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ProxySQL> show tables ;
+--------------------------------------------+
| tables                                     |
+--------------------------------------------+
| global_variables                           |
| mysql_collations                           |
| mysql_group_replication_hostgroups         |
| mysql_query_rules                          |
| mysql_replication_hostgroups               |
| mysql_servers                              |
| mysql_users                                |
...
| scheduler                                  |
+--------------------------------------------+
15 rows in set (0.00 sec)

name	ip
mysql1	192.168.90.2
mysql2	192.168.90.3
mysql3	192.168.90.4

mysql> insert into mysql_servers (hostgroup_id,hostname,port) values (2,'192.168.90.2',3306);
Query OK, 1 row affected (0.00 sec)
mysql> insert into mysql_servers (hostgroup_id,hostname,port) values (2,'192.168.90.3',3306);
Query OK, 1 row affected (0.00 sec)
mysql> insert into mysql_servers (hostgroup_id,hostname,port) values (2,'192.168.90.4',3306);
Query OK, 1 row affected (0.00 sec)
mysql> select * from mysql_servers;
+--------------+--------------+------+--------+--------+-------------+-----------------+---------------------+---------+----------------+---------+
| hostgroup_id | hostname     | port | status | weight | compression | max_connections | max_replication_lag | use_ssl | max_latency_ms | comment |
+--------------+--------------+------+--------+--------+-------------+-----------------+---------------------+---------+----------------+---------+
| 2            | 192.168.90.2 | 3306 | ONLINE | 1      | 0           | 1000            | 0                   | 0       | 0              |         |
| 2            | 192.168.90.3 | 3306 | ONLINE | 1      | 0           | 1000            | 0                   | 0       | 0              |         |
| 2            | 192.168.90.4 | 3306 | ONLINE | 1      | 0           | 1000            | 0                   | 0       | 0              |         |
+--------------+--------------+------+--------+--------+-------------+-----------------+---------------------+---------+----------------+---------+
ProxySQL> show create table mysql_group_replication_hostgroups\G
*************************** 1. row ***************************
      table: mysql_group_replication_hostgroups
Create Table: CREATE TABLE mysql_group_replication_hostgroups (
   writer_hostgroup INT CHECK (writer_hostgroup>=0) NOT NULL PRIMARY KEY,
   backup_writer_hostgroup INT CHECK (backup_writer_hostgroup>=0 AND backup_writer_hostgroup<>writer_hostgroup) NOT NULL,
   reader_hostgroup INT NOT NULL CHECK (reader_hostgroup<>writer_hostgroup AND backup_writer_hostgroup<>reader_hostgroup AND reader_hostgroup>0),
   offline_hostgroup INT NOT NULL CHECK (offline_hostgroup<>writer_hostgroup AND offline_hostgroup<>reader_hostgroup AND backup_writer_hostgroup<>offline_hostgroup AND offline_hostgroup>=0),
   active INT CHECK (active IN (0,1)) NOT NULL DEFAULT 1,
   max_writers INT NOT NULL CHECK (max_writers >= 0) DEFAULT 1,
   writer_is_also_reader INT CHECK (writer_is_also_reader IN (0,1)) NOT NULL DEFAULT 0,
   max_transactions_behind INT CHECK (max_transactions_behind>=0) NOT NULL DEFAULT 0,
   comment VARCHAR,
   UNIQUE (reader_hostgroup),
   UNIQUE (offline_hostgroup),
   UNIQUE (backup_writer_hostgroup))

Column Name	Description
writer_hostgroup	the id of the hostgroup that will contain all the members that are writer MGR写节点都应被包含在这个组中
backup_writer_hostgroup	if the group is running in multi-primary mode, there are multi writers (read_only=0) but if the amount of these writer is larger than the max_writers, the extra nodes are located in that backup writer group 在MGR多写的模式下，如果可以提供写属性的节点超过实际使用的写节点数，剩下的节点将在这个备用写节点组中存放。
reader_hostgroup	the id of the hostgroup that will contain all the members in read_only 该组将会包含所有具有只读属性的MGR节点
offline_hostgroup	the id of the hostgroup that will contain the host not being online or not being part of the Group 改组将会包含所有无法提供服务或者不处于online情况下的节点
active	when enabled, ProxySQL monitors the Group and move the server according in the appropriate hostgroups 当该列属性启动时，ProxySQL将会监察整个集权，并根据hostgroup和节点的属性，进行匹配。
max_writers	limit the amount of nodes in the writer hostgroup in case of group in multi-primary mode 控制MGR多写模式下实际对外提供写服务的节点数量
writer_is_also_reader	boolean value, 0 or 1, when enabled, a node in the writer hostgroup will also belongs the the reader hostgroup 布尔值0或1，当启动时写节点组中的节点会同时出现在读组中
max_transactions_behind	if the value is greater than 0, it defines how much a node can be lagging in applying the transactions from the Group, see this post for more info 定义节点最大落后整个集群的事务数量（ProxySQL内部，非MGR中的）

