8.2 新特性 - 透明的读写分离

前言

MySQL 8.0 官方推出过一个高可用方案 ReplicaSet 主要由 Router、MySQL Shell、MySQL Server 三个组件组成。

MySQL Shell 负责管理 ReplicaSet 包括部署、切换、节点加入等，都可以通过内置 AdminAPI 自动化完成。

MySQL Router 是一款轻量级中间件，可在应用程序和 ReplicaSet 之间提供透明路由和读写分离功能。

8.0 时期的 Router 读写需要配置两个端口，应用如果想要使用读写分离的特性，需要额外适配。

-- MySQL 经典协议
- Read/Write Connections: localhost:6446, /data/myrouter/mysql.sock
- Read/Only Connections:  localhost:6447, /data/myrouter/mysqlro.sock-- MySQL X 协议
- Read/Write Connections: localhost:6448, /data/myrouter/mysqlx.sock
- Read/Only Connections:  localhost:6449, /data/myrouter/mysqlxro.sock

到了 MySQL 8.2 版本 Router 自动可以识别读取和写入，按照配置规则分配到不同的实例，无需使用额外端口。

1. 安装部署

让我们一起从 0 部署一套 MySQL 8.2 ReplicaSet 集群吧 ！

• 系统版本：CentOS Linux release 7.8.2003 (Core)
• MySQL Server：8.0.32

IP	hostname	Role
172.16.104.56	172-16-104-56	Master
172.16.104.57	172-16-104-56	Secondary

vi /etc/hosts
172.16.104.56 172-16-104-56
172.16.104.57 172-16-104-57

1.1 下载安装包

MySQL 官网下载地址：https://downloads.mysql.com/archives/community

压缩包里面包含 MySQL Server 和 MySQL Router 组件。安装 MySQL Server 步骤参考下文👇

MySQL 部署：MySQL 自动化安装部署

1.2 MySQL Shell

官方下载地址：MySQL Shell download

mv mysql-shell-8.0.31-linux-glibc2.12-x86-64bit /usr/local/mysqlsh
export PATH=/usr/local/mysqlsh/bin/:$PATH
echo 'PATH=$PATH:/usr/local/mysqlsh/bin/' >> /etc/profile

进入 MySQL Shell 使用 \py & \js 可以切换命令模式，本篇文章使用 python 模式演示：

1.3 配置 MySQL 实例

部署好 MySQL 实例后，需要创建一个用户，提供给 MySQL Shell 使用，这里演示创建的用户是：rw_shell

GRANT CLONE_ADMIN, CONNECTION_ADMIN, CREATE USER, EXECUTE, FILE, GROUP_REPLICATION_ADMIN, PERSIST_RO_VARIABLES_ADMIN, PROCESS, RELOAD, REPLICATION CLIENT, REPLICATION SLAVE, REPLICATION_APPLIER, REPLICATION_SLAVE_ADMIN, ROLE_ADMIN, SELECT, SHUTDOWN, SYSTEM_VARIABLES_ADMIN ON *.* TO 'rw_shell'@'%' WITH GRANT OPTION;
GRANT DELETE, INSERT, UPDATE ON mysql.* TO 'rw_shell'@'%' WITH GRANT OPTION;
GRANT ALTER, ALTER ROUTINE, CREATE, CREATE ROUTINE, CREATE TEMPORARY TABLES, CREATE VIEW, DELETE, DROP, EVENT, EXECUTE, INDEX, INSERT, LOCK TABLES, REFERENCES, SHOW VIEW, TRIGGER, UPDATE ON mysql_innodb_cluster_metadata.* TO 'rw_shell'@'%' WITH GRANT OPTION;
GRANT ALTER, ALTER ROUTINE, CREATE, CREATE ROUTINE, CREATE TEMPORARY TABLES, CREATE VIEW, DELETE, DROP, EVENT, EXECUTE, INDEX, INSERT, LOCK TABLES, REFERENCES, SHOW VIEW, TRIGGER, UPDATE ON mysql_innodb_cluster_metadata_bkp.* TO 'rw_shell'@'%' WITH GRANT OPTION;
GRANT ALTER, ALTER ROUTINE, CREATE, CREATE ROUTINE, CREATE TEMPORARY TABLES, CREATE VIEW, DELETE, DROP, EVENT, EXECUTE, INDEX, INSERT, LOCK TABLES, REFERENCES, SHOW VIEW, TRIGGER, UPDATE ON mysql_innodb_cluster_metadata_previous.* TO 'rw_shell'@'%' WITH GRANT OPTION;

配置 MySQL 实例，检查是否符合创建 ReplicaSet 的条件，如果发现需要修改的地方，就会提示确认修改。
执行次命令会让用户输入密码，保存后会进入检查阶段。

dba.configure_replica_set_instance('rw_shell@172-16-104-55:3306', {"clusterAdmin": "rw_shell@'%'"})
dba.configure_replica_set_instance('rw_shell@172-16-104-56:3306', {"clusterAdmin": "rw_shell@'%'"})

MySQL Shell 会检查数据库参数是否满足创建 ReplicaSet 条件，并提出修改建议：

此阶段执行完成后，表示实例都具备组成 ReplicaSet 条件，可进入下一步。

1.4 启动 ReplicaSet

使用 MySQL Shell 连接到主实例，否则测试中会报 session 错误。

An open session is required to perform this operation.

