本章是《Docker下MySQL主从三部曲》的终篇,前面的章节我们能够制作镜像来搭建主从同步环境,本章我们来观察binlog参数MASTER_LOG_POS;
原文地址:https://blog.csdn.net/boling_cavalry/article/details/79782008
在设置从库同步的时候一般会使用以下SQL:
CHANGE MASTER TO MASTER_HOST='172.17.0.2', \
MASTER_USER='rep', \
MASTER_PASSWORD='888888', \
MASTER_LOG_FILE='mysql-bin.000001', \
MASTER_LOG_POS=745;
今天我们的实战和上面的MASTER_LOG_FILE、MASTER_LOG_POS两个参数有关;
上一章制作从库镜像时并未设置MASTER_LOG_FILE和MASTER_LOG_POS,但是之前的文章《Docker下手工配置MySQL主从》中却又设置了这两个参数,那么在设置主从同步的时候,究竟该不该设置这两个参数呢?
前面两章实战我们已经验证过了,不设置这两个参数并不会影响主从同步,所以可以不设置,那么就剩下一个问题:设置了MASTER_LOG_FILE和MASTER_LOG_POS有什么影响?
在master容器的MySQL命令行执行show master status:
mysql> show master status;
+------------------+----------+--------------+------------------+-------------------+
| File | Position | Binlog_Do_DB | Binlog_Ignore_DB | Executed_Gtid_Set |
+------------------+----------+--------------+------------------+-------------------+
| mysql-bin.000003 | 154 | | | |
+------------------+----------+--------------+------------------+-------------------+
1 row in set (0.00 sec)
如上所示,bin log文件名为mysql-bin.000003,在/etc/mysql/mysql.conf.d/mysqld.cnf中定义的文件路径如下:
[mysqld]
pid-file = /var/run/mysqld/mysqld.pid
socket = /var/run/mysqld/mysqld.sock
datadir = /var/lib/mysql
#log-error = /var/log/mysql/error.log
# By default we only accept connections from localhost
#bind-address = 127.0.0.1
# Disabling symbolic-links is recommended to prevent assorted security risks
symbolic-links=0
根据以上配置信息,我们在/var/lib/mysql目录下找到了bin log文件mysql-bin.000003,如下:
root@ae594a28192d:/var/lib/mysql# pwd
/var/lib/mysql
root@ae594a28192d:/var/lib/mysql# ls -al
total 191468
drwxr-xr-x 5 mysql mysql 4096 Apr 2 01:12 .
drwxr-xr-x 19 root root 4096 Mar 14 07:47 ..
-rw-r----- 1 mysql mysql 56 Apr 2 01:12 auto.cnf
-rw------- 1 mysql mysql 1675 Apr 2 01:12 ca-key.pem
-rw-r--r-- 1 mysql mysql 1107 Apr 2 01:12 ca.pem
-rw-r--r-- 1 mysql mysql 1107 Apr 2 01:12 client-cert.pem
-rw------- 1 mysql mysql 1675 Apr 2 01:12 client-key.pem
-rw-r----- 1 mysql mysql 1353 Apr 2 01:12 ib_buffer_pool
-rw-r----- 1 mysql mysql 50331648 Apr 2 01:13 ib_logfile0
-rw-r----- 1 mysql mysql 50331648 Apr 2 01:12 ib_logfile1
-rw-r----- 1 mysql mysql 79691776 Apr 2 01:13 ibdata1
-rw-r----- 1 mysql mysql 12582912 Apr 2 01:13 ibtmp1
drwxr-x--- 2 mysql mysql 4096 Apr 2 01:12 mysql
-rw-r----- 1 mysql mysql 177 Apr 2 01:12 mysql-bin.000001
-rw-r----- 1 mysql mysql 3039401 Apr 2 01:12 mysql-bin.000002
-rw-r----- 1 mysql mysql 154 Apr 2 01:12 mysql-bin.000003
