MySQL GTID详解

MySQL在5.6版本推出了GTID复制，相比传统的复制，GTID复制对于运维更加友好，这个事物是谁产生，产生多少事物，非常直接的标识出来。

今天将讨论一下关于从库show slave status 中的Retrieved_Gtid_Set 和 Executed_Gtid_Set.

Retrieved_Gtid_Set : 从库已经接收到主库的事务编号

Executed_Gtid_Set : 从库自身已经执行的事务编号

下面将解释这两列的含义：

首先看看master和slave的server-uuid

Master:

[root@localhost][db1]> show variables like '%uuid%';       
+---------------+--------------------------------------+
| Variable_name | Value                                |
+---------------+--------------------------------------+
| server_uuid   | 2a09ee6e-645d-11e7-a96c-000c2953a1cb |
+---------------+--------------------------------------+
1 row in set (0.00 sec)

Slave

[root@localhost][(none)]> show variables like '%uuid%';
+---------------+--------------------------------------+
| Variable_name | Value                                |
+---------------+--------------------------------------+
| server_uuid   | 8ce853fc-6f8a-11e7-8940-000c29e3f5ab |
+---------------+--------------------------------------+
1 row in set (0.01 sec)

其中主库的server-id是10,从库的server-id是20.

搭建好主从以后，如果没有数据写入，那么show slave status是下面这样的:

Replicate_Ignore_Server_Ids: 
             Master_Server_Id: 10
                  Master_UUID: 2a09ee6e-645d-11e7-a96c-000c2953a1cb
             Master_Info_File: mysql.slave_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: 
            Executed_Gtid_Set: 
                Auto_Position: 1
         Replicate_Rewrite_DB: 
                 Channel_Name: 
           Master_TLS_Version:

如果在主库创建表，并且写入2条数据，是下面这样的:

[root@localhost][db1]> create table t2 ( id int);
Query OK, 0 rows affected (0.07 sec)

[root@localhost][db1]> insert into t2 select 1;
Query OK, 1 row affected (0.07 sec)
Records: 1  Duplicates: 0  Warnings: 0

[root@localhost][db1]> insert into t2 select 2;
Query OK, 1 row affected (0.02 sec)
Records: 1  Duplicates: 0  Warnings: 0

这里auto_commit=1,可以看到创建表加插入2条数据，一共执行了3个事务.

从库：show slave statusG

Replicate_Ignore_Server_Ids: 
             Master_Server_Id: 10
                  Master_UUID: 2a09ee6e-645d-11e7-a96c-000c2953a1cb
             Master_Info_File: mysql.slave_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: 2a09ee6e-645d-11e7-a96c-000c2953a1cb:1-3
            Executed_Gtid_Set: 2a09ee6e-645d-11e7-a96c-000c2953a1cb:1-3
                Auto_Position: 1

主库：show master status

+------------------+----------+--------------+------------------+------------------------------------------+
| File             | Position | Binlog_Do_DB | Binlog_Ignore_DB | Executed_Gtid_Set                        |
+------------------+----------+--------------+------------------+------------------------------------------+
| mysql-bin.000001 |      912 |              |                  | 2a09ee6e-645d-11e7-a96c-000c2953a1cb:1-3 |
+------------------+----------+--------------+------------------+------------------------------------------+
1 row in set (0.00 sec)

其中主库的 Executed_Gtid_Set为：2a09ee6e-645d-11e7-a96c-000c2953a1cb:1-3

看到从库的Retrieved_Gtid_Set为: 2a09ee6e-645d-11e7-a96c-000c2953a1cb:1-3

Executed_Gtid_Set为： 2a09ee6e-645d-11e7-a96c-000c2953a1cb:1-3

也就是说主库产生了3个事务，从库接收到了主库的3个事务，且都已全部执行。

其中 2a09ee6e-645d-11e7-a96c-000c2953a1cb 是主库的server-uuid. 可以从从库解析binlog看出:

# at 154
#170823  0:38:38 server id 10  end_log_pos 219 CRC32 0x6268641f         GTID    last_committed=0        sequence_number=1
SET @@SESSION.GTID_NEXT= '2a09ee6e-645d-11e7-a96c-000c2953a1cb:1'/*!*/;
# at 219
#170823  0:38:38 server id 10  end_log_pos 316 CRC32 0x6c837618         Query   thread_id=103   exec_time=0     error_code=0
use `db1`/*!*/;
SET TIMESTAMP=1503419918/*!*/;
SET @@session.pseudo_thread_id=103/*!*/;
SET @@session.foreign_key_checks=1, @@session.sql_auto_is_null=0, @@session.unique_checks=1, @@session.autocommit=1/*!*/;
SET @@session.sql_mode=1436549152/*!*/;
SET @@session.auto_increment_increment=1, @@session.auto_increment_offset=1/*!*/;
/*!C utf8 *//*!*/;
SET @@session.character_set_client=33,@@session.collation_connection=33,@@session.collation_server=33/*!*/;
SET @@session.lc_time_names=0/*!*/;
SET @@session.collation_database=DEFAULT/*!*/;
create table t2 ( id int)
/*!*/;

