18.怎样查看MGR复制延迟？

1.查看集群状态信息

 MySQL  db01:3306 ssl  JS > dba.getCluster().status()
{
    "clusterName": "ClusterTest", 
    "defaultReplicaSet": {
        "name": "default", 
        "primary": "db01:3306", 
        "ssl": "REQUIRED", 
        "status": "OK", 
        "statusText": "Cluster is ONLINE and can tolerate up to ONE failure.", 
        "topology": {
            "db01:3306": {
                "address": "db01:3306", 
                "memberRole": "PRIMARY", 
                "mode": "R/W", 
                "readReplicas": {}, 
                "replicationLag": null,    ## 这里如果有时间显示，就代表的是延迟时间
                "role": "HA", 
                "status": "ONLINE", 
                "version": "8.0.25"
            }, 
            "db02:3306": {
                "address": "db02:3306", 
                "memberRole": "SECONDARY", 
                "mode": "R/O", 
                "readReplicas": {}, 
                "replicationLag": null, 
                "role": "HA", 
                "status": "ONLINE", 
                "version": "8.0.25"
            }, 
            "db03:3306": {
                "address": "db03:3306", 
                "memberRole": "SECONDARY", 
                "mode": "R/O", 
                "readReplicas": {}, 
                "replicationLag": null, 
                "role": "HA", 
                "status": "ONLINE", 
                "version": "8.0.25"
            }
        }, 
        "topologyMode": "Single-Primary"
    }, 
    "groupInformationSourceMember": "db01:3306"
}

2.也可以通过如下命令查看：

root@mysqldb 14:02:  [test]> SELECT MEMBER_ID AS id, COUNT_TRANSACTIONS_IN_QUEUE AS trx_tobe_certified, COUNT_TRANSACTIONS_REMOTE_IN_APPLIER_QUEUE AS relaylog_tobe_applied, COUNT_TRANSACTIONS_CHECKED AS trx_chkd, COUNT_TRANSACTIONS_REMOTE_APPLIED AS trx_done, COUNT_TRANSACTIONS_LOCAL_PROPOSED AS proposed FROM performance_schema.replication_group_member_stats;
+--------------------------------------+--------------------+-----------------------+----------+----------+----------+
| id                                   | trx_tobe_certified | relaylog_tobe_applied | trx_chkd | trx_done | proposed |
+--------------------------------------+--------------------+-----------------------+----------+----------+----------+
| 02e3192d-2eec-11ee-9dc3-000c2995c6c1 |                  0 |                     0 |       44 |        4 |       44 |
| 307f5f45-3544-11ee-8fa9-000c293f8c20 |                  0 |                     0 |        3 |        3 |        0 |
| bb4a87c4-2f41-11ee-8804-000c292fd49a |                  0 |                     0 |        9 |       11 |        0 |
+--------------------------------------+--------------------+-----------------------+----------+----------+----------+
3 rows in set (0.00 sec)

这里主要查看的是表performance_schema.replication_group_member_stats相关资源进行查看.

3.也可以通过查看接受到的事务和已执行完的事务之间的差距来判断

root@mysqldb 20:42:  [test]> SELECT RECEIVED_TRANSACTION_SET FROM performance_schema.replication_connection_status WHERE channel_name = 'group_replication_applier' UNION ALL SELECT variable_value FROM performance_schema.global_variables WHERE variable_name = 'gtid_executed';
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| RECEIVED_TRANSACTION_SET                                                                                                                                                           |
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| 02e3192d-2eec-11ee-9dc3-000c2995c6c1:1-3,
62864011-2f71-11ee-b8e3-000c2995c6c1:1-2231:1002226,
71a06ea2-38c6-11ee-a40a-000c2995c6c1:1-50,
aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaa1:1-7 |
| 02e3192d-2eec-11ee-9dc3-000c2995c6c1:1-3,
62864011-2f71-11ee-b8e3-000c2995c6c1:1-2231:1002226,
71a06ea2-38c6-11ee-a40a-000c2995c6c1:1-50,
aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaa1:1-7 |
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
2 rows in set (0.01 sec)