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Taxonomy upgrade extras: mysqlBackupRestoreRecoverymysql_bmanpitrAbout

The MySQL Backup Manager (mysql_bman) is a wrapper script for standard MySQL backup tools. The Problem with MySQL backup tools is, that they have many options and thus are overcomplicated and errors are easy made.

mysql_bman has the intention to make backups for MySQL easier and technically correct. This means it should per default not allow non-consistent backups or complain if some functions or parameters are used in the wrong way to guarantee proper backups.

In addition it has added some nice features which are missing in standard MySQL backup tools or which are only known from Enterprise backup solutions.

Where to download mysql_bman

The Backup Manager for MySQL (mysql_bman) can be downloaded from our website.

What mysql_bman user say about

Mathias Brem DBA@DBAOnline on LinkedIn:

Ow! Nice!
mysql backup manager is a very nice tool! Congratulations for FromDual! I made a shell script for catalog and maintained backups by xtrabackup, but mysql_bman is the best!

Xtrabackup + mysql_bman!!!!

Where can mysql_bman help you

The intention of mysql_bman is to assist you in bigger MySQL set-ups where you have to follow some backup policies and where you need a serious backup concept.

mysql_bman example

To give you an impression of the power of the MySQL Backup Manager let us have a look at a little example:

shell> mysql_bman --target=bman:secret@192.168.1.42 --type=full --mode=logical --policy=daily \ --no-compress --backupdir=/mnt/slowdisk \ --archive --archivedir=/mnt/nfsmount

With this backup method we do a logical full backup (mysqldump is triggered in the background). The backup is stored in the location for backups with the daily policy and is NOT compressed to speed up the backup by saving CPU power AND because the backup device is a de-duplicating drive. Then the backup is archived to and NFS mount.

Backup types

To achieve this we have defined different backup types:

TypeDescriptionfullfull logical backup (mysqldump) of all schemasbinlogbinary-log backupconfigconfiguration file backup (my.cnf)structurestructure backupcleanupclean-up of backup pieces older than n daysschemabackup of one or more schemasprivilegeprivilege dump (SHOW GRANTS FOR)

A backup type is specified with the option --type=<backup_type>.

Backup modes

A backup can either be logical or physical. A logical backup is typically what you do with mysqldump. A physical backup is typically a physical file copy without looking into the data. That is what for example xtrabackup does.

The backup mode is specified with the option --mode=<backup_mode>. The following backup modes are available:

ModeDescriptionlogicaldo a logical backup (mysqldump).physicaldo a physical backup (mysqlbackup/innobackup/xtrabackup)Backup policies

Further we have introduced different backup policies. Policies are there to distinguish how different backups should be treated.

The following backup policies exist:

PolicyDescriptiondailydirectory to store daily backupsweeklydirectory to store weekly backupsmonthlydirectory to store monthly backupsquarterlydirectory to store quarterly backupsyearlydirectory to store yearly backups

For example you could plan to do a daily MySQL backup with binary logs with a retention policy of 7 days. But once a week you want to do a weekly backup consisting of a full backup, a configuration backup and a structure dump. But this weekly backup you want to keep for 6 months. And because of legal reasons you want to do a yearly backup with a retention policy of 10 years.

A backup policy is specified with the --policy=<backup_policy> option. This leads us to the retention time:

Options

The retention time which should be applied to a specific backup policy you can specify with the option --retention=<period_in_days>. The retention option means that a backup is not deleted before this amount of days when you run a clean-up job with mysql_bman.

Let us do an example:

shell> mysql_bman --type=cleanup --policy=daily --retention=30

This means that all backups in the daily policy should be deleted when they are older than 30 days.

Target

With the --target option you specify the connect string to the database to backup. This database can be located either local (all backup types can be used) or remote (only client/server backup types can be used).

A target looks as follows: user/password@host:port (similar to URI specification) whereas you can omit password and port.

Backup location, archiving, compressing and clean-up

The --backupdir option is to control location of the backup files. The policy folders are automatically created under this --backupdir location.
If you have a second layer of backup stores (e.g. tapes or slow backup drives or deduplicated drives or NFS drives) you can use the --archive option to copy your backup files to this second layer storage which is specified with the --archivedir option. For restore performance reasons it is recommended to always keep one or two generations of backups on you fast local drive. If you want to remove the backuped files from the --backupdir destination after the archive job use the --cleanup option.
If you want to omit to compress backups, either to safe time or because your location uses deduplicated drives you can use the --no-compress option.

Per schema backup

Especially for hosting companies a full database backup is typically not the right backup strategy because a restore of one specific customer (= schema) is very complicated. For this case we have the --per-schema option. mysql_bman will do a backup of the whole database schema by schema. Keep in mind: This breaks consistency among schemas!

Sometimes you want to do a schema backup only for some specific schemas for this you can use the --schema option. This option allows you to specify schemas to backup or not to backup. --schema=+a,+b means backup schema a and b. --schema=-a,-b means backup all schemas except a and b.
The second variant is less error prone because you do not forget to backup a new database.

