Backing Up and Restoring Individual Partitions

Percona XtraBackup features partial backups, which means that you may backup individual partitions as well because from the storage engines perspective partitions are regular tables with specially formatted names. The only requirement for this feature is having the innodb_file_per_table option enabled in the server.

There is only one caveat about using this kind of backup: you can’t copy back the prepared backup. Restoring partial backups should be done by importing the tables, and not by using the traditional --copy-back option. Although there are some scenarios where restoring can be done by copying back the files, this may be lead to database inconsistencies in many cases and it is not the recommended way to do it.

Creating the backup

There are three ways of specifying which part of the whole data will be backed up: regular expressions (--include), enumerating the tables in a file (--tables-file) or providing a list of databases (--databases). In this example --include option will be used.

The regular expression provided to this option will be matched against the fully qualified tablename, including the database name, in the form databasename.tablename.

For example, this will back up the partition p4 from the table name located in the database imdb:

$ innobackupex --include='^imdb[.]name#P#p4' /mnt/backup/

This will create a timestamped directory with the usual files that innobackupex creates, but only the data files related to the tables matched.

Output of the innobackupex will list the skipped tables

...
[01] Skipping ./imdb/person_info.ibd
[01] Skipping ./imdb/name#P#p5.ibd
[01] Skipping ./imdb/name#P#p6.ibd
...
imdb.person_info.frm is skipped because it does not match ^imdb[.]name#P#p4.
imdb.title.frm is skipped because it does not match ^imdb[.]name#P#p4.
imdb.company_type.frm is skipped because it does not match ^imdb[.]name#P#p4.
...

Note that this option is passed to xtrabackup --tables and is matched against each table of each database, the directories of each database will be created even if they are empty.

Preparing the backup

For preparing partial backups, the procedure is analogous to restoring individual tables : apply the logs and use the --export option:

$ innobackupex --apply-log --export /mnt/backup/2012-08-28_10-29-09

You may see warnings in the output about tables that don’t exists. This is because InnoDB-based engines stores its data dictionary inside the tablespace files besides the .frm files. innobackupex will use xtrabackup to remove the missing tables (those that haven’t been selected in the partial backup) from the data dictionary in order to avoid future warnings or errors:

InnoDB: in InnoDB data dictionary has tablespace id 51,
InnoDB: but tablespace with that id or name does not exist. It will be removed from data dictionary.
120828 10:25:28  InnoDB: Waiting for the background threads to start
120828 10:25:29 Percona XtraDB (http://www.percona.com) 1.1.8-20.1 started; log sequence number 10098323731
xtrabackup: export option is specified.
xtrabackup: export metadata of table 'imdb/name#P#p4' to file `./imdb/name#P#p4.exp` (1 indexes)
xtrabackup:     name=PRIMARY, id.low=73, page=3

You should also see the notification of the creation of a file needed for importing (.exp file) for each table included in the partial backup:

xtrabackup: export option is specified.
xtrabackup: export metadata of table 'imdb/name#P#p4' to file `./imdb/name#P#p4.exp` (1 indexes)
xtrabackup:     name=PRIMARY, id.low=73, page=3

Note that you can use the --export option with --apply-log to an already-prepared backup in order to create the .exp files.

Finally, check the for the confirmation message in the output:

120828 19:25:38  innobackupex: completed OK!

Restoring from the backups

Restoring should be done by importing the tables in the partial backup to the server.

Note

Improved table/partition import is only available in Percona Server and MySQL 5.6, this means that partitions which were backed up from different server can be imported as well. For versions older than MySQL 5.6 only partitions from that server can be imported with some important limitations. There should be no DROP/CREATE/TRUNCATE/ALTER TABLE commands issued between taking the backup and importing the partition.

First step is to create new table in which data will be restored

mysql> CREATE TABLE `name_p4` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` text NOT NULL,
`imdb_index` varchar(12) DEFAULT NULL,
`imdb_id` int(11) DEFAULT NULL,
`name_pcode_cf` varchar(5) DEFAULT NULL,
`name_pcode_nf` varchar(5) DEFAULT NULL,
`surname_pcode` varchar(5) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=2812744 DEFAULT CHARSET=utf8

To restore the partition from the backup tablespace needs to be discarded for that table:

mysql>  ALTER TABLE name_p4 DISCARD TABLESPACE;

Next step is to copy the .exp and ibd files from the backup to MySQL data directory:

$ cp /mnt/backup/2012-08-28_10-29-09/imdb/name#P#p4.exp /var/lib/mysql/imdb/name_p4.exp
$ cp /mnt/backup/2012-08-28_10-29-09/imdb/name#P#p4.ibd /var/lib/mysql/imdb/name_p4.ibd

Note

Make sure that the copied files can be accessed by the user running the MySQL.

If you’re running the Percona Server make sure that variable innodb_import_table_from_xtrabackup is enabled:

mysql> SET GLOBAL innodb_import_table_from_xtrabackup=1;

Last step is to import the tablespace:

mysql>  ALTER TABLE name_p4 IMPORT TABLESPACE;

Restoring from the backups in version 5.6

The problem with server versions up to 5.5 is that there is no server support to import either individual partitions or all partitions of a partitioned table, so partitions could only be imported as independent tables. In MySQL and Percona Server 5.6 it is possible to exchange individual partitions with independent tables through ALTER TABLE ... EXCHANGE PARTITION command.

Note

In Percona Server 5.6 variable innodb_import_table_from_xtrabackup has been removed in favor of MySQL Transportable Tablespaces implementation.

When importing an entire partitioned table, first import all (sub)partitions as independent tables:

mysql> CREATE TABLE `name_p4` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` text NOT NULL,
`imdb_index` varchar(12) DEFAULT NULL,
`imdb_id` int(11) DEFAULT NULL,
`name_pcode_cf` varchar(5) DEFAULT NULL,
`name_pcode_nf` varchar(5) DEFAULT NULL,
`surname_pcode` varchar(5) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=2812744 DEFAULT CHARSET=utf8

To restore the partition from the backup tablespace needs to be discarded for that table:

mysql>  ALTER TABLE name_p4 DISCARD TABLESPACE;

Next step is to copy the .cfg and .ibd files from the backup to MySQL data directory:

$ cp /mnt/backup/2013-07-18_10-29-09/imdb/name#P#p4.cfg /var/lib/mysql/imdb/name_p4.cfg
$ cp /mnt/backup/2013-07-18_10-29-09/imdb/name#P#p4.ibd /var/lib/mysql/imdb/name_p4.ibd

Last step is to import the tablespace:

mysql>  ALTER TABLE name_p4 IMPORT TABLESPACE;

We can now create the empty partitioned table with exactly the same schema as the table being imported:

mysql> CREATE TABLE name2 LIKE name;

Then swap empty partitions from the newly created table with individual tables corresponding to partitions that have been exported/imported on the previous steps

mysql> ALTER TABLE name2 EXCHANGE PARTITION p4 WITH TABLE name_p4;

In order for this operation to be successful following conditions have to be met.

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