How can I optimize a mysqldump of a large database?

How can I optimize a mysqldump of a large database ?

I have a symfony application with an InnoDB database that is ~2GB with 57 tables. The majority of the size of the database resides in a single table (~1.2GB). I am currently using mysqldump to backup the database nightly. Due to my comcast connection, oftentimes if I am running a dump manually my connection to the server will timeout before the dump is complete causing me to have to rerun the dump. [I currently run a cron that does the dump nightly, this is just for dumps that I run manually.] Is there a way to speed up the dumps for the connection timeout issue, but also to limit the time the server is occupied with this process? BTW, I am currently working on reducing the size of the overall database to resolve this issue.

The main bottleneck in the dump like this is drive I/O. You are reading a load of data and writing it again. You can speed this up in a number of ways: Make sure your output is going to a different drive(s) than the one(s) the database files are stored on - this will make a massive difference with spinning disks as the drive heads will not be constantly flicking between the location being read from and the location being written to. The output of mysqldump will be very compressible, so if you can not separate the output from the input as mentioned above pipe the output through gzip or similar. This will reduce the amount of writing being done (so reduce the overall IO load, and the amount of head movement) at the expense of some CPU time (which you may have a lot of spare at these times anyway). Also, pass the output through a pipe utility (like pv) that supports large write buffers to group blocks written to the drives together more, again to reduce the effect of head-movement latency - this will make quite a difference if using the --quick option to reduce the RAM impact of backing up large tables). Only run your backup process when IO load is otherwise low. You may be fixing the wrong issue though: it might be easier to address the connection drops instead (though reducing the I/O load imposed by your backups will help reduce the effect you have on other users so is worth trying anyway). Could you run your manual backups through screen (or similar tools like tmux)? That way if your connection to the server drops you can just reconnect and reattach to the screen session without any processes getting interrupted. If you are sending the data directly over the connection (i.e. you are running mysqldump on your local machine against a remote database, so the dump appears locally) you might be better off running the dump on the server first, compressing as needed, then transferring the data over the network using a tool (such as rsync) which supports partial transfers so you can resume the transfer (instead of restarting) if a connection drop interrupts it. As part of your "reducing the size of the overall database to resolve this issue" I would guess that a large chunk of your data does not change. You might be able to move a large chunk of the 1.2Gb from that main table off into another and remove that from those that are copied by the mysqldump call. You don't need to backup this data every time if it never changes. Splitting data between tables and databases this way is usually referred to as data partitioning and can also allow you to spread the data and I/O load over multiple drives. High-end database have built in support for automatic partitioning, though in mysql you will probably have to do it manually and alter your data access layer to account for it. Straying off-topic for this site (so you should probably nip over to ServerFault or SuperUser to ask if you need more detail): If you seem to be losing connections due to inactivity, check the options in your SSH server and SSH client to make sure keep-alive packets are enabled and being sent often enough. If seeing drops even if the connection is active you could also try using OpenVPN or similar to wrap the connection - it should handle a short drop, even a complete drop if your entire connection is down for a few seconds, such that the SSH client and server don't notice.

