Assuming a good portion of the data on your MySQL server remains unchanged over time, you can increase the speed and reduce the required storage space for your regular backups by backing up not all the data on the server each time, but only the changes to the data which have taken place over time. In order to that, after making first a full backup that contains all data, you can do one of the following:
Performing a series of differential backups. Each differential backups includes all the changes made to the data since the last full backup was performed. To restore data up to, for example, time
t
, you simply restore first the full backup, and then, on top of it, the differential backup taken for timet
.Perform a series of incremental backup. Each incremental backup only includes the changes since the previous backup, which can itself be a full or incremental backup. The first backup in an incremental series is always then a differential backup; but after that, each incremental backup only contains the changes made since that last incremental backup. Each subsequent incremental backup is thus usually smaller in size than a differential backup, and is faster to make; that allows you to make very frequent incremental backups, and then enables you to restore the database to a more precise point in time when necessary. However, restoring data with incremental backups might take longer and more work: in general, to restore data up to, for example, time
t
, you start with restoring the full backup, and then restore the incremental backups one by one, until you are finished with the incremental backup taken for time t.
MySQL Enterprise Backup supports both incremental and differential backups. You should decide on which backup strategy to adopt by looking at such factors like how much storage space you have, how quickly you have to be able to restore data, and so on.
MySQL Enterprise Backup treats differential backup as a special case of incremental backup that has a full backup as its base. To create a differential backup, simply follow the instructions below for performing incremental backups, and make sure you specify a full backup as the base of your incremental backup; you should also ignore any instructions that only apply to the handling of multiple incremental backups.
For MySQL Enterprise Backup 8.0.17 and later, you can
create a differential backup easily using the option
--incremental-base=history:last_full_backup
.
See Section 18.7, “Incremental Backup Options”, for
descriptions of the mysqlbackup options used
for incremental backups. An Incremental backup is enabled with
one of the two options:
--incremental
and
--incremental-with-redo-log-only
option. See
Creating Incremental Backups Using Only the Redo Log
for their differences.
When creating an incremental backup, you have to indicate to
mysqlbackup the point in time of the previous
full or incremental backup. For convenience, you can use the
--incremental-base
option to
automatically derive the necessary log
sequence number (LSN) from the metadata stored in a
previous backup directory or on the server. Or, you can specify
an explicit LSN value using the
--start-lsn
option,
providing to mysqlbackup the ending LSN from
a previous full or incremental backup (see
Other Considerations for Incremental Backups on
some limitation that applies when using the
--start-lsn
option).
To prepare the backup data to be restored, you combine all incremental backups with an original full backup. Typically, you perform a new full backup after a designated period of time, after which you can discard the older incremental backup data.
Creating Incremental Backups Using Only the Redo Log
The --incremental-with-redo-log-only
might offer some benefits over the
--incremental
option for creating an
incremental backup:
The changes to InnoDB tables are determined based on the contents of the
InnoDB
redo log. Since the redo log files have a fixed size that you know in advance, it can require less I/O to read the changes from them than to scan the InnoDB tablespace files to locate the changed pages, depending on the size of your database, amount of DML activity, and size of the redo log files.Since the redo log files act as a circular buffer, with records of older changes being overwritten as new DML operations take place, you must take new incremental backups on a predictable schedule dictated by the size of the log files and the amount of redo data generated for your workload. Otherwise, the redo log might not reach back far enough to record all the changes since the previous incremental backup, in which case mysqlbackup will quickly determine that it cannot proceed and will return an error. Your backup script should be able to catch that error and then perform an incremental backup with the
--incremental
option instead.For example:
To calculate the size of the redo log, issue the command
SHOW VARIABLES LIKE 'innodb_log_file%'
and, based on the output, multiply theinnodb_log_file_size
setting by the value ofinnodb_log_files_in_group
. To compute the redo log size at the physical level, look into thedatadir
directory of the MySQL instance and sum up the sizes of the files matching the patternib_logfile*
.The InnoDB LSN value corresponds to the number of bytes written to the redo log. To check the LSN at some point in time, issue the command
SHOW ENGINE INNODB STATUS
and look under theLOG
heading. While planning your backup strategy, record the LSN values periodically and subtract the earlier value from the current one to calculate how much redo data is generated each hour, day, and so on.
