How to recover a single InnoDB table from a Full Backup

Sometimes we need to restore only some tables from a full backup maybe because your data loss affect a small number of your tables. In this particular scenario is faster to recover single tables than a full backup. This is easy with MyISAM but if your tables are InnoDB the process is a little bit different story.

With Oracle’s stock MySQL you cannot move your ibd files freely from one server to another or from one database to another. The reason is that the table definition is stored in the InnoDB shared tablespace (ibdata) and the transaction IDs and log sequence numbers that are stored in the tablespace files also differ between servers. Therefore our example will be very straightforward: we’ll delete some rows from a table in order to recover the table later.

Most of these limitations are solved on Percona Server . More info about this in the conclusion section of this post. This post will be focus on how to recover a single tablespace using stock MySQL server.

First, you must meet certain prerequisites to be able to restore a ibd tablespace:

• The ibd file must be from a consistent backup with all insert buffer entries merged and have no uncommitted transactions in order to not be dependent of the shared tablespace ibdata. That is, shutting down with innodb_fast_shutdown=0. We’ll use XtraBackup to avoid the server shutdown.
• You must not drop, truncate or alter the schema of the table after the backup has been taken.
• The variable innodb_file_per_table must be enabled.

Then, our first step is to get a consistent backup.

First we need to copy all the data to an output directory:

The –export option is the magic trick that will help us to get a consistent backup with complete independent ibd files without shutting down the service. In the second step the use of –export option runs a recovery process on the backup with innodb_fast_shutdown=0 and therefore merging all the insert buffers.

# innobackupex --defaults-file=/etc/my.cnf --export /tmp/

Then apply the logs to get a consistent backup:

# innobackupex --defaults-file=/etc/my.cnf --apply-log --export /tmp/2012-01-22_14-13-20/

Now we’re going to delete some data from one table. In this case we’re going to delete the salary information from the user 10008:

mysql> SELECT * FROM salaries WHERE emp_no=10008;
+--------+--------+------------+------------+
| emp_no | salary | from_date | to_date |
+--------+--------+------------+------------+
| 10008 | 46671 | 1998-03-11 | 1999-03-11 |
| 10008 | 48584 | 1999-03-11 | 2000-03-10 |
| 10008 | 52668 | 2000-03-10 | 2000-07-31 |
+--------+--------+------------+------------+

mysql> DELETE FROM salaries WHERE emp_no=10008;

The next step is where we are going to save a lot of time and some headaches Instead of recovering all the InnoDB data we are going to recover only the “salaries” table:

• Discard the tablespace of the salaries table:

mysql> ALTER TABLE salaries DISCARD TABLESPACE;

• Copy the salaries.ibd files from the backup to the database data directory:

# cp /tmp/2012-01-22_14-13-20/employees/salaries.ibd /var/lib/mysql/data/employees/

• Import the new tablespace:

mysql> ALTER TABLE salaries IMPORT TABLESPACE;

mysql> SELECT * FROM salaries WHERE emp_no=10008;
+--------+--------+------------+------------+
| emp_no | salary | from_date | to_date |
+--------+--------+------------+------------+
| 10008 | 46671 | 1998-03-11 | 1999-03-11 |
| 10008 | 48584 | 1999-03-11 | 2000-03-10 |
| 10008 | 52668 | 2000-03-10 | 2000-07-31 |
+--------+--------+------------+------------+

The salary history from the user is back again!

Conclusion:

As we learned , you can also recover single InnoDB table as with MyISAM but knowing in advance that there are some prerequisites to comply.

Percona Server relaxes a lot of limitations and is able to import tables from different Server instance, when table was altered or truncated in the meanwhile. Though this only works if table was
“exported” with Xtrabackup as this exports essential information from main tablespace which is not stored in .ibd file. innodb_import_table_from_xtrabackup=1 should be enabled for such advanced import process to work. You can read more about this feature in Percona Server Documentation

In the next blog post I’ll explain how to do recovery using Percona Data Recovery toolkit.