Chapter 6. Backup and Recovery

Table of Contents

6.1. Backup and Recovery Types
6.2. Database Backup Methods
6.3. Example Backup and Recovery Strategy
6.3.1. Backup Policy
6.3.2. Using Backups for Recovery
6.3.3. Backup Strategy Summary
6.4. Using mysqldump for Backups
6.4.1. Dumping Data in SQL Format with mysqldump
6.4.2. Reloading SQL-Format Backups
6.4.3. Dumping Data in Delimited-Text Format with mysqldump
6.4.4. Reloading Delimited-Text Format Backups
6.4.5. mysqldump Tips
6.5. Using MySQL Backup
6.5.1. Quick Guide to MySQL Backup
6.5.2. How MySQL Backup Works
6.5.3. MySQL Backup Status Reporting and Monitoring
6.6. Point-in-Time (Incremental) Recovery Using the Binary Log
6.6.1. Point-in-Time Recovery Using Event Times
6.6.2. Point-in-Time Recovery Using Event Positions
6.7. MyISAM Table Maintenance and Crash Recovery
6.7.1. Using myisamchk for Crash Recovery
6.7.2. How to Check MyISAM Tables for Errors
6.7.3. How to Repair MyISAM Tables
6.7.4. MyISAM Table Optimization
6.7.5. Setting Up a MyISAM Table Maintenance Schedule

It is important to back up your databases so that you can recover your data and be up and running again in case problems occur, such as system crashes, hardware failures, or users deleting data by mistake. Backups are also essential as a safeguard before upgrading a MySQL installation, and they can be used to transfer a MySQL installation to another system or to set up replication slave servers.

MySQL offers a variety of backup strategies from which you can choose the methods that best suit the requirements for your installation. This chapter discusses several backup and recovery topics with which you should be familiar:

Additional Resources

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

6.1. Backup and Recovery Types

This section describes the characteristics of different types of backups.

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.

Logical backup methods have these characteristics:

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

  • Backup is slower than physical methods because the server must access database information and convert it to logical format. If the output is written on the client side, the server must also send it to the backup program.

  • Output is larger than for physical backup, particularly 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.

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

  • To restore logical backups, 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 ranges 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.

  • 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 file system-level commands (such as cp, scp, tar, rsync), mysqlhotcopy for MyISAM tables, or ibbackup for InnoDB tables.

  • For restore, files copied at the file system level or with mysqlhotcopy can be copied back to their original locations with file system commands; ibbackup 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:

  • The backup is less intrusive to other clients, which can connect to the MySQL server during the backup and may be able to access data depending on what operations they need to perform.

  • Care must be taken to impose appropriate locking so that data modifications do not take place that would compromise backup integrity.

Offline backup methods have these characteristics:

  • Clients can be affected adversely because the server is unavailable during backup.

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

A similar distinction between online and offline applies for recovery operations, and similar characteristics apply. However, it is more likely that clients will be affected for online recovery than for online backup because recovery requires stronger locking. During backup, clients might be able to read data while it is being backed up. Recovery modifies data and does not just read it, so clients must be prevented from accessing data while it is being restored.

Local Versus Remote Backups

A local backup is performed on the same host where the MySQL server runs, whereas a remote backup is done from a different host. For some types of backups, the backup can be initiated from a remote host even if the output is written locally on the server. 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 local or 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 copied files might be remote.

Snapshot Backups

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

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 during a given time span (from one point in time to another). MySQL has different ways to perform full backups, such as those described earlier in this section. Incremental backups are made possible by enabling the server's binary log, which the server uses to record data changes.

Full Versus Point-in-Time (Incremental) Recovery

A full recovery restores all data from a full backup. This restores the server instance to the state that it had when the backup was made. If that state is not sufficiently current, a full recovery can be followed by recovery of incremental backups made since the full backup, to bring the server to a more up-to-date state.

Incremental recovery is recovery of changes made during a given time span. This is also called point-in-time recovery because it makes a server's state current up to a given time. Point-in-time recovery is based on the binary log and typically follows a full recovery from the backup files that restores the server to its state when the backup was made. Then the data changes written in the binary log files are applied as incremental recovery to redo data modifications and bring the server up to the desired point in time.

Table Maintenance

Data integrity can be compromised if tables become corrupt. MySQL provides programs for checking MyISAM tables and repairing them should problems be found. See Section 6.7, “MyISAM Table Maintenance and Crash Recovery”.

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 file system utilities. Other third-party solutions may be available.

6.2. Database Backup Methods

This section summarizes some general methods for making backups.

Making Backups by Copying Table Files

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 (*.frm, *.MYD, and *.MYI files). To get a consistent backup, stop the server or do a LOCK TABLES on the relevant tables followed by FLUSH TABLES for the tables. See Section 12.3.5, “LOCK TABLES and UNLOCK TABLES Syntax”, and Section, “FLUSH Syntax”. You need only a read lock; this allows other clients to continue to query the tables while you are making a copy of the files in the database directory. The FLUSH TABLES statement is needed to ensure that the all active index pages are written to disk before you start the backup.

Making Delimited-Text File Backups

To create a text file containing a table's data, you can use SELECT * INTO OUTFILE 'file_name' FROM tbl_name. The file is created on the MySQL server host, not the client host. For this statement, the output file cannot already exist because allowing files to be overwritten constitutes a security risk. See Section 12.2.9, “SELECT Syntax”. 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.

To reload the output data file, use LOAD DATA INFILE or mysqlimport.

Making Backups with mysqldump or mysqlhotcopy

The mysqldump program and the mysqlhotcopy script can make backups. mysqldump is more general because it can back up all kinds of tables. mysqlhotcopy works only with some storage engines. (See Section 4.5.4, “mysqldump — A Database Backup Program”, and Section 4.6.10, “mysqlhotcopy — A Database Backup Program”.)

Create a full backup of your database using mysqldump:

shell> mysqldump db_name > dump_file
shell> mysqldump --tab=/path/to/some/dir db_name

The first command dumps the database to the named file as CREATE TABLE and INSERT statements. The second command creates two files per table in the named output directory. One file contains the table contents as tab-delimited text. Other other contains a CREATE TABLE statement for the table.

Create a full backup of your database using mysqlhotcopy:

shell> mysqlhotcopy db_name /path/to/some/dir

You can also create a binary backup simply by copying all table files, as long as the server isn't updating anything. The mysqlhotcopy script uses this method. (But note that table file copying methods do not work if your database contains InnoDB tables. mysqlhotcopy does not work for InnoDB tables because InnoDB does not necessarily store table contents in database directories. Also, even if the server is not actively updating data, InnoDB may still have modified data cached in memory and not flushed to disk.

For InnoDB tables, it is possible to perform an online backup that takes no locks on tables using the --single-transaction option to mysqldump. See Section 4.5.4, “mysqldump — A Database Backup Program”.

Making Incremental Backups by Enabling the Binary Log

MySQL supports incremental backups: You must start the server with the --log-bin option to enable binary logging; see Section 5.2.4, “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 6.6, “Point-in-Time (Incremental) Recovery Using the Binary Log”. The next time you do a full backup, you should also rotate the binary log using FLUSH LOGS, mysqldump --flush-logs, or mysqlhotcopy --flushlog. See Section 4.5.4, “mysqldump — A Database Backup Program”, and Section 4.6.10, “mysqlhotcopy — A Database Backup Program”.

Making Backups Using Replication Slaves

If you are backing up a slave replication server, you should back up its and files 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 INFILE commands, you should also back up any SQL_LOAD-* files that may exist in the directory specified by the --slave-load-tmpdir option. (This location defaults to the value of the tmpdir system variable if not specified.) The slave needs these files to resume replication of any interrupted LOAD DATA INFILE operations.

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”.

MySQL Enterprise The MySQL Enterprise Monitor provides numerous advisors that issue immediate warnings should replication issues arise. For more information, see

Recovering Corrupt Tables

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, try the following procedure. It is assumed that you have enabled binary logging by starting MySQL with the --log-bin option.

  1. Restore the table from a mysqldump backup or binary backup.

  2. Execute the following command to re-run the updates in the binary logs:

    shell> mysqlbinlog binlog.[0-9]* | mysql

    In some cases, you may want to re-run only certain binary logs, from certain positions (usually you want to re-run all binary logs from the date of the restored backup, excepting possibly some incorrect statements). See Section 6.6, “Point-in-Time (Incremental) Recovery Using the Binary Log”.