可以看见server-id为10，gtid-next为2a09ee6e-645d-11e7-a96c-000c2953a1cb:1，执行了建表，剩下的

2a09ee6e-645d-11e7-a96c-000c2953a1cb:2 与 2a09ee6e-645d-11e7-a96c-000c2953a1cb:3 执行的查询我没有写出来。

这里也体现了文章开始提到的：这个事物由谁产生，产生多少事物，非常直接的标识了出来。

那么对于文章开头那个诡异的gtid是怎么出来的呢？先说说已经执行的事务：

Executed_Gtid_Set: 2a09ee6e-645d-11e7-a96c-000c2953a1cb:1-33,
8ce853fc-6f8a-11e7-8940-000c29e3f5ab:1

这里的2a09ee6e-645d-11e7-a96c-000c2953a1cb:1-33好理解，就是已经执行主库的1-33的事务，那么8ce853fc-6f8a-11e7-8940-000c29e3f5ab:1呢?其实也简单，有两种情况：

NO.1 从库有数据写入（即从库插入数据）

[root@localhost][db1]> insert into t2 select 1;
Query OK, 1 row affected (0.03 sec)
Records: 1  Duplicates: 0  Warnings: 0

show slave statusG;

Replicate_Ignore_Server_Ids: 
             Master_Server_Id: 10
                  Master_UUID: 2a09ee6e-645d-11e7-a96c-000c2953a1cb
             Master_Info_File: mysql.slave_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: 2a09ee6e-645d-11e7-a96c-000c2953a1cb:1-3
            Executed_Gtid_Set: 2a09ee6e-645d-11e7-a96c-000c2953a1cb:1-3,
8ce853fc-6f8a-11e7-8940-000c29e3f5ab:1
                Auto_Position: 1
         Replicate_Rewrite_DB:

可以看到已经执行的事务有来自主库的2a09ee6e-645d-11e7-a96c-000c2953a1cb:1-3,也有从库自己写入的数据：8ce853fc-6f8a-11e7-8940-000c29e3f5ab:1。我们可以解析binlog看看

mysqlbinlog -vv mysql-bin.000001 --include-gtids='8ce853fc-6f8a-11e7-8940-000c29e3f5ab:1'

# at 896
#170823  0:59:19 server id 20  end_log_pos 961 CRC32 0x0492528a         GTID    last_committed=3        sequence_number=4
SET @@SESSION.GTID_NEXT= '8ce853fc-6f8a-11e7-8940-000c29e3f5ab:1'/*!*/;
# at 961
#170823  0:59:19 server id 20  end_log_pos 1032 CRC32 0xbf545cca        Query   thread_id=25    exec_time=0     error_code=0
SET TIMESTAMP=1503421159/*!*/;
SET @@session.pseudo_thread_id=25/*!*/;
SET @@session.foreign_key_checks=1, @@session.sql_auto_is_null=0, @@session.unique_checks=1, @@session.autocommit=1/*!*/;
SET @@session.sql_mode=1436549152/*!*/;
SET @@session.auto_increment_increment=1, @@session.auto_increment_offset=1/*!*/;
/*!C utf8 *//*!*/;
SET @@session.character_set_client=33,@@session.collation_connection=33,@@session.collation_server=33/*!*/;
SET @@session.lc_time_names=0/*!*/;
SET @@session.collation_database=DEFAULT/*!*/;
BEGIN
/*!*/;
# at 1032
#170823  0:59:19 server id 20  end_log_pos 1079 CRC32 0x2f2de3ec        Rows_query
# insert into t2 select 1
# at 1079
#170823  0:59:19 server id 20  end_log_pos 1123 CRC32 0x18fe1c5c        Table_map: `db1`.`t2` mapped to number 109
# at 1123
#170823  0:59:19 server id 20  end_log_pos 1163 CRC32 0x163a708e        Write_rows: table id 109 flags: STMT_END_F

