MySQL 5.7 MGR单主确定主节点是哪个，我们可以通过成员ID来判断，然后结合read_only参数来确认。
[root@localhost ~]# mysql -uroot -p -P 3306 -h 127.0.0.1 mysql: [Warning] Using a password on the command line interface can be insecure. Welcome to the MySQL monitor. Commands end with ; or g. Your MySQL connection id is 857246 Server version: 5.7.26-29-log Percona Server (GPL)
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mysql> status -------------- mysql Ver 14.14 Distrib 5.7.26-29, for Linux (x86_64) using EditLine wrapper
Connection id: 857246 Current database: Current user: root@127.0.0.1 SSL: Not in use Current pager: stdout Using outfile: '' Using delimiter: ; Server version: 5.7.26-29-log Percona Server (GPL) Protocol version: 10 Connection: 127.0.0.1 via TCP/IP Server characterset: utf8mb4 Db characterset: utf8mb4 Client characterset: utf8 Conn. characterset: utf8 TCP port: 3306 Uptime: 39 days 8 hours 53 min 39 sec
Threads: 4 Questions: 4989552 Slow queries: 731837 Opens: 930 Flush tables: 1 Open tables: 924 Queries per second avg: 1.466 --------------
mysql> SHOW STATUS LIKE 'group_replication_primary_member'; ---------------------------------- -------------------------------------- | Variable_name | Value | ---------------------------------- -------------------------------------- | group_replication_primary_member | 59d7f183-b8f6-11e9-863b-005056875165 | ---------------------------------- -------------------------------------- 1 row in set (0.00 sec)
mysql> select * from performance_schema.replication_group_members; --------------------------- -------------------------------------- ------------- ------------- -------------- | CHANNEL_NAME | MEMBER_ID | MEMBER_HOST | MEMBER_PORT | MEMBER_STATE | --------------------------- -------------------------------------- ------------- ------------- -------------- | group_replication_applier | 500dd0aa-b8f6-11e9-85ba-005056875a61 | 196.55.7.37 | 3306 | ONLINE | | group_replication_applier | 59d7f183-b8f6-11e9-863b-005056875165 | 196.55.7.36 | 3306 | ONLINE | | group_replication_applier | 69e1c26d-b8f6-11e9-91c1-00505687032a | 196.55.7.38 | 3306 | ONLINE | --------------------------- -------------------------------------- ------------- ------------- -------------- 3 rows in set (0.00 sec)
mysql> show variables like '%read_only'; ----------------------- ------- | Variable_name | Value | ----------------------- ------- | innodb_read_only | OFF | | read_only | OFF | | super_read_only | OFF | | transaction_read_only | OFF | | tx_read_only | OFF | ----------------------- ------- 5 rows in set (0.01 sec)
mysql>