Instance name

MySQL does not know the concept of naming an instance (mysqld). But for bigger environments it could be useful to uniquely name each instance. For this purpose we have introduced the option --instance-name=<give_it_a_name>. This instance name should be unique within your whole company. But we do not enforce it atm. The instance name is used to name backup files and later to identify the backup history of an instance in our backup catalog and to allow us to track the files for restore.

mysql_bman configuration file

Specifying everything on the command line is cumbersome. Thus mysql_bman considers a configuration file specified with the --config=<config_file> option.
A mysql_bman configuration file looks for example as follows:

policy = daily target = root/secret@127.0.0.1:3306 type = schema schema = -mysql policy = daily archive = on archivedir = /mnt/tape per-schema = on no-compress = on
Simulate what happens

For the Sissies among us (as for example me) we have the --simulate option. This option simulates nearly all steps as far as possible without executing really anything. This option is either for testing some features or for debugging purposes.

Logging

If you want to track your backup history you can specify with the --log option where your mysql_bman log file should be located.

Using Catalog

It will be very useful when you can store your backups metadata in the database so you can check them in the future and to find out the backup criteria (type, mode, instance-name, ... etc) for specific backup processes. This could be achieved by using the catalog feature.

To activate this feature you have to create a database for the catalog "default name is bman_catalog" then create its tables by using the option --create in a special mysql_bman command (check examples below).
Finally, to store your backup metadata in the catalog what you only have to do is adding the option --catalog=catalog_connection_string to the normal mysql_bman command.
Check the examples below for using catalog in mysql_bman.

More help

A little more help you can get with the following command:

shell> mysql_bman --help
Examples

Do a full (logical = default) backup and store it in the daily policy folder:

shell> mysql_bman --target=root/secret@127.0.0.1:3306 --type=full --policy=daily

Do a full physical backup and store it in the weekly policy folder:

shell> mysql_bman --target=root/secret@127.0.0.1 --type=full --mode=physical --policy=weekly

Do a binary-log backup omitting the password in the target and store it in the daily policy folder:

shell> mysql_bman --target=bman@192.168.1.42:3307 --type=binlog --policy=daily

Do a MySQL configuration backup and store it in the weekly policy folder:

shell> mysql_bman --target=root/secret@127.0.0.1:3306 --type=config --policy=weekly

Do a structure backup and store it in the monthly policy folder and name the file with the instance name:

shell> mysql_bman --target=root/secret@127.0.0.1:3306 --type=structure --policy=monthly --instance-name=prod-db

Do a weekly structure backup and archive it to an other backup location:

shell> mysql_bman --target=root/secret@127.0.0.1:3306 --type=structure --policy=weekly --archive --archivedir=/mnt/tape

Do a schema backup omitting the mysql schema:

shell> mysql_bman --target=root/secret@127.0.0.1:3306 --type=schema --schema=-mysql --policy=daily --archive --archivedir=/mnt/tape

Do a schema backup only of foodmart and world and write it to their own files. Omit compressing these backups because they are located for example on deduplicated drives:

shell> mysql_bman --target=root/secret@127.0.0.1:3306 --type=schema --schema=+foodmart,+world --per-schema --policy=daily --no-compress

Creation of a backup catalog (assuming you have created already a catalog database with the default name "bman_catalog"):

shell> mysql_bman --catalog=root/secret@127.0.0.1:3306 --create

Backups against catalog:

shell> mysql_bman --target=root/secret@127.0.0.1:3306 --catalog=root/secret@127.0.0.1:3306 --instance-name=test --type=full --policy=daily

Privilege backup:

shell> mysql_bman --target=root/secret@127.0.0.1:3306 --type=privilege --policy=daily --mode=logical

It's not usual to find an easy source on how to setup MySQL replication, I thought it might be useful at least for the beginners to write a direct and simple howto blog on setting up Master/Slave replication in MySQL using the classic method (binary log information). Check out my post GTID In Action for information about transaction-based replication using GTID.

Before going through the replication setup steps, I think it's better to explain first how Replication works in MySQL.

MySQL replication mainly consists of three-part process:

• The master server records all data changes to its binary logs (binary log events) and send it to the slave using a thread called (Binlog dump thread) once the slave connects to the master.
• The slave copies the binary log events sent by the master's binlog dump thread to its relay logs using a thread called (Slave I/O thread).
• The slave applies these changes from the relay logs to its data by replaying (executing) all events using a thread called (Slave SQL thread).

Now, lets go through the setup process which is divided into 3 main sections (assuming you have already installed MySQL on master and slave servers):

• Master's side configurations.
• Slave's side configurations.
• Replication checking and troubleshooting.