ProxySQL> insert into mysql_group_replication_hostgroups (writer_hostgroup,backup_writer_hostgroup,
reader_hostgroup, offline_hostgroup,active,max_writers,writer_is_also_reader,max_transactions_behind)
values (2,4,3,1,1,1,0,100);
ProxySQL> save mysql servers to disk;
Query OK, 0 rows affected (0.01 sec)
ProxySQL> load mysql servers to runtime;
Query OK, 0 rows affected (0.00 sec)
# mysql -p < addition_to_sys.sql
mysql> select * from gr_member_routing_candidate_status;
+------------------+-----------+---------------------+----------------------+
| viable_candidate | read_only | transactions_behind | transactions_to_cert |
+------------------+-----------+---------------------+----------------------+
| YES              | YES       |                  40 |                    0 |
+------------------+-----------+---------------------+----------------------+
mysql> GRANT SELECT on sys.* to 'monitor'@'%' identified by 'monitor';
ProxySQL>  select hostgroup_id, hostname, status  from runtime_mysql_servers;
+--------------+--------------+--------+
| hostgroup_id | hostname     | status |
+--------------+--------------+--------+
| 2            | 192.168.90.2 | ONLINE |
| 3            | 192.168.90.3 | ONLINE |
| 3            | 192.168.90.4 | ONLINE |
+--------------+--------------+--------+
ProxySQL> SHOW TABLES FROM monitor ;
+------------------------------------+
| tables                             |
+------------------------------------+
| mysql_server_connect               |
| mysql_server_connect_log           |
| mysql_server_group_replication_log |
| mysql_server_ping                  |
| mysql_server_ping_log              |
| mysql_server_read_only_log         |
| mysql_server_replication_lag_log   |
+------------------------------------+
7 rows in set (0.00 sec)
ProxySQL> select * from mysql_server_group_replication_log order by time_start_us desc  limit 5 ;
+--------------+------+------------------+-----------------+------------------+-----------+---------------------+-------+
| hostname     | port | time_start_us    | success_time_us | viable_candidate | read_only | transactions_behind | error |
+--------------+------+------------------+-----------------+------------------+-----------+---------------------+-------+
| 192.168.90.4 | 3306 | 1490187314429511 | 1887            | YES              | NO        | 0                   | NULL  |
| 192.168.90.3 | 3306 | 1490187314429141 | 1378            | YES              | YES       | 0                   | NULL  |
| 192.168.90.2 | 3306 | 1490187314428743 | 1478            | NO               | NO        | 0                   | NULL  |
| 192.168.90.4 | 3306 | 1490187309406886 | 3639            | YES              | NO        | 0                   | NULL  |
| 192.168.90.3 | 3306 | 1490187309406486 | 2444            | YES              | YES       | 0                   | NULL  |
+--------------+------+------------------+-----------------+------------------+-----------+---------------------+-------+

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ProxySQL在MySQL的代理和负载均衡中一直处于领先地位。其中包含了诸如缓存查询，多路复用，流量镜像，读写分离，路由等等的强力功能。在最新的功能性增强中，包含了对MGR的原生支持，不在需要使用第三方脚本进行适配。

This implementation supports Groups in Single-Primary and in Multi-Primary mode. It is even possible to setup a Multi-Primary Group but dedicate writes on only one member.

最新的增强中，提供了对单写和多写集群组的支持，甚至可以在多写组上指定只由某个成员进行写入操作。

René, the main developer of ProxySQL, went even further. For example in a 7 nodes clusters (Group of 7 members) where all nodes are writers (Multi-Primary mode), it’s possible to decide to have only 2 writers, 3 readers and 2 backup-writers. This mean that ProxySQL will see all the nodes as possible writers but will only route writes on 2 nodes (add them in the  writer hostgroup, because we decided to limit it to 2 writers for example), then it will add the others in the backup-writers group, this group defines the other writer candidates. An finally add 2 in the readers hostgroup.

