This section describes the performance considerations for backup operations with the MySQL Enterprise Backup product. When optimizing and tuning the backup procedure, measure both the raw performance (how long it takes the backup to complete) and the amount of overhead on the database server. When measuring backup performance, consider:
The limits imposed by your backup procedures. For example, if you take a backup every 8 hours, the backup must take less than 8 hours to finish.
The limits imposed by your network and storage infrastructure. For example, if you need to fit many backups on a particular storage device, you might use compressed backups, even if that made the backup process slower.
The tradeoff between backup time and restore time. You might choose a set of options resulting in a slightly slower backup, if those options enable the restore to be much faster. See Section 7.2, “Optimizing Restore Performance” for performance information for the restore process.
After taking a full backup, subsequent backups can be performed more
quickly by doing incremental backups, where only the changed data is
backed up. For an incremental backup, specify the
to mysqlbackup. See
Section 4.1.8, “Incremental Backup Options” for information about
these options. For usage instructions for the backup and apply
stages of incremental backups, see
Section 3.3.2, “Making an Incremental Backup” and
Example 5.3, “Applying an Incremental Backup to a Full Backup”.
Compressing the backup data before transmitting it to another server involves additional CPU overhead on the database server where the backup takes place, but less network traffic and less disk I/O on the server that is the final destination for the backup data. Consider the load on your database server, the bandwidth of your network, and the relative capacities of the database and destination servers when deciding whether or not to use compression. See Section 3.3.3, “Making a Compressed Backup” and Section 4.1.7, “Compression Options” for information about creating compressed backups.
Compression involves a tradeoff between backup performance and restore performance. In an emergency, the time needed to uncompress the backup data before restoring it might be unacceptable. There might also be storage issues if there is not enough free space on the database server to hold both the compressed backup and the uncompressed data. Thus, the more critical the data is, the more likely that you might choose not to use compression: accepting a slower, larger backup to ensure that the restore process is as fast and reliable as possible.
The single-file backup by itself is not necessarily faster than the traditional type of backup that produces a directory tree of output files. Its performance advantage comes from combining different steps that you might otherwise have to perform in sequence, such as combining the backup data into a single output file and transferring it to another server. See Section 126.96.36.199, “Work with Single-File Backups” for the options related to single-file backups, and Section 3.3.5, “Making a Single-File Backup” for usage instructions.
Prior to MySQL 5.5, it was common practice to keep the redo logs fairly small to avoid long startup times when the MySQL server was killed rather than shut down normally. In MySQL 5.5 and higher, the performance of crash recovery is significantly improved, as explained in Improvements to Crash Recovery Performance. With those releases, you can make your redo log files bigger if that helps your backup strategy and your database workload.
As discussed later, there are a number of reasons why you might
prefer to run with the setting
The mysqlbackup command can take advantage of modern multicore CPUs and operating system threads to perform backup operations in parallel. See Section 4.1.11, “Performance / Scalability / Capacity Options” for the options to control how many threads are used for different aspects of the backup process. If you see that there is unused system capacity during backups, consider increasing the values for these options and testing whether doing so increases backup performance:
When tuning and testing backup performance using a RAID storage
configuration, consider the combination of option settings
--write-threads=3. Compare against the combination
When tuning and testing backup performance using a non-RAID
storage configuration, consider the combination of option
When you increase the values for any of the 3
“threads” options, also increase the value of the
--limit-memory option, to give the
extra threads enough memory to do their work.
If the CPU is not too busy (less than 80% CPU utilization),
increase the value of the
If the storage device that you are backing up from (the source
drive) can handle more I/O requests, increase the value of the
If the storage device that you are backing up to (the
destination drive) can handle more I/O requests, increase the
value of the
Depending on your operating system, you can measure resource
utilization using commands such as top,
dtrace, or a graphical performance monitor. Do
not increase the number of read or write threads
iowait once the system
value reaches approximately 20%.
Although the mysqlbackup command backs up
InnoDB tables without interrupting database use, the final
stage that copies non-InnoDB files (such as MyISAM tables and
.frm files) temporarily puts the database
into a read-only state, using the statement
TABLES WITH READ LOCK. For best backup performance
and minimal impact on database processing:
Do not run long
SELECT queries or other
SQL statements at the time of the backup run.