Making Backups Using a File System Snapshot

If you are using a Veritas file system, you can make a backup like this:

  1. From a client program, execute FLUSH TABLES WITH READ LOCK.

  2. From another shell, execute mount vxfs snapshot.

  3. From the first client, execute UNLOCK TABLES.

  4. Copy files from the snapshot.

  5. Unmount the snapshot.

Similar snapshot capabilities may be available in other file systems, such as LVM or ZFS.

6.3. Example Backup and Recovery Strategy

This section discusses a procedure for performing backups that enables you to recover data after several types of crashes:

  • Operating system crash

  • Power failure

  • File system crash

  • Hardware problem (hard drive, motherboard, and so forth)

The example commands do not include options such as --user and --password for the mysqldump and mysql client programs. You should include such options as necessary to enable client programs to connect to the MySQL server.

Assume that data is stored in the InnoDB storage engine, which has support for transactions and automatic crash recovery. Assume also that the MySQL server is under load at the time of the crash. If it were not, no recovery would ever be needed.

For cases of operating system crashes or power failures, we can assume that MySQL's disk data is available after a restart. The InnoDB data files might not contain consistent data due to the crash, but InnoDB reads its logs and finds in them the list of pending committed and noncommitted transactions that have not been flushed to the data files. InnoDB automatically rolls back those transactions that were not committed, and flushes to its data files those that were committed. Information about this recovery process is conveyed to the user through the MySQL error log. The following is an example log excerpt:

InnoDB: Database was not shut down normally.
InnoDB: Starting recovery from log files...
InnoDB: Starting log scan based on checkpoint at
InnoDB: log sequence number 0 13674004
InnoDB: Doing recovery: scanned up to log sequence number 0 13739520
InnoDB: Doing recovery: scanned up to log sequence number 0 13805056
InnoDB: Doing recovery: scanned up to log sequence number 0 13870592
InnoDB: Doing recovery: scanned up to log sequence number 0 13936128
InnoDB: Doing recovery: scanned up to log sequence number 0 20555264
InnoDB: Doing recovery: scanned up to log sequence number 0 20620800
InnoDB: Doing recovery: scanned up to log sequence number 0 20664692
InnoDB: 1 uncommitted transaction(s) which must be rolled back
InnoDB: Starting rollback of uncommitted transactions
InnoDB: Rolling back trx no 16745
InnoDB: Rolling back of trx no 16745 completed
InnoDB: Rollback of uncommitted transactions completed
InnoDB: Starting an apply batch of log records to the database...
InnoDB: Apply batch completed
InnoDB: Started
mysqld: ready for connections

For the cases of file system crashes or hardware problems, we can assume that the MySQL disk data is not available after a restart. This means that MySQL fails to start successfully because some blocks of disk data are no longer readable. In this case, it is necessary to reformat the disk, install a new one, or otherwise correct the underlying problem. Then it is necessary to recover our MySQL data from backups, which means that backups must already have been made. To make sure that is the case, design and implement a backup policy.

6.3.1. Backup Policy

To be useful, backups must be scheduled regularly. A full backup (a snapshot of the data at a point in time) can be done in MySQL with several tools. For example, InnoDB Hot Backup provides online nonblocking physical backup of the InnoDB data files, and mysqldump provides online logical backup. This discussion uses mysqldump.

MySQL Enterprise For expert advice on backups and replication, subscribe to the MySQL Enterprise Monitor. For more information, see

Assume that we make a full backup of all our InnoDB tables in all databases using the following command on Sunday at 1 p.m., when load is low:

shell> mysqldump --single-transaction --all-databases > backup_sunday_1_PM.sql

The resulting .sql file produced by mysqldump contains a set of SQL INSERT statements that can be used to reload the dumped tables at a later time.

This backup operation acquires a global read lock on all tables at the beginning of the dump (using FLUSH TABLES WITH READ LOCK). As soon as this lock has been acquired, the binary log coordinates are read and the lock is released. If long updating statements are running when the FLUSH statement is issued, the backup operation may stall until those statements finish. After that, the dump becomes lock-free and does not disturb reads and writes on the tables.

It was assumed earlier that the tables to back up are InnoDB tables, so --single-transaction uses a consistent read and guarantees that data seen by mysqldump does not change. (Changes made by other clients to InnoDB tables are not seen by the mysqldump process.) If the backup operation includes nontransactional tables, consistency requires that they do not change during the backup. For example, for the MyISAM tables in the mysql database, there must be no administrative changes to MySQL accounts during the backup.

Full backups are necessary, but it is not always convenient to create them. They produce large backup files and take time to generate. They are not optimal in the sense that each successive full backup includes all data, even that part that has not changed since the previous full backup. It is more efficient to make an initial full backup, and then to make incremental backups. The incremental backups are smaller and take less time to produce. The tradeoff is that, at recovery time, you cannot restore your data just by reloading the full backup. You must also process the incremental backups to recover the incremental changes.

To make incremental backups, we need to save the incremental changes. In MySQL, these changes are represented in the binary log, so the MySQL server should always be started with the --log-bin option to enable that log. With binary logging enabled, the server writes each data change into a file while it updates data. Looking at the data directory of a MySQL server that was started with the --log-bin option and that has been running for some days, we find these MySQL binary log files:

-rw-rw---- 1 guilhem  guilhem   1277324 Nov 10 23:59 gbichot2-bin.000001
-rw-rw---- 1 guilhem  guilhem         4 Nov 10 23:59 gbichot2-bin.000002
-rw-rw---- 1 guilhem  guilhem        79 Nov 11 11:06 gbichot2-bin.000003
-rw-rw---- 1 guilhem  guilhem       508 Nov 11 11:08 gbichot2-bin.000004
-rw-rw---- 1 guilhem  guilhem 220047446 Nov 12 16:47 gbichot2-bin.000005
-rw-rw---- 1 guilhem  guilhem    998412 Nov 14 10:08 gbichot2-bin.000006
-rw-rw---- 1 guilhem  guilhem       361 Nov 14 10:07 gbichot2-bin.index

Each time it restarts, the MySQL server creates a new binary log file using the next number in the sequence. While the server is running, you can also tell it to close the current binary log file and begin a new one manually by issuing a FLUSH LOGS SQL statement or with a mysqladmin flush-logs command. mysqldump also has an option to flush the logs. The .index file in the data directory contains the list of all MySQL binary logs in the directory.

The MySQL binary logs are important for recovery because they form the set of incremental backups. If you make sure to flush the logs when you make your full backup, the binary log files created afterward contain all the data changes made since the backup. Let's modify the previous mysqldump command a bit so that it flushes the MySQL binary logs at the moment of the full backup, and so that the dump file contains the name of the new current binary log:

shell> mysqldump --single-transaction --flush-logs --master-data=2 \
         --all-databases > backup_sunday_1_PM.sql

After executing this command, the data directory contains a new binary log file, gbichot2-bin.000007, because the --flush-logs option causes the server to flush its logs. The --master-data option causes mysqldump to write binary log information to its output, so the resulting .sql dump file includes these lines:

-- Position to start replication or point-in-time recovery from

Because the mysqldump command made a full backup, those lines mean two things:

  • The dump file contains all changes made before any changes written to the gbichot2-bin.000007 binary log file or newer.

  • All data changes logged after the backup are not present in the dump file, but are present in the gbichot2-bin.000007 binary log file or newer.

On Monday at 1 p.m., we can create an incremental backup by flushing the logs to begin a new binary log file. For example, executing a mysqladmin flush-logs command creates gbichot2-bin.000008. All changes between the Sunday 1 p.m. full backup and Monday 1 p.m. will be in the gbichot2-bin.000007 file. This incremental backup is important, so it is a good idea to copy it to a safe place. (For example, back it up on tape or DVD, or copy it to another machine.) On Tuesday at 1 p.m., execute another mysqladmin flush-logs command. All changes between Monday 1 p.m. and Tuesday 1 p.m. will be in the gbichot2-bin.000008 file (which also should be copied somewhere safe).

