【MySQL】基于GTID的半同步主从复制（实践）
一、GTID简介
什么是GTID?
全局事务标识符GTID的全称为Global Transaction Identifier，是在整个复制环境中对一个事务的唯一标识。
它是MySQL 5.6加入的一个强大特性，目的在于能够实现主从自动定位和切换，而不像以前需要指定文件和位置。
1、全局唯一，一个事务对应一个GTID
2、替代传统的binlog+pos复制；使用master_auto_position=1自动匹配GTID断点进行复制
3、MySQL5.6开始支持
4、在传统的主从复制中，slave端不用开启binlog；但是在GTID主从复制中，必须开启binlog
5、slave端在接受master的binlog时，会校验GTID值
6、为了保证主从数据的一致性，多线程同时执行一个GTID
二、工作原理
GTID长什么样子？
de35d2ef-cd37-11ed-93d8-000c2954bc91:1-4
uuid号：每个MySQL实例的唯一编号
使用GTID复制时，主库上提交事务时创建事务对应的GTID，从库在应用中继日志时用GTID识别和跟踪每个事务。在启动新从库或因故障转移到新主库时可以使用GTID来标识复制的位置，极大地简化了这些任务。
简而言之，在新的主从切换的时候，新的从服务器知道哪些事务已经做了，哪些没有做。
工作原理：
1、master更新数据时，会在事务前产生GTID，一同记录到binlog日志中。
2、slave端的i/o线程将变更的binlog，写入到本地的relay log中。
3、sql线程从relayog中获取GTID，然后对比slave端的binlog是否有记录。
4、如果有记录，说明该GTID的事务已经执行，slave会忽略。
5、如果没有记录，slave就会从relay log中执行该GTID的事务，并记录到binlog。
6、在解析过程中会判断是否有主键，如果没有就用二级索引，如果没有就用全部扫描
三、实践
查看master上的配置
[root@jd-mysql ~]# cat /etc/my.cnf
[mysqld_safe]
[client]
socket=/data/mysql/mysql.sock
[mysqld]
socket=/data/mysql/mysql.sock
port = 3306
open_files_limit = 8192
innodb_buffer_pool_size = 512M
character-set-server=utf8mb4
#skip-grant-tables
#二进制日志开启
log_bin
server_id = 1
#开启半同步，需要提前安装半同步的插件
rpl_semi_sync_master_enabled=1
rpl_semi_sync_master_timeout=1000 # 1 second
#gtid功能
gtid-mode=ON
enforce-gtid-consistency=ON
[mysql]
auto-rehash
prompt=\u@\d \R:\m mysql>
改了配置，首先一定记得刷新服务！
[root@jd-mysql mysql]# service mysqld restart
Shutting down MySQL.. SUCCESS!
Starting MySQL. SUCCESS!
配置slave的配置
[root@jd-mysql-2 ~]# cat /etc/my.cnf
[mysqld_safe]
[client]
socket=/data/mysql/mysql.sock
[mysqld]
socket=/data/mysql/mysql.sock
port = 3306
open_files_limit = 8192
innodb_buffer_pool_size = 512M
character-set-server=utf8
#log bin 二进制日志
log_bin
server_id = 2
#开启gtid功能
gtid-mode=ON
enforce-gtid-consistency=ON
log_slave_updates=ON
#开启半同步，需要提前安装半同步的插件
rpl_semi_sync_slave_enabled=1
[mysql]
auto-rehash
prompt=\u@\d \R:\m mysql>
记得刷新服务！
[root@jd-mysql-2 mysql]# service mysqld restart
Shutting down MySQL.. SUCCESS!
Starting MySQL. SUCCESS!
