mysql官网不支持夸大版本升级，比如跳过5.6直接升级到5.7，但由于一些客观原因，项目需要从5.5直接升级到5.7，以下是具体操作
1、备份之前mysql，（数据量少，可直接拷贝安装目录及data目录和配置文件，本例使用的为Percona XtraBackup工具进行的备份）
2、将data目录移出mysql5.5安装目录
3、解压mysql5.7版本
4、修改5.7需要配置文件my.cnf，添加datadir，指向5.5数据目录
5、初始化，该步骤可选，（新安装数据库，或者数据目录不存在，可执行如下命令初始化数据目录，本例中不需要执行如下操作）
bin/mysqld --initialize --user=mysql
6、执行ssl相关操作
bin/mysql_ssl_rsa_setup
7、启动mysql
8、此时数据目录还是5.5的，需要执行mysql_upgrade进行升级，使用方法与mysql命令登录命令行一样,mysql会自动检测当前表并自动修复
mysql_upgrade -uroot -p
9、修复完成后，若发现mysql启动有server-key.pem相关的ssl错误，则是server-key.pem文件权限问题
chmod 644 server-key.pem
10、但此时若执行mysqlpum备份数据，可能会出现异常
mysqlpump --user=root --password mytest > mytest.sql
错误信息：
mysqlpump: [ERROR] (1577) Cannot proceed because system tables used by Event Scheduler were found damaged at server start Dump process encountered error and will not continue. mysqlpump: [ERROR] (1577) Cannot proceed because system tables used by Event Scheduler were found damaged at server start Dump process encountered error and will not continue. mysqlpump: [ERROR] (1577) Cannot proceed because system tables used by Event Scheduler were found damaged at server start Dump process encountered error and will not continue. mysqlpump: [ERROR] (1577) Cannot proceed because system tables used by Event Scheduler were found damaged at server start Dump process encountered error and will not continue. mysqlpump: [ERROR] (1577) Cannot proceed because system tables used by Event Scheduler were found damaged at server start Dump process encountered error and will not continue. mysqlpump: [ERROR] (1577) Cannot proceed because system tables used by Event Scheduler were found damaged at server start Dump process encountered error and will not continue. mysqlpump: [ERROR] (1577) Cannot proceed because system tables used by Event Scheduler were found damaged at server start Dump process encountered error and will not continue. mysqlpump: [ERROR] (1577) Cannot proceed because system tables used by Event Scheduler were found damaged at server start Dump process encountered error and will not continue. mysqlpump: [ERROR] (1577) Cannot proceed because system tables used by Event Scheduler were found damaged at server start Dump process encountered error and will not continue.
解决方法：重启mysql服务 （本例中是这样解决的问题）
重新执行mysqlpump
Dump progress: 1/28 tables, 0/353 rows Dump progress: 36/343 tables, 0/19746 rows Dump progress: 180/343 tables, 6151/19746 rows Dump completed in 3675 milliseconds
数据被正确备份下来，且备份速度很快，从备份文件可以看到，内容与mysqldump备份有很多不同
本次只是简单尝试mysqlpump，待后续再对mysqlpump做深入了解