一个简单的binlog恢复测试

日常的数据备份及恢复测试，是DBA工作重中之重的事情，所以要做好备份及测试，日常的备份常见有mysqldump+binlog备份、xtrabackup+binlog备份，无论那一种，几乎都少不了对binlog的备份，说明了binlog在数据恢复中的重要性，下面做个小测试，是工作中不少运维或者新人DBA容易犯的错。

创建一个测试表tb1：

<test>(root@localhost) [xuanzhi]> show create table tb1\G
*************************** . row ***************************
       Table: tb1
Create Table: CREATE TABLE `tb1` (
  `id` int() NOT NULL AUTO_INCREMENT,
  `name` char() CHARACTER SET latin1 DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8
 row in set (0.00 sec)

<test>(root@localhost) [xuanzhi]> 

往表里插入两条数据：

<test>(root@localhost) [xuanzhi]> insert into tb1 (name)  value ('aa'),('bb');
Query OK, 2 rows affected (0.01 sec)
Records: 2  Duplicates: 0  Warnings: 0

<test>(root@localhost) [xuanzhi]> show master logs;
+----------------------+-----------+
| Log_name             | File_size |
+----------------------+-----------+
| localhost-bin.000001 |       329 |
+----------------------+-----------+
1 row in set (0.00 sec)

<test>(root@localhost) [xuanzhi]> 

这个时候对数据备份，如果是xtrabackup备份的话，会在有xtrabackup_binlog_info文件中记录此时备份是到那个binlog文件和pos点的，如果是mysqldump备份，则需要带上--master-data=2这个参数，下面我们的数据量少，用mysqldump备份：

[root@localhost ~]# mysqldump -uroot -p123456  -R --events --triggers=true --master-data= --single-transaction xuanzhi > xuanzhi.sql
Warning: Using a password on the command line interface can be insecure.
[root@localhost ~]# grep -i "CHANGE MASTER" xuanzhi.sql
-- CHANGE MASTER TO MASTER_LOG_FILE='localhost-bin.000001', MASTER_LOG_POS=;
[root@localhost ~]# 

备份完后，继续模拟数据库有写入，而还是写在localhost-bin.000001

<test>(root@localhost) [xuanzhi]> insert into tb1 (name)  value ('cc'),('dd');
Query OK, 2 rows affected (0.00 sec)
Records: 2  Duplicates: 0  Warnings: 0

<test>(root@localhost) [xuanzhi]> show master logs;
+----------------------+-----------+
| Log_name             | File_size |
+----------------------+-----------+
| localhost-bin.000001 |       538 |
+----------------------+-----------+
1 row in set (0.00 sec)

<test>(root@localhost) [xuanzhi]> flush logs;
Query OK, 0 rows affected (0.01 sec)

<test>(root@localhost) [xuanzhi]> insert into tb1 (name)  value ('ee');
Query OK, 1 row affected (0.00 sec)

<test>(root@localhost) [xuanzhi]> show master logs;
+----------------------+-----------+
| Log_name             | File_size |
+----------------------+-----------+
| localhost-bin.000001 |       589 |
| localhost-bin.000002 |       321 |
+----------------------+-----------+
2 rows in set (0.00 sec)

<test>(root@localhost) [xuanzhi]> 

上面我们进行flush logs是为了模拟现在已经有多个binlog文件了，恢复时进行多个binlog一起恢复。

进行误操，把xunazhi库drop了：

<test>(root@localhost) [xuanzhi]> drop database xuanzhi;
Query OK, 1 row affected (0.02 sec)

<test>(root@localhost) [(none)]> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| test               |
+--------------------+
4 rows in set (0.00 sec)

<test>(root@localhost) [(none)]> 

创建数据xuanzhi，把备份导入：

<test>(root@localhost) [(none)]> create database xuanzhi;
Query OK, 1 row affected (0.00 sec)

[root@localhost ~]# mysql -uroot -p123456 xuanzhi <./xuanzhi.sql
Warning: Using a password on the command line interface can be insecure.
[root@localhost ~]# 

查看数据：

<test>(root@localhost) [(none)]> use xuanzhi
Database changed
<test>(root@localhost) [xuanzhi]> select * from tb1;
+----+------+
| id | name |
+----+------+
|  1 | aa   |
|  2 | bb   |
+----+------+
2 rows in set (0.00 sec)

<test>(root@localhost) [xuanzhi]> 

可以看到备份前的数据恢复了，我们现在要结合Binlog来恢复，但前提要找出误操作前的pos点，也就是drop database xuanzhi前的pos点：

[root@localhost ~]# mysqlbinlog -v --base64-output=DECODE-ROWS localhost-bin. |grep -C   -i "drop database"
### INSERT INTO `xuanzhi`.`tb1`
### SET
###   @=
###   @='ee'
# at
# :: server id   end_log_pos  CRC32 0x825a2f99    Xid =
COMMIT/*!*/;
# at
# :: server id   end_log_pos  CRC32 0x8c139cac    Query   thread_id=     exec_time=     error_code=
SET TIMESTAMP=/*!*/;
drop database xuanzhi
/*!*/;
DELIMITER ;
# End of log file
ROLLBACK /* added by mysqlbinlog */;
/*!50003 SET COMPLETION_TYPE=@OLD_COMPLETION_TYPE*/;
/*!50530 SET @@SESSION.PSEUDO_SLAVE_MODE=0*/;
[root@localhost ~]# mysql -uroot -p123456 xuanzhi <./xuanzhi.sql
Warning: Using a password on the command line interface can be insecure.
[root@localhost ~]# 

