what's meaning of last_lsn?

When i use innobackup to backup my database.It will write database’s checkpoint to file named xtrabackup_checkpoint.In the file ,i don’t know the meaning of last_lsn .
What is difference of last_lsn and to_lsn? Where can i use it?
Please help me!


This pages has related information:

http://www.mysqlperformanceblog.com/2012/02/17/the-relations hip-between-innodb-log-checkpointing-and-dirty-buffer-pool-p ages/
http://www.percona.com/files/percona-live/justin-innodb-inte rnals.pdf

In short, LSN (log sequence number) are offsets from the redo logs - so simply put, last_lsn is the offset where the last transaction written to the redo logs was written. to_lsn on the other hand, should be paired to a from_lsn, mostly useful on incremental backups, etc.