELECT /*!40001 SQL_NO_CACHE */ * FROM `customer`
2018-11-28T05:20:35.251932Z       29 Query    SET SESSION character_set_results = 'binary'
2018-11-28T05:20:35.252069Z       29 Query    use `tpcc_test`
2018-11-28T05:20:35.252158Z       29 Query    select @@collation_database
2018-11-28T05:20:35.252290Z       29 Query    SHOW TRIGGERS LIKE 'customer'
2018-11-28T05:20:35.252706Z       29 Query    SET SESSION character_set_results = 'utf8'
2018-11-28T05:20:35.252771Z       29 Query    ROLLBACK TO SAVEPOINT sp                               #这张表备份结束之后，回滚保存点............

以上的过程可以看到，mysqldump是在一个事务中备份的，因此在备份表时会产生undo日志，若是表数据太大，则undo日志也会很大，因此mysqldump在备份每张表时都设置savepoint，这样当这个表备份完成之后，就会回滚保存点，然后purge线程就会回收undo日志

[root@test3 ~]# mysqldump -uroot -p123456 -d --databases lianxi > dep.sql    #这样只备份出lianxi这个库中表的建表语句和创建库的语句[root@test3 ~]# mysqldump -uroot -p123456 -d lianxi tb2 > dep.sql            #如果这里只备份库下面的表，则还是没有建库语句，只有创建表的语句

[root@test3 ~]# mysqldump -uroot -p123456 -R lianxi tb2 > dep.sql

[root@test3 ~]# mysql -uroot -p123456 financesys < financesys.sql
mysql: [Warning] Using a password on the command line interface can be insecure.
ERROR 1118 (42000) at line 25: Row size too large (> 8126). Changing some columns to TEXT or BLOB may help. In current row format, BLOB prefix of 0 bytes is stored inline.

mysql> set global innodb_strict_mode=off;
Query OK, 0 rows affected (0.00 sec)
[root@test3 ~]# mysql -uroot -p123456 financesys < financesys.sql        #再导入就可以了
mysql: [Warning] Using a password on the command line interface can be insecure.

从MySQL5.5.X版本开始，你可以开启InnoDB严格检查模式，尤其采用了页数据压缩功能后，最好是开启该功能。开启此功能后，当创建表（CREATE TABLE）、更改表（ALTER TABLE）和创建索引（CREATE INDEX）语句时，如果写法有错误，不会有警告信息，而是直接抛出错误，这样就可直接将问题扼杀在摇篮里。开启InnoDB严格检查模式涉及的参数是innodb_strict_mode，默认为OFF，支持动态开启，开启方式如下：
set global innodb_strict_mode=1;连接地址

[root@test2 data]# mysqldump -uroot -p7abec53701c3eefb --databases financesys > financesys1.sql
mysqldump: Error 2013: Lost connection to MySQL server during query when dumping table `fi_factincome` at row: 1303198

备份失败的原因：在向磁盘上备份的时候，数据的流向是这样的：MySQL Server 端从数据文件中检索出数据，然后分批将数据返回给mysqldump 客户端，然后 mysqldump 将数据写入到磁盘上。一般地，向 磁盘 上写入数据的速度较之Server端检索发送数据的速度要慢得多，这就会导致 mysqldump 无法及时的接受 Server 端发送过来的数据，Server 端的数据就会积压在内存中等待发送，这个等待不是无限期的，当 Server 的等待时间超过 net_write_timeout（默认是60秒）时它就失去了耐心，mysqldump 的连接会被断开，同时抛出错误 Got error: 2013: Lost connection。其实该错误不是说数据库文件太多而导致出错，而是单张表数据量太大导致备份失败