从上面可以看到，误操作前的pos点是321，那我们现在通过binlog来进行数据恢复：

[root@localhost mysql-5.6]# mysqlbinlog --start-position= --stop-position= localhost-bin. localhost-bin. |mysql -uroot -p123456 xuanzhi
Warning: Using a password on the command line interface can be insecure.
[root@localhost mysql-5.6]# 

--start-position是备份后记录下的pos点， --stop-position是误操前的pos点，如果批多个binlog文件，那么start-position是第一个binlog文件的pos点，stop-position是最后一个binlog的pos点，下面我们看下数据是否恢复回来了：

<test>(root@localhost) [xuanzhi]> select * from tb1;
+----+------+
| id | name |
+----+------+
|  1 | aa   |
|  2 | bb   |
|  3 | cc   |
|  4 | dd   |
|  5 | ee   |
+----+------+
5 rows in set (0.00 sec)

<test>(root@localhost) [xuanzhi]> 

这里要提的是进行恢复前，要把需要恢复的binlog备份好，或者移动拷贝一份到另一个目录，因为进行数据导入时也会继续写binlog。假如你没有误操作的情况下，就是想测试一下数据的恢复，很多人的操作是导入备份，再从备份里记录的binlog文件名和pos点进行binlog恢复，发现步骤都很完美，也没报错，恢复后就是只有备份时的数据，没有备份后的数据，下面测试一下给大家看：

<test>(root@localhost) [xuanzhi]> insert into tb1 (name)  value ('aa'),('bb');
Query OK, 2 rows affected (0.01 sec)
Records: 2  Duplicates: 0  Warnings: 0

<test>(root@localhost) [xuanzhi]> select * from tb1;
+----+------+
| id | name |
+----+------+
|  1 | aa   |
|  2 | bb   |
+----+------+
2 rows in set (0.00 sec)
<test>(root@localhost) [xuanzhi]> show master logs;
+----------------------+-----------+
| Log_name             | File_size |
+----------------------+-----------+
| localhost-bin.000001 |       329 |
+----------------------+-----------+
1 row in set (0.00 sec)

<test>(root@localhost) [xuanzhi]> 

进行备份操作：

[root@localhost ~]# mysqldump -uroot -p123456 -R --events --triggers=true --master-data= --single-transaction xuanzhi > xuanzhi.sql
Warning: Using a password on the command line interface can be insecure.
[root@localhost ~]# grep -i "change master" xuanzhi.sql
-- CHANGE MASTER TO MASTER_LOG_FILE='localhost-bin.000001', MASTER_LOG_POS=;
[root@localhost ~]# 

继续写localhost-bin.000001后进行flush logs生成新的binlog再继续写数据，这里只是想模拟localhost-bin.000001写满了切localhost-bin.000002，结合多个binlog一起恢复

<test>(root@localhost) [xuanzhi]> insert into tb1 (name)  value ('cc'),('dd');
Query OK,  rows affected (0.00 sec)
Records:   Duplicates:   Warnings: 

<test>(root@localhost) [xuanzhi]> flush logs;
Query OK,  rows affected (0.00 sec)

<test>(root@localhost) [xuanzhi]> insert into tb1 (name)  value ('dd');
Query OK,  row affected (0.01 sec)

<test>(root@localhost) [xuanzhi]> show master logs;
+----------------------+-----------+
| Log_name             | File_size |
+----------------------+-----------+
| localhost-bin. |        |
| localhost-bin. |        |
+----------------------+-----------+
 rows in set (0.00 sec)

<test>(root@localhost) [xuanzhi]> 

下面进行恢复测试，正常来说先把备份导入：

[root@localhost ~]# mysql -uroot -p123456 xuanzhi <./xuanzhi.sql
Warning: Using a password on the command line interface can be insecure.
[root@localhost ~]# 

查看数据，只有备份的那两条记录：

<test>(root@localhost) [xuanzhi]> select * from tb1;
+----+------+
| id | name |
+----+------+
|   | aa   |
|   | bb   |
+----+------+
 rows in set (0.00 sec)

<test>(root@localhost) [xuanzhi]> 

那现在通过localhost-bin.000001，localhost-bin.000002来恢复后面那3条数据，那么起始pos是那个呢，就是上面备份完后备份文件里的那个pos，我们进到binlog的存放路径：

可以看到备份后的数据是没有恢复回来的。为什么呢？因为导入备份的时候，又开始写binlog了，而你恢复时用的binlog也就是现在导入备份时正在写的binlog。大体过程是这样的：

1、导入备份后，备份的所有操作都写进最后一个binlog了，也就是上面的localhost-bin.000002

2、进行binlog恢复，从备份文件里的pos点开始，按理来说是可以恢复到最新数据的，但是上面导入了备份，导入时的所有操作都会记录到localhost-bin.000002

3、备份导入时会有DROP TABLE和CREATE TABLE的动作写进binlog里，所以最终得到的数据，还是备份时的数据。

总结：

        一、在恢复全备数据之前必须将该binlog文件移出，否则恢复过程中，会继续写入语句到binlog，最终导致增量恢复数据部分变得比较混乱

        二、做好数据文件及binlog的备份至关重要，但不是备份完就算了，要定期进行数据恢复测试或演练

        三、恢复时建议对外停止更新，即禁止更新数据库

作者：陆炫志

出处：xuanzhi的博客 http://www.cnblogs.com/xuanzhi201111

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