Prior to MySQL 5.5, it was common practice to keep the redo logs fairly small to avoid a long startup time when the MySQL server was killed rather than shut down normally. With MySQL 5.5 and higher, the performance of crash recovery is significantly improved, as described in Optimizing InnoDB Configuration Variables, so that you can make your redo log files bigger if that helps your backup strategy and your database workload.
This type of incremental backup is not so forgiving of too-low
--start-lsn
values as the standard--incremental
option is. For example, you cannot make a full backup and then make a series of--incremental-with-redo-log-only
backups all using the same--start-lsn
value. Make sure to specify the precise end LSN of the previous backup as the start LSN of the next incremental backup; do not use arbitrary values.NoteTo ensure the LSN values match up exactly between successive incremental backups, it is recommended that you always use the
--incremental-base
option when you use the--incremental-with-redo-log-only
option.To judge whether this type of incremental backup is practical and efficient for a particular MySQL instance:
Measure how fast the data changes within the InnoDB redo log files. Check the LSN periodically to decide how much redo data accumulates over the course of some number of hours or days.
Compare the rate of redo log accumulation with the size of the redo log files. Use this ratio to see how often to take an incremental backup, in order to avoid the likelihood of the backup failing because the historical data are not available in the redo log. For example, if you are producing 1GB of redo log data per day, and the combined size of your redo log files is 7GB, you would schedule incremental backups more frequently than once a week. You might perform incremental backups every day or two, to avoid a potential issue when a sudden flurry of updates produced more redo log data than usual.
Benchmark incremental backup times using both the
--incremental
and--incremental-with-redo-log-only
options, to confirm if the redo log backup technique performs faster and with less overhead than the traditional incremental backup method. The result could depend on the size of your data, the amount of DML activity, and the size of your redo log files. Do your testing on a server with a realistic data volume and a realistic workload. For example, if you have huge redo log files, reading them in the course of an incremental backup could take as long as reading the InnoDB data files using the traditional incremental technique. Conversely, if your data volume is large, reading all the data files to find the few changed pages could be less efficient than processing the much smaller redo log files.Backup compression (i.e., use of the compression options) is not supported when you perform incremental backups with the redo log only. If backup compression is important to you, do not use the
--incremental-with-redo-log-only
option.
Incremental Backup Using Page Tracking
For MySQL Enterprise Backup 8.0.18 and later: mysqlbackup supports creating incremental backups using the page tracking functionality of the MySQL Server, by which mysqlbackup looks for changed pages in the InnoDB data files that have been modified since the last backup and then copies them. In general, incremental backups using page tracking are faster than other kinds of incremental backups performed by mysqlbackup if the majority of the data in the database has not been modified. Using this feature requires the following to be done on the server before the base backup for the incremental backup is made:
Install the
mysqlbackup
component, which comes with the MySQL Enterprise Server 8.0 installation, by running this command at a mysql client connected to the server:INSTALL COMPONENT "file://component_mysqlbackup";
Start page tracking with the following user-defined function (UDF):
SELECT mysqlbackup_page_track_set(true);
The LSN value starting from which changed pages have been tracked is returned by this UDF:
SELECT mysqlbackup_page_track_get_start_lsn();
You can stop page tracking with the following UDF:
SELECT mysqlbackup_page_track_set(false);
The above-mentioned UDFs regarding page tracking require the
BACKUP_ADMIN
privilege to run.