ProxySQL的主要开发者René，更进一步的可以（利用ProxySQL）做到例如在一个七个节点的多写集群中，指定2组写节点，2组备用写节点，3个只读节点的操作。即ProxySQL虽然识别出来所有的节点皆为写节点，但只路由写操作到选定的两个写节点（通过Hostgroup的方式），同时将另外两个写节点添加到备用写节点组中，最后三个读节点加入读组。（本段中的组皆为ProxySQL中的hostgroup含义）。

It’s also possible to limit the access to a member that is slower in applying the replicated transactions (applying queue reaching a threshold).

除此之外，还可以限制连接访问集群中超出最大设定落后事务值的慢节点。

It is time to have a look at this new ProxySQL version. The version supporting MySQL Group Replication is 1.4.0 and currently is only available on github (but stay tuned for a new release soon).

ProxySQL从1.4.0版本开始增加对MGR的原生支持，若发行版中没有，可以从GitHub中编译获取。

So let’s have a look at what is new for users. When you connect to the admin interface of ProxySQL, you can see a new table: mysql_group_replication_hostgroups

下面我们看下对于用户来说有哪些明显的变化，开始进行admin端口连接后会发现比之前多了一个mysql_group_replication_hostgroups表

This is the table we will use to setup in which hostgroup a node will belongs.

我们将在这个表中进行节点的归属组（hostgroup）的设置。

To illustrate how ProxySQL supports MySQL Group Replication, I will use a cluster of 3 nodes:

为了阐明ProxySQL 对MGR支持的原理，下面我会用到一个三节点的集群。

So first, as usual we need to add our 3 members into the mysql_servers table:

首先，我们照旧插入三个节点的信息到mysql_servers表中。

Now we can setup ProxySQL’s behavior with our Group Replication cluster, but before let’s check the definition of the new mysql_group_replication_hostgroups table:

在设置MGR节点在ProxySQL中的行为之前，先查看下新加入的mysql_group_replication_hostgroups表的DDL。

There are many new columns, let’s have a look at their meaning:

看一下之前没有出现过的新列的含义

Now that we are (or should be) more familiar with that table, we will set it up like this:

熟悉了表的定义后，整个拓补将会如下图所示：

So let’s add this:

下面我们将MGR集群的分组定义和关键参数写入mysql_group_replication_hostgroups表中

We should not forget to save our mysql servers to disk and load them on runtime:

然后将新更改的配置保存到磁盘上，并加载到运行环境。

It’s also important with the current version of MySQL Group Replication to add a view and its dependencies in sys schema: addition_to_sys.sql:

同时，我们需要在MGR中添加如下的视图，及其依赖的存储过程。

So now from every members of the group, we can run the following statement. ProxySQL based its internal monitoring this same view:

如此，我们便可以从MGR集群中任意一个节点上执行下面的语句获取MGR成员的基本信息，ProxySQL 也是根据这个办法进行监测节点的健康与落后情况。

We also must not forget to create in our cluster the  monitor user needed by ProxySQL:

同时，我们需要讲sys库的读权限赋给ProxySQL配置的监控MySQL的账户：

We can immediately check how ProxySQL has distributed the servers in the hostgroups :

接下来，我们马上检查下ProxySQL是如何将MGR节点分发到ProxySQL各个组中：

The Writer (Primary-Master) is mysql1 (192.168.90.2 in hostgroup 2) and the others are in the read hostgroup (id=3).

写节点被分配到之前定义好的ID为2的写组中，其他所有的节点被分配到ID为3的只读组中。（单写模式）

As you can see, there is no more need to create a scheduler calling an external script with complex rules to move the servers in the right hostgroup.

这样，我们就省掉了通过定时器去调用第三方复杂定义的脚本将MGR节点匹配并分配到对应的ProxySQL组中的操作。

Now to use the proxy, it’s exactly as usual, you need to create users associated to default hostgroup or add routing rules.

接下来，你就可以按照之前的做法对ProxySQL进行配置，例如关联用户到默认ProxySQL组中，或者添加查询路由规则。

An extra table has also been added for monitoring:

另外，ProxySQL比之前多了一个监控MySQL实例的表，具体信息如下面所示：

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