MEB: Taking Incremental Backup using last successful backup
- by Sagar Jauhari
Introduction
In MySQL Enterprise Backup v3.7.0 (MEB 3.7.0) a new option '–incremental-base' was introduced. Using
this option a user can take in incremental backup without specifying
the '–start-lsn' option. Description of this option can be found here. Instead of '–start-lsn' the user can provide the location of
the last full backup or incremental backup using the 'dir:'
prefix. MEB would extract the end LSN of this backup from the
mysql.backup_history table as well as the backup_variables.txt file
(for verification) to use it as the start LSN of the incremental
backup.
Because of popular demand, in MEB 3.7.1 the option '-incremental-base'
has been extended further. The idea is to allow the user to take an
incremental backup as easily as possible using the
'–incremental-base' option. With the new option MEB queries the
backup_history table for the last successful backup and uses its end
LSN as the start LSN for the new incremental backup. It should be
noted that the last successful backup is used irrespective of the
location of the backup.
Details
A new prefix 'history:' has been introduced for the –incremental-base
option and currently the only permissible value is the string
"last_backup". So using the new option an incremental backup can be
taken with the following command:
$ mysqlbackup --incremental --incremental-backup-dir=/media/mysqlbackup-repo/ --incremental-base=history:last_backup backup
When MEB attempts to extract the end LSN of the last successful backup
from the mysql.backup_history table, it also scans the corresponding
backup destination for the old backup and tries to read the meta files
at this backup destination. If a valid backup still exists at the
backup destination and the meta files can be read, MEB compares the
end LSN found in the mysql.backup_history table with the end LSN found
in the backup meta files of the old backup. Assuming that the host
MySQL server is alive and mysql.backup_history can be accessed by MEB,
the behaviour of MEB with respect to verification of the old end LSN
can be summarized as follows:
If 'BD' is the backup destination of the last successful backup in
mysql.backup_history table and 'BHT' is the mysql.backup_history table
if can_read_files_at_BD:
if end_lsn_found_at_BD == end_lsn_of_last_backup_in_BHT:
continue_with_backup()
else
return_with_error()
else
continue_with_backup()
Advantages
Apart from ease of usability an important advantage of this option is
that the user can do repeated incremental backups without changing the
command line. This is possible using the '–with-timestamp' option along
with this new option. For example, the following command
$ mysqlbackup --with-timestamp --incremental --incremental-backup-dir=/media/mysqlbackup-repo/ --incremental-base=history:last_backup backup
can be used to perform successive
incremental backups in the directory /media/mysqlbackup-repo .
Limitations
The option '--incremental-base=history:last_backup'
should not be used when the user takes different kinds
of concurrent backups on the same MySQL server (say different
partial backups at multiple locations).
should not be used after any temporary or experimental
backups performed on the server (which where successful!).
needs to be used with precaution since any intermediate
successful backup without the –no-connection will be used as the
base backup for the next incremental backup.
will give an error in case a valid backup exists at the
location of the last successful backup and whose end LSN is
different from that of the last successful backup found in the
backup_history table.
Date: 2012-06-19
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