MySQL Enterprise Backup 3.10 User's Guide  /  ...  /  Limitations of MySQL Enterprise Backup

A.1 Limitations of MySQL Enterprise Backup

  • The group commit feature in MySQL 5.6 and higher changes the frequency of flush operations for the InnoDB redo log, which could affect the point in time associated with the backup data from InnoDB tables. See Section B.3, “Compatibility Notes for MySQL Versions” for details.

  • For MySQL 5.5 and earlier, when restoring an individual InnoDB table, as described in Section 4.4, “Backing Up and Restoring a Single .ibd File”, the table must not have been dropped or truncated in the MySQL server after the backup. Dropping or truncating an InnoDB table changes its internal table ID, and when the table is re-created the ID will not match the table ID from the backup data. This restriction does not apply to MySQL 5.6 and later, as long as the restoration is made from one Generally Available (GA) version to another in the same series of MySQL servers.

  • In Linux, Unix, and OS X systems, the mysqlbackup command does not record file ownership or permissions of the files that are backed up. Upon restore, these files might have different ownership, for example being owned by root rather than mysql. They might also have different read/write permissions, for example being readable by anyone rather than just the file owner. When planning your backup strategy, survey the files in the MySQL data directory to ensure they have consistent owner and permission settings. When executing a restore operation, use an appropriate combination of su, umask, chown, and chmod on the restored files to set up the same owners and privileges as on the original files.

  • In some cases, backups of non-transactional tables such as MyISAM tables could contain additional uncommitted data. If autocommit is turned off, and both InnoDB tables and non-transactional tables are modified within the same transaction, data can be written to the non-transactional table before the binary log position is updated. The binary log position is updated when the transaction is committed, but the non-transactional data is written immediately. If the backup occurs while such a transaction is open, the backup data contains the updates made to the non-transactional table.

  • If the mysqlbackup process is interrupted, such as by a Unix kill -9 command, a FLUSH TABLES WITH READ LOCK operation might remain running. In this case, use the KILL QUERY statement from the mysql command line to kill the FLUSH TABLES WITH READ LOCK statement. This issue is more likely to occur if the FLUSH TABLES operation is stalled by a long-running query or transaction. Refer to Chapter 5, mysqlbackup Command Reference for guidelines about backup timing and performance.

  • Do not run the DDL operations ALTER TABLE, TRUNCATE TABLE, OPTIMIZE TABLE, REPAIR TABLE, or RESTORE TABLE while a backup operation is going on. The resulting backup might be corrupted.

    The only ALTER TABLE operations that can be safely run in parallel with a backup are those that do not influence the physical representation of records on disk, such as changing column names or default column values.

  • The maximum number of subdirectories allowed in the --backup-dir path is 21. This limit could be exceeded by a deeply nested backup directory, or by an anomalous condition such as symbolic links forming an infinite recursive path.

  • When statement-based binary log format is used on the MySQL server (which is the default behavior), if you take a backup when there are temporary tables in the database and you use those temporary tables to update or insert into normal tables, application of the MySQL binlog to a backup could then fail—that is, you might not be able to roll forward the backup to a particular point in time using the MySQL binlog. This is because temporary tables are not copied to the backup, as the physical filenames #sql*.frm do not correspond to the logical table names that MySQL writes to the binlog. To avoid the problem, use row-based or mixed format for the binary log by setting the value for the --binlog-format option to ROW or MIXED on the server.

  • The engines column in the mysql.backup_history table does not correctly reflect the storage engines of the backed-up databases.

  • When saving any tables into the data directory, the MySQL server performs conversions for any special characters in any database or table names to come up with the file names for storage. Here are two examples of MySQL commands including special characters (. and -) in their database and file names:

    mysql> CREATE TABLE `db.2`.`t.2` (c1 INT) ENGINE=InnoDB;
    mysql> CREATE TABLE `db-3`.`t-3` (c1 INT) ENGINE=InnoDB;

    The tables created by these commands are stored in the file system as these files:


    Currently, mysqlbackup does not perform the same conversion with database and table names supplied using the --include-tables and --exclude-tables options. Using, for example, --include-tables="db\.2\.t\.2|db-3\.t-3" will no not select the tables described above.

    As a workaround, for a backup that does not use transportable tablespace (TTS) (that is, the --use-tts option is not used during the creation of the backup), users can look up the file names for the desired tables in the data directories of the databases and, in the arguments for the --include-tables and --exclude-tables options, use the converted names for the database directories as database names and the converted file names (without the file extension) as table names . For example, for the tables mentioned above, select them for inclusion in a backup with the option argument --include-tables="db@002e2\.t@002e2|db@002d3\.t@002d3". Using the same argument with the option --exclude-tables excludes the two tables in the backup.

    However, the suggested workaround does not work for TTS backups; therefore, do not use TTS if you want to do a partial backup that includes tables with special characters in their names.

  • Compressed InnoDB tables from MySQL server 5.6.10 and earlier cannot be restored with MySQL Enterprise Backup 3.9.0 or later, due to a bug with the InnoDB storage engine (see Bug# 72851 on the MySQL Bug System).

  • While it is possible to backup to or restore from a Network Attached Storage (NAS) device using MySQL Enterprise Backup, due to networking issues that might arise, the consistency of the backups and the performance of the backup or restore operations might be compromised.

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