BINLOG '
52KcWR0UAAAALwAAADcEAACAABdpbnNlcnQgaW50byB0MiBzZWxlY3QgMezjLS8=
52KcWRMUAAAALAAAAGMEAAAAAG0AAAAAAAEAA2RiMQACdDIAAQMAAVwc/hg=
52KcWR4UAAAAKAAAAIsEAAAAAG0AAAAAAAEAAgAB//4BAAAAjnA6Fg==
'/*!*/;
### INSERT INTO `db1`.`t2`
### SET
###   @1=1 /* INT meta=0 nullable=1 is_null=0 */
# at 1163
#170823  0:59:19 server id 20  end_log_pos 1194 CRC32 0xe3347ac1        Xid = 68
COMMIT/*!*/;
SET @@SESSION.GTID_NEXT= 'AUTOMATIC' /* added by mysqlbinlog */ /*!*/;

从binlog中可以清楚看到是从库进行了写入。

NO.2 主从切换(这里使用的是MHA切换主从)

             Master_Server_Id: 20
                  Master_UUID: 8ce853fc-6f8a-11e7-8940-000c29e3f5ab
             Master_Info_File: mysql.slave_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: 8ce853fc-6f8a-11e7-8940-000c29e3f5ab:1
            Executed_Gtid_Set: 2a09ee6e-645d-11e7-a96c-000c2953a1cb:1-3,
8ce853fc-6f8a-11e7-8940-000c29e3f5ab:1
                Auto_Position: 1

可以看到主从切换以后主库的server-id是20。这里的意思是接收到主库8ce853fc-6f8a-11e7-8940-000c29e3f5ab:1,并已经执行了这个事物，这个事物其实就是之前从库写入的那条数据。对于2a09ee6e-645d-11e7-a96c-000c2953a1cb:1-3就是之前主库执行的3个事务，如果此时在主库再插入一条数据，那么变化如下：

Retrieved_Gtid_Set: 8ce853fc-6f8a-11e7-8940-000c29e3f5ab:1-2
Executed_Gtid_Set: 2a09ee6e-645d-11e7-a96c-000c2953a1cb:1-3,
8ce853fc-6f8a-11e7-8940-000c29e3f5ab:1-2

下面说说GTID不连续问题，类似 2a09ee6e-645d-11e7-a96c-000c2953a1cb:37-45 ，这个是由于binlog被清理后导致的，我们可以测试一下，然后查看gtid_purge变量。

binlog不可能永远驻留在服务上，需要定期进行清理(通过expire_logs_days可以控制定期清理间隔)，否则迟早它会把磁盘用尽。gtid_purged用于记录已经被清除了的binlog事务集合，它是gtid_executed的子集。只有gtid_executed为空时才能手动设置该变量，此时会同时更新gtid_executed为和gtid_purged相同的值。gtid_executed为空意味着要么之前没有启动过基于GTID的复制，要么执行过RESET MASTER。执行RESET MASTER时同样也会把gtid_purged置空，即始终保持gtid_purged是gtid_executed的子集。

[root@localhost][db1]> show master logs;
+------------------+-----------+
| Log_name         | File_size |
+------------------+-----------+
| mysql-bin.000001 |      3530 |
+------------------+-----------+
1 row in set (0.00 sec)

[root@localhost][db1]> flush logs;
Query OK, 0 rows affected (0.05 sec)

[root@localhost][db1]> show master logs;
+------------------+-----------+
| Log_name         | File_size |
+------------------+-----------+
| mysql-bin.000001 |      3577 |
| mysql-bin.000002 |       234 |
+------------------+-----------+
2 rows in set (0.00 sec)

[root@localhost][db1]> PURGE BINARY LOGS TO 'mysql-bin.000002';
Query OK, 0 rows affected (0.01 sec)

[root@localhost][db1]> show master logs;
+------------------+-----------+
| Log_name         | File_size |
+------------------+-----------+
| mysql-bin.000002 |       234 |
+------------------+-----------+
1 row in set (0.00 sec)

然后只要从库有重新启动，才会读取。MySQL服务器启动时，通过读binlog文件，初始化gtid_executed和gtid_purged,使它们的值能和上次MySQL运行时一致。

gtid_executed 本机被执行并写入日志的gtid
gtid_purged 该变量中记录的是本机上已经执行过，但是已经被purge binary logs to命令清理的gtid_set

没启动前：

 Retrieved_Gtid_Set: 8ce853fc-6f8a-11e7-8940-000c29e3f5ab:1-9
  Executed_Gtid_Set: 2a09ee6e-645d-11e7-a96c-000c2953a1cb:1-3,
8ce853fc-6f8a-11e7-8940-000c29e3f5ab:1-9

