Incremental Backups with innobackupex

As not all information changes between each backup, the incremental backup strategy uses this to reduce the storage needs and the duration of making a backup.

This can be done because each InnoDB page has a log sequence number, LSN, which acts as a version number of the entire database. Every time the database is modified, this number gets incremented.

An incremental backup copies all pages since a specific LSN.

Once the pages have been put together in their respective order, applying the logs will recreate the process that affected the database, yielding the data at the moment of the most recently created backup.

Creating an Incremental Backups with innobackupex

First, you need to make a full backup as the BASE for subsequent incremental backups:

$ innobackupex /data/backups

This will create a timestamped directory in /data/backups. Assuming that the backup is done last day of the month, BASEDIR would be /data/backups/2013-03-31_23-01-18, for example.

Note

You can use the innobackupex --no-timestamp option to override this behavior and the backup will be created in the given directory.

If you check at the xtrabackup-checkpoints file in BASE-DIR, you should see something like:

backup_type = full-backuped
from_lsn = 0
to_lsn = 1291135

To create an incremental backup the next day, use the --incremental option and provide the BASEDIR:

$ innobackupex --incremental /data/backups --incremental-basedir=BASEDIR

and another timestamped directory will be created in /data/backups, in this example, /data/backups/2013-04-01_23-01-18 containing the incremental backup. We will call this INCREMENTAL-DIR-1.

If you check at the xtrabackup-checkpoints file in INCREMENTAL-DIR-1, you should see something like:

backup_type = incremental
from_lsn = 1291135
to_lsn = 1352113

Creating another incremental backup the next day will be analogous, but this time the previous incremental one will be base:

$ innobackupex --incremental /data/backups --incremental-basedir=INCREMENTAL-DIR-1

yielding (in this example) /data/backups/2013-04-02_23-01-18. We will use INCREMENTAL-DIR-2 instead for simplicity.

At this point, the xtrabackup-checkpoints file in INCREMENTAL-DIR-2 should contain something like:

backup_type = incremental
from_lsn = 1352113
to_lsn = 1358967

As it was said before, an incremental backup only copy pages with a LSN greater than a specific value. Providing the LSN would have produced directories with the same data inside:

innobackupex --incremental /data/backups --incremental-lsn=1291135
innobackupex --incremental /data/backups --incremental-lsn=1358967

This is a very useful way of doing an incremental backup, since not always the base or the last incremental will be available in the system.

Warning

This procedure only affects XtraDB or InnoDB-based tables. Other tables with a different storage engine, e.g. MyISAM, will be copied entirely each time an incremental backup is performed.

Preparing an Incremental Backup with innobackupex

Preparing incremental backups is a bit different than full ones. This is, perhaps, the stage where more attention is needed:

  • First, only the committed transactions must be replayed on each backup. This will merge the base full backup with the incremental ones.
  • Then, the uncommitted transaction must be rolled back in order to have a ready-to-use backup.

If you replay the committed transactions and rollback the uncommitted ones on the base backup, you will not be able to add the incremental ones. If you do this on an incremental one, you won’t be able to add data from that moment and the remaining increments.

Having this in mind, the procedure is very straight-forward using the --redo-only option, starting with the base backup:

innobackupex --apply-log --redo-only BASE-DIR

You should see an output similar to:

120103 22:00:12 InnoDB: Shutdown completed; log sequence number 1291135
120103 22:00:12 innobackupex: completed OK!

Then, the first incremental backup can be applied to the base backup, by issuing:

innobackupex --apply-log --redo-only BASE-DIR --incremental-dir=INCREMENTAL-DIR-1

You should see an output similar to the previous one but with corresponding LSN:

120103 22:08:43 InnoDB: Shutdown completed; log sequence number 1358967
120103 22:08:43 innobackupex: completed OK!

If no --incremental-dir is set, innobackupex will use the most recent subdirectory created in the basedir.

At this moment, BASE-DIR contains the data up to the moment of the first incremental backup. Note that the full data will always be in the directory of the base backup, as we are appending the increments to it.

Repeat the procedure with the second one:

innobackupex --apply-log BASE-DIR --incremental-dir=INCREMENTAL-DIR-2

If the “completed OK!” message was shown, the final data will be in the base backup directory, BASE-DIR.

Note

--redo-only should be used when merging all incrementals except the last one. That’s why the previous line doesn’t contain the --redo-only option. Even if the --redo-only was used on the last step, backup would still be consistent but in that case server would perform the rollback phase.

You can use this procedure to add more increments to the base, as long as you do it in the chronological order that the backups were done. If you merge the incrementals in the wrong order, the backup will be useless. If you have doubts about the order that they must be applied, you can check the file xtrabackup_checkpoints at the directory of each one, as shown in the beginning of this section.

Once you merge the base with all the increments, you can prepare it to roll back the uncommitted transactions:

innobackupex --apply-log BASE-DIR

Now your backup is ready to be used immediately after restoring it. This preparation step is optional. However, if you restore without doing the prepare, the database server will begin to rollback uncommitted transactions, the same work it would do if a crash had occurred. This results in delay as the database server starts, and you can avoid the delay if you do the prepare.

Note that the iblog* files will not be created by innobackupex, if you want them to be created, use xtrabackup –prepare on the directory. Otherwise, the files will be created by the server once started.

Restoring Incremental Backups with innobackupex

After preparing the incremental backups, the base directory contains the same as a full one. For restoring it you can use:

innobackupex --copy-back BASE-DIR

and you may have to change the ownership as detailed on Restoring a Full Backup with innobackupex.

Incremental Streaming Backups using xbstream and tar

Incremental streaming backups can be performed with the xbstream streaming option. Currently backups are packed in custom xbstream format. With this feature taking a BASE backup is needed as well.

Taking a base backup:

innobackupex /data/backups

Taking a local backup:

innobackupex --incremental --incremental-lsn=LSN-number --stream=xbstream ./ > incremental.xbstream

Unpacking the backup:

xbstream -x < incremental.xbstream

Taking a local backup and streaming it to the remote server and unpacking it:

innobackupex  --incremental --incremental-lsn=LSN-number --stream=xbstream ./ | /
ssh user@hostname " cat - | xbstream -x -C > /backup-dir/"
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