The MySQL binary logs take up disk space. To free up space, purge them from time to time. One way to do this is by deleting the binary logs that are no longer needed, such as when we make a full backup:

shell> mysqldump --single-transaction --flush-logs --master-data=2 \
         --all-databases --delete-master-logs > backup_sunday_1_PM.sql


Deleting the MySQL binary logs with mysqldump --delete-master-logs can be dangerous if your server is a replication master server, because slave servers might not yet fully have processed the contents of the binary log. The description for the PURGE BINARY LOGS statement explains what should be verified before deleting the MySQL binary logs. See Section, “PURGE BINARY LOGS Syntax”.

6.3.2. Using Backups for Recovery

Now, suppose that we have a catastrophic crash on Wednesday at 8 a.m. that requires recovery from backups. To recover, first we restore the last full backup we have (the one from Sunday 1 p.m.). The full backup file is just a set of SQL statements, so restoring it is very easy:

shell> mysql < backup_sunday_1_PM.sql

At this point, the data is restored to its state as of Sunday 1 p.m.. To restore the changes made since then, we must use the incremental backups; that is, the gbichot2-bin.000007 and gbichot2-bin.000008 binary log files. Fetch the files if necessary from where they were backed up, and then process their contents like this:

shell> mysqlbinlog gbichot2-bin.000007 gbichot2-bin.000008 | mysql

We now have recovered the data to its state as of Tuesday 1 p.m., but still are missing the changes from that date to the date of the crash. To not lose them, we would have needed to have the MySQL server store its MySQL binary logs into a safe location (RAID disks, SAN, ...) different from the place where it stores its data files, so that these logs were not on the destroyed disk. (That is, we can start the server with a --log-bin option that specifies a location on a different physical device from the one on which the data directory resides. That way, the logs are safe even if the device containing the directory is lost.) If we had done this, we would have the gbichot2-bin.000009 file (and any subsequent files) at hand, and we could apply them using mysqlbinlog and mysql to restore the most recent data changes with no loss up to the moment of the crash:

shell> mysqlbinlog gbichot2-bin.000009 ... | mysql

For more information about using mysqlbinlog to process binary log files, see Section 6.6, “Point-in-Time (Incremental) Recovery Using the Binary Log”.

6.3.3. Backup Strategy Summary

In case of an operating system crash or power failure, InnoDB itself does all the job of recovering data. But to make sure that you can sleep well, observe the following guidelines:

  • Always run the MySQL server with the --log-bin option, or even --log-bin=log_name, where the log file name is located on some safe media different from the drive on which the data directory is located. If you have such safe media, this technique can also be good for disk load balancing (which results in a performance improvement).

  • Make periodic full backups, using the mysqldump command shown earlier in Section 6.3.1, “Backup Policy”, that makes an online, nonblocking backup.

  • Make periodic incremental backups by flushing the logs with FLUSH LOGS or mysqladmin flush-logs.

6.4. Using mysqldump for Backups

This section describes how to use mysqldump to produce dump files, and how to reload dump files. A dump file can be used in several ways:

  • As a backup to enable data recovery in case of data loss.

  • As a source of data for setting up replication slaves.

  • As a source of data for experimentation:

    • To make a copy of a database that you can use without changing the original data.

    • To test potential upgrade incompatibilities.

mysqldump produces two types of output, depending on whether the --tab option is given:

  • Without --tab, mysqldump writes SQL statements to the standard output. This output consists of CREATE statements to create dumped objects (databases, tables, stored routines, and so forth), and INSERT statements to load data into tables. The output can be saved in a file and reloaded later using mysql to recreate the dumped objects. Options are available to modify the format of the SQL statements, and to control which objects are dumped.

  • With --tab, mysqldump produces two output files for each dumped table. The server writes one file as tab-delimited text, one line per table row. This file is named tbl_name.txt in the output directory. The server also sends a CREATE TABLE statement for the table to mysqldump, which writes it as a file named tbl_name.sql in the output directory.

6.4.1. Dumping Data in SQL Format with mysqldump

This section describes how to use mysqldump to create SQL-format dump files. For information about reloading such dump files, see Section 6.4.2, “Reloading SQL-Format Backups”.

By default, mysqldump writes information as SQL statements to the standard output. You can save the output in a file:

shell> mysqldump [arguments] > file_name

To dump all databases, invoke mysqldump with the --all-databases option:

shell> mysqldump --all-databases > dump.sql

To dump only specific databases, name them on the command line and use the --databases option:

shell> mysqldump --databases db1 db2 db3 > dump.sql

The --databases option causes all names on the command line to be treated as database names. Without this option, mysqldump treats the first name as a database name and those following as table names.

With --all-databases or --databases, mysqldump writes CREATE DATABASE and USE statements prior to the dump output for each database. This ensures that when the dump file is reloaded, it creates each database if it does not exist and makes it the default database so database contents are loaded into the same database from which they came. If you want to cause the dump file to force a drop of each database before recreating it, use the --add-drop-database option as well. In this case, mysqldump writes a DROP DATABASE statement preceding each CREATE DATABASE statement.

To dump a single database, name it on the command line:

shell> mysqldump --databases test > dump.sql

In the single-database case, it is allowable to omit the --databases option:

shell> mysqldump test > dump.sql

The difference between the two preceding commands is that without --databases, the dump output contains no CREATE DATABASE or USE statements. This has several implications:

  • When you reload the dump file, you must specify a default database name so that the server knows which database to reload.

  • For reloading, you can specify a database name different from the original name, which enables you to reload the data into a different database.

  • If the database to be reloaded does not exist, you must create it first.

  • Because the output will contain no CREATE DATABASE statement, the --add-drop-database option has no effect. If you use it, it produces no DROP DATABASE statement.

To dump only specific tables from a database, name them on the command line following the database name:

shell> mysqldump test t1 t3 t7 > dump.sql

6.4.2. Reloading SQL-Format Backups

To reload a dump file written by mysqldump that consists of SQL statements, use it as input to the mysql client. If the dump file was created by mysqldump with the --all-databases or --databases option, it contains CREATE DATABASE and USE statements and it is not necessary to specify a default database into which to load the data:

shell> mysql < dump.sql

Alternatively, from within mysql, use a source command:

mysql> source dump.sql

If the file is a single-database dump not containing CREATE DATABASE and USE statements, create the database first (if necessary):

shell> mysqladmin create db1

Then specify the database name when you load the dump file:

shell> mysql db1 < dump.sql

Alternatively, from within mysql, create the database, select it as the default database, and load the dump file:

mysql> USE db1;
mysql> source dump.sql

6.4.3. Dumping Data in Delimited-Text Format with mysqldump

This section describes how to use mysqldump to create delimited-text dump files. For information about reloading such dump files, see Section 6.4.4, “Reloading Delimited-Text Format Backups”.

If you invoke mysqldump with the --tab=dir_name option, it uses dir_name as the output directory and dumps tables individually in that directory using two files for each table. The table name is the basename for these files. For a table named t1, the files are named t1.sql and t1.txt. The .sql file contains a CREATE TABLE statement for the table. The .txt file contains the table data, one line per table row.

The following command dumps the contents of the db1 database to files in the /tmp database:

shell> mysqldump --tab=/tmp db1

The .txt files containing table data are written by the server, so they are owned by the system account used for running the server. The server uses SELECT ... INTO OUTFILE to write the files, so you must have the FILE privilege to perform this operation, and an error occurs if a given .txt file already exists.

The server sends the CREATE definitions for dumped tables to mysqldump, which writes them to .sql files. These files therefore are owned by the user who executes mysqldump.

It is best that --tab be used only for dumping a local server. If you use it with a remote server, the --tab directory must exist on both the local and remote hosts, and the .txt files will be written by the server in the remote directory (on the server host), whereas the .sql files will be written by mysqldump in the local directory (on the client host).

For mysqldump --tab, the server by default writes table data to .txt files one line per row with tabs between column values, no quotation marks around column values, and newline as the line terminator. (These are the same defaults as for SELECT ... INTO OUTFILE.)

To enable data files to be written using a different format, mysqldump supports these options:

Depending on the value you specify for any of these options, it might be necessary on the command line to quote or escape the value appropriately for your command interpreter. Alternatively, specify the value using hex notation. Suppose that you want mysqldump to quote column values within double quotation marks. To do so, specify double quote as the value for the --fields-enclosed-by option. But this character is often special to command interpreters and must be treated specially. For example, on Unix, you can quote the double quote like this:


On any platform, you can specify the value in hex:


It is common to use several of the data-formatting options together. For example, to dump tables in comma-separated values format with lines terminated by carriage-return/newline pairs (\r\n), use this command (enter it on a single line):

shell> mysqldump --tab=/tmp --fields-terminated-by=,
         --fields-enclosed-by='"' --lines-terminated-by=0x0d0a db1

Should you use any of the data-formatting options to dump table data, you will need to specify the same format when you reload data files later, to ensure proper interpretation of the file contents.