重启并插入数据：

            Master_Server_Id: 20
                  Master_UUID: 8ce853fc-6f8a-11e7-8940-000c29e3f5ab
             Master_Info_File: mysql.slave_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: 8ce853fc-6f8a-11e7-8940-000c29e3f5ab:10
            Executed_Gtid_Set: 2a09ee6e-645d-11e7-a96c-000c2953a1cb:1-3,
8ce853fc-6f8a-11e7-8940-000c29e3f5ab:1-10
                Auto_Position: 1

[root@localhost][(none)]> show variables like 'gtid_purged'; 
+---------------+------------------------------------------------------------------------------------+
| Variable_name | Value                                                                              |
+---------------+------------------------------------------------------------------------------------+
| gtid_purged   | 2a09ee6e-645d-11e7-a96c-000c2953a1cb:1-3,
8ce853fc-6f8a-11e7-8940-000c29e3f5ab:1-9 |
+---------------+------------------------------------------------------------------------------------+
1 row in set (0.01 sec)

可以看到 2a09ee6e-645d-11e7-a96c-000c2953a1cb:1-3 与 8ce853fc-6f8a-11e7-8940-000c29e3f5ab:1-9 都在mysql-bin.000001里，已经被清除了。

下面的两个实验，将会告诉我们如果主日志被清除，但从还没获得这些日志，该怎么处理：

实验一：如果slave所需要事务对应的GTID在master上已经被purge了

根据show global variables like '%gtid%'的命令结果我们可以看到，和GTID相关的变量中有一个gtid_purged。从字面意思以及官方文档可以知道该变量中记录的是本机上已经执行过，但是已经被purge binary logs to命令清理的gtid_set。
本节中我们就要试验下，如果master上把某些slave还没有fetch到的gtid event purge后会有什么样的结果。

以下指令在master上执行

master [localhost] {msandbox} (test) > show global variables like '%gtid%';
+---------------------------------+----------------------------------------+
| Variable_name | Value |
+---------------------------------+----------------------------------------+
| binlog_gtid_simple_recovery | OFF |
| enforce_gtid_consistency | ON |
| gtid_executed | 24024e52-bd95-11e4-9c6d-926853670d0b:1 |
| gtid_mode | ON |
| gtid_owned | |
| gtid_purged | |
| simplified_binlog_gtid_recovery | OFF |
+---------------------------------+----------------------------------------+
7 rows in set (0.01 sec)
master [localhost] {msandbox} (test) > flush logs;create table gtid_test2 (ID int) engine=innodb;
Query OK, 0 rows affected (0.04 sec)
Query OK, 0 rows affected (0.02 sec)
master [localhost] {msandbox} (test) > flush logs;create table gtid_test3 (ID int) engine=innodb;
Query OK, 0 rows affected (0.04 sec)
Query OK, 0 rows affected (0.04 sec)
master [localhost] {msandbox} (test) > show master status;
+------------------+----------+--------------+------------------+------------------------------------------+
| File | Position | Binlog_Do_DB | Binlog_Ignore_DB | Executed_Gtid_Set |
+------------------+----------+--------------+------------------+------------------------------------------+
| mysql-bin.000005 | 359 | | | 24024e52-bd95-11e4-9c6d-926853670d0b:1-3 |
+------------------+----------+--------------+------------------+------------------------------------------+
1 row in set (0.00 sec)
master [localhost] {msandbox} (test) > purge binary logs to 'mysql-bin.000004';
Query OK, 0 rows affected (0.03 sec)
master [localhost] {msandbox} (test) > show global variables like '%gtid%';
+---------------------------------+------------------------------------------+
| Variable_name | Value |
+---------------------------------+------------------------------------------+
| binlog_gtid_simple_recovery | OFF |
| enforce_gtid_consistency | ON |
| gtid_executed | 24024e52-bd95-11e4-9c6d-926853670d0b:1-3 |
| gtid_mode | ON |
| gtid_owned | |
| gtid_purged | 24024e52-bd95-11e4-9c6d-926853670d0b:1 |
| simplified_binlog_gtid_recovery | OFF |
+---------------------------------+------------------------------------------+
7 rows in set (0.00 sec)

在slave2上重新做一次主从，以下命令在slave2上执行

slave2 [localhost] {msandbox} ((none)) > change master to master_host='127.0.0.1',master_port =21288,master_user='rsandbox',master_password='rsandbox',master_auto_position=1;
Query OK, 0 rows affected, 2 warnings (0.04 sec)
slave2 [localhost] {msandbox} ((none)) > start slave;
Query OK, 0 rows affected (0.01 sec)
slave2 [localhost] {msandbox} ((none)) > show slave statusG
*************************** 1. row ***************************
......
Slave_IO_Running: No
Slave_SQL_Running: Yes
......
Last_Errno: 0
Last_Error:
Skip_Counter: 0
Exec_Master_Log_Pos: 0
Relay_Log_Space: 151
......
Last_IO_Errno: 1236
Last_IO_Error: Got fatal error 1236 from master when reading data from binary log: 'The slave is connecting using CHANGE MASTER TO MASTER_AUTO_POSITION = 1, but the master has purged binary logs containing GTIDs that the slave requires.'
Last_SQL_Errno: 0
Last_SQL_Error:
......
Auto_Position: 1
1 row in set (0.00 sec)