Keep your MyISAM tables relatively small and primarily for read-only or read-mostly work.
Then the locked phase at the end of a
mysqlbackup run is short (maybe a few
seconds), and does not disturb the normal processing of
mysqld much. If the preceding conditions
are not met in your database application, use the
--only-innodb-with-frm option to back up only
InnoDB tables, or use the
--no-locking option to back up
non-InnoDB files. Note that MyISAM,
and other files copied under the
setting cannot be guaranteed to be consistent, if they are
updated during this final phase of the backup.
For a large database, a backup run might take a long time. Always check that mysqlbackup has completed successfully, either by verifying that the mysqlbackup command returned exit code 0, or by observing that mysqlbackup has printed the text “mysqlbackup completed OK!”.
The mysqlbackup command is not the same as the former “MySQL Backup” open source project from the MySQL 6.0 source tree. The MySQL Enterprise Backup product supersedes the MySQL Backup initiative.
Schedule backups during periods when no DDL operations involving tables are running. See Section A.1, “Limitations of mysqlbackup Command” for restrictions on backups at the same time as DDL operations.
For data processing operations, you might know the conventional
advice that Unix sockets are faster than TCP/IP for communicating
with the database. Although the mysqlbackup
command supports the options
--protocol=pipe, these options do
not have a significant effect on backup or restore performance.
These processes involve file-copy operations rather than
client/server network traffic. The database communication controlled
--protocol option is
low-volume. For example, mysqlbackup retrieves
information about database parameters through the database
connection, but not table or index data.
If certain tables or databases contain non-critical information, or are rarely updated, you can leave them out of your most frequent backups and back them up on a less frequent schedule. See Section 4.1.9, “Partial Backup Options” for information about the relevant options, and Section 3.3.4, “Making a Partial Backup” for instructions about leaving out data from specific tables, databases, or storage engines. Partial backups are faster because they copy, compress, and transmit a smaller volume of data.
To minimize the overall size of
files, consider enabling the MySQL configuration option
innodb_file_per_table. This option
can minimize data size for
InnoDB tables in
It prevents the
InnoDB system tablespace from
ballooning in size, allocating disk space that can afterwards
only be used by MySQL. For example, sometimes huge amounts of
data are only needed temporarily, or are loaded by mistake or
during experimentation. Without the
the system tablespace expands to hold all this data, and never
It immediately frees the disk space taken up by an
InnoDB table and its indexes when the table
is dropped or truncated. Each table and its associated indexes
are represented by a .ibd
file that is deleted or emptied by these DDL operations.
It allows unused space within a
.ibd file to
be reclaimed by the
TABLE statement, when substantial amounts of data are
removed or indexes are dropped.
It enables partial backups where you back up some
InnoDB tables and not others, as discussed in
Section 3.3.4, “Making a Partial Backup”.
Avoid creating indexes that are not used by queries. Because indexes
take up space in the backup data, unnecessary indexes slow down the
backup process. (The copying and scanning mechanisms used by
mysqlbackup do not rely on indexes to do their
work.) For example, it is typically not helpful to create an index
on each column of a table, because only one index is used by any
query. Because the primary key columns are included in each
InnoDB secondary index, it wastes space to define
primary keys composed of numerous or lengthy columns, or multiple
secondary indexes with different permutations of the same columns.
If you store the backup data on a separate machine, and that machine is not as busy the machine hosting the database server, you can offload some postprocessing work (the apply-log phase) to that separate machine. Section 188.8.131.52, “Apply-Log Operations for Existing Backup Data”
There is always a performance tradeoff between doing the apply-log
phase immediately after the initial backup (makes restore faster),
or postponing it until right before the restore (makes backup
faster). In an emergency, restore performance is the most important
consideration. Thus, the more crucial the data is, the more
important it is to run the apply-log phase immediately after the
backup. Either combine the backup and apply-log phases on the same
server by specifying the
backup-and-apply-log option, or perform
the fast initial backup, transfer the backup data to another server,
and then perform the apply-log phase using one of the options from
Section 184.108.40.206, “Apply-Log Operations for Existing Backup Data”.