Master's side configuration:

• Add the following variables to the MySQL configuration file (my.cnf): [mysqld] server-id=1 ## must be unique log-bin=mysql-bin binlog_format=ROW
• Restart MySQL so that configuration changes take place: shell> /etc/init.d/mysql restart
• Create a MySQL user to be used by the slave: SQL> GRANT REPLICATION SLAVE ON *.* TO 'slave_user_name'@'slave_ip' IDENTIFIED BY 's3cret';
• Take a full snapshot from the master's databases: shell> mysqldump -u root -p --all-databases --flush-privileges --single-transaction --master-data=2 --flush-logs --triggers --routines --events --hex-blob >/path/to/backupdir/full_backup-$TIMESTAMP.sql
  

  Note:

  If you have MyISAM tables you should omit the option --single-transaction while --master-data=2 will automatically turn on --lock-all-tables option which is required for MyISAM tables).
• After preparing the backup file transfer it to the slave server.
• If you are setting up fresh M/S servers (no data is there on the master) you don't have to backup the master databases and all what you need is to execute the following command on the master server just to know the master's coordinates which will be used later on the slave's: SQL> SHOW MASTER STATUS\G *************************** 1. row *************************** File: mysql-bin.000275 Position: 120 Binlog_Do_DB: Binlog_Ignore_DB: Executed_Gtid_Set:

And that is it on the master's, let's do the slave's work.

Slave's side configuration:

• Add the following variables to the my.cnf file: [mysqld] server-id=2 ## must be unique. relay_log=relay-log skip-slave-start ## useful to make any checks before starting the slave (this way, slave must be started manually after each mysql restart)
• Restart MySQL so that configuration changes take place: shell> /etc/init.d/mysql restart
• Restore the full backup taken from the master (if performed): shell> mysql -u root -p < /path/to/backupdir/full_backup-$TIMESTAMP.sql.
• Get the master's coordinates information from the backup file: shell> head -n 50 /path/to/backupdir/full_backup-$TIMESTAMP.sql|grep "CHANGE MASTER TO"
  

  OR from the output of "SHOW MASTER STATUS;" in case of no backups taken (check the final step in the "Master's side configuration").

• Set the master information on the slave's: SQL> CHANGE MASTER TO -> MASTER_HOST='master_ip', -> MASTER_PORT=3306, -> MASTER_USER='slave_user_name', ## The user which was created on the master -> MASTER_PASSWORD='s3cret', -> MASTER_LOG_FILE='mysql-bin.000275', ## taken from the above step -> MASTER_LOG_POS=120; ## taken from the above step
• Start replication: SQL> START SLAVE;

Replication checking and troubleshooting:

• Once the slave is started, check the replication status on the slave by the following command: SQL> SHOW SLAVE STATUS\G *************************** 1. row *************************** Slave_IO_State: Waiting for master to send event Master_Host: 127.0.0.1 Master_User: slave_user_name Master_Port: 3306 Connect_Retry: 60 Master_Log_File: mysql-bin.000275 Read_Master_Log_Pos: 120 Relay_Log_File: mysql-relay.000001 Relay_Log_Pos: 283 Relay_Master_Log_File: mysql-bin.000275 Slave_IO_Running: Yes Slave_SQL_Running: Yes . . . Last_SQL_Error: . . .
• If the Slave_IO_State= connecting .... then make sure that the slave user information is set correctly and there is no firewall restrictions between the two servers (master and slave) this could be checked by connecting to the master's MySQL from the salve server by the replication user (in this example, slave_user_name).
• If both Slave_IO_Running and Slave_SQL_Running = Yes, then the replication had been set up correctly.
• If the Slave_SQL_Running = No, check the value of Last_SQL_Error for more details about the SQL error.
• If you know that error and you want to ignore it, you can execute "SET GLOBAL sql_slave_skip_counter = 1;" on the slave and then start the slave again "START SLAVE;".
• To restrict all normal users from changing data on the slave - which might break the replication - the option "read-only" should be added in the slave's my.cnf file.
• the server option "server-id" must be unique among all servers inside the replication (masters and slaves).
• If your database size is big (100GB or so) Xtrabackup tool could be used instead of mysqldump - when preparing the master snapshot - for faster backup and restore operations. For more information on how to use Xtrabackup, check out this link.
• For more information on how to setup MySQL replication, check out the manual documentation.
• For more information on how to troubleshoot MySQL replication, check out the Replication Troubleshooting - Classic VS GTID blog.

Taxonomy upgrade extras: replication

It's not usual to find an easy source on how to setup MySQL replication, I thought it might be useful at least for the beginners to write a direct and simple howto blog on setting up Master/Slave replication in MySQL using the classic method (binary log information). Check out my post GTID In Action for information about transaction-based replication using GTID.

Before going through the replication setup steps, I think it's better to explain first how Replication works in MySQL.

MySQL replication mainly consists of three-part process:

• The master server records all data changes to its binary logs (binary log events) and send it to the slave using a thread called (Binlog dump thread) once the slave connects to the master.
• The slave copies the binary log events sent by the master's binlog dump thread to its relay logs using a thread called (Slave I/O thread).
• The slave applies these changes from the relay logs to its data by replaying (executing) all events using a thread called (Slave SQL thread).