-rw-r----- 1 mysql mysql 57 Apr 2 01:12 mysql-bin.index
drwxr-x--- 2 mysql mysql 4096 Apr 2 01:12 performance_schema
-rw------- 1 mysql mysql 1675 Apr 2 01:12 private_key.pem
-rw-r--r-- 1 mysql mysql 451 Apr 2 01:12 public_key.pem
-rw-r--r-- 1 mysql mysql 1107 Apr 2 01:12 server-cert.pem
-rw------- 1 mysql mysql 1675 Apr 2 01:12 server-key.pem
drwxr-x--- 2 mysql mysql 12288 Apr 2 01:12 sys
root@ae594a28192d:/var/lib/mysql#
设置同步时,若MASTER_LOG_FILE有误会怎么样?来试试: 1. 进入MySQL第一从库容器,再进入MySQL命令行; 2. 执行stop slave;停止同步; 3. 执行以下SQL重新设置同步参数,其中MASTER_LOG_FILE已被改成一个不存在的文件名“mysql-bin.999999”:
CHANGE MASTER TO MASTER_HOST='masterhost', \
MASTER_USER='rep', \
MASTER_PASSWORD='888888', \
MASTER_LOG_FILE='mysql-bin.999999', \
MASTER_LOG_POS=154;
4. 执行start slave;开始同步; 5. 执行show slave status\G查看同步状态,发现”Last_IO_Error”字段的值如下,提示找不到binlog文件:
Last_IO_Error: Got fatal error 1236 from master when reading data from binary log: 'Could not find first log file name in binary log index file'
6. 此时在主库的MySQL命令行执行SQL新增一条记录:insert into test_table(name) values (‘tom’);; 7. 回到第一从库查看test_table表,发现数据没有同步过来; 8. 去第二从库查看test_table表,数据同步正常:
小结:MASTER_LOG_FILE的值与主库同步的binlog名不一致会导致同步失败;
接下来看看MASTER_LOG_POS参数的作用,我们把之前的容器全部清除再重新来验证: 1. 在docker-compose.yml文件所在目录下执行docker-compose down,将一主二从容器全部删除; 2. 在docker-compose.yml文件所在目录下执行docker-compose up -d,像《Docker下MySQL主从三部曲之一:极速体验》一样重新创建一主二从; 3. 进入第一从库,在MySQL命令行执行stop slave;,将主从同步停止; 4. 在MySQL主库的命令行执行以下命令,创建数据库、表、新增记录:
create database test001;
use test001;
CREATE TABLE `test_table` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(100) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
insert into test_table(name) values ('jerry');
5. 执行show master status;,查出binlog文件名为mysql-bin.000003; 6. 推出MySQL命令行,执行mysqlbinlog /var/lib/mysql/mysql-bin.000003 > ~/mysql-bin.000003.txt将binlog文件转成可读的文本文件; 7. 打开文件~/mysql-bin.000003.txt,看到如下内容:
SET @@session.collation_database=DEFAULT/*!*/;
create database test001
/*!*/;
# at 322
#180402 12:37:52 server id 1 end_log_pos 387 CRC32 0xa2118048 Anonymous_GTID last_committed=1 sequence_number=2 rbr_only=no
SET @@SESSION.GTID_NEXT= 'ANONYMOUS'/*!*/;
# at 387
#180402 12:37:52 server id 1 end_log_pos 628 CRC32 0x4eb6b868 Query thread_id=4 exec_time=1 error_code=0
use `test001`/*!*/;
SET TIMESTAMP=1522672672/*!*/;
CREATE TABLE `test_table` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(100) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8
/*!*/;
