手动创建binary log files和手动编辑binary log index file会有什么影响

基本环境：官方社区版MySQL 5.7.19

一、了解Binary Log结构

1.1、High-Level Binary Log Structure and Contents

• Binlog包括binary log files和index file
• 每个binary log文件的前4字节是Magic Number，紧接着是一组描述数据修改的Events
　　• The magic number bytes are 0xfe 0x62 0x69 0x6e = 0xfe 'b''i''n'
　　• 每个Event包括header bytes和data bytes
　　　　header bytes：Event类型，什么时候，由哪个server生成等信息
　　　　data bytes：特定的数据修改
　　• 第一个Event是Description Event，描述文件的格式版本
　　• 其他Events按照binlog_version(1、3、4)进行记录
　　• 最后一个Event是Log-rotation Event，指定下一个binary log的文件名称
• index文件里面是当前binary log的一个列表

1.2、Binary Log结构示意图

# Binary Log结构示意图(binlog_version=)
               |<----------------------------------Events---------------------------------->|
               |<---------Fisrt Event--------->|<------Mid Events----->|<---Final Event---->|
+--------------+-------------------------------+--------+-----+--------+--------------------+
| Magic Number | FDE(Format Description Event) | Event1 | ... | EventN | Log-rotation Event |
+--------------+-------------------------------+--------+-----+--------+--------------------+
               |<-event header->|<-event data->|

上图是binlog_version=4(MySQL 5.0 and up)的示意图

二、index file添加一行不存在的binary log记录

查看当前binary log

# 查看当前binary log
[root@ZST1 logs]# ll
total
-rw-r-----.  mysql mysql  Jan  : mysql-bin.
-rw-r-----.  mysql mysql  Jan  : mysql-bin.
-rw-r-----.  mysql mysql  Jan  : mysql-bin.
-rw-r-----.  mysql mysql  Jan  : mysql-bin.
-rw-r-----.  mysql mysql  Jan  : mysql-bin.index
[root@ZST1 logs]# cat mysql-bin.index
/data/mysql/mysql3308/logs/mysql-bin.
/data/mysql/mysql3308/logs/mysql-bin.
/data/mysql/mysql3308/logs/mysql-bin.
/data/mysql/mysql3308/logs/mysql-bin.
[root@ZST1 logs]# 

mysql-bin.index 添加一行已经删除的记录/data/mysql/mysql3308/logs/mysql-bin.000001，重新启动数据库服务

# 查看error log
[root@ZST1 ~]# more /data/mysql/mysql3308/data/error.log
...
--12T03::.467474Z  [Note] InnoDB: Loading buffer pool(s) from /data/mysql/mysql3308/data/ib_buffer_pool
mysqld: File '/data/mysql/mysql3308/logs/mysql-bin.000001' not found (Errcode:  - No such file or directory)
--12T03::.546276Z  [ERROR] Failed to open log (file '/data/mysql/mysql3308/logs/mysql-bin.000001', errno )
--12T03::.546294Z  [ERROR] Could not open log file
--12T03::.563485Z  [Warning] Failed to set up SSL because of the following SSL library error: SSL context is not usable without certificate and private key
--12T03::.563528Z  [Note] Server hostname (bind-address): '*'; port:
数据库服务最终启动起来

mysql-bin.index 添加一行未来的记录/data/mysql/mysql3308/logs/mysql-bin.000017，重新启动数据库服务

# 查看error log
[root@ZST1 ~]# more /data/mysql/mysql3308/data/error.log
...
--12T03::.921370Z  [Note] InnoDB: Loading buffer pool(s) from /data/mysql/mysql3308/data/ib_buffer_pool
mysqld: File '/data/mysql/mysql3308/logs/mysql-bin.000017' not found (Errcode:  - No such file or directory)
--12T03::.017490Z  [ERROR] Failed to open log (file '/data/mysql/mysql3308/logs/mysql-bin.000017', errno )
--12T03::.017509Z  [ERROR] Could not open log file
--12T03::.017532Z  [ERROR] Can not init tc log
--12T03::.017545Z  [ERROR] Aborting
数据库服务最终退出

启动过程会读取index file中的第一条和最后一条记录，然后检查对应的文件是否存在。如果第一条不存在，error log中会有报错，但服务正常启动；如果最后一条不存在，error log中会有报错，服务退出。即使你打乱index file中列表顺序，或者写入其他信息，它始终只验证index file的第一条和最后一条~