Now, lets go through the setup process which is divided into 3 main sections (assuming you have already installed MySQL on master and slave servers):

• Master's side configurations.
• Slave's side configurations.
• Replication checking and troubleshooting.

Master's side configuration:

• Add the following variables to the MySQL configuration file (my.cnf): [mysqld] server-id=1 ## must be unique log-bin=mysql-bin binlog_format=ROW
• Restart MySQL so that configuration changes take place: shell> /etc/init.d/mysql restart
• Create a MySQL user to be used by the slave: SQL> GRANT REPLICATION SLAVE ON *.* TO 'slave_user_name'@'slave_ip' IDENTIFIED BY 's3cret';
• Take a full snapshot from the master's databases: shell> mysqldump -u root -p --all-databases --flush-privileges --single-transaction --master-data=2 --flush-logs --triggers --routines --events --hex-blob >/path/to/backupdir/full_backup-$TIMESTAMP.sql
  

  Note:

  If you have MyISAM tables you should omit the option --single-transaction while --master-data=2 will automatically turn on --lock-all-tables option which is required for MyISAM tables).
• After preparing the backup file transfer it to the slave server.
• If you are setting up fresh M/S servers (no data is there on the master) you don't have to backup the master databases and all what you need is to execute the following command on the master server just to know the master's coordinates which will be used later on the slave's: SQL> SHOW MASTER STATUS\G *************************** 1. row *************************** File: mysql-bin.000275 Position: 120 Binlog_Do_DB: Binlog_Ignore_DB: Executed_Gtid_Set:

And that is it on the master's, let's do the slave's work.

Slave's side configuration:

• Add the following variables to the my.cnf file: [mysqld] server-id=2 ## must be unique. relay_log=relay-log skip-slave-start ## useful to make any checks before starting the slave (this way, slave must be started manually after each mysql restart)
• Restart MySQL so that configuration changes take place: shell> /etc/init.d/mysql restart
• Restore the full backup taken from the master (if performed): shell> mysql -u root -p < /path/to/backupdir/full_backup-$TIMESTAMP.sql.
• Get the master's coordinates information from the backup file: shell> head -n 50 /path/to/backupdir/full_backup-$TIMESTAMP.sql|grep "CHANGE MASTER TO"
  

  OR from the output of "SHOW MASTER STATUS;" in case of no backups taken (check the final step in the "Master's side configuration").

• Set the master information on the slave's: SQL> CHANGE MASTER TO -> MASTER_HOST='master_ip', -> MASTER_PORT=3306, -> MASTER_USER='slave_user_name', ## The user which was created on the master -> MASTER_PASSWORD='s3cret', -> MASTER_LOG_FILE='mysql-bin.000275', ## taken from the above step -> MASTER_LOG_POS=120; ## taken from the above step
• Start replication: SQL> START SLAVE;

Replication checking and troubleshooting:

• Once the slave is started, check the replication status on the slave by the following command: SQL> SHOW SLAVE STATUS\G *************************** 1. row *************************** Slave_IO_State: Waiting for master to send event Master_Host: 127.0.0.1 Master_User: slave_user_name Master_Port: 3306 Connect_Retry: 60 Master_Log_File: mysql-bin.000275 Read_Master_Log_Pos: 120 Relay_Log_File: mysql-relay.000001 Relay_Log_Pos: 283 Relay_Master_Log_File: mysql-bin.000275 Slave_IO_Running: Yes Slave_SQL_Running: Yes . . . Last_SQL_Error: . . .
• If the Slave_IO_State= connecting .... then make sure that the slave user information is set correctly and there is no firewall restrictions between the two servers (master and slave) this could be checked by connecting to the master's MySQL from the salve server by the replication user (in this example, slave_user_name).
• If both Slave_IO_Running and Slave_SQL_Running = Yes, then the replication had been set up correctly.
• If the Slave_SQL_Running = No, check the value of Last_SQL_Error for more details about the SQL error.
• If you know that error and you want to ignore it, you can execute "SET GLOBAL sql_slave_skip_counter = 1;" on the slave and then start the slave again "START SLAVE;".
• To restrict all normal users from changing data on the slave - which might break the replication - the option "read-only" should be added in the slave's my.cnf file.
• the server option "server-id" must be unique among all servers inside the replication (masters and slaves).
• If your database size is big (100GB or so) Xtrabackup tool could be used instead of mysqldump - when preparing the master snapshot - for faster backup and restore operations. For more information on how to use Xtrabackup, check out this link.
• For more information on how to setup MySQL replication, check out the manual documentation.
• For more information on how to troubleshoot MySQL replication, check out the Replication Troubleshooting - Classic VS GTID blog.

Taxonomy upgrade extras: replication

It's not usual to find an easy source on how to setup MySQL replication, I thought it might be useful at least for the beginners to write a direct and simple howto blog on setting up Master/Slave replication in MySQL using the classic method (binary log information). Check out my post GTID In Action for information about transaction-based replication using GTID.