INSIGHT INTO DOING BACKUPS WITH mysqldump IMHO Doing backups has become more of an art form if you know just how to approach it You have options Option 1 : mysqldump an entire mysql instance This is the easiest one, the no-brainer !!! mysqldump -h... -u... -p... --hex-blob --routines --triggers --all-databases | gzip > MySQLData.sql.gz Everything written in one file: table structures, indexes, triggers, stored procedures, users, encrypted passwords. Other mysqldump options can also export different styles of INSERT commands, log file and position coordinates from binary logs, database creation options, partial data (--where option), and so forth. Option 2 : mysqldump separate databases into separate data files Start by creating a list of databases (2 techniques to do this) Technique 1 mysql -h... -u... -p... -A --skip-column-names -e"SELECT schema_name FROM information_schema.schemata WHERE schema_name NOT IN ('information_schema','mysql')" > ListOfDatabases.txt Technique 2 mysql -h... -u... -p... -A --skip-column-names -e"SELECT DISTINCT table_schema FROM information_schema.tables WHERE table_schema NOT IN ('information_schema','mysql')" > ListOfDatabases.txt Technique 1 is the fastest way. Technique 2 is the surest and safest. Technique 2 is better because, sometimes, users create folders for general purposes in /var/lib/mysql (datadir) which are not database related. The information_schema would register the folder as a database in the information_schema.schemata table. Technique 2 would bypass folders that do not contain mysql data. Once you compile the list of databases, you can proceed to loop through the list and mysqldump them, even in parallel if so desired. for DB in `cat ListOfDatabases.txt` do mysqldump -h... -u... -p... --hex-blob --routines --triggers ${DB} | gzip > ${DB}.sql.gz & done wait If there are too many databases to launch at one time, parallel dump them 10 at a time: COMMIT_COUNT=0 COMMIT_LIMIT=10 for DB in `cat ListOfDatabases.txt` do mysqldump -h... -u... -p... --hex-blob --routines --triggers ${DB} | gzip > ${DB}.sql.gz & (( COMMIT_COUNT++ )) if [ ${COMMIT_COUNT} -eq ${COMMIT_LIMIT} ] then COMMIT_COUNT=0 wait fi done if [ ${COMMIT_COUNT} -gt 0 ] then wait fi Option 3 : mysqldump separate tables into separate data files Start by creating a list of tables mysql -h... -u... -p... -A --skip-column-names -e"SELECT CONCAT(table_schema,'.',table_name) FROM information_schema.tables WHERE table_schema NOT IN ('information_schema','mysql')" > ListOfTables.txt Then dump all tables in groups of 10 COMMIT_COUNT=0 COMMIT_LIMIT=10 for DBTB in `cat ListOfTables.txt` do DB=`echo ${DBTB} | sed 's/\./ /g' | awk '{print $1}'` TB=`echo ${DBTB} | sed 's/\./ /g' | awk '{print $2}'` mysqldump -h... -u... -p... --hex-blob --triggers ${DB} ${TB} | gzip > ${DB}_${TB}.sql.gz & (( COMMIT_COUNT++ )) if [ ${COMMIT_COUNT} -eq ${COMMIT_LIMIT} ] then COMMIT_COUNT=0 wait fi done if [ ${COMMIT_COUNT} -gt 0 ] then wait fi   Option 4 : USE YOUR IMAGINATION Try variations of the aforementioned Options plus techniques for clean snapshots Examples Order the list of tables by the size of each tables ascending or descending. Using separate process, run "FLUSH TABLES WITH READ LOCK; SELECT SLEEP(86400)" before launching mysqldumps. Kill this process after mysqldumps are complete. This is helpful if a database contains both InnoDB and MyISAM Save the mysqldumps in dated folders and rotate out old backup folders. Load whole instance mysqldumps into standalone servers. CAVEAT Only Option 1 brings everything. The drawback is that mysqldumps created this way can only be reloaded into the same majot release version of mysql that the mysqldump was generated. In other words, a mysqldump from a MySQL 5.0 database cannot be loaded in 5.1 or 5.5. The reason ? The mysql schema is total different among major releases. Options 2 and 3 do not include saving usernames and passwords. Here is the generic way to dump the SQL Grants for users that is readble and more portable mysql -h... -u... -p... --skip-column-names -A -e"SELECT CONCAT('SHOW GRANTS FOR ''',user,'''@''',host,''';') FROM mysql.user WHERE user<>''" | mysql -h... -u... -p... --skip-column-names -A | sed 's/$/;/g' > MySQLGrants.sql Option 3 does not save the stored procedures, so you can do the following mysqldump -h... -u... -p... --no-data --no-create-info --routines > MySQLStoredProcedures.sql & Another point that should be noted is concerning InnoDB. If your have a large InnoDB buffer pool, it makes sense to flush it as best you can before performing any backups. Otherwise, MySQL spends the time flushing tables with leftover dirty page out of the buffer pool. Here is what I suggest: About 1 hour before performing the backup run this SQL command SET GLOBAL innodb_max_dirty_pages_pct = 0; In MySQL 5.5 default innodb_max_dirty_pages_pct is 75. In MySQL 5.1 and back, default innodb_max_dirty_pages_pct is 90. By setting innodb_max_dirty_pages_pct to 0, this will hasten the flushing of dirty pages to disk. This will prevent or at least lessen the impact of cleaning up any incomplete two-phase commits of InnoDB data prior to performing any mysqldump against any InnoDB tables. FINAL WORD ON mysqldump Most people shy away from mysqldump in favor of other tools and those tools are indeed good. Such tools include MAATKIT (parallel dump/restore scripts, from Percona [Deprecated but great]) XtraBackup (TopNotch Snapshot Backup from Percona) CDP R1Soft (MySQL Module Option that takes point-in-time snapshots) MySQL Enterprise Backup (formerly InnoDB Hot Backups [commercial]) If you have the spirit of a true MySQL DBA, you can embrace mysqldump and have the complete mastery over it that can be attained. May all your backups be a reflection of your skills as a MySQL DBA.

