The group commit feature in MySQL 5.6 and higher changes the frequency of flush operations for the
InnoDBredo log, which could affect the point in time associated with the backup data from
InnoDBtables. 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 5.4, “Backing Up and Restoring a Single
.ibdFile”, 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
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
chmodon 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
MyISAMtables could contain additional uncommitted data. If autocommit is turned off, and both
InnoDBtables and non-transactional tables are modified within the same transaction, data can be written to the non-transactional table before the binlog position is updated. The binlog 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 -9command, a
FLUSH TABLES WITH READ LOCKoperation might remain running. In this case, use the
KILL QUERYstatement from the mysql command line to kill the
FLUSH TABLES WITH READ LOCKstatement. This issue is more likely to occur if the
FLUSH TABLESoperation is stalled by a long-running query or transaction. Refer to Chapter 4, mysqlbackup Command Reference for guidelines about backup timing and performance.
Do not run the DDL operations
REPAIR TABLE, or
RESTORE TABLEwhile a backup operation is going on. The resulting backup might be corrupted.
ALTER TABLEoperations 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-dirpath 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*.frmdo 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-formatoption to “ROW” or “MIXED” on the server.
Currently, if the regular expression for the
--includeoption does not match any table names, all file-per-table tables are included in the backup.
enginescolumn in the
mysql.backup_historytable does not correctly reflect the storage engines of the backed-up databases.
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).