Before going through the replication setup steps, I think it's better to explain first how Replication works in MySQL.

MySQL replication mainly consists of three-part process:

• The master server records all data changes to its binary logs (binary log events) and send it to the slave using a thread called (Binlog dump thread) once the slave connects to the master.
• The slave copies the binary log events sent by the master's binlog dump thread to its relay logs using a thread called (Slave I/O thread).
• The slave applies these changes from the relay logs to its data by replaying (executing) all events using a thread called (Slave SQL thread).

Now, lets go through the setup process which is divided into 3 main sections (assuming you have already installed MySQL on master and slave servers):

• Master's side configurations.
• Slave's side configurations.
• Replication checking and troubleshooting.

Master's side configuration:

• Add the following variables to the MySQL configuration file (my.cnf): [mysqld] server-id=1 ## must be unique log-bin=mysql-bin binlog_format=ROW
• Restart MySQL so that configuration changes take place: shell> /etc/init.d/mysql restart
• Create a MySQL user to be used by the slave: SQL> GRANT REPLICATION SLAVE ON *.* TO 'slave_user_name'@'slave_ip' IDENTIFIED BY 's3cret';
• Take a full snapshot from the master's databases: shell> mysqldump -u root -p --all-databases --flush-privileges --single-transaction --master-data=2 --flush-logs --triggers --routines --events --hex-blob >/path/to/backupdir/full_backup-$TIMESTAMP.sql
  

  Note:

  If you have MyISAM tables you should omit the option --single-transaction while --master-data=2 will automatically turn on --lock-all-tables option which is required for MyISAM tables).
• After preparing the backup file transfer it to the slave server.
• If you are setting up fresh M/S servers (no data is there on the master) you don't have to backup the master databases and all what you need is to execute the following command on the master server just to know the master's coordinates which will be used later on the slave's: SQL> SHOW MASTER STATUS\G *************************** 1. row *************************** File: mysql-bin.000275 Position: 120 Binlog_Do_DB: Binlog_Ignore_DB: Executed_Gtid_Set:

And that is it on the master's, let's do the slave's work.

Slave's side configuration:

• Add the following variables to the my.cnf file: [mysqld] server-id=2 ## must be unique. relay_log=relay-log skip-slave-start ## useful to make any checks before starting the slave (this way, slave must be started manually after each mysql restart)
• Restart MySQL so that configuration changes take place: shell> /etc/init.d/mysql restart
• Restore the full backup taken from the master (if performed): shell> mysql -u root -p < /path/to/backupdir/full_backup-$TIMESTAMP.sql.
• Get the master's coordinates information from the backup file: shell> head -n 50 /path/to/backupdir/full_backup-$TIMESTAMP.sql|grep "CHANGE MASTER TO"
  

  OR from the output of "SHOW MASTER STATUS;" in case of no backups taken (check the final step in the "Master's side configuration").

• Set the master information on the slave's: SQL> CHANGE MASTER TO -> MASTER_HOST='master_ip', -> MASTER_PORT=3306, -> MASTER_USER='slave_user_name', ## The user which was created on the master -> MASTER_PASSWORD='s3cret', -> MASTER_LOG_FILE='mysql-bin.000275', ## taken from the above step -> MASTER_LOG_POS=120; ## taken from the above step
• Start replication: SQL> START SLAVE;

Replication checking and troubleshooting:

• Once the slave is started, check the replication status on the slave by the following command: SQL> SHOW SLAVE STATUS\G *************************** 1. row *************************** Slave_IO_State: Waiting for master to send event Master_Host: 127.0.0.1 Master_User: slave_user_name Master_Port: 3306 Connect_Retry: 60 Master_Log_File: mysql-bin.000275 Read_Master_Log_Pos: 120 Relay_Log_File: mysql-relay.000001 Relay_Log_Pos: 283 Relay_Master_Log_File: mysql-bin.000275 Slave_IO_Running: Yes Slave_SQL_Running: Yes . . . Last_SQL_Error: . . .
• If the Slave_IO_State= connecting .... then make sure that the slave user information is set correctly and there is no firewall restrictions between the two servers (master and slave) this could be checked by connecting to the master's MySQL from the salve server by the replication user (in this example, slave_user_name).
• If both Slave_IO_Running and Slave_SQL_Running = Yes, then the replication had been set up correctly.
• If the Slave_SQL_Running = No, check the value of Last_SQL_Error for more details about the SQL error.
• If you know that error and you want to ignore it, you can execute "SET GLOBAL sql_slave_skip_counter = 1;" on the slave and then start the slave again "START SLAVE;".
• To restrict all normal users from changing data on the slave - which might break the replication - the option "read-only" should be added in the slave's my.cnf file.
• the server option "server-id" must be unique among all servers inside the replication (masters and slaves).
• If your database size is big (100GB or so) Xtrabackup tool could be used instead of mysqldump - when preparing the master snapshot - for faster backup and restore operations. For more information on how to use Xtrabackup, check out this link.
• For more information on how to setup MySQL replication, check out the manual documentation.
• For more information on how to troubleshoot MySQL replication, check out the Replication Troubleshooting - Classic VS GTID blog.

