7.2 Database Backup Methods
This section summarizes some general methods for making backups.
Customers of MySQL Enterprise Edition can use the MySQL Enterprise Backup product to do physical backups of entire instances or selected databases, tables, or both. This product includes features for incremental and compressed backups. Backing up the physical database files makes restore much faster than logical techniques such as the
InnoDB tables are copied using a hot backup mechanism. (Ideally, the
InnoDB tables should represent a substantial majority of the data.) Tables from other storage engines are copied using a warm backup mechanism. For an overview of the MySQL Enterprise Backup product, see Section 29.2, “MySQL Enterprise Backup Overview”.
For storage engines that represent each table using its own files, tables can be backed up by copying those files. For example,
MyISAM tables are stored as files, so it is easy to do a backup by copying files (
*.MYI files). To get a consistent backup, stop the server or lock and flush the relevant tables:
FLUSH TABLES tbl_list WITH READ LOCK;
You need only a read lock; this enables other clients to continue to query the tables while you are making a copy of the files in the database directory. The flush is needed to ensure that the all active index pages are written to disk before you start the backup. See Section 13.3.5, “LOCK TABLES and UNLOCK TABLES Statements”, and Section 126.96.36.199, “FLUSH Statement”.
You can also create a binary backup simply by copying all table files, as long as the server isn't updating anything. (But note that table file copying methods do not work if your database contains
InnoDB tables. Also, even if the server is not actively updating data,
InnoDB may still have modified data cached in memory and not flushed to disk.)
To create a text file containing a table's data, you can use
SELECT * INTO OUTFILE '. The file is created on the MySQL server host, not the client host. For this statement, the output file cannot already exist because permitting files to be overwritten constitutes a security risk. See Section 13.2.9, “SELECT Statement”. This method works for any kind of data file, but saves only table data, not the table structure.
Another way to create text data files (along with files containing
CREATE TABLE statements for the backed up tables) is to use mysqldump with the
--tab option. See Section 7.4.3, “Dumping Data in Delimited-Text Format with mysqldump”.
MySQL supports incremental backups: You must start the server with the
--log-bin option to enable binary logging; see Section 5.4.4, “The Binary Log”. The binary log files provide you with the information you need to replicate changes to the database that are made subsequent to the point at which you performed a backup. At the moment you want to make an incremental backup (containing all changes that happened since the last full or incremental backup), you should rotate the binary log by using
FLUSH LOGS. This done, you need to copy to the backup location all binary logs which range from the one of the moment of the last full or incremental backup to the last but one. These binary logs are the incremental backup; at restore time, you apply them as explained in Section 7.5, “Point-in-Time (Incremental) Recovery”. The next time you do a full backup, you should also rotate the binary log using
FLUSH LOGS or mysqldump --flush-logs. See Section 4.5.4, “mysqldump — A Database Backup Program”.
If you have performance problems with your master server while making backups, one strategy that can help is to set up replication and perform backups on the slave rather than on the master. See Section 16.3.1, “Using Replication for Backups”.
If you are backing up a slave replication server, you should back up its master info and relay log info repositories (see Section 16.2.4, “Relay Log and Replication Applier Metadata Repositories”) when you back up the slave's databases, regardless of the backup method you choose. These information files are always needed to resume replication after you restore the slave's data. If your slave is replicating
LOAD DATA statements, you should also back up any
SQL_LOAD-* files that exist in the directory that the slave uses for this purpose. The slave needs these files to resume replication of any interrupted
LOAD DATA operations. The location of this directory is the value of the
slave_load_tmpdir system variable. If the server was not started with that variable set, the directory location is the value of the
tmpdir system variable.
If you have to restore
MyISAM tables that have become corrupt, try to recover them using
REPAIR TABLE or myisamchk -r first. That should work in 99.9% of all cases. If myisamchk fails, see Section 7.6, “MyISAM Table Maintenance and Crash Recovery”.
If you are using a Veritas file system, you can make a backup like this:
Similar snapshot capabilities may be available in other file systems, such as LVM or ZFS.