6.4.4. Reloading Delimited-Text Format Backups

For backups produced with mysqldump --tab, each table is represented in the output directory by an .sql file containing the CREATE TABLE statement for the table, and a .txt file containing the table data. To reload a table, first change location into the output directory. Then process the .sql file with mysql to create an empty table and process the .txt file to load the data into the table:

shell> mysql db1 < t1.sql
shell> mysqlimport db1 t1.txt

An alternative to using mysqlimport to load the data file is to use the LOAD DATA INFILE statement from within the mysql client:

mysql> USE db1;
mysql> LOAD DATA INFILE 't1.txt' INTO TABLE t1;

If you used any data-formatting options with mysqldump when you initially dumped the table, you must use the same options with mysqlimport or LOAD DATA INFILE to ensure proper interpretation of the data file contents:

shell> mysqlimport --fields-terminated-by=,
         --fields-enclosed-by='"' --lines-terminated-by=0x0d0a db1 t1.txt


mysql> USE db1;
mysql> LOAD DATA INFILE 't1.txt' INTO TABLE t1
    -> LINES TERMINATED BY '\r\n';

6.4.5. mysqldump Tips

This section surveys techniques that enable you to use mysqldump to solve specific problems:

  • How to make a copy a database

  • How to copy a database from one server to another

  • How to dump stored programs (stored procedures and functions, triggers, and events)

  • How to dump definitions and data separately Making a Copy of a Database

shell> mysqldump db1 > dump.sql
shell> mysqladmin create db2
shell> mysql db2 < dump.sql

Do not use --databases on the mysqldump command line because that causes USE db1 to be included in the dump file, which overrides the effect of naming db2 on the mysql command line. Copy a Database from one Server to Another

On Server 1:

shell> mysqldump --databases db1 > dump.sql

Copy the dump file from Server 1 to Server 2.

On Server 2:

shell> mysql < dump.sql

Use of --databases with the mysqldump command line causes the dump file to include CREATE DATABASE and USE statements that create the database if it does exist and make it the default database for the reloaded data.

Alternatively, you can omit --databases from the mysqldump command. Then you will need to create the database on Server 2 (if necessary) and specify it as the default database when you reload the dump file.

On Server 1:

shell> mysqldump db1 > dump.sql

On Server 2:

shell> mysqladmin create db1
shell> mysql db1 < dump.sql

You can specify a different database name in this case, so omitting --databases from the mysqldump command enables you to dump data from one database and load it into another. Dumping Stored Programs

Several options control how mysqldump handles stored programs (stored procedures and functions, triggers, and events):

The --triggers option is enabled by default so that when tables are dumped, they are accompanied by any triggers they have. The other options are disabled by default and must be specified explicitly to dump the corresponding objects. To disable any of these options explicitly, use its skip form: --skip-events, --skip-routines, or --skip-triggers. Dumping Table Definitions and Content Separately

The --no-data option tells mysqldump not to dump table data, resulting in the dump file containing only statements to create the tables. Conversely, the --no-create-info option tells mysqldump to suppress CREATE statements from the output, so that the dump file contains only table data.

For example, to dump table definitions and data separately for the test database, use these commands:

shell> mysqldump --no-data test > dump-defs.sql
shell> mysqldump --no-create-info test > dump-data.sql

For a definition-only dump, add the --routines and --events options to also include stored routine and event definitions:

shell> mysqldump --no-data --routines --events test > dump-defs.sql Using mysqldump to Test for Upgrade Incompatibilities

When contemplating a MySQL upgrade, it is prudent to install the newer version separately from your current production version. Then you can dump the database and database object definitions from the production server and load them into the new server to verify that they are handled properly. (This is also useful for testing downgrades.)

On the production server:

shell> mysqldump --all-databases --no-data --routines --events > dump-defs.sql

On the upgraded server:

shell> mysql < dump-defs.sql

Because the dump file does not contain table data, it can be processed quickly. This enables you to spot potential incompatibilities without waiting for lengthy data-loading operations. Look for warnings or errors while the dump file is being processed.

After you have verified that the definitions are handled properly, dump the data and try to load it into the upgraded server.

On the production server:

shell> mysqldump --all-databases --no-create-info > dump-data.sql

On the upgraded server:

shell> mysql < dump-data.sql

Now check the table contents and run some test queries.

6.5. Using MySQL Backup

MySQL Backup is available as of MySQL 6.0.5. This feature comprises the BACKUP DATABASE and RESTORE statements. They provide a way to make a copy of a database or set of databases at a given point in time, and a way to restore each database to its state as of that time.

A backup operation can include tables for different storage engines and the backup image will still be consistent. That is, you need not care which storage engines you're using. BACKUP DATABASE saves the data in a consistent backup image with respect to its “validity point.

The validity point ties the backup to the binary log. Restoring a backup can be combined with use of the binary log to accomplish point-in-time recovery: If the restore operation is done because data loss has occurred after the backup was made (that is, after the validity point), restored databases can be brought up to the time of data loss by executing the data changes in the binary log between the times when the backup was made and when the data loss occurred.

A goal of the BACKUP DATABASE and RESTORE statements is to enable other database operations to proceed concurrently, to make it unnecessary to take databases offline or prevent clients from accessing them. BACKUP DATABASE must block some operations from occurring (such as dropping tables from a database while it is being backed up), but the attempt is made to keep blocking to a minimum. Generally, blocked operations are those involving Data Definition Language (DDL) statements. RESTORE must do more blocking because it writes database contents rather than just reading them.

The following discussion covers these aspects of BACKUP DATABASE and RESTORE:

  • Quick guide to making backups and restoring them


  • Status reporting and monitoring for backup and restore operations

For additional information about the BACKUP DATABASE and RESTORE statements, see these sections of the manual:

6.5.1. Quick Guide to MySQL Backup

Use the BACKUP DATABASE and RESTORE statements like this:

  • BACKUP DATABASE backs up one or more databases to a named file:

    BACKUP DATABASE world TO '/tmp/mybackupfile';

    To back up more than one database, separate the names by commas:

    BACKUP DATABASE world, sakila TO '/tmp/mybackupfile';

    To select all databases for backup, use the * selector as a shortcut:

    BACKUP DATABASE * TO '/tmp/mybackupfile';
  • RESTORE restores databases using the contents of the backup file:

    RESTORE FROM '/tmp/mybackupfile';

BACKUP DATABASE backs up database and table definitions, table data, stored routines, triggers, events, and views. TEMPORARY tables are not included. Tablespace backup support is limited to the Falcon storage engine.

Prior to MySQL 6.0.7, BACKUP DATABASE did not save any privileges in the backup image file and RESTORE did not restore privileges. As of MySQL 6.0.7, privileges are saved and restored according to these rules:

  • BACKUP DATABASE saves privileges for the backed-up databases in the backup image file. The privileges are stored in the form of GRANT statements.

  • Only privileges are the database level or below (table, column, routine) are saved. Global privileges are not saved because they are not specific to the databases included in the backup.

  • Privileges that specify the database name using a pattern (containing the '%' or '_' wildcard character) are not saved because they might apply to databases not included in the backup.

  • For restore operations, only those privileges are restored that pertain to accounts that exist on the MySQL server performing the restore. Other privileges are ignored with a warning. (These warnings can be displayed with SHOW WARNINGS.) Suppose that a backup contains this GRANT statement:

    GRANT SELECT, INSERT ON db1.* to 'someuser'@'localhost'

    The privileges specified by this statement will be restored if the 'someuser'@'localhost' account exists, and ignored with a warning otherwise.

    Restoration of privileges for accounts that do not exist is not done because that would implicitly create accounts that have no password, which is a security risk.

Storage of GRANT statement in backup image files has a security implication: Backup images should be stored in a secure location so that unauthorized users cannot modify the GRANT statements contained therein to change the privileges granted by restore operations.