One of our customers had a question related to the right value of Galera Cache size (gcache.size) in Galera Cluster for MySQL which I would like to share with you.

The question was: My maintenance window takes 4 hours for my 5TB DB. How can I avoid an SST ?!

Basically, having too small GCache size will lead to SST (Snapshot State Transfer) instead of IST (Incremental State Transfer), thus we can avoid the SST by setting the GCache to the appropriate value.

To check the current value of the GCache size:

mysql> SHOW GLOBAL VARIABLES LIKE 'wsrep_provider_options'\G Variable_name: wsrep_provider_options Value: base_host = 192.168.1.12; . . . gcache.page_size = 128M; gcache.size = 128M; gcs.fc_debug = 0; . . .

The value of GCache size could be changed by adding the following line in the my.cnf file and restarting the node (it could NOT be changed online):

#my.cnf [mysqld] wsrep_provider_options="gcache.size=256M"

But the question is how can we calculate the right value for GCache size to cover the maintenance window and at the same time not larger than what it needs?

To answer that question we should first find out how much GCache can handle which could be calculated by the following formula:

Hold time = GCache size / Replication Rate.

Where:

• Replication Rate = Amount of replicated data / time.
• Amount of replicated data = (wsrep_replicated_bytes + wsrep_received_bytes) after the maintenance window - (wsrep_replicated_bytes + wsrep_received_bytes) before the maintenance window.

The amount of replicated data for the customer's case = 7200MB.

Now, we can find out how much GCache (default 128M) can handle for the customer's case:

Hold time = 128MB / (7200MB / 4h) = 128MB / 0.5 MB = 256s.

Then, we can calculate the right GCache size value to handle the maintenance window by the following formula:
GCache = Maintenance window * Replication Rate = 14400s * 0.5 MB.
GCache = 7200MB.

In other words, the right GCache size should be equivalent to (or not less than) the amount of replicated data.

A shorter way using the binary logs size

Is there any relation between (wsrep_replicated_bytes + wsrep_received_bytes) and the binary log traffic? Lets check that by the following test scenario:

• Starting a Galera Cluster where the newest binary log file size will be empty (120 bytes) and the same for the status variables: mysql> SHOW GLOBAL STATUS LIKE 'wsrep_replicated_bytes'; +------------------------+-------+ | Variable_name | Value | +------------------------+-------+ | wsrep_replicated_bytes | 0 | +------------------------+-------+ 1 row in set (0.00 sec) mysql> SHOW GLOBAL STATUS LIKE 'wsrep_received_bytes'; +----------------------+-------+ | Variable_name | Value | +----------------------+-------+ | wsrep_received_bytes | 368 | +----------------------+-------+ 1 row in set (0.00 sec)
• Execute some DML statements on the current node (to increase wsrep_replicated_bytes) and on another node (to increase wsrep_received_bytes), then check the status values:
  mysql> SHOW GLOBAL STATUS LIKE 'wsrep_replicated_bytes'; +------------------------+----------+ | Variable_name | Value | +------------------------+----------+ | wsrep_replicated_bytes | 80125192 | +------------------------+----------+ 1 row in set (0.00 sec) mysql> SHOW GLOBAL STATUS LIKE 'wsrep_received_bytes'; +------------------------+----------+ | Variable_name | Value | +------------------------+----------+ | wsrep_received_bytes | 40062948 | +------------------------+----------+ 1 row in set (0.00 sec)
  

  The Amount of replicated data = (80125192 + 40062948) - (0 + 368) = 120187772 Bytes.

• Checking the increase of the binary log file: shell> ll /var/lib/mysql/mysql-bin.000243 -rw-rw---- 1 mysql mysql 113769454 Mar 20 13:42 mysql-bin.000243

Notes:

• The variable log_slave_updates MUST to be enabled on ALL nodes, otherwise, the option wsrep_received_bytes will not be reflected on the binary logs, thus will lead to WRONG calculations!!
• Since the cluster is freshly started, MySQL started to write into a new binary log file while in an already running cluster we can force MySQL to start from new binary log file by issuing the SQL command "FLUSH BINARY LOGS;" so that we can use the total size of the binary logs generated after that during the maintenance.
Conclusion:

Although the binary log traffic will be always less than the amount of replicated data but they are nearly close, thus we can use it to get a rough estimation about the right GCache size value, hence the formula will be as follows:

• GCache size = Maintenance window * Replication Rate.
• GCache size = (wsrep_replicated_bytes + wsrep_received_bytes) after the maintenance window - (wsrep_replicated_bytes + wsrep_received_bytes) before the maintenance window.
• GCache size = binary log traffic which occurs during the maintenance window.

