小于1G的数据库，用mysqldump
大于1G的数据库，用xtrabackup
备份策略
###### mysql backup at 2019/01/09 by dba,每天凌晨2点备份一次 ######
0 2 * * * /bin/sh /data/scripts/mysql_backup.sh >/dev/null
###### mysql backup at 2019/01/09 by dba,每天上午10点，晚上22点各备份一次 ######
0 10,22 * * * /bin/sh /data/scripts/mysql_backup.sh >/dev/null
###### mysql backup at 2019/01/09 by dba,每隔4小时备份一次 ######
0 */4 * * * /bin/sh /data/scripts/mysql_backup.sh >/dev/null
###### mysql backup at 2019/01/09 by dba,每隔6小时备份一次 ######
0 */6 * * * /bin/sh /data/scripts/mysql_backup.sh >/dev/null