1.背景

MySQL Group Replication（MGR）是MySQL官方在5.7.17版本引進的一個資料庫高可用與高擴充套件的解決方案，以外掛形式提供，實現了分散式下資料的最終一致性，總結MGR特點如下：

* 高一致性：基於分散式paxos協議實現組複製，保證資料一致性；

* 高容錯性：自動檢測機制，只要不是大多數節點都當機就可以繼續工作，內建防腦裂保護機制；

* 高擴充套件性：節點的增加與移除會自動更新組成員資訊，新節點加入後，自動從其他節點同步增量資料，直到與其他節點資料一致；

* 高靈活性：提供單主模式和多主模式，單主模式在主庫當機後能夠自動選主，所有寫入都在主節點進行，多主模式支援多節點寫入。

2. 環境：

3臺伺服器搭建3節點MGR叢集，MySQL版本5.7.27，作業系統版本CentOS 7.3。

* 192.168.8.71

* 192.168.8.72

* 192.168.8.73

3.安裝步驟

3.1 安裝MySQL5.7

MySQL官方版5.7.27，採用Linux Generic安裝方式，直接下載壓縮包，解壓到目錄/usr/local/mysql。

3.2 修改配置檔案

編輯配置檔案/etc/my.cnf，3個節點除了server_id、loose-group_replication_local_address、report_host 三個引數不一樣外，其他保持一致。

[mysqld]

port=3306

basedir=/usr/local/mysql

datadir=/usr/local/mysql/data

server_id=1

gtid_mode=ON

enforce_gtid_consistency=ON

binlog_checksum=NONE

log_bin=binlog

log_slave_updates=ON

binlog_format=ROW

master_info_repository=TABLE

relay_log_info_repository=TABLE

transaction_write_set_extraction=XXHASH64

loose-group_replication_group_name="aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa"

loose-group_replication_start_on_boot=OFF

loose-group_replication_local_address= "192.168.8.71:33061"

loose-group_replication_group_seeds= "192.168.8.71:33061,192.168.8.72:33061,192.168.8.73:33061"

loose-group_replication_bootstrap_group=OFF

report_host=192.168.8.71

report_port=3306

3.3 初始化資料庫（所有節點執行）

略

3.4 啟動資料庫，安裝MGR外掛，設定複製賬號（所有節點執行）

--安裝MGR外掛

mysql>INSTALL PLUGIN group_replication SONAME 'group_replication.so';

--設定複製賬號

mysql> SET SQL_LOG_BIN=0;

mysql> CREATE USER repl@'%' IDENTIFIED BY 'repl';

mysql> GRANT REPLICATION SLAVE ON *.* TO repl@'%';

mysql> FLUSH PRIVILEGES;

mysql> SET SQL_LOG_BIN=1;

mysql> CHANGE MASTER TO MASTER_USER='repl', MASTER_PASSWORD='repl' FOR CHANNEL 'group_replication_recovery';

3.5 啟動MGR單主模式

# 啟動MGR，在主庫(192.168.8.71)上執行

mysql> SET GLOBAL group_replication_bootstrap_group=ON;

mysql> START GROUP_REPLICATION;

mysql> SET GLOBAL group_replication_bootstrap_group=OFF;

# 檢視MGR組資訊

mysql> SELECT * FROM performance_schema.replication_group_members;

+---------------------------+--------------------------------------+--------------+-------------+--------------+

+---------------------------+--------------------------------------+--------------+-------------+--------------+

+---------------------------+--------------------------------------+--------------+-------------+--------------+

1 row in set (0.00 sec)

# 其他節點加入MGR，在從庫（192.168.8.72，192.168.8.73）上執行

mysql> START GROUP_REPLICATION;

# 檢視MGR組資訊

mysql> SELECT channel_name,

-> member_id,

-> member_host,

-> member_port,

-> member_state,

-> IF(global_status.variable_name IS NOT NULL, 'PRIMARY', 'SECONDARY') AS member_role

-> FROM performance_schema.replication_group_members

-> LEFT JOIN performance_schema.global_status

-> ON global_status.variable_name = 'group_replication_primary_member'

-> AND global_status.variable_value = replication_group_members.member_id;

+---------------------------+--------------------------------------+--------------+-------------+--------------+-------------+

+---------------------------+--------------------------------------+--------------+-------------+--------------+-------------+

+---------------------------+--------------------------------------+--------------+-------------+--------------+-------------+

3 rows in set (0.00 sec)

可以看到，3個節點狀態為online，並且主節點為192.168.8.71，只有主節點可以寫入，其他節點只讀，MGR單主模式搭建成功

3.6 切換到多主模式

MGR切換模式需要重新啟動組複製，因些需要在所有節點上先關閉組複製，設定 group_replication_single_primary_mode=OFF 等引數，再啟動組複製。

# 停止組複製(所有節點執行)：

mysql> stop group_replication;

mysql> set global group_replication_single_primary_mode=OFF;

mysql> set global group_replication_enforce_update_everywhere_checks=ON;

# 隨便選擇某個節點執行

mysql> SET GLOBAL group_replication_bootstrap_group=ON;

mysql> START GROUP_REPLICATION;

mysql> SET GLOBAL group_replication_bootstrap_group=OFF;

# 其他節點執行

mysql> START GROUP_REPLICATION;

# 檢視組資訊，所有節點的 MEMBER_ROLE 都為 PRIMARY

mysql> SELECT channel_name,

-> member_id,

-> member_host,

-> member_port,

-> member_state,

-> IF(global_status.variable_name IS NOT NULL, 'PRIMARY', 'SECONDARY') AS member_role

-> FROM performance_schema.replication_group_members

-> LEFT JOIN performance_schema.global_status

-> ON global_status.variable_name = 'group_replication_primary_member'

-> AND global_status.variable_value = replication_group_members.member_id;

+---------------------------+--------------------------------------+--------------+-------------+--------------+-------------+

+---------------------------+--------------------------------------+--------------+-------------+--------------+-------------+

+---------------------------+--------------------------------------+--------------+-------------+--------------+-------------+

3 rows in set (0.00 sec)

可以看到所有節點狀態都是online，角色都是PRIMARY，MGR多主模式搭建成功。

3.7 切回單主模式

# 所有節點執行

mysql> stop group_replication;

mysql> set global group_replication_enforce_update_everywhere_checks=OFF;

mysql> set global group_replication_single_primary_mode=ON;

# 主節點（192.168.8.71）執行

SET GLOBAL group_replication_bootstrap_group=ON;

START GROUP_REPLICATION;

SET GLOBAL group_replication_bootstrap_group=OFF;

# 從節點（192.168.8.72、192.168.8.73）執行

START GROUP_REPLICATION;

# 檢視MGR組資訊

mysql> SELECT channel_name,

-> member_id,

-> member_host,

-> member_port,

-> member_state,

-> IF(global_status.variable_name IS NOT NULL, 'PRIMARY', 'SECONDARY') AS member_role

-> FROM performance_schema.replication_group_members

-> LEFT JOIN performance_schema.global_status

-> ON global_status.variable_name = 'group_replication_primary_member'

-> AND global_status.variable_value = replication_group_members.member_id;

+---------------------------+--------------------------------------+--------------+-------------+--------------+-------------+

+---------------------------+--------------------------------------+--------------+-------------+--------------+-------------+

+---------------------------+--------------------------------------+--------------+-------------+--------------+-------------+

MySQL MGR 叢集搭建（單主模式）

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