When the --incremental
option is
used without any value specified, mysqlbackup
performs an incremental backup using the page tracking
functionality. User can also specifies
--incremental=page-track
to make mysqlbackup use the page tracking
functionality. However, the prerequisites for making use of the
page tracking functionality for incremental backups are:
Page tracking is functioning properly on the server, and it has been enabled (with
SELECT mysqlbackup_page_track_set(true)
) before the base backup was created; if that is not the case, mysqlbackup throws an error when--incremental=page-track
, or it performs a full-scan incremental backup instead when--incremental
is unspecified.The number of changed pages is less than 50% of the total number of pages; if that is not the case, mysqlbackup throws an error when
--incremental=page-track
, or it performs a full-scan incremental backup instead when--incremental
is unspecified.
mysqlbackup needs to be started with enough memory to process
all the tracked pages in memory. If there is not enough
memory, mysqlbackup throws an error and
then exits. A rough guideline is as follows: the default value
of 300 [MB] for the --limit-memory
option
allows mysqlbackup to handle about 600GB of
changed data.
Full-scan versus Optimistic Incremental Backup
When the --incremental
option is set
to full-scan
, mysqlbackup
performs a full-scan incremental backup, in which it scans all
InnoDB data files in the server's data directory to find pages
that have been changed since the last backup was made and then
copies those pages. A full-scan incremental backup might not be
very efficient when not many tables have been modified since the
last back up.
An optimistic incremental backup, on the other hand, only scans
for changed pages in InnoDB data files that have been modified
since the last backup, thus saving some unnecessary scan time.
An optimistic incremental backup can be performed by specifying
--incremental=optimistic
.
While an optimistic increment backup might shorten the backup
time, it has the following limitations:
Since this feature makes use of the modification times of the files in the server's data directory, two things must have remained unchanged since the previous backup: (1) the system time on the server, and (2) the location of the data directory. Otherwise, the backup might fail, or an inconsistent incremental backup might be produced.
Optimistic incremental backups cannot be performed with the
--incremental-with-redo-log-only
, for which mysqlbackup reads the redo log files instead of scanning the files in the data directory.If the
--start-lsn
option is used, a full scan is performed even if--incremental=optimistic
is specified since, in that case, mysqlbackup cannot determine the point in time for which the previous backup is consistent, and thus has no time frame to determine which files have been modified recently.
For these and other cases in which an optimistic incremental backup is not desirable, perform a full-scan incremental backup, or an incremental backup using page tracking (for MySQL Enterprise Backup 8.0.18 and later). See Section 4.1.2, “Grant MySQL Privileges to Backup Administrator” on the privileges required for mysqlbackup to perform an optimistic incremental backup. Also see Using Optimistic Backups and Optimistic Incremental Backups Together on how to utilize the two features together in a backup schedule.
For MySQL Enterprise Backup 8.0.17 and earlier, full-scan
backup is the default method for incremental backups, which is
utilized if no value is specified for
--incremental
.
Other Considerations for Incremental Backups
The incremental backup feature is primarily intended for InnoDB tables, or non-InnoDB tables that are read-only or rarely updated. Incremental backups detect changes at the level of pages in the InnoDB data files, as opposed to table rows; each page that has changed is backed up. Thus, the space and time savings are not exactly proportional to the percentage of changed InnoDB rows or columns.
For non-InnoDB files, the entire file is included in an incremental backup if that file has changed since the previous backup, which means the savings for backup resources are less significant when comparing with the case with InnoDB tables.
When making an incremental backup that is based on a backup
(full or incremental) created using the
--no-locking
option, use the
--skip-binlog
option to
skip the backing up of the binary log, as binary log information
will be unavailable to mysqlbackup in that
situation.
No binary log files are copied into the incremental backup if
the --start-lsn
option is
used. To include binary log files for the period covered by the
incremental backup, use the
--incremental-base
option instead,
which provides the necessary information for
mysqlbackup to ensure that no gap exists
between binary log data included in the previous backup and the
current incremental backup.
