Pantek Library
Hosting Provided By
CybrHost
High Speed Hosting
Applications: MySQL > doc > refman > 4.1 > enbackup-and-recovery.html (Request Expert MySQL Support)
Skip navigation links

Additional languages

    Chapter 6. Backup and Recovery

    Table of Contents     [+/-]

    6.1. Database Backups
    6.2. Example Backup and Recovery Strategy     [+/-]
    6.3. Point-in-Time Recovery     [+/-]
    6.4. Table Maintenance and Crash Recovery     [+/-]

    It is important to back up your databases in case problems occur so that you can recover your data and be up and running again. MySQL offers a variety of backup strategies from which you can choose to select whatever methods best suit the requirements for your installation.

    Briefly summarized, backup concepts with which you should be familiar include the following:

    More generally, the following discussion amplifies on the properties of different backup methods.

    • Logical versus physical (raw) backups. Logical backups save information represented as logical database structure (CREATE DATABASE, CREATE TABLE statements) and content (INSERT statements or delimited-text files). Physical backups consist of raw copies of the directories and files that store database contents.

      Do you need more help?X

      Logical backup methods have these characteristics:

      • The backup is done by going through the MySQL server to obtain database structure and content information.

      • Backup is slower than physical methods because the server must access database information, convert it to logical format, and send it to the backup program.

      • Output is larger than for physical backup, paticularly when saved in text format.

      • Backup and restore granularity is available at the server level (all databases), database level (all tables in a particular database), or table level. This is true regardless of storage engine.

      • The backup does not include log or configuration files, or other database-related files that are not part of databases.

      • Backups stored in logical format are machine independent and highly portable.

      • Logical backups are performed with the MySQL server running (the server is not taken offline).

        Can we help you?X

      • Logical backup tools include the mysqldump program and the SELECT ... INTO OUTFILE statement. These work for any storage engine, even MEMORY.

        For restore, SQL-format dump files can be processed using the mysql client. To load delimited-text files, use the LOAD DATA INFILE statement or the mysqlimport client.

      Physical backup methods have these characteristics:

      • The backup consists of exact copies of database directories and files. Typically this is a copy of all or part of the MySQL data directory. Data from MEMORY tables cannot be backed up this way because their contents are not stored on disk.

      • Physical backup methods are faster than logical because they involve only file copying without conversion.

      • Output is more compact than for logical backup.

      • Backup and restore granularity extends from the level of the entire data directory down to the level of individual files. This may or may not provide for table-level granularity, depending on storage engine. (Each MyISAM table corresponds uniquely to a set of files, but an InnoDB table shares file storage with other InnoDB tables.)

      • In addition to databases, the backup can include any related files such as log or configuration files.

        Can't find what you're looking for?X

      • Backups are portable only to other machines that have identical or similar hardware characteristics.

      • Backups can be performed while the MySQL server is not running. If the server is running, it is necessary to perform appropriate locking so that the server does not change database contents during the backup.

      • Physical backup tools include filesystem-level commands (such as cp, scp, tar, rsync), mysqlhotcopy for MyISAM tables, ibbackup for InnoDB tables, or START BACKUP for NDB tables.

        For restore, files copied at the filesystem level or with mysqlhotcopy can be copied back to their original locations with filesystem commands; ibback restores InnoDB tables, and ndb_restore restores NDB tables.

    • Online versus offline backups. Online backups take place while the MySQL server is running so that the database information can be obtained from the server. Offline backups take place while the server is stopped. (This distinction can also be described as “hot” versus “cold” backups; a “warm” backup is one where the server remains running but locked against modifying data while you access database files externally.)

      Online backup methods have these characteristics:

      Offline backup methods have these characteristics:

      • Affects clients adversely because the server is unavailable during backup.

      • Simpler backup procedure because there is no possibility of interference from client activity.

    • Local versus remote backups. A local backup is performed on the same host where the MySQL server runs, whereas a remote backup is initiated from a different host.

      • mysqldump can connect to local or remote servers. For SQL output (CREATE and INSERT statements), local or remote dumps can be done and generate output on the client. For delimited-text output (with the --tab option), data files are created on the server host.

      • mysqlhotcopy performs only local backups: It connects to the server to lock it against data modifications and then copies local table files.

      • SELECT ... INTO OUTFILE can be initiated from a remote client host, but the output file is created on the server host.

      • Physical backup methods typically are initiated locally on the MySQL server host so that the server can be taken offline, although the destination for file copies might be remote.

        Confused? Frustrated?X

    • Snapshot backups. Some filesystem implementations enable “snapshots” to be taken. These provide logical copies of the filesystem at a given point in time, without having to physically copy the entire filesystem. (For example, the implementation may use copy-on-write techniques so that only parts of the filesystem modified after the snapshot time need be copied.) MySQL itself does not provide the capability for taking filesystem snapshots. It is available through third-party solutions such as Veritas or LVM.

    • Full versus incremental backups. A full backup includes all data managed by a MySQL server at a given point in time. An incremental backup consists of the changes made to the data since the full backup. MySQL has different ways to perform full backups, such as those described in previous items. Incremental backups are made possible by enabling the server's binary log, which the server uses to record data changes.

    • Point-in-time recovery. One use for the binary log is to achieve point-in-time recovery. This is done by recovering first from the backup files to restore the server to its state when the backup was made, and then by re-executing changes in subsequently written binary log files to redo data modifications up to the desired point in time.

    • Backup scheduling, compression, and encryption. Backup scheduling is valuable for automating backup procedures. Compression of backup output reduces space requirements, and encryption of the output provides better security against unauthorized access of backed-up data. MySQL itself does not provide these capabilities. ibbackup can compress InnoDB backups, and compression or encryption of backup output can be achieved using filesystem utilities. Other third-party solutions may be available.

    • Table maintenance. Data integrity can be compromised if tables become corrupt. MySQL provides programs for checking tables and repairing them should problems be found. These programs apply primarily to MyISAM and ISAM tables. See Section 6.4, “Table Maintenance and Crash Recovery”.

    Additional resources

    Resources related to backup or to maintaining data availability include the following:


    Contact Us  Legal Notices  Order Services Online 
    Pantek Home  Privacy Policy  IT news  Site Map  Pantek Library