One of our customers had a question related to the right value of Galera Cache size (gcache.size) in Galera Cluster for MySQL which I would like to share with you.

The question was: My maintenance window takes 4 hours for my 5TB DB. How can I avoid an SST ?!

Basically, having too small GCache size will lead to SST (Snapshot State Transfer) instead of IST (Incremental State Transfer), thus we can avoid the SST by setting the GCache to the appropriate value.

To check the current value of the GCache size:

mysql> SHOW GLOBAL VARIABLES LIKE 'wsrep_provider_options'\G Variable_name: wsrep_provider_options Value: base_host = 192.168.1.12; . . . gcache.page_size = 128M; gcache.size = 128M; gcs.fc_debug = 0; . . .

The value of GCache size could be changed by adding the following line in the my.cnf file and restarting the node (it could NOT be changed online):

#my.cnf [mysqld] wsrep_provider_options="gcache.size=256M"

But the question is how can we calculate the right value for GCache size to cover the maintenance window and at the same time not larger than what it needs?

To answer that question we should first find out how much GCache can handle which could be calculated by the following formula:

Hold time = GCache size / Replication Rate.

Where:

• Replication Rate = Amount of replicated data / time.
• Amount of replicated data = (wsrep_replicated_bytes + wsrep_received_bytes) after the maintenance window - (wsrep_replicated_bytes + wsrep_received_bytes) before the maintenance window.

The amount of replicated data for the customer's case = 7200MB.

Now, we can find out how much GCache (default 128M) can handle for the customer's case:

Hold time = 128MB / (7200MB / 4h) = 128MB / 0.5 MB = 256s.

Then, we can calculate the right GCache size value to handle the maintenance window by the following formula:
GCache = Maintenance window * Replication Rate = 14400s * 0.5 MB.
GCache = 7200MB.

In other words, the right GCache size should be equivalent to (or not less than) the amount of replicated data.

A shorter way using the binary logs size

Is there any relation between (wsrep_replicated_bytes + wsrep_received_bytes) and the binary log traffic? Lets check that by the following test scenario:

• Starting a Galera Cluster where the newest binary log file size will be empty (120 bytes) and the same for the status variables: mysql> SHOW GLOBAL STATUS LIKE 'wsrep_replicated_bytes'; +------------------------+-------+ | Variable_name | Value | +------------------------+-------+ | wsrep_replicated_bytes | 0 | +------------------------+-------+ 1 row in set (0.00 sec) mysql> SHOW GLOBAL STATUS LIKE 'wsrep_received_bytes'; +----------------------+-------+ | Variable_name | Value | +----------------------+-------+ | wsrep_received_bytes | 368 | +----------------------+-------+ 1 row in set (0.00 sec)
• Execute some DML statements on the current node (to increase wsrep_replicated_bytes) and on another node (to increase wsrep_received_bytes), then check the status values:
  mysql> SHOW GLOBAL STATUS LIKE 'wsrep_replicated_bytes'; +------------------------+----------+ | Variable_name | Value | +------------------------+----------+ | wsrep_replicated_bytes | 80125192 | +------------------------+----------+ 1 row in set (0.00 sec) mysql> SHOW GLOBAL STATUS LIKE 'wsrep_received_bytes'; +------------------------+----------+ | Variable_name | Value | +------------------------+----------+ | wsrep_received_bytes | 40062948 | +------------------------+----------+ 1 row in set (0.00 sec)
  

  The Amount of replicated data = (80125192 + 40062948) - (0 + 368) = 120187772 Bytes.

• Checking the increase of the binary log file: shell> ll /var/lib/mysql/mysql-bin.000243 -rw-rw---- 1 mysql mysql 113769454 Mar 20 13:42 mysql-bin.000243

Notes:

• The variable log_slave_updates MUST to be enabled on ALL nodes, otherwise, the option wsrep_received_bytes will not be reflected on the binary logs, thus will lead to WRONG calculations!!
• Since the cluster is freshly started, MySQL started to write into a new binary log file while in an already running cluster we can force MySQL to start from new binary log file by issuing the SQL command "FLUSH BINARY LOGS;" so that we can use the total size of the binary logs generated after that during the maintenance.
Conclusion:

Although the binary log traffic will be always less than the amount of replicated data but they are nearly close, thus we can use it to get a rough estimation about the right GCache size value, hence the formula will be as follows:

• GCache size = Maintenance window * Replication Rate.
• GCache size = (wsrep_replicated_bytes + wsrep_received_bytes) after the maintenance window - (wsrep_replicated_bytes + wsrep_received_bytes) before the maintenance window.
• GCache size = binary log traffic which occurs during the maintenance window.

One of our customers had a question related to the right value of Galera Cache size (gcache.size) in Galera Cluster for MySQL which I would like to share with you.

The question was: My maintenance window takes 4 hours for my 5TB DB. How can I avoid an SST ?!

Basically, having too small GCache size will lead to SST (Snapshot State Transfer) instead of IST (Incremental State Transfer), thus we can avoid the SST by setting the GCache to the appropriate value.