For anything else not explicitly listed, assume that it is not backed up. This includes but is not limited to items such as UDF definitions and files, logs, and option files.

BACKUP DATABASE currently does not back up the contents of the mysql database. This database contains the grant tables that define user accounts and their privileges, as well as other system information. To make a full server instance backup that includes account information in addition to data, use the BACKUP DATABASE statement together with the mysqldump program. In the following instructions, path represents the full path name to the directory where you store your backup files.

  1. Use mysqldump to back up the mysql database. This is a blocking operation that prevents changes to the database during the dump, but the mysql database normally is relatively small and can be dumped quickly:

    shell> mysqldump --databases mysql > path/mysql-db.sql
  2. Use BACKUP DATABASE to back up the data from other databases. This is a nonblocking operation:

    mysql> BACKUP DATABASE * TO 'path/other-dbs.bak';

Restore the server instance later like this:

  1. To restore the user accounts, reload the mysql database dump file using the mysql client:

    shell> mysql -u root -p < path/mysql-db.sql
  2. To restore the data for other databases, use RESTORE with the image file produced by BACKUP DATABASE:

    mysql> RESTORE FROM 'path/other-dbs.bak';

For more information about the operation of the BACKUP DATABASE and RESTORE statements, see Section, “BACKUP DATABASE Syntax”, and Section, “RESTORE Syntax”.

6.5.2. How MySQL Backup Works

A backup operation creates a backup of one or more databases at a given point in time and saves it as a backup image, a file that contains the backup data (table contents) and metadata (definitions for databases, tables, and other objects, and server information).

The backup is intended to provide a consistent snapshot of the backed-up data as of the point at which the operation began, and it is intended to provide online operation as much as possible that allows other server activity to proceed without blocking.

A backup operation begins at time t1 and ends at time t2, producing a backup image that contains the backup state (database state) at time t, where t1 < t < t2. The time t is called the validity point of the backup image. It represents the time when all storage engines are synchronized for the backup. Restoring this image restores the state to be the same as it was at time t.

Consistency of the backup means that these constraints must be true:

  • Data from transactional tables is included only for committed transactions.

  • Data from nontransactional tables is included only for completed statements.

  • Referential integrity is maintained between all backed-up tables within a given backup image.

The referential-integrity constraint does not necessarily hold if two tables are related but only one of them is included in a backup. Restoring the backup then would restore only the backed-up table, which can produce tables for which referential integrity no longer holds.

For a backup to proceed properly, certain types of server activity must be blocked, so the backup system incorporates a commit blocker and a Backup Metadata Lock.

The commit blocker has these properties:

  • Changes for nontransactional tables must be blocked.

  • Changes for transactional tables are not blocked, but only changes that have been committed when the backup occurs appear in the backup. Changes that occur during the backup operation are not included in the backup image.

When a backup or restore operation is in progress, it is not allowable to modify the structure of database objects. Consequently, during the operation, the Backup Metadata Lock blocks statements that change database metadata from executing. A backup image stores metadata for the following types of objects:

  • Databases

  • Tablespaces

  • Privileges

  • Tables

  • Views

  • Stored programs (functions, procedures, events, triggers)

This requires that the following metadata changes be frozen during backup operation:

  • Databases being backed up should not disappear or be changed.

  • BACKUP DATABASE * ..., new databases should not appear.

  • The list of objects inside each database should not change.

  • Metadata for objects in the databases should not change.

  • The set of privileges for each database should not change.

  • Users for which privileges are stored should not disappear or change.

  • Tablespaces used by tables being backed up should not disappear or change.

To achieve these requirements, the Backup Metadata Lock blocks the following statements:


Currently, all instances of statements that change metadata are blocked, even for database or table objects that are not included in the backup. Eventually, the goal is to block only metadata-changing statements for objects in the backup.

Blocking works in both directions. A backup or restore blocks DDL statements, but if a backup or restore operation is initiated while DDL statements are in progress, the operation waits until the statements have finished.

Implementation of BACKUP DATABASE and RESTORE uses an architecture with the following design:

  • The MySQL server communicates with the backup kernel.

  • The backup kernel is responsible for communicating with backup engines and for handling metadata (definitions for databases, tables, and other objects, as well as server information).

  • Each backup engine provides backup and restore drivers for the backup kernel to use.

  • An engine's backup and restore drivers perform actual transfer of data (table contents).

The backup system chooses from among the backup engines available to it:

  • There is a default backup engine to be used if a better one is not found. This engine provides default backup and restore drivers that use a blocking algorithm. For example, the backup driver locks all tables at the start of the backup and unlocks them after the last one is processed (which may occur before the operation is complete).

  • A consistent-snapshot engine implements the same kind of backup as that made by mysqldump --single-transaction.

    The backup driver for the snapshot engine works with only those storage engines that support consistent read via the handler interface, which currently includes only InnoDB and Falcon. The backup driver creates a logical backup because it reads rows one at a time and returns them to the backup kernel to be stored in the backup image.

A backup image must have contents that are consistent with the binary log coordinates taken from the time of the backup. Otherwise, point-in-time recovery using the backup image plus the binary log contents will not work correctly. BACKUP DATABASE synchronizes with binary logging to make sure that the backup image and binary log are consistent with each other. This way, if data loss occurs later, use of the backup image combined with the binary log makes point-in-time recovery possible:

  1. Restore the backup image

  2. Re-execute binary log contents beginning from the coordinates of the backup's validity point up to the desired point of recovery

6.5.3. MySQL Backup Status Reporting and Monitoring

MySQL provides information about the status or progress of BACKUP DATABASE or RESTORE operations in the following ways:

  • SHOW PROCESSLIST displays information while a thread performing a backup or restore is executing.

  • Upon successful completion, the BACKUP DATABASE and RESTORE statements return a result set with the backup number. (This number is the ID for the corresponding row or rows in the metadata tables described later.) Warnings produced during the operation can be displayed with SHOW WARNINGS.

    If errors occur during a backup or restore operation, they are written to the error log, recorded in the progress tables, and are available via the SHOW ERRORS and SHOW WARNINGS statements.

    If a fatal error occurs, the BACKUP DATABASE or RESTORE statement reports it to the user.

  • The server maintains backup_history and backup_progress tables in the mysql database that contain metadata indicating backup status and progress. It is also possible to write log information to files. For information about selecting log destinations, see Section, “MySQL Backup Log Control”. For a description of what is logged, see Section, “MySQL Backup Log Contents”.

    If you upgrade to MySQL 6.0.5 or later from an older version, be sure to run mysql_upgrade to ensure that the backup log tables exist. From MySQL 6.0.5 through 6.0.7, these tables were named online_backup and online_backup_progress.

    Currently, there are no INFORMATION_SCHEMA tables corresponding to the backup_history and backup_progress tables. MySQL Backup Log Control

MySQL Backup provides status and progress logging. This capability can be enabled or disabled. If logging is enabled, tables in the mysql database or log files can be used as the destinations for log output. These features are similar to those provided for the general query log and slow query log (see Section 5.2.1, “Selecting General Query and Slow Query Log Output Destinations”), although the options and variables are different.

This section describes how to control MySQL Backup logging. For a description of what is logged, see Section, “MySQL Backup Log Contents”.


The features described here are available as of MySQL 6.0.8. Before 6.0.8, MySQL Backup logs to the online_backup and online_backup_progress tables in the mysql database. Logging to files is not supported and logging cannot be disabled.

Log control at server startup. The --log-backup-output option specifies the destination for log output, if logging is enabled, but the option does not in itself enable the logs. The syntax for this option is --log-backup-output[=value,...]:

  • If --log-backup-output is given with a value, the value can be a comma-separated list of one or more of the words TABLE (log to tables), FILE (log to files), or NONE (do not log to tables or files). NONE, if present, takes precedence over any other specifiers.

  • If --log-backup-output is omitted or given without a value, the default logging destination is TABLE.

The --backup_history_log and --backup_progress_log variables control how logging is done to the history and progress logs for the selected log destinations. (By default, both logs are enabled.) These options take an optional argument of 1 or 0 to enable or disable the log. If either log is enabled, the server opens the corresponding log file and writes startup messages to it. However, further logging to the file does not occur unless the FILE log destination is selected.


  • With no logging arguments, MySQL Backup logs to the log tables by default.