Examples of Incremental Backups
These examples use mysqlbackup to make an
incremental backup of a MySQL server, including all databases
and tables. We show two alternatives, one using the
--incremental-base
option and the
other using the
--start-lsn
option.
With the --incremental-base
option, you do not
have to keep track of LSN values between one backup and the
next. Instead, you can do one of the following:
Tell mysqlbackup to query the
end_lsn
value from the last successful non-TTS backup as recorded in thebackup_history
table on the server using--incremental-base
=history:last_backup
orhistory:last_full_backup
(for release 8.0.17 and later).Advanced: For directory backups, specify the directory of the previous backup (either full or incremental) with
--incremental-base=dir:
, and mysqlbackup will figure out the starting point for this backup based on the metadata of the earlier one. Because you need a known set of directory names, you might want to use hardcoded names or generate a sequence of names in your own backup script, rather than using thedirectory_path
--with-timestamp
option. If your last backup was a single-file, you can still use--incremental-base=dir:
to provide the location of the temporary directory you supplied with thedirectory_path
--backup-dir
option during the last backup
In the following example, the
--incremental-base=history:last_backup
option is used, given which mysqlbackup
fetches the LSN of the last successful (non-TTS) full or partial
backup from the mysql.backup_history
table
and performs an incremental backup basing on that.
mysqlbackup --defaults-file=/home/dbadmin/my.cnf \
--incremental --incremental-base=history:last_backup \
--backup-dir=/home/dbadmin/temp_dir \
--backup-image=incremental_image1.bi \
backup-to-image
In the following example, an incremental backup similar to the one in the last example but optimistic in nature is performed.
mysqlbackup --defaults-file=/home/dbadmin/my.cnf \
--incremental=optimistic --incremental-base=history:last_backup \
--backup-dir=/home/dbadmin/temp_dir \
--backup-image=incremental_image1.bi
backup-to-image
Advanced: Use the following command to
create an incremental directory backup using the
--incremental-base=dir:
option; the backup is saved at the location specified by
directory_path
--incremental-backup-dir
:
mysqlbackup --defaults-file=/home/dbadmin/my.cnf --incremental \
--incremental-base=dir:/incr-backup/wednesday \
--incremental-backup-dir=/incr-backup/thursday \
backup
You can also use the --start-lsn
option to specify where the incremental backup should start. You
have to record the LSN of the previous backup reported by
mysqlbackup at the end of the backup:
mysqlbackup: Was able to parse the log up to lsn 2654255716
The number is also recorded in the
meta/backup_variables.txt
file in the
folder specified by --backup-dir
during the backup. Supply then that number to
mysqlbackup using the
--start-lsn
option. The incremental backup then
includes all changes that came after the
specified LSN.
To create an incremental backup image with the
--start-lsn
option, use the following command,
specifying with --backup-dir
the
backup directory, which, in this case, is a directory for
storing the metadata for the backup and some temporary files:
mysqlbackup --defaults-file=/home/dbadmin/my.cnf --incremental \
--start-lsn=2654255716 \
--with-timestamp \
--backup-dir=/incr-tmp \
--backup-image=/incr-backup/incremental_image.bi \
backup-to-image
In the following example though, because
--backup-image
does not provide a
full path to the image file to be created, the incremental
backup image is created under the folder specified by
--backup-dir
:
mysqlbackup --defaults-file=/home/dbadmin/my.cnf --incremental \
--start-lsn=2654255716 \
--with-timestamp \
--backup-dir=/incr-images \
--backup-image=incremental_image1.bi \
backup-to-image
Maintaining a backup schedule:
On a regular schedule determined by date or amount of database activity, take more incremental or differential backups.
Optionally, periodically start the cycle over again by taking a full, uncompressed or compressed backup. Typically, this milestone happens when you can archive and clear out your oldest backup data.
On how to restore your database using the incremental backups, see Section 5.1.3, “Restoring an Incremental Backup”