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前文有说到，在做数据库升级之前，一定要多加小心谨慎，避免兼容问题。这也就要求DBA除了知道新版本特性之外，还需要知道为这些特性，做了哪些修改。MySQL手记5 — 数据库升级准备
4月27日，MySQL官方发布了8.0.20的GA版本，新增了许多振奋人心的特性，同时，也带了了很多差异，需要进行测试。较为关注的是Percona Xtrabackup在对MySQL8.0.20进行备份恢复的时候，会出现报错：
一、环境准备
1.1 MySQL 8.0.20
下载MySQL官方的8.0.20版本进行安装，建库建表：
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mysql> create database wstestdb;
mysql> use wstestdb
mysql> CREATE TABLE if not exists `test1` (
`id` int NOT NULL AUTO_INCREMENT,
`name` varchar(30) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
mysql> insert into test1 values(1,'aaa');
1.2 下载安装最新版本Percona Xtrabackup
截止5月4日，最新版本为percona-xtrabackup-8.0.11，下载解压后，进入到bin目录下，执行：
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./xtrabackup --defaults-file=/soft/my5501.cnf --user=root --password=abc1abc --host=127.0.0.1 --port=5501 --parallel=4 --databases=wstestdb --backup
其中：
–defaults-file：MySQL实例的配置文件
其余项目为MySQL实例的连接、需要备份的数据库信息，最后使用–backup指明需要进行备份。
二、xtrabackup备份报错
打印信息：
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[root@mysql-01 bin]# ./xtrabackup --defaults-file=/soft/my5501.cnf --user=root --password=abc1abc --host=127.0.0.1 --port=5501 --parallel=4 --databases=wstestdb --backup
xtrabackup: recognized server arguments: --datadir=/data/mysql5501 --innodb_undo_tablespaces=3 --tmpdir=/tmp --log_bin=/data/mysql5501/mysql5501 --server-id=1845501 --innodb_file_per_table=1 --innodb_flush_log_at_trx_commit=1 --innodb_page_size=16k --innodb_buffer_pool_size=256M --innodb_data_file_path=ibdata1:400M:autoextend --innodb_log_files_in_group=2 --innodb_log_buffer_size=200M --innodb_open_files=2000 --innodb_io_capacity=1200 --innodb_read_io_threads=32 --innodb_write_io_threads=32 --innodb_max_dirty_pages_pct=75
xtrabackup: recognized client arguments: --port=5501 --user=root --password=* --host=127.0.0.1 --port=5501 --parallel=4 --databases=wstestdb --backup=1
./xtrabackup version 8.0.11 based on MySQL server 8.0.18 Linux (x86_64) (revision id: 486c270)
200504 09:29:43 version_check Connecting to MySQL server with DSN 'dbi:mysql:;mysql_read_default_group=xtrabackup;host=127.0.0.1;port=5501' as 'root' (using password: YES).
200504 09:29:43 version_check Connected to MySQL server
200504 09:29:43 version_check Executing a version check against the server...
200504 09:29:43 version_check Done.
200504 09:29:43 Connecting to MySQL server host: 127.0.0.1, user: root, password: set, port: 5501, socket: not set
Using server version 8.0.20
xtrabackup: uses posix_fadvise().
xtrabackup: cd to /data/mysql5501
xtrabackup: open files limit requested 0, set to 1048576
xtrabackup: using the following InnoDB configuration:
xtrabackup: innodb_data_home_dir = .
xtrabackup: innodb_data_file_path = ibdata1:400M:autoextend
xtrabackup: innodb_log_group_home_dir = ./
xtrabackup: innodb_log_files_in_group = 2
xtrabackup: innodb_log_file_size = 50331648
Number of pools: 1
200504 09:29:44 Connecting to MySQL server host: 127.0.0.1, user: root, password: set, port: 5501, socket: not set
xtrabackup: Redo Log Archiving is not set up.
Unknown redo log format (4). Please follow the instructions at http://dev.mysql.com/doc/refman/8.0/en/ upgrading-downgrading.html.
xtrabackup: Error: recv_find_max_checkpoint() failed.
报错信息为：
xtrabackup: Redo Log Archiving is not set up.
Unknown redo log format (4). Please follow the instructions at http://dev.mysql.com/doc/refman/8.0/en/ upgrading-downgrading.html.
xtrabackup: Error: recv_find_max_checkpoint() failed.
原因
MySQL8.0.20的Release Notes中有这样的介绍：
InnoDB: Redo log records for modifications to undo tablespaces increased in size in MySQL 8.0 due to a change in undo tablespace ID values, which required additional bytes. The change in redo log record size caused a performance regression in workloads with heavy write I/O. To address this issue, the redo log format was modified to reduce redo log record size for modifications to undo tablespaces. (Bug #29536710)
为了在redo log中记录undo表空间的修改信息（记录undo表空间的ID），所以会增加redo log的大小，导致影响到I/O性能。为了解决这个问题，redo log的格式被修改了，以减小其记录所占的大小。
Percona-xtrabackup-8.0.11是基于MySQL 8.0.18进行开发的，所以当前若使用MySQL 8.0.20版本，暂时不要使用Percona Xtrabackup进行备份操作。
参考：https://forums.percona.com/discussion/comment/55828
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