  • To write log entries to the log tables and log files, use --log-backup-output=TABLE,FILE to select both log destinations.

Log control at runtime. Several system variables are associated with log tables and files and enable runtime control over logging:

  • The log_backup_output system variable indicates the current logging destinations. It can be modified at runtime to change the destinations.

  • The backup_history_log and backup_progress_log variables indicate whether the history and progress logs are enabled (ON) or disabled (OFF). You can set these variables at runtime to control whether the logs are enabled.

  • The backup_history_log_file and backup_progress_log_file variables indicate the names of the history and progress log files. You can set these variables at runtime to change the names of the log files. MySQL Backup Log Contents

If you enable backup logging to tables, MySQL Backup uses the backup_history and backup_progress tables in the mysql database. For logging to files, MySQL Backup uses the backup_history.log and backup_progress.log files in the MySQL data directory by default. The log file names can be changed by setting the global backup_history_log_file and backup_progress_log_file system variables. For information about selecting log Section, “MySQL Backup Log Control”.

For logging to files, the server writes lines with a field for each column in the corresponding log table. The server also writes an initial line to the file at startup to indicate the names of the fields.

If the table destination is selected for backup logging, the server uses these tables:

  • The backup_history table contains a row for each backup and restore operation. A row is created when an operation completes. The rows in this table serve as a history of all backup and restore operations performed on the server. The table can be queried to obtain detailed information about the operations or as a means of creating a summary of the operations. The rows are not removed from the table by the server. Any table maintenance, such as removing old rows, is intended to be performed by the database administrator.

  • The backup_progress table contains progress data describing the steps in the most recent backup or restore operation. There may be multiple rows for the operation. Rows are added to this table over the course of the operation and are not updated. This enables the table to be used to track the current progress of the operation. Each row in the table represents a step in the operation and may contain informational statements, errors, and other pertinent information. The data in this table has a limited lifetime. At the start of each operation, the table is truncated and new data is added. The database administrator should not need to perform maintenance for this data.

Backup log contents can be culled with the PURGE BACKUP LOGS statement (see Section, “PURGE BACKUP LOGS Syntax”.)

The backup_history table has this structure:

CREATE TABLE backup_history (
    backup_id           BIGINT UNSIGNED NOT NULL,
    process_id          INT UNSIGNED NOT NULL,
    binlog_start_pos    INT UNSIGNED NOT NULL,
    binlog_file         CHAR(64) NOT NULL,
    backup_state        ENUM('complete', 'starting', 'validity point',
                             'running', 'error', 'cancel') NOT NULL,
    operation           ENUM('backup', 'restore') NOT NULL,
    error_num           INT NOT NULL,
    num_objects         INT UNSIGNED NOT NULL,
    total_bytes         BIGINT UNSIGNED NOT NULL,
    validity_point_time DATETIME NOT NULL,
    start_time          DATETIME NOT NULL,
    stop_time           DATETIME NOT NULL,
    host_or_server_name CHAR (30) NOT NULL,
    username            CHAR (30) NOT NULL,
    backup_file         CHAR (100) NOT NULL,
    backup_file_path    VARCHAR (512) NOT NULL,
    user_comment        VARCHAR (200) NOT NULL,
    command             VARCHAR (512) NOT NULL,
    engines             VARCHAR (100) NOT NULL

The backup_history columns are used as follows:

  • backup_id

    The ID for the table row. BACKUP DATABASE and RESTORE return a result set containing a backup ID, which is the value that tells you which row in the backup_history table corresponds to the backup or restore operation.

  • process_id

    The process ID that the operation ran as.

  • binlog_start_pos, binlog_file

    For a backup, the starting binary log position and the file name at the time the validity point is generated (the time when all storage engines are synchronized). If the binary log is not enabled, the values are 0 and '' (the empty string.

  • backup_state

    The status of the operation.

  • operation

    The type of operation.

  • error_num

    The error from this operation (0 = no error).

  • num_objects

    The number of objects in the backup.

  • total_bytes

    For a backup, the number of bytes written to the backup image file (after any compression or encryption). For a restore, the number of bytes read from the backup image file.

  • validity_point_time

    For a backup, this is the time that the validity point was generated.

  • start_time, stop_time

    The date and time when the operation started and stopped.

  • host_or_server_name

    The server name where the operation ran.

  • username

    The name of the user who ran the operation.

  • backup_file

    The name of the backup image file. As of MySQL 6.0.8, this column contains the file basename.

  • backup_file_path

    The directory containing the image file. This column was added in MySQL 6.0.8.

  • user_comment

    The comment from the user entered at the command line.

  • command

    The statement used to perform the operation.

  • drivers

    The names of the drivers used in the operation. Before MySQL 6.0.7, this column was named engines.

The backup_progress table has this structure:

CREATE TABLE backup_progress (
    object      CHAR (30) NOT NULL,
    error_num   INT NOT NULL,
    notes       CHAR(100) NOT NULL

The backup_progress columns are used as follows:

  • backup_id

    The backup_id value of the backup_history table row with which the rows in the backup_progress table are associated.

  • object

    The object being operated on.

  • error_num

    The error from this operation (0 = no error).

  • notes

    Commentary from the backup engine.

6.6. Point-in-Time (Incremental) Recovery Using the Binary Log

Point-in-time recovery refers to recovery of data changes made since a given point in time. Typically, this type of recovery is performed after restoring a full backup that brings the server to its state as of the time the backup was made. (The full backup can be made in several ways, such as those listed in Section 6.2, “Database Backup Methods”.) Point-in-time recovery then brings the server up to date incrementally from the time of the full backup to a more recent time.

Point-in-time recovery is based on these principles:

  • The source of information for point-in-time recovery is the set of incremental backups represented by the binary log files generated subsequent to the full backup operation. Therefore, the server must be started with the --log-bin option to enable binary logging (see Section 5.2.4, “The Binary Log”).

    To restore data from the binary log, you must know the name and location of the current binary log files. By default, the server creates binary log files in the data directory, but a path name can be specified with the --log-bin option to place the files in a different location. Section 5.2.4, “The Binary Log”.

    To see a listing of all binary log files, use this statement:

    mysql> SHOW BINARY LOGS;

    To determine the name of the current binary log file, issue the following statement:

  • The mysqlbinlog utility converts the events in the binary log files from binary format to text so that they can be executed or viewed. mysqlbinlog has options for selecting sections of the binary log based on event times or position of events within the log. See Section 4.6.8, “mysqlbinlog — Utility for Processing Binary Log Files”.

  • Executing events from the binary log causes the data modifications they represent to be redone. This enables recovery of data changes for a given span of time. To execute events from the binary log, process mysqlbinlog output using the mysql client:

    shell> mysqlbinlog binlog_files | mysql -u root -p
  • Viewing log contents can be useful when you need to determine event times or positions to select partial log contents prior to executing events. To view events from the log, send mysqlbinlog output into a paging program:

    shell> mysqlbinlog binlog_files | more

    Alternatively, save the output in a file and view the file in a text editor:

    shell> mysqlbinlog binlog_files > tmpfile
    shell> ... edit tmpfile ...
  • Saving the output in a file is useful as a preliminary to executing the log contents with certain events removed, such as an accidental DROP DATABASE. You can delete from the file any statements not to be executed before executing its contents. After editing the file, execute the contents as follows:

    shell> mysql -u root -p < tmpfile

If you have more than one binary log to execute on the MySQL server, the safe method is to process them all using a single connection to the server. Here is an example that demonstrates what may be unsafe:

shell> mysqlbinlog binlog.000001 | mysql -u root -p # DANGER!!
shell> mysqlbinlog binlog.000002 | mysql -u root -p # DANGER!!

Processing binary logs this way using different connections to the server causes problems if the first log file contains a CREATE TEMPORARY TABLE statement and the second log contains a statement that uses the temporary table. When the first mysql process terminates, the server drops the temporary table. When the second mysql process attempts to use the table, the server reports “unknown table.