三、手动创建一个binary log，但不添加到index file

如果touch_seq < max(exists_seq)，正常启动，最新的new_seq=max(exists_seq)+1
如果max(exists_seq) < touch_seq < pow(2,31)-1，正常启动，最新的new_seq=touch_seq+1，当new_seq > pow(2,31)-1001 时会往error log中写入警告
如果touch_seq = pow(2,31)-1，mysqld退出
如果touch_seq > pow(2,31)-1，正常启动，会往error log中写入警告

3.1、MySQL binlog后面的编号最大是多大

最大编号参考文章：MySQL binlog后面的编号最大是多大

原文结论：
1、MySQL binlog的最大sequence是：pow(2,31)-1 = 2147483647
2、当 pow(2,31)-1001 < sequence < pow(2,31)-1 会往error log中写入警告
3、binlog的sequence达到最大值(2147483647)时，不管有没有mysql-bin.000001类似这样的文件，mysqld都是退出
4、在MySQL产生binlog时会读取当前日件文目录下的log-bin的base name获取下一个日志文件的后面的Seq。所以日志目录下文件太多，会影响MySQL的启动及日志切换。这里也有一个大的隐患，运行中给放一个较大的日志文件，在下次日志文件切换时有可能很快就接近于最大值，造成mysqld crash退出
5、一定要监控error log的输出，并足够重视

查看源码(5.7.19)

# 源码信息 sql/binlog.cc
#define MAX_LOG_UNIQUE_FN_EXT 0x7FFFFFFF
#define LOG_WARN_UNIQUE_FN_EXT_LEFT 1000

  /* check if reached the maximum possible extension number */
  if (max_found == MAX_LOG_UNIQUE_FN_EXT)
  {
    sql_print_error("Log filename extension number exhausted: %06lu. \
Please fix this by archiving old logs and \
updating the index files.", max_found);
    error= ;
    goto end;
  }

  /* print warning if reaching the end of available extensions. */
  if ((next > (MAX_LOG_UNIQUE_FN_EXT - LOG_WARN_UNIQUE_FN_EXT_LEFT)))
    sql_print_warning("Next log extension: %lu. \
Remaining log filename extensions: %lu. \
Please consider archiving some logs.", next, (MAX_LOG_UNIQUE_FN_EXT - next));

mysql> select conv('7FFFFFFF',,);
+------------------------+
| conv('7FFFFFFF',,) |
+------------------------+
|              |
+------------------------+

源码逻辑正是上面的结论1、2、3。如果我们的binlog的sequence疯涨到2147483647，那很不幸mysqld会退出。。。但如果我们在正常情况下，touch一个大于2147483647的binary log的文件会出现什么情况呢？

3.2、MySQL binlog后面的编号最大到底是多大

首先我们从2147483648开始

# reset master
mydba@192.168.85.132, [replcrash]> reset master;
Query OK,  rows affected (0.01 sec)
# 查看binary log
mydba@192.168.85.132, [replcrash]> show binary logs;
+------------------+-----------+
| Log_name         | File_size |
+------------------+-----------+
| mysql-bin. |        |
+------------------+-----------+
row in set (0.00 sec)
# touch ^
[root@ZST1 logs]# touch mysql-bin.
[root@ZST1 logs]# chown -R mysql:mysql *
# flush执行5次
mydba@192.168.85.132, [replcrash]> flush binary logs;
Query OK,  rows affected (0.01 sec)
# 查看binary log
mydba@192.168.85.132, [replcrash]> show binary logs;
+----------------------+-----------+
| Log_name             | File_size |
+----------------------+-----------+
| mysql-bin.     |        |
| mysql-bin. |        |
| mysql-bin. |        |
| mysql-bin. |        |
| mysql-bin. |        |
| mysql-bin. |        |
+----------------------+-----------+
rows in set (0.00 sec)
# 查看error log
[root@ZST1 data]# cat error.log
--08T09::.235149Z  [Warning] Next log extension: . Remaining log filename extensions: . Please consider archiving some logs.
--08T09::.868883Z  [Warning] Next log extension: . Remaining log filename extensions: . Please consider archiving some logs.
--08T09::.670811Z  [Warning] Next log extension: . Remaining log filename extensions: . Please consider archiving some logs.
--08T09::.401541Z  [Warning] Next log extension: . Remaining log filename extensions: . Please consider archiving some logs.
--08T09::.075702Z  [Warning] Next log extension: . Remaining log filename extensions: . Please consider archiving some logs.
[root@ZST1 logs]# 