Backups and Recover

Backups and Recovery

This is the most important task of an database administrator, you must protect your data at all costs, this means regular backups and regular restores even to another system just to check the integrity of those backups. There is no point in putting yourself in a position where you are holding your breathe when a restore is happening only to find out that the backup is corrupt, try if possible to perform regular restores if not then at least you should be performing a disaster recovery test once per year. Not being able to restore could be a disaster for your company and your job.
To check your backups you can use one or more of the below which I have used in the past

• use a reporting database if the customers don't need real time data and you have the money and time, Production data could be restored every day to this system which is a very good test
• use a performance test server with Production data, ideal to test releases of your software against Production data which is generally has more volume then a test system, restore perhaps once a week
• at least perform a DR once per year to prove the backup solution is working, for example you may have forgotten to backup something not only regarding the database but from the systems as well

Backups and restoring
First lets start with a few terms associated with backups

logical backup	this type of backup is created by saving information that represents the logical database structures using SQL statements like create database, create table and insert. This type of backup is ideal when you want to upgrade from one version of MySQL to another however it is a slower method of backing up.
physical backup	this type of backup is a backup of the actual database files or disk partitions, this type of backup can be very fast to backup and restore.
full backup	a full backup is a standalone backup containing everything in the database, this could then be restored on another server. A full backup can be either logical or physical.
incremental backup	this type of backup only contains the data that has changed from the last backup. The advantage of this type of backup is that it is faster as there is not some much data to backup, however the disadvantage is that it takes longer to recover.
consistent backup	this is a backup at an exact moment in time, generally you shutdown the database (or quiescent mode) then take the backup.
hot backup	this type of backup is taken when the database is running, during the backup both reads and writes are not blocked
warm backup	this type of backup is taken when the database is running, however reads are not blocked but writes are prohibited from making any modifications to the database.
cold backup	similar to a consistent backup as the database is shutdown before the backup begins
point-in-time restore	is a restoration of a database to a specified date and time , some databases use a full backup and recovery logs to restore to that point-in-time, others can only use the last full backup which means that data might have to be re-keyed into the system.

As well as obtaining a backup in your maintenance window you should also be aware on how long a restore will take thus to make sure that you meet you SLA agreements during a DR or if you have to recovery a database due to corruption or user error.
The $64,000 question is how often you should take your backups, and this i am afraid depends, so company are happy for once a month backups other may take two backups per day. The answer generally has to come from the business on what they are prepared to lose, amount of data lost or what has to be re-keyed into the system again. If you have a small company that say has to re-key in 20-50 invoices then that's no big deal, however if you have a trading company that many have to re-key in 10's of thousands of entries/trades then that becomes a problem. You have to add the time it takes to restore the system plus the time it takes to recover the system so that users are able to use it, it is this time that you give to the business to make there decision on what is a acceptable time period that the business can be down for, the shorter the time the more money that will have to be thrown at the solution, if you are talking about zero downtime then we would have to implement a high availability solution which could cost a lot of money, if you are happy with 1 days downtime then this should be enough to restore and recovery a database and to re-key in some entries to make the database consistent with the companies paper work.
As you saw above there are a number of ways to backup a database, depending on the the available time to perform a backup will make you decide on what method to use, if you have a short maintenance window with a large database then a incremental backup maybe the only option, but you have a large maintenance window with a small database then you could perform a full backup, remember what ever option you use with have a impact on the recovery time.
One point to make is that you backups should be taken off-site if held on tape or copied across to an other system in another location, if an incident happened on the original system for example a fire you don't want to lose your backups as well, the storing of off-site data should be part of you DR plan.
Enough of talking about backups lets see how you can actually take one, there are a number of backup tools that MySQL can use, see the table below

Backup tools for MySQL
Backup method	Storage engine	Impact	Backup speed	Recovery speed	Recovery granularity
mysqldump	ALL	WARM	MEDUIM	SLOWEST	MOST FLEXIBLE
mysqldump	INNODB	HOT	MEDUIM	SLOWEST	MOST FLEXIBLE
select into outfile	ALL	WARM	SLOW	SLOW	MOST FLEXIBLE
mk-parallel-backup	ALL	WARM	MEDUIM	MEDUIM	FLEXIBLE
ibbackup	INNODB	HOT	FAST	FAST	FLEXIBLE
ibbackup	ALL	WARM	FAST	FAST	FLEXIBLE
backup command in mysqld	ALL	HOT	FAST	FAST	FLEXIBLE
filesystem (copy files)	ALL	COLD	FASTEST	FASTEST	NOT FLEXIBLE
snapshot (using LVM, ZFS, VMWare)	ALL	ALMOST HOT	FAST	FAST	LEAST FLEXIBLE
mysqlhotcopy	MyISAM	MOSTLY COLD	FAST	FAST	FLEXIBLE