To avoid problems like this, use a single connection to execute the contents of all binary logs that you want to process. Here is one way to do so:

shell> mysqlbinlog binlog.000001 binlog.000002 | mysql -u root -p

Another approach is to write all the logs to a single file and then process the file:

shell> mysqlbinlog binlog.000001 >  /tmp/statements.sql
shell> mysqlbinlog binlog.000002 >> /tmp/statements.sql
shell> mysql -u root -p -e "source /tmp/statements.sql"

MySQL Enterprise For maximum data recovery, the MySQL Enterprise Monitor advises subscribers to synchronize to disk at each write. For more information, see

6.6.1. Point-in-Time Recovery Using Event Times

To indicate the start and end times for recovery, specify the --start-datetime and --stop-datetime options for mysqlbinlog, in DATETIME format. As an example, suppose that exactly at 10:00 a.m. on April 20, 2005 an SQL statement was executed that deleted a large table. To restore the table and data, you could restore the previous night's backup, and then execute the following command:

shell> mysqlbinlog --stop-datetime="2005-04-20 9:59:59" \
         /var/log/mysql/bin.123456 | mysql -u root -p

This command recovers all of the data up until the date and time given by the --stop-datetime option. If you did not detect the erroneous SQL statement that was entered until hours later, you will probably also want to recover the activity that occurred afterward. Based on this, you could run mysqlbinlog again with a start date and time, like so:

shell> mysqlbinlog --start-datetime="2005-04-20 10:01:00" \
         /var/log/mysql/bin.123456 | mysql -u root -p

In this command, the SQL statements logged from 10:01 a.m. on will be re-executed. The combination of restoring of the previous night's dump file and the two mysqlbinlog commands restores everything up until one second before 10:00 a.m. and everything from 10:01 a.m. on.

To use this method of point-in-time recovery, you should examine the log to be sure of the exact times to specify for the commands. To display the log file contents without executing them, use this command:

shell> mysqlbinlog /var/log/mysql/bin.123456 > /tmp/mysql_restore.sql

Then open the /tmp/mysql_restore.sql file with a text editor to examine it.

Excluding specific changes by specifying times for mysqlbinlog does not work well if multiple statements executed at the same time as the one to be excluded.

6.6.2. Point-in-Time Recovery Using Event Positions

Instead of specifying dates and times, the --start-position and --stop-position options for mysqlbinlog can be used for specifying log positions. They work the same as the start and stop date options, except that you specify log position numbers rather than dates. Using positions may enable you to be more precise about which part of the log to recover, especially if many transactions occurred around the same time as a damaging SQL statement. To determine the position numbers, run mysqlbinlog for a range of times near the time when the unwanted transaction was executed, but redirect the results to a text file for examination. This can be done like so:

shell> mysqlbinlog --start-datetime="2005-04-20 9:55:00" \
         --stop-datetime="2005-04-20 10:05:00" \
         /var/log/mysql/bin.123456 > /tmp/mysql_restore.sql

This command creates a small text file in the /tmp directory that contains the SQL statements around the time that the deleterious SQL statement was executed. Open this file with a text editor and look for the statement that you do not want to repeat. Determine the positions in the binary log for stopping and resuming the recovery and make note of them. Positions are labeled as log_pos followed by a number. After restoring the previous backup file, use the position numbers to process the binary log file. For example, you would use commands something like these:

shell> mysqlbinlog --stop-position=368312 /var/log/mysql/bin.123456 \
         | mysql -u root -p

shell> mysqlbinlog --start-position=368315 /var/log/mysql/bin.123456 \
         | mysql -u root -p

The first command recovers all the transactions up until the stop position given. The second command recovers all transactions from the starting position given until the end of the binary log. Because the output of mysqlbinlog includes SET TIMESTAMP statements before each SQL statement recorded, the recovered data and related MySQL logs will reflect the original times at which the transactions were executed.

6.7. MyISAM Table Maintenance and Crash Recovery

This section discusses how to use myisamchk to check or repair MyISAM tables (tables that have .MYD and .MYI files for storing data and indexes). For general myisamchk background, see Section 4.6.3, “myisamchk — MyISAM Table-Maintenance Utility”. Other table-repair information can be found at Section 2.11.4, “Rebuilding or Repairing Tables or Indexes”.

You can use myisamchk to check, repair, or optimize database tables. The following sections describe how to perform these operations and how to set up a table maintenance schedule. For information about using myisamchk to get information about your tables, see Section, “myisamchk Table Information”.

Even though table repair with myisamchk is quite secure, it is always a good idea to make a backup before doing a repair or any maintenance operation that could make a lot of changes to a table.

myisamchk operations that affect indexes can cause FULLTEXT indexes to be rebuilt with full-text parameters that are incompatible with the values used by the MySQL server. To avoid this problem, follow the guidelines in Section, “myisamchk General Options”.

MyISAM table maintenance can also be done using the SQL statements that perform operations similar to what myisamchk can do:

For additional information about these statements, see Section 12.4.2, “Table Maintenance Statements”.

These statements can be used directly or by means of the mysqlcheck client program. One advantage of these statements over myisamchk is that the server does all the work. With myisamchk, you must make sure that the server does not use the tables at the same time so that there is no unwanted interaction between myisamchk and the server.

6.7.1. Using myisamchk for Crash Recovery

This section describes how to check for and deal with data corruption in MySQL databases. If your tables become corrupted frequently, you should try to find the reason why. See Section B.5.4.2, “What to Do If MySQL Keeps Crashing”.

For an explanation of how MyISAM tables can become corrupted, see Section 13.5.4, “MyISAM Table Problems”.

If you run mysqld with external locking disabled (which is the default), you cannot reliably use myisamchk to check a table when mysqld is using the same table. If you can be certain that no one will access the tables through mysqld while you run myisamchk, you only have to execute mysqladmin flush-tables before you start checking the tables. If you cannot guarantee this, you must stop mysqld while you check the tables. If you run myisamchk to check tables that mysqld is updating at the same time, you may get a warning that a table is corrupt even when it is not.

If the server is run with external locking enabled, you can use myisamchk to check tables at any time. In this case, if the server tries to update a table that myisamchk is using, the server will wait for myisamchk to finish before it continues.

If you use myisamchk to repair or optimize tables, you must always ensure that the mysqld server is not using the table (this also applies if external locking is disabled). If you do not stop mysqld, you should at least do a mysqladmin flush-tables before you run myisamchk. Your tables may become corrupted if the server and myisamchk access the tables simultaneously.

When performing crash recovery, it is important to understand that each MyISAM table tbl_name in a database corresponds to the three files in the database directory shown in the following table.

tbl_name.frmDefinition (format) file
tbl_name.MYDData file
tbl_name.MYIIndex file

Each of these three file types is subject to corruption in various ways, but problems occur most often in data files and index files.

myisamchk works by creating a copy of the .MYD data file row by row. It ends the repair stage by removing the old .MYD file and renaming the new file to the original file name. If you use --quick, myisamchk does not create a temporary .MYD file, but instead assumes that the .MYD file is correct and generates only a new index file without touching the .MYD file. This is safe, because myisamchk automatically detects whether the .MYD file is corrupt and aborts the repair if it is. You can also specify the --quick option twice to myisamchk. In this case, myisamchk does not abort on some errors (such as duplicate-key errors) but instead tries to resolve them by modifying the .MYD file. Normally the use of two --quick options is useful only if you have too little free disk space to perform a normal repair. In this case, you should at least make a backup of the table before running myisamchk.

6.7.2. How to Check MyISAM Tables for Errors

To check a MyISAM table, use the following commands:

  • myisamchk tbl_name

    This finds 99.99% of all errors. What it cannot find is corruption that involves only the data file (which is very unusual). If you want to check a table, you should normally run myisamchk without options or with the -s (silent) option.

  • myisamchk -m tbl_name

    This finds 99.999% of all errors. It first checks all index entries for errors and then reads through all rows. It calculates a checksum for all key values in the rows and verifies that the checksum matches the checksum for the keys in the index tree.

  • myisamchk -e tbl_name

    This does a complete and thorough check of all data (-e means “extended check”). It does a check-read of every key for each row to verify that they indeed point to the correct row. This may take a long time for a large table that has many indexes. Normally, myisamchk stops after the first error it finds. If you want to obtain more information, you can add the -v (verbose) option. This causes myisamchk to keep going, up through a maximum of 20 errors.

  • myisamchk -e -i tbl_name

    This is like the previous command, but the -i option tells myisamchk to print additional statistical information.

In most cases, a simple myisamchk command with no arguments other than the table name is sufficient to check a table.

6.7.3. How to Repair MyISAM Tables

The discussion in this section describes how to use myisamchk on MyISAM tables (extensions .MYI and .MYD).