在master上新建一个授权用户，给slave来复制二进制日志
root@(none) 16:41 mysql>grant replication slave on *.* to 'jiangda'@'192.168.1.%' identified by 'Jiangda123#';
Query OK, 0 rows affected, 1 warning (1.01 sec)
在slave上配置master info的信息
CHANGE MASTER TO MASTER_HOST=‘192.168.1.150’ ,
MASTER_USER=‘jiangda’,
MASTER_PASSWORD=‘Jiangda123#’,
MASTER_PORT=3306,
master_auto_position=1;
root@(none) 16:43 mysql>stop slave;
Query OK, 0 rows affected (0.00 sec)
root@(none) 16:43 mysql>reset slave all;
Query OK, 0 rows affected (0.01 sec)
root@(none) 16:43 mysql>CHANGE MASTER TO MASTER_HOST='192.168.1.150' ,
-> MASTER_USER='jiangda',
-> MASTER_PASSWORD='Jiangda123#',
-> MASTER_PORT=3306,
-> master_auto_position=1;
Query OK, 0 rows affected, 2 warnings (0.01 sec)
root@(none) 16:43 mysql>start slave;
Query OK, 0 rows affected (0.00 sec)
root@(none) 16:43 mysql>show slave status\G;
*************************** 1. row ***************************
Slave_IO_State: Waiting for master to send event
Master_Host: 192.168.1.150
Master_User: jiangda
Master_Port: 3306
Connect_Retry: 60
Master_Log_File: jd-mysql-bin.000003
Read_Master_Log_Pos: 450
Relay_Log_File: jd-mysql-2-relay-bin.000002
Relay_Log_Pos: 669
Relay_Master_Log_File: jd-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: 450
Relay_Log_Space: 881
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: de35d2ef-cd37-11ed-93d8-000c2954bc91
Master_Info_File: /data/mysql/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: de35d2ef-cd37-11ed-93d8-000c2954bc91:1
Executed_Gtid_Set: de35d2ef-cd37-11ed-93d8-000c2954bc91:1
Auto_Position: 1
Replicate_Rewrite_DB:
Channel_Name:
Master_TLS_Version:
1 row in set (0.00 sec)
ERROR:
No query specified
在master上查看
root@(none) 16:42 mysql>show variables like "%semi_sync%";
+-------------------------------------------+------------+
| Variable_name | Value |
+-------------------------------------------+------------+
| rpl_semi_sync_master_enabled | ON |
| rpl_semi_sync_master_timeout | 1000 |
| rpl_semi_sync_master_trace_level | 32 |
| rpl_semi_sync_master_wait_for_slave_count | 1 |
| rpl_semi_sync_master_wait_no_slave | ON |
| rpl_semi_sync_master_wait_point | AFTER_SYNC |
+-------------------------------------------+------------+
6 rows in set (0.00 sec)
在slave上查看
root@(none) 16:43 mysql>show variables like "%semi_sync%";
+---------------------------------+-------+
| Variable_name | Value |
+---------------------------------+-------+
| rpl_semi_sync_slave_enabled | ON |
| rpl_semi_sync_slave_trace_level | 32 |
+---------------------------------+-------+
2 rows in set (0.00 sec)
验证GTID的半同步主从复制
在master上操作：
root@(none) 16:37 mysql>create database dada;
Query OK, 1 row affected (0.03 sec)
root@(none) 16:37 mysql>use dada;
Database changed
root@dada 16:38 mysql>create table t1(id int);
Query OK, 0 rows affected (0.02 sec)
root@dada 16:38 mysql>insert into t1(id) values(1),(2);
Query OK, 2 rows affected (0.10 sec)
Records: 2 Duplicates: 0 Warnings: 0
在slave上查看:
root@(none) 16:36 mysql>use dada;
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
root@dada 16:38 mysql>show tables;
+------------------+
| Tables_in_dada |
+------------------+
| t1 |
+------------------+
1 row in set (0.01 sec)
root@dada 16:39 scmysql>select * from t1;
+------+
| id |
+------+
| 1 |
| 2 |
+------+
2 rows in set (0.00 sec)
root@dada 16:44 mysql>show slave status\G;
*************************** 1. row ***************************
Slave_IO_State: Waiting for master to send event
Master_Host: 192.168.1.150
Master_User: jiangda
Master_Port: 3306
Connect_Retry: 60
Master_Log_File: jd-mysql-bin.000003
Read_Master_Log_Pos: 1043
Relay_Log_File: jd-mysql-2-relay-bin.000002
Relay_Log_Pos: 1262
Relay_Master_Log_File: jd-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: 1043
Relay_Log_Space: 1474
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: de35d2ef-cd37-11ed-93d8-000c2954bc91
Master_Info_File: /data/mysql/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: de35d2ef-cd37-11ed-93d8-000c2954bc91:1-4
Executed_Gtid_Set: de35d2ef-cd37-11ed-93d8-000c2954bc91:1-4
Auto_Position: 1
Replicate_Rewrite_DB:
Channel_Name:
Master_TLS_Version:
1 row in set (0.00 sec)
ERROR:
No query specified
四、总结
业务量小：推荐使用gtid的半同步主从复制，只要2~3台服务器
业务量大： 推荐使用组复制，至少3，5,7，9台服务器
但是当我们需要实现级联同步时，即以这样的一个模式，A>B>C实现三级同步时，AB库除了需要设置log-bin参数还需要添加一个参数：log-slave-updates
log-slave-updates参数默认时关闭的状态，如果不手动设置，那么bin-log只会记录直接在该库上执行的SQL语句，由replication机制的SQL线程读取relay-log而执行的SQL语句并不会记录到bin-log，那么就无法实现上述的三级级联同步。