Last checkpoint at ：redo log记录的更新已经刷新到磁盘上的检查点LSN，该LSN之前的redo log上记录的更新已全部刷新到磁盘上，可以被覆盖重复使用。
7、查看ib_logfile里的内容的方法
[root@mydb ~]# strings /var/lib/mysql/ib_logfile0
相关参数
innodb_log_file_size ：每个redo log文件大小
innodb_log_files_in_group ：redo log日志组成员个数
innodb_log_group_home_dir ：redo log存放目录
innodb_page_size ：InnoDB表空间的页面大小，默认16K
innodb_flush_log_at_timeout ：日志刷新频率，单位秒
Write and flush the logs every N seconds. innodb_flush_log_at_timeout allows the timeout period between flushes to be increased in order to reduce flushing and avoid impacting performance of binary log group commit. The default setting for innodb_flush_log_at_timeout is once per second.
The redo log is a disk-based data structure used during crash recovery to correct data written by incomplete transactions.
重做日志是在崩溃恢复期间用于纠正由未完成事务写入的数据的基于磁盘的数据结构。
By default, the redo log is physically represented on disk as a set of files, named ib_logfile0 and ib_logfile1. MySQL writes to the redo log files in a circular fashion.
A disk-based data structure used during crash recovery, to correct data written by incomplete transactions. During normal operation, it encodes requests to change InnoDB table data, which result from SQL statements or low-level API calls through NoSQL interfaces. Modifications that did not finish updating the data files before an unexpected shutdown are replayed automatically.
The redo log is physically represented as a set of files, typically named ib_logfile0 and ib_logfile1. The data in the redo log is encoded in terms of records affected; this data is collectively referred to as redo. The passage of data through the redo logs is represented by the ever-increasing LSN value. The original 4GB limit on maximum size for the redo log is raised to 512GB in MySQL 5.6.3.