# 再次reset master
mydba@192.168.85.132, [replcrash]> reset master;
Query OK,  rows affected (0.02 sec)
# 查看binary log
mydba@192.168.85.132, [replcrash]> show binary logs;
+----------------------+-----------+
| Log_name             | File_size |
+----------------------+-----------+
| mysql-bin. |        |
+----------------------+-----------+
row in set (0.00 sec)

可以看到，执行flush binary logs后，sequence一直往后+1(next)。error log中会有警告日志，next > (MAX_LOG_UNIQUE_FN_EXT - LOG_WARN_UNIQUE_FN_EXT_LEFT)恒成立；Remaining log filename extensions后面的数值看着有点怪异~
第二次reset后的sequence从2147483649开始，并不是从000001开始，不知道什么原因。
我们继续加大sequence，直到接近9223372036854775808

# touch ^-
[root@ZST1 logs]# touch mysql-bin.
[root@ZST1 logs]# chown -R mysql:mysql *
# flush执行5次
mydba@192.168.85.132, [replcrash]> flush binary logs;
Query OK,  rows affected (0.01 sec)
# 查看binary log
mydba@192.168.85.132, [replcrash]> show binary logs;
+-------------------------------+-----------+
| Log_name                      | File_size |
+-------------------------------+-----------+
| mysql-bin.              |        |
| mysql-bin. |        |
| mysql-bin. |        |
| mysql-bin. |        |
| mysql-bin. |        |
| mysql-bin. |        |
+-------------------------------+-----------+
rows in set (0.00 sec)
# 查看error log
[root@ZST1 data]# cat error.log
--08T09::.879612Z  [Warning] Next log extension: . Remaining log filename extensions: . Please consider archiving some logs.
--08T09::.082530Z  [Warning] Next log extension: . Remaining log filename extensions: . Please consider archiving some logs.
--08T09::.934636Z  [Warning] Next log extension: . Remaining log filename extensions: . Please consider archiving some logs.
--08T09::.544604Z  [Warning] Next log extension: . Remaining log filename extensions: . Please consider archiving some logs.
--08T09::.134664Z  [Warning] Next log extension: . Remaining log filename extensions: . Please consider archiving some logs.
[root@ZST1 logs]# 

当sequence达到9223372036854775808后，再flush binary log，看不出产生新binary log~

[root@ZST1 logs]# mysqlbinlog -v --base64-output=decode-rows mysql-bin.
/*!50530 SET @@SESSION.PSEUDO_SLAVE_MODE=1*/;
/*!50003 SET @OLD_COMPLETION_TYPE=@@COMPLETION_TYPE,COMPLETION_TYPE=0*/;
DELIMITER /*!*/;
# at
# :: server id   end_log_pos  CRC32 0x798b200f    Start: binlog v , server v 5.7.-log created  ::
# Warning: this binlog is either in use or was not closed properly.
# at
# :: server id   end_log_pos  CRC32 0xf3252c32    Previous-GTIDs
# [empty]
# at
# :: server id   end_log_pos  CRC32 0x6054f256    Rotate to mysql-bin.  pos:
SET @@SESSION.GTID_NEXT= 'AUTOMATIC' /* added by mysqlbinlog */ /*!*/;
DELIMITER ;
# End of log file
/*!50003 SET COMPLETION_TYPE=@OLD_COMPLETION_TYPE*/;
/*!50530 SET @@SESSION.PSEUDO_SLAVE_MODE=0*/;
[root@ZST1 logs]# 

解析binlog可以在末尾看到Rotate to mysql-bin.9223372036854775808  pos: 4
也就是说再怎么切，也只能切到9223372036854775808，这个文件感觉有点不太正常，不受max_binlog_size限制，解析出的日志莫名不完整~
恢复原始：手工删除 mysql-bin.2147483647 这类大文件，然后修改 mysql-bin.index；或者直接清空logs文件夹，再重新启动数据库服务

四、参考文档

MySQL binlog后面的编号最大是多大：http://wubx.net/mysql-binlog-max-sequence/
High-Level Binary Log Structure and Contents：https://dev.mysql.com/doc/internals/en/binary-log-structure-and-contents.html
Binary Log Versions：https://dev.mysql.com/doc/internals/en/binary-log-versions.html
Event Structure：https://dev.mysql.com/doc/internals/en/event-structure.html