实验二：忽略purged的部分，强行同步

那么实际生产应用当中，偶尔会遇到这样的情况：某个slave从备份恢复后（或者load data infile）后，DBA可以人为保证该slave数据和master一致；或者即使不一致，这些差异也不会导致今后的主从异常（例如：所有master上只有insert没有update）。这样的前提下，我们又想使slave通过replication从master进行数据复制。此时我们就需要跳过master已经被purge的部分，那么实际该如何操作呢？
我们还是以实验一的情况为例：

先确认master上已经purge的部分。从下面的命令结果可以知道master上已经缺失24024e52-bd95-11e4-9c6d-926853670d0b:1这一条事务的相关日志

master [localhost] {msandbox} (test) > show global variables like '%gtid%';
+---------------------------------+------------------------------------------+
| Variable_name | Value |
+---------------------------------+------------------------------------------+
| binlog_gtid_simple_recovery | OFF |
| enforce_gtid_consistency | ON |
| gtid_executed | 24024e52-bd95-11e4-9c6d-926853670d0b:1-3 |
| gtid_mode | ON |
| gtid_owned | |
| gtid_purged | 24024e52-bd95-11e4-9c6d-926853670d0b:1 |
| simplified_binlog_gtid_recovery | OFF |
+---------------------------------+------------------------------------------+
7 rows in set (0.00 sec)

在slave上通过set global gtid_purged='xxxx'的方式，跳过已经purge的部分

slave2 [localhost] {msandbox} ((none)) > stop slave;
Query OK, 0 rows affected (0.04 sec)
slave2 [localhost] {msandbox} ((none)) > set global gtid_purged = '24024e52-bd95-11e4-9c6d-926853670d0b:1';
Query OK, 0 rows affected (0.05 sec)
slave2 [localhost] {msandbox} ((none)) > start slave;
Query OK, 0 rows affected (0.01 sec)
slave2 [localhost] {msandbox} ((none)) > show slave statusG
*************************** 1. row ***************************
Slave_IO_State: Waiting for master to send event
......
Master_Log_File: mysql-bin.000005
Read_Master_Log_Pos: 359
Relay_Log_File: mysql_sandbox21290-relay-bin.000004
Relay_Log_Pos: 569
Relay_Master_Log_File: mysql-bin.000005
Slave_IO_Running: Yes
Slave_SQL_Running: Yes
......
Exec_Master_Log_Pos: 359
Relay_Log_Space: 873
......
Master_Server_Id: 1
Master_UUID: 24024e52-bd95-11e4-9c6d-926853670d0b
Master_Info_File: /data/mysql/rsandbox_mysql-5_6_23/node2/data/master.info
SQL_Delay: 0
SQL_Remaining_Delay: NULL
Slave_SQL_Running_State: Slave has read all relay log; waiting for the slave I/O thread to update it
......
Retrieved_Gtid_Set: 24024e52-bd95-11e4-9c6d-926853670d0b:2-3
Executed_Gtid_Set: 24024e52-bd95-11e4-9c6d-926853670d0b:1-3
Auto_Position: 1
1 row in set (0.00 sec)

可以看到此时slave已经可以正常同步，并补齐了24024e52-bd95-11e4-9c6d-926853670d0b:2-3范围的binlog日志。

https://blog.csdn.net/woailyoo0000/article/details/88981380

相关阅读:
[WCF安全系列]从两种安全模式谈起
为自定义配置的编辑提供”智能感知”的支持
在Entity Framework中使用存储过程（二）：具有继承关系实体的存储过程如何定义？
[WCF安全系列]实例演示：TLS/SSL在WCF中的应用[HTTPS]
[WCF安全系列]谈谈WCF的客户端认证[Windows认证]
在Entity Framework中使用存储过程（三）：逻辑删除的实现与自增长列值返回
[转] Leaving patterns & practices
两个简单的扩展方法：TrimPrefix和TrimSuffix
Oracle 系统表
让IoC动态解析自定义配置（提供基于Unity的实现）

原文地址：https://www.cnblogs.com/softidea/p/12781094.html