5.9.2.2. Using Backups for Recovery
Now, suppose that we have a catastrophic crash on Wednesday at
8 a.m. that requires recovery from backups. To recover, first
we restore the last full backup we have (the one from Sunday 1
p.m.). The full backup file is just a set of SQL statements,
so restoring it is very easy:
shell> mysql < backup_sunday_1_PM.sql
At this point, the data is restored to its state as of Sunday
1 p.m.. To restore the changes made since then, we must use
the incremental backups; that is, the
gbichot2-bin.000007 and
gbichot2-bin.000008 binary log files.
Fetch the files if necessary from where they were backed up,
and then process their contents like this:
shell> mysqlbinlog gbichot2-bin.000007 gbichot2-bin.000008 | mysql
We now have recovered the data to its state as of Tuesday 1
p.m., but still are missing the changes from that date to the
date of the crash. To not lose them, we would have needed to
have the MySQL server store its MySQL binary logs into a safe
location (RAID disks, SAN, ...) different from the place where
it stores its data files, so that these logs were not on the
destroyed disk. (That is, we can start the server with a
--log-bin option that specifies a location on
a different physical device from the one on which the data
directory resides. That way, the logs are safe even if the
device containing the directory is lost.) If we had done this,
we would have the gbichot2-bin.000009
file at hand, and we could apply it using
mysqlbinlog and mysql to
restore the most recent data changes with no loss up to the
moment of the crash.