The mysqldump program has been around a long time, it provides a logical backup of the entire database, individual databases, individual tables or even subsets of data using the --where option, it is often called a data dump. The output is in ascii format which means that you can open it in vi or notepad and change the contains if desired. I am not going to detail all options of the mysqldump command but show you a few examples

mysqldump

## backup all databases mysqldump --user=root --password --all-databases > backup_<date>_all.sql ## backup a specific database mysqldump --user=root --password <database_name> > backup_<date>_<database_name>.sql ## backup multiple databases mysqldump --user=root --password <database_name>,<database_name> > backup_<date>.sql ## backup a table from a database mysqldump --user=root --password <database_name> <table_name> > backup_<date>_<database_name>_<table_name>.sql ## backup some specific data mysqldump --user=root --password <database_name> <table_name> --where "last_name='VALLE' order by first_name > backup_<date>.sql ## dumping from one database to another mysqldump --databases <database_name> | mysql -h <destination_host> <database_name>

restore a mysqldump

## all databases mysql --user=root --password < backup.sql ## specific database mysql --user=<user> --password <database_name> < backup_<dataabse_name>.sql

You can use the into outfile clause of the select statement to backup individual tables, the command used to load the dump created is load data infile

select into outfile / load data infile

## dump of the accounts table select * into outfile '/tmp/accounts.txt' from accounts; ## load the dump load data infile '/tmp/accounts.txt' into table accounts;

The Maatkit parallel dump and restore toolkit can be downloaded from http://www.maatkit.org basically it's a wrapper around mysqldump which provides the programs mk-parallel-dump and mk-parallel-restore, what this means is that if you have a 16 core server and you are dumping 32 tables, the script will start up 16 separate copies of mysqldump with each process dumping a separate table.

mk-parallel-dump, mk-parallel-restore

## backup a database mk-parallel-dump --basdir=/backups ## restore a database mk-parallel-restore /backups

Snapshots for a filesystem depend on what operating system or software you are using, here are some links to my web pages regarding LVM, ZFS and VMWare

• LVM snapshotting
• ZFS snapshotting
• VMWare snapshots

New in MySQL 5.6 is the online logical host backup, you can also use compression and encryption which is important when using sensitive data.

backup	backup database <database_name> to '<database_name>-backup.sql'
restore	restore from '<database_name>-backup.sql'
history	select * from backup_history where backup_id = 321\G

There currently is a number of limitations of this command

• no backup of the internal mysql datadisk
• no native driver for InnoDB tables
• no native driver for Maria or Falcon
• no backup of partitions
• no incremental backups

The mysqlhotcopy is a perl script written to provide a consistent backup of MyISAM and ARCHIVE tables, it does some limitations one of which when run it uses the lock tables command to create read locks on the tables being backed up, this allows for a consistent backup. again there are a number of options that you can use so have a look at the man page, here are a few examples

mysqlhotcopy

## backup a database mysqlhotcopy <database_name> /backups ## backup multiple databases mysqlhotcopy <database_name> accounts /backups ## backup a database to to another server mysqlhotcopy --method=scp <database_name> \ username@backup.server:/backup ## use pattern match to backup databases and tables mysqlhotcopy <database_name>./^employees/ /backup

Lastly ibbackup is a 3rd party software which allows you to perform non-blocking hot backups of InnoDB tables, it is entirely command-line driven which means that it is ideal for scripts, here is a link to the web site http://www.innodb.com/doc/hot_backup/manual.html
Recovering from Crashes
Most often you have to recover to a point-in-time after the last backup, the normal procedure is as follows

• restore the latest backup
• recovery the data to a point-in-time using recovery log files

MySQL server uses a binary format for the log files to save space, this means that you cannot view these files directly, a utility called mysqlbinlog is supplied to convert these log files into a text format that you can view. So the process for performing a point-in-time restore for MySQL is

• restore the database using the last backup
• determine the first binary log and starting position needed
• determine the last binary log needed
• convert the binary log to text format with the mysqlbinlog utility using options to specify the start and stop time
• check the text file to make sure it's what you need
• import the converted binary log(s)

convert the log files	## convert to a specific binary log file mysqlbinlog mysql-bin.010310 > mysql-bin.010310.sql ## use a date to end at a specific time mysqlbinlog --stop-datetime='201204-29 17:00:00' mysql-bin.010312 > mysql-bin.010312.sql ## other options are --stop-datetime --start-datatime --start-position --stop-position
restore the converted file	mysql --user=root -password < mysql-bin.010310.sql