Create an incremental backup¶
xtrabackup supports incremental backups, which means that they can copy only all the data that has changed since the last backup.
Note
Incremental backups on the MyRocks storage engine do not determine if an earlier full backup or incremental backup contains the same files. Percona XtraBackup copies all the MyRocks files each time it takes a backup.
You can perform many incremental backups between each full backup, so you can set up a backup process such as a full backup once a week and an incremental backup every day, or full backups every day and incremental backups every hour.
Incremental backups work because each InnoDB page contains a log sequence number, or LSN. The LSN is the system version number for the entire database. Each page’s LSN shows how recently it was changed.
An incremental backup copies each page which LSN is newer than the previous incremental or full backup’s LSN. An algorithm finds the pages that match the criteria. The algorithm reads the data pages and checks the page LSN.
Use the changed page tracking algorithm¶
Percona XtraBackup 8.0.30 removes the algorithm that used the changed page tracking feature in Percona Server for MySQL. Percona Server for MySQL 8.0.27 deprecated the changed page tracking feature.
With PXB 8.0.27 or earlier, another algorithm enabled the Percona Server for MySQL changed page tracking feature. The algorithm generates a bitmap file. The xtrabackup binary uses that bitmap file to read only those pages needed for the incremental backup. This method potentially saves resources. The backup enables the algorithm by default if the xtrabackup binary discovers the bitmap file. You can override the algorithm with --incremental-force-scan which forces a read of all pages even if the bitmap file is available.
Create an incremental backup¶
To make an incremental backup, begin with a full backup as usual. The
xtrabackup binary writes a file called xtrabackup_checkpoints into
the backup’s target directory. This file contains a line showing the
to_lsn, which is the database’s LSN at the end of the backup.
Create the full backup with a following command:
$ xtrabackup --backup --target-dir=/data/backups/base
If you look at the xtrabackup_checkpoints file, you should see similar
content depending on your LSN nuber:
Expected output
backup_type = full-backuped
from_lsn = 0
to_lsn = 1626007
last_lsn = 1626007
compact = 0
recover_binlog_info = 1
Now that you have a full backup, you can make an incremental backup based on it. Use the following command:
$ xtrabackup --backup --target-dir=/data/backups/inc1 \
--incremental-basedir=/data/backups/base
The /data/backups/inc1/ directory should now contain delta files, such
as ibdata1.delta and test/table1.ibd.delta. These represent the
changes since the LSN 1626007. If you examine the
xtrabackup_checkpoints file in this directory, you should see similar
content to the following:
Expected output
backup_type = incremental
from_lsn = 1626007
to_lsn = 4124244
last_lsn = 4124244
compact = 0
recover_binlog_info = 1
from_lsn is the starting LSN of the backup and for incremental it has to be the same as to_lsn (if it is the last checkpoint) of the previous/base backup.
It’s now possible to use this directory as the base for yet another incremental backup:
$ xtrabackup --backup --target-dir=/data/backups/inc2 \
--incremental-basedir=/data/backups/inc1
This folder also contains the xtrabackup_checkpoints:
Expected output
backup_type = incremental
from_lsn = 4124244
to_lsn = 6938371
last_lsn = 7110572
compact = 0
recover_binlog_info = 1
Note
In this case you can see that there is a difference between the to_lsn (last checkpoint LSN) and last_lsn (last copied LSN), this means that there was some traffic on the server during the backup process.
The next step is to prepare the backup in order to restore it.
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