好的，下面是一篇关于通过 CHANGE REPLICATION SOURCE TO 语句实现复制拓扑动态调整的技术文章，以讲座的形式呈现。
复制拓扑的动态调整：CHANGE REPLICATION SOURCE TO 语句详解
大家好，今天我们来探讨一个非常重要的数据库管理话题：复制拓扑的动态调整。在生产环境中，数据库的复制拓扑结构并非一成不变，随着业务的发展，我们可能需要调整复制关系，例如：
- 主库切换（Failover/Switchover）
- 读写分离架构的调整
- 添加新的只读副本
- 替换故障的副本
而 CHANGE REPLICATION SOURCE TO 语句就是实现这些动态调整的关键工具。本文将深入剖析这个语句的用法、原理，并结合实际案例进行讲解。
一、CHANGE REPLICATION SOURCE TO 语句的基本语法
CHANGE REPLICATION SOURCE TO 语句用于修改副本服务器（原为slave）的复制源信息。其基本语法如下：
CHANGE REPLICATION SOURCE TO
SOURCE_HOST = 'host_name_or_IP_address',
SOURCE_PORT = port_number,
SOURCE_USER = 'user_name',
SOURCE_PASSWORD = 'password',
SOURCE_LOG_FILE = 'binary_log_file_name',
SOURCE_LOG_POS = binary_log_position,
[SOURCE_SSL = {0|1}]
[SOURCE_SSL_CA = 'ca_file_name']
[SOURCE_SSL_CAPATH = 'ca_directory_name']
[SOURCE_SSL_CERT = 'cert_file_name']
[SOURCE_SSL_CIPHER = 'cipher_list']
[SOURCE_SSL_KEY = 'key_file_name']
[SOURCE_SSL_VERIFY_SERVER_CERT = {0|1}]
[SOURCE_HEARTBEAT_INTERVAL = interval]
[SOURCE_CONNECT_RETRY = interval]
[SOURCE_RETRY_COUNT = count]
[SOURCE_AUTO_POSITION = {0|1}]
[GET_SERVER_PUBLIC_KEY = {0|1}]
[PUBLIC_KEY_PATH = 'file_name']
[DEFAULT_AUTH = 'plugin_name']
[CHANNEL = 'channel_name'];
下面对一些重要的参数进行解释：
| 参数 | 描述 |
|---|---|
SOURCE_HOST |
新的复制源服务器的主机名或 IP 地址。 |
SOURCE_PORT |
新的复制源服务器的端口号。 |
SOURCE_USER |
用于连接到新的复制源服务器的用户名。 该用户必须具有 REPLICATION SLAVE 权限。 |
SOURCE_PASSWORD |
用于连接到新的复制源服务器的密码。 |
SOURCE_LOG_FILE |
新的复制源服务器的二进制日志文件名。 |
SOURCE_LOG_POS |
新的复制源服务器的二进制日志位置。 |
SOURCE_SSL |
是否启用 SSL 连接。 |
SOURCE_SSL_CA |
SSL 证书颁发机构 (CA) 文件。 |
SOURCE_SSL_CERT |
SSL 证书文件。 |
SOURCE_SSL_KEY |
SSL 密钥文件。 |
SOURCE_AUTO_POSITION |
是否启用基于 GTID 的复制。设置为 1 表示启用，设置为 0 表示禁用。强烈建议使用 GTID 复制。 |
SOURCE_HEARTBEAT_INTERVAL |
副本服务器向复制源服务器发送心跳信号的间隔（秒）。 |
SOURCE_CONNECT_RETRY |
如果连接失败，副本服务器尝试重新连接复制源服务器的间隔（秒）。 |
SOURCE_RETRY_COUNT |
副本服务器尝试重新连接复制源服务器的最大次数。 |
CHANNEL |
指定复制通道的名称。 默认情况下，复制使用默认通道。 可以使用通道来管理多个复制源。 |
注意： 在 MySQL 8.0.23 之后，MASTER_ 前缀的参数名已被弃用，并被 SOURCE_ 前缀的参数名取代。为了兼容性，MySQL 仍然支持 MASTER_ 前缀，但建议使用 SOURCE_ 前缀。
二、基于位点 (Binary Log Position) 的复制切换
这是最传统的复制切换方式，需要手动指定新的复制源的二进制日志文件名和位置。
场景：假设我们有一个主库 db-master-01 和一个从库 db-slave-01。现在由于某种原因，db-master-01 需要进行维护，我们需要将 db-slave-01 切换到新的主库 db-master-02。
步骤：
-
在原主库
