一.背景

有的项目初期阶段数据库只是单台节点，中期或后期阶段，需要具备数据冗余或者读写分离功能，这个时候需要对单数据库进行扩容，实现高可用

二.实现方案

• 方案1

  搭建一套新的集群，对现有单节点数据库执行lock table write进行写锁，随后导出数据再导入至新的集群中，并修改应用程序配置指明新的数据库；这个过程较为繁琐，同时影响业务，工作人员在规定的时间完成会有很大压力

• 方案2

  新部署一台数据库节点，在线扩容为集群形式，这里以主从为例

三.实现案例

1. 基础环境

2. slave节点关联master

mysql> change master to master_host='39.107.13.9',master_port=38383,master_user='wtc',master_password='wtc.com',master_log_file='mysql-bin.000001',master_log_pos=177;
Query OK, 0 rows affected, 2 warnings (0.03 sec)

3. 检测slave状态

mysql> show slave status\G;
*************************** 1. row ***************************
               Slave_IO_State: Waiting for master to send event
                  Master_Host: 39.107.13.12
                  Master_User: wtc
                  Master_Port: 38383
                Connect_Retry: 60
              Master_Log_File: mysql-bin.000003
          Read_Master_Log_Pos: 3931784
               Relay_Log_File: relay-log.000004
                Relay_Log_Pos: 3500131
        Relay_Master_Log_File: mysql-bin.000003
             Slave_IO_Running: Yes
            Slave_SQL_Running: Yes
              Replicate_Do_DB: 
          Replicate_Ignore_DB: 
           Replicate_Do_Table: 
       Replicate_Ignore_Table: 
      Replicate_Wild_Do_Table: 
  Replicate_Wild_Ignore_Table: 
                   Last_Errno: 0
                   Last_Error: 
                 Skip_Counter: 0
          Exec_Master_Log_Pos: 3499918
              Relay_Log_Space: 3933277
              Until_Condition: None
               Until_Log_File: 
                Until_Log_Pos: 0
           Master_SSL_Allowed: No
           Master_SSL_CA_File: 
           Master_SSL_CA_Path: 
              Master_SSL_Cert: 
            Master_SSL_Cipher: 
               Master_SSL_Key: 
        Seconds_Behind_Master: 0
Master_SSL_Verify_Server_Cert: No
                Last_IO_Errno: 0
                Last_IO_Error: 
               Last_SQL_Errno: 0
               Last_SQL_Error: 
  Replicate_Ignore_Server_Ids: 
             Master_Server_Id: 1
                  Master_UUID: 122574bd-7926-11ec-85dc-00163e366a62
             Master_Info_File: /opt/app/mysql/data/master.info
                    SQL_Delay: 0
          SQL_Remaining_Delay: NULL
      Slave_SQL_Running_State: Slave has read all relay log; waiting for more updates
           Master_Retry_Count: 86400
                  Master_Bind: 
      Last_IO_Error_Timestamp: 
     Last_SQL_Error_Timestamp: 
               Master_SSL_Crl: 
           Master_SSL_Crlpath: 
           Retrieved_Gtid_Set: 
            Executed_Gtid_Set: 
                Auto_Position: 0
         Replicate_Rewrite_DB: 
                 Channel_Name: 
           Master_TLS_Version: 
1 row in set (0.00 sec)

3.确认数据

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| sys                |
| wtc                |
+--------------------+
5 rows in set (0.00 sec)

mysql> use wtc
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Database changed
mysql> select count(1) from wtc_table;
+----------+
| count(1) |
+----------+
|   100000 |
+----------+

四. 问题深入

1. 若新增节点想构成双主集群，应该如何做？