\c rw_shell@172-16-104-56:3306

创建 ReplicaSet 默认当前进入的实例为主库实例：

rs = dba.create_replica_set("prd_op_service")

添加复制节点：

rs.add_instance("172-16-104-57:3306")

至此，ReplicaSet 已配置完成，下图为拓扑信息：

{"replicaSet": {"name": "prd_op_service", "primary": "172-16-104-56:3306", "status": "AVAILABLE", "statusText": "All instances available.", "topology": {"172-16-104-56:3306": {"address": "172-16-104-56:3306", "instanceRole": "PRIMARY", "mode": "R/W", "status": "ONLINE"}, "172-16-104-57:3306": {"address": "172-16-104-57:3306", "instanceRole": "SECONDARY", "mode": "R/O", "replication": {"applierStatus": "APPLIED_ALL", "applierThreadState": "Waiting for an event from Coordinator", "applierWorkerThreads": 4, "receiverStatus": "ON", "receiverThreadState": "Waiting for source to send event", "replicationLag": null, "replicationSsl": "TLS_AES_128_GCM_SHA256 TLSv1.3", "replicationSslMode": "REQUIRED"}, "status": "ONLINE"}}, "type": "ASYNC"}
}

1.5 启动 8.2 Router

解压二进制包，开箱即用。

xz -d mysql-router-8.2.0-linux-glibc2.12-x86_64.tar.xz
tar -xvf mysql-router-8.2.0-linux-glibc2.12-x86_64.tar

创建 router 专用用户：

rs.setup_router_account('op_router')

更新 router 配置信息：

./mysqlrouter \--bootstrap rw_shell@172-16-104-56:3306 \--directory /data/myrouter \--conf-use-sockets \--account op_router \--user=root

此时 Router 输出的配置信息：

After this MySQL Router has been started with the generated configuration$ ./mysqlrouter -c /data/myrouter/mysqlrouter.confInnoDB ReplicaSet 'prd_op_service' can be reached by connecting to:## MySQL Classic protocol- Read/Write Connections: localhost:6446, /data/myrouter/mysql.sock
- Read/Only Connections:  localhost:6447, /data/myrouter/mysqlro.sock
- Read/Write Split Connections: localhost:6450, /data/myrouter/mysqlsplit.sock## MySQL X protocol- Read/Write Connections: localhost:6448, /data/myrouter/mysqlx.sock
- Read/Only Connections:  localhost:6449, /data/myrouter/mysqlxro.sock

从输出结果看，相比于之前的版本，多了一个 6450 端口。

启动 mysqlrouter 服务：

./mysqlrouter -c /data/myrouter/mysqlrouter.conf &

2. 测试路由

使用 6450 端口连接 MySQL：

mysql -urw_shell -P6450 -h172.16.104.56 -p

rw_shell@mysql 17:21:  [(none)]>select @@hostname;
+---------------+
| @@hostname    |
+---------------+
| 172-16-104-57 |
+---------------+
1 row in set (0.01 sec)rw_shell@mysql 17:22:  [(none)]>begin;
Query OK, 0 rows affected (0.01 sec)rw_shell@mysql 17:22:  [(none)]>select @@hostname;
+---------------+
| @@hostname    |
+---------------+
| 172-16-104-56 |
+---------------+
1 row in set (0.01 sec)rw_shell@mysql 17:22:  [(none)]>commit;
Query OK, 0 rows affected (0.00 sec)rw_shell@mysql 17:22:  [(none)]>
rw_shell@mysql 17:22:  [(none)]>select @@hostname;
+---------------+
| @@hostname    |
+---------------+
| 172-16-104-57 |
+---------------+
1 row in set (0.01 sec)

从上面的实验，我们可以看到，默认情况下，如果执行读取操作，我们将到达复制节点，但如果启动事务，我们将到主节点，而无需更改端口并使用相同的连接。

rw_shell@mysql 17:25:  [(none)]>select @@hostname;
+---------------+
| @@hostname    |
+---------------+
| 172-16-104-57 |
+---------------+
1 row in set (0.01 sec)rw_shell@mysql 17:25:  [(none)]>start transaction read only;
Query OK, 0 rows affected (0.02 sec)rw_shell@mysql 17:26:  [(none)]>select @@hostname;
+---------------+
| @@hostname    |
+---------------+
| 172-16-104-57 |
+---------------+
1 row in set (0.01 sec)

启动事务类型为只读事务的话，也会直接到复制节点。

rw_shell@mysql 17:32:  [(none)]>ROUTER SET access_mode='read_only';
Query OK, 0 rows affected (0.00 sec)rw_shell@mysql 17:32:  [(none)]>select @@hostname;
+---------------+
| @@hostname    |
+---------------+
| 172-16-104-57 |
+---------------+
1 row in set (0.02 sec)rw_shell@mysql 17:33:  [(none)]>ROUTER SET access_mode='read_write';
Query OK, 0 rows affected (0.00 sec)rw_shell@mysql 17:33:  [(none)]>select @@hostname;
+---------------+
| @@hostname    |
+---------------+
| 172-16-104-56 |
+---------------+
1 row in set (0.02 sec)

可以通过 ROUTER SET 语句，定义接下来 SQL 访问类型。

总结

MySQL 8.2 版本的 router 读写分离支持使用一个端口，无需业务适应更改，是一项非常很有价值的功能，可以优化数据库性能和可扩展性，而无需对应用程序进行任何更改。

参考资料：https://lefred.be/content/mysql-8-2-transparent-read-write-splitting/