db-master-01上停止写入操作，并获取当前的二进制日志文件名和位置：mysql> FLUSH TABLES WITH READ LOCK; -- 阻止新的写入 mysql> SHOW MASTER STATUS; +------------------+----------+--------------+------------------+-------------------+ | File | Position | Binlog_Do_DB | Binlog_Ignore_DB | Executed_Gtid_Set | +------------------+----------+--------------+------------------+-------------------+ | mysql-bin.000005 | 1234 | | | | +------------------+----------+--------------+------------------+-------------------+ 1 row in set (0.00 sec) mysql> UNLOCK TABLES; -- 释放锁记录下
File(mysql-bin.000005) 和Position(1234) 的值。 -
在新的主库
db-master-02上开启二进制日志，并创建一个用于复制的用户：-- 在 db-master-02 上 CREATE USER 'repl'@'%' IDENTIFIED BY 'your_password'; GRANT REPLICATION SLAVE ON *.* TO 'repl'@'%'; FLUSH PRIVILEGES; -- 确保开启二进制日志 SHOW VARIABLES LIKE 'log_bin'; -- 如果 log_bin 为 OFF，则需要在配置文件中开启，并重启 MySQL 服务 -
将数据从
db-master-01同步到db-master-02。可以使用 mysqldump 或其他数据迁移工具。 确保
db-master-02拥有db-master-01的全量数据。 -
在从库
db-slave-01上停止复制进程：mysql> STOP SLAVE; -- MySQL 5.7 及更早版本 mysql> STOP REPLICA; -- MySQL 8.0 及更高版本 -
在从库
db-slave-01上修改复制源信息：CHANGE REPLICATION SOURCE TO SOURCE_HOST = 'db-master-02', SOURCE_PORT = 3306, SOURCE_USER = 'repl', SOURCE_PASSWORD = 'your_password', SOURCE_LOG_FILE = 'mysql-bin.000005', -- 注意：这里使用db-master-01上获取的binlog文件名 SOURCE_LOG_POS = 1234; -- 注意：这里使用db-master-01上获取的binlog位置注意： 这里
SOURCE_LOG_FILE和SOURCE_LOG_POS的值来自于 原主库db-master-01，而不是新的主库db-master-02。因为db-slave-01已经同步到了db-master-01的这个位点，所以需要从这个位置开始同步db-master-02上的数据。需要确保db-master-02上存在mysql-bin.000005这个二进制日志文件，并且包含db-master-01停止写入后的数据。如果db-master-02是通过备份恢复的，那么这个条件通常是满足的。 -
在从库
db-slave-01上启动复制进程：mysql> START SLAVE; -- MySQL 5.7 及更早版本 mysql> START REPLICA; -- MySQL 8.0 及更高版本 -
检查复制状态：
mysql> SHOW SLAVE STATUSG -- MySQL 5.7 及更早版本 mysql> SHOW REPLICA STATUSG -- MySQL 8.0 及更高版本 -- 关注以下几个关键字段： -- Slave_IO_Running: Yes -- Slave_SQL_Running: Yes -- Last_Errno: 0 -- Last_Error: (空) -- Seconds_Behind_Master: 0 (或接近 0)如果
Slave_IO_Running和Slave_SQL_Running都为Yes，且Last_Errno为0，Last_Error为空，Seconds_Behind_Master接近0，则表示复制切换成功。
这种方式的缺点：
- 需要手动获取二进制日志文件名和位置，容易出错。
- 需要确保新的主库包含原主库的二进制日志，并且在指定的位置之后的数据与原主库一致。
- 切换过程较为繁琐，容易出现人为错误。
三、基于 GTID (Global Transaction Identifier) 的复制切换
GTID 是 MySQL 5.6 引入的全局事务标识符，它可以唯一标识一个事务。基于 GTID 的复制简化了复制切换的过程，避免了手动指定二进制日志文件名和位置的麻烦。
前提条件：
- 主库和从库都必须启用 GTID。
- 主库和从库的
gtid_mode必须设置为ON或ON_PERMISSIVE。 - 主库和从库的
enforce_gtid_consistency必须设置为ON。
场景： 同样假设我们有一个主库 db-master-01 和一个从库 db-slave-01。现在由于某种原因，db-master-01 需要进行维护，我们需要将 db-slave-01 切换到新的主库 db-master-02。
步骤：
-
在原主库
db-master-01上停止写入操作，并记录当前的 GTID 集：mysql> FLUSH TABLES WITH READ LOCK; mysql> SELECT @@global.gtid_executed; 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