You can also (and should, if possible) use the CHECK TABLE and REPAIR TABLE statements to check and repair MyISAM tables. See Section, “CHECK TABLE Syntax”, and Section, “REPAIR TABLE Syntax”.

Symptoms of corrupted tables include queries that abort unexpectedly and observable errors such as these:

  • tbl_name.frm is locked against change

  • Can't find file tbl_name.MYI (Errcode: nnn)

  • Unexpected end of file

  • Record file is crashed

  • Got error nnn from table handler

To get more information about the error, run perror nnn, where nnn is the error number. The following example shows how to use perror to find the meanings for the most common error numbers that indicate a problem with a table:

shell> perror 126 127 132 134 135 136 141 144 145
MySQL error code 126 = Index file is crashed
MySQL error code 127 = Record-file is crashed
MySQL error code 132 = Old database file
MySQL error code 134 = Record was already deleted (or record file crashed)
MySQL error code 135 = No more room in record file
MySQL error code 136 = No more room in index file
MySQL error code 141 = Duplicate unique key or constraint on write or update
MySQL error code 144 = Table is crashed and last repair failed
MySQL error code 145 = Table was marked as crashed and should be repaired

Note that error 135 (no more room in record file) and error 136 (no more room in index file) are not errors that can be fixed by a simple repair. In this case, you must use ALTER TABLE to increase the MAX_ROWS and AVG_ROW_LENGTH table option values:


If you do not know the current table option values, use SHOW CREATE TABLE.

For the other errors, you must repair your tables. myisamchk can usually detect and fix most problems that occur.

The repair process involves up to four stages, described here. Before you begin, you should change location to the database directory and check the permissions of the table files. On Unix, make sure that they are readable by the user that mysqld runs as (and to you, because you need to access the files you are checking). If it turns out you need to modify files, they must also be writable by you.

This section is for the cases where a table check fails (such as those described in Section 6.7.2, “How to Check MyISAM Tables for Errors”), or you want to use the extended features that myisamchk provides.

The options that you can use for table maintenance with myisamchk are described in Section 4.6.3, “myisamchk — MyISAM Table-Maintenance Utility”.

If you are going to repair a table from the command line, you must first stop the mysqld server. Note that when you do mysqladmin shutdown on a remote server, the mysqld server is still alive for a while after mysqladmin returns, until all statement-processing has stopped and all index changes have been flushed to disk.

Stage 1: Checking your tables

Run myisamchk *.MYI or myisamchk -e *.MYI if you have more time. Use the -s (silent) option to suppress unnecessary information.

If the mysqld server is stopped, you should use the --update-state option to tell myisamchk to mark the table as “checked.

You have to repair only those tables for which myisamchk announces an error. For such tables, proceed to Stage 2.

If you get unexpected errors when checking (such as out of memory errors), or if myisamchk crashes, go to Stage 3.

Stage 2: Easy safe repair

First, try myisamchk -r -q tbl_name (-r -q means “quick recovery mode”). This attempts to repair the index file without touching the data file. If the data file contains everything that it should and the delete links point at the correct locations within the data file, this should work, and the table is fixed. Start repairing the next table. Otherwise, use the following procedure:

  1. Make a backup of the data file before continuing.

  2. Use myisamchk -r tbl_name (-r means “recovery mode”). This removes incorrect rows and deleted rows from the data file and reconstructs the index file.

  3. If the preceding step fails, use myisamchk --safe-recover tbl_name. Safe recovery mode uses an old recovery method that handles a few cases that regular recovery mode does not (but is slower).


If you want a repair operation to go much faster, you should set the values of the sort_buffer_size and key_buffer_size variables each to about 25% of your available memory when running myisamchk.

If you get unexpected errors when repairing (such as out of memory errors), or if myisamchk crashes, go to Stage 3.

Stage 3: Difficult repair

You should reach this stage only if the first 16KB block in the index file is destroyed or contains incorrect information, or if the index file is missing. In this case, it is necessary to create a new index file. Do so as follows:

  1. Move the data file to a safe place.

  2. Use the table description file to create new (empty) data and index files:

    shell> mysql db_name
    mysql> SET autocommit=1;
    mysql> TRUNCATE TABLE tbl_name;
    mysql> quit
  3. Copy the old data file back onto the newly created data file. (Do not just move the old file back onto the new file. You want to retain a copy in case something goes wrong.)


If you are using replication, you should stop it prior to performing the above procedure, since it involves file system operations, and these are not logged by MySQL.

Go back to Stage 2. myisamchk -r -q should work. (This should not be an endless loop.)

You can also use the REPAIR TABLE tbl_name USE_FRM SQL statement, which performs the whole procedure automatically. There is also no possibility of unwanted interaction between a utility and the server, because the server does all the work when you use REPAIR TABLE. See Section, “REPAIR TABLE Syntax”.

Stage 4: Very difficult repair

You should reach this stage only if the .frm description file has also crashed. That should never happen, because the description file is not changed after the table is created:

  1. Restore the description file from a backup and go back to Stage 3. You can also restore the index file and go back to Stage 2. In the latter case, you should start with myisamchk -r.

  2. If you do not have a backup but know exactly how the table was created, create a copy of the table in another database. Remove the new data file, and then move the .frm description and .MYI index files from the other database to your crashed database. This gives you new description and index files, but leaves the .MYD data file alone. Go back to Stage 2 and attempt to reconstruct the index file.

6.7.4. MyISAM Table Optimization

To coalesce fragmented rows and eliminate wasted space that results from deleting or updating rows, run myisamchk in recovery mode:

shell> myisamchk -r tbl_name

You can optimize a table in the same way by using the OPTIMIZE TABLE SQL statement. OPTIMIZE TABLE does a table repair and a key analysis, and also sorts the index tree so that key lookups are faster. There is also no possibility of unwanted interaction between a utility and the server, because the server does all the work when you use OPTIMIZE TABLE. See Section, “OPTIMIZE TABLE Syntax”.

myisamchk has a number of other options that you can use to improve the performance of a table:

  • --analyze or -a: Perform key distribution analysis. This improves join performance by enabling the join optimizer to better choose the order in which to join the tables and which indexes it should use.

  • --sort-index or -S: Sort the index blocks. This optimizes seeks and makes table scans that use indexes faster.

  • --sort-records=index_num or -R index_num: Sort data rows according to a given index. This makes your data much more localized and may speed up range-based SELECT and ORDER BY operations that use this index.

For a full description of all available options, see Section 4.6.3, “myisamchk — MyISAM Table-Maintenance Utility”.

6.7.5. Setting Up a MyISAM Table Maintenance Schedule

It is a good idea to perform table checks on a regular basis rather than waiting for problems to occur. One way to check and repair MyISAM tables is with the CHECK TABLE and REPAIR TABLE statements. See Section 12.4.2, “Table Maintenance Statements”.

Another way to check tables is to use myisamchk. For maintenance purposes, you can use myisamchk -s. The -s option (short for --silent) causes myisamchk to run in silent mode, printing messages only when errors occur.

It is also a good idea to enable automatic MyISAM table checking. For example, whenever the machine has done a restart in the middle of an update, you usually need to check each table that could have been affected before it is used further. (These are “expected crashed tables.”) To cause the server to check MyISAM tables automatically, start it with the --myisam-recover-options option. See Section 5.1.2, “Server Command Options”.

You should also check your tables regularly during normal system operation. For example, you can run a cron job to check important tables once a week, using a line like this in a crontab file:

35 0 * * 0 /path/to/myisamchk --fast --silent /path/to/datadir/*/*.MYI

This prints out information about crashed tables so that you can examine and repair them as necessary.

To start with, execute myisamchk -s each night on all tables that have been updated during the last 24 hours. As you see that problems occur infrequently, you can back off the checking frequency to once a week or so.

Normally, MySQL tables need little maintenance. If you are performing many updates to MyISAM tables with dynamic-sized rows (tables with VARCHAR, BLOB, or TEXT columns) or have tables with many deleted rows you may want to defragment/reclaim space from the tables from time to time. You can do this by using OPTIMIZE TABLE on the tables in question. Alternatively, if you can stop the mysqld server for a while, change location into the data directory and use this command while the server is stopped:

shell> myisamchk -r -s --sort-index --sort_buffer_size=16M */*.MYI