Appendix B Limitations of MySQL Enterprise Backup

Please refer to the MySQL Enterprise Backup version history in Appendix D, MySQL Enterprise Backup Release Notes for a list of fixed mysqlbackup bugs. Here are a list of limitaions 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 C.5, “Compatibility Notes for Specific MySQL Versions” for details.

• 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 by, for example, 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 Section 7.1, “Optimizing Backup Performance” for guidelines about backup timing and performance.

• Do not run the DDL operations (for example, ALTER TABLE, TRUNCATE TABLE, OPTIMIZE TABLE, REPAIR TABLE, RESTORE TABLE or CREATE INDEX) while a backup operation is going on. The resulting backup might become corrupted.

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

• Hot backups for large databases with heavy writing workloads (say, in the order of gigabytes per minute) can take a very long time to complete due to the huge redo log files that are generated on the server while the backup is running. However, when it is a relatively small subset of tables in the database that are being modified frequently, the Optimistic Backup feature can be used to improve performance and reduce backup size, as well as backup and recovery times. See Section 4.3.6, “Making an Optimistic Backup” for details.

• 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 known issue 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.

• When creating a backup using transportable tablespace (TTS) for a server containing tables with a mix of the Antelope and Barracuda file formats, do not apply full locking on the tables (that is, do not specify --use-tts=with-full-locking). Instead, just specify --use-tts or --use-tts=with-minimum-locking, both of which will apply minimum locking to the tables (Bug #20583946).

• Tables created on the MySQL server with the ANSI_QUOTES SQL mode cannot be backed up using transportable tablespace (TTS).

• When a file of an unrecognized file type exists under a subdirectory in the server's data directory, it will be backed up by mysqlbackup unless the --only-known-file-types option is used. However, if the name of the file does not have an extension, it will cause mysqlbackup to throw an error when it tries to restore the backup to a server.

• If a table on the server is dropped while mysqlbackup is backing up that table, mysqlbackup throws an error and exits.

• Offline backups using MySQL Enterprise Backup 3.12.2 sometimes fail, with occasional crashes of mysqlbackup.

• Cloud operations by MySQL Enterprise Backup are not supported on macOS and Windows platforms, and also on Linux platforms when generic Linux builds are used for both the server and MySQL Enterprise Backup (i.e., when both the server and MySQL Enterprise Backup have been installed using generic Linux tarballs).

• Using the --src-entry option with the extract command on cloud backups will cause the command to fail. Cloud backups can only be extracted in full.

• Due to some issues, cloud backup and restore using Amazon S3 is currently not supported by MySQL Enterprise Backup 3.12.

• A compressed directory backup fails when a general tablespace bears the same basename as the database's system tablespace (usually ibdata1) and exists in the same directory with it (usually the server's data directory). A compressed single-file backup created under the same situation will be corrupted, and cannot be restored. To avoid the problem, the server administrator should not put into the same directory the system tablespace and a general tablespace of the same basename; if that is unavoidable, do not perform a compressed backup for the database.

• When working with a replication set up whose source server also belongs to a separate Group Replication setup, over time, create backups consistently either from the source or the replica, but not from both. Otherwise, there will be conflicts between the id values generated by the source and the replica, causing backups to fail.