# at 628
#180402 12:37:57 server id 1 end_log_pos 693 CRC32 0x37e9fbe9 Anonymous_GTID last_committed=2 sequence_number=3 rbr_only=ye
s
/*!50718 SET TRANSACTION ISOLATION LEVEL READ COMMITTED*//*!*/;
SET @@SESSION.GTID_NEXT= 'ANONYMOUS'/*!*/;
# at 693
#180402 12:37:57 server id 1 end_log_pos 768 CRC32 0x0a4b387b Query thread_id=4 exec_time=0 error_code=0
SET TIMESTAMP=1522672677/*!*/;
BEGIN
/*!*/;
# at 768
#180402 12:37:57 server id 1 end_log_pos 827 CRC32 0x45fec29f Table_map: `test001`.`test_table` mapped to number 108
# at 827
#180402 12:37:57 server id 1 end_log_pos 874 CRC32 0x620435ef Write_rows: table id 108 flags: STMT_END_F
BINLOG '
JSTCWhMBAAAAOwAAADsDAAAAAGwAAAAAAAEAB3Rlc3QwMDEACnRlc3RfdGFibGUAAgMPAiwBAp/C
/kU=
JSTCWh4BAAAALwAAAGoDAAAAAGwAAAAAAAEAAgAC//wBAAAABQBqZXJyee81BGI=
'/*!*/;
# at 874
#180402 12:37:57 server id 1 end_log_pos 905 CRC32 0x6128e936 Xid = 29
COMMIT/*!*/;
SET @@SESSION.GTID_NEXT= 'AUTOMATIC' /* added by mysqlbinlog */ /*!*/;
DELIMITER ;
# End of log file
从上述内容可以看到,每次写入操作之后都会有个# at xxx这样的标记,这就是MASTER_LOG_POS对应的数字; 8. 将上面的几个关键点整理成下面的表格:
at值 | at前面的操作 |
---|---|
154 | 此位置之后会执行创建数据库的操作 |
322 | 创建数据库 |
628 | 创建表 |
874 | 向表中新增一条记录 |
接下来我们修改MASTER_LOG_POS参数试试: 1. 进入第一从库容器的MySQL命令行; 2. 执行下面的SQL,令MASTER_LOG_POS等于628,也就是不包含创建数据库和创建表的binlog内容:
CHANGE MASTER TO MASTER_HOST='masterhost', \
MASTER_USER='rep', \
MASTER_PASSWORD='888888', \
MASTER_LOG_FILE='mysql-bin.000003', \
MASTER_LOG_POS=628;
3. 进入第一从库,在MySQL命令行执行start slave;,将主从同步启动; 4. 执行show slave status\G查看同步状态,看到Last_SQL_Error字段的内容如下:
Last_SQL_Error: Error executing row event: 'Table 'test001.test_table' doesn't exist'
如上所示,MASTER_LOG_POS参数指定的AT数字之后的binlog才会被执行,之前的是不执行的; 5. MySQL命令行执行stop slave;,将主从同步停止; 6. 执行下面的SQL,令MASTER_LOG_POS等于154,也就是创建数据库之前的位置:
CHANGE MASTER TO MASTER_HOST='masterhost', \
MASTER_USER='rep', \
MASTER_PASSWORD='888888', \
MASTER_LOG_FILE='mysql-bin.000003', \
MASTER_LOG_POS=154;
7. MySQL命令行执行start slave;,将主从同步启动; 8. 查看同步状态,已经正常,再去查数据库数据,也已经同步过来了:
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| performance_schema |
| sys |
| test001 |
+--------------------+
5 rows in set (0.00 sec)
mysql> use test001;
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
mysql> select * from test_table;
+----+-------+
| id | name |
+----+-------+
| 1 | jerry |
+----+-------+
1 row in set (0.00 sec)
到这里,对MASTER_LOG_POS参数的实战就结束了,该参数与binlog中的“at”标记对应,如果设置不当,会导致前面的SQL操作丢失,在遇到有依赖的同步操作时就会有问题;
至此,Docker下MySQL主从三部曲就全部结束了,希望能够给您的Docker实战带来一些参考,助您做出更实用的镜像