To check the current value of the GCache size:

mysql> SHOW GLOBAL VARIABLES LIKE 'wsrep_provider_options'\G Variable_name: wsrep_provider_options Value: base_host = 192.168.1.12; . . . gcache.page_size = 128M; gcache.size = 128M; gcs.fc_debug = 0; . . .

The value of GCache size could be changed by adding the following line in the my.cnf file and restarting the node (it could NOT be changed online):

#my.cnf [mysqld] wsrep_provider_options="gcache.size=256M"

But the question is how can we calculate the right value for GCache size to cover the maintenance window and at the same time not larger than what it needs?

To answer that question we should first find out how much GCache can handle which could be calculated by the following formula:

Hold time = GCache size / Replication Rate.

Where:

• Replication Rate = Amount of replicated data / time.
• Amount of replicated data = (wsrep_replicated_bytes + wsrep_received_bytes) after the maintenance window - (wsrep_replicated_bytes + wsrep_received_bytes) before the maintenance window.

The amount of replicated data for the customer's case = 7200MB.

Now, we can find out how much GCache (default 128M) can handle for the customer's case:

Hold time = 128MB / (7200MB / 4h) = 128MB / 0.5 MB = 256s.

Then, we can calculate the right GCache size value to handle the maintenance window by the following formula:
GCache = Maintenance window * Replication Rate = 14400s * 0.5 MB.
GCache = 7200MB.

In other words, the right GCache size should be equivalent to (or not less than) the amount of replicated data.

A shorter way using the binary logs size

Is there any relation between (wsrep_replicated_bytes + wsrep_received_bytes) and the binary log traffic? Lets check that by the following test scenario:

• Starting a Galera Cluster where the newest binary log file size will be empty (120 bytes) and the same for the status variables: mysql> SHOW GLOBAL STATUS LIKE 'wsrep_replicated_bytes'; +------------------------+-------+ | Variable_name | Value | +------------------------+-------+ | wsrep_replicated_bytes | 0 | +------------------------+-------+ 1 row in set (0.00 sec) mysql> SHOW GLOBAL STATUS LIKE 'wsrep_received_bytes'; +----------------------+-------+ | Variable_name | Value | +----------------------+-------+ | wsrep_received_bytes | 368 | +----------------------+-------+ 1 row in set (0.00 sec)
• Execute some DML statements on the current node (to increase wsrep_replicated_bytes) and on another node (to increase wsrep_received_bytes), then check the status values:
  mysql> SHOW GLOBAL STATUS LIKE 'wsrep_replicated_bytes'; +------------------------+----------+ | Variable_name | Value | +------------------------+----------+ | wsrep_replicated_bytes | 80125192 | +------------------------+----------+ 1 row in set (0.00 sec) mysql> SHOW GLOBAL STATUS LIKE 'wsrep_received_bytes'; +------------------------+----------+ | Variable_name | Value | +------------------------+----------+ | wsrep_received_bytes | 40062948 | +------------------------+----------+ 1 row in set (0.00 sec)
  

  The Amount of replicated data = (80125192 + 40062948) - (0 + 368) = 120187772 Bytes.

• Checking the increase of the binary log file: shell> ll /var/lib/mysql/mysql-bin.000243 -rw-rw---- 1 mysql mysql 113769454 Mar 20 13:42 mysql-bin.000243

Notes:

• The variable log_slave_updates MUST to be enabled on ALL nodes, otherwise, the option wsrep_received_bytes will not be reflected on the binary logs, thus will lead to WRONG calculations!!
• Since the cluster is freshly started, MySQL started to write into a new binary log file while in an already running cluster we can force MySQL to start from new binary log file by issuing the SQL command "FLUSH BINARY LOGS;" so that we can use the total size of the binary logs generated after that during the maintenance.
Conclusion:

Although the binary log traffic will be always less than the amount of replicated data but they are nearly close, thus we can use it to get a rough estimation about the right GCache size value, hence the formula will be as follows:

• GCache size = Maintenance window * Replication Rate.
• GCache size = (wsrep_replicated_bytes + wsrep_received_bytes) after the maintenance window - (wsrep_replicated_bytes + wsrep_received_bytes) before the maintenance window.
• GCache size = binary log traffic which occurs during the maintenance window.

Sometimes, it is required to enable the general query log (which is disabled by default). If the general query log is enabled the server writes to this log information when clients connect or disconnect, and each SQL statement received from the client.

The question is, does enabling the general query log affects the MySQL performance ?
Also, it is possible to record the output of this log into either file or table in the mysql database (mysql.general_log), what is the performance impact of each one?

Let's do some simple benchmark for those scenarios to measure the actual impact on the mysql performance.

System Information: HW configurations:

• CPU: Intel® Core™ i7-3520M Processor (4M Cache, up to 3.60 GHz).
• 2 cores, 4 threads, HT enabled.
• Memory: 8GB RAM (1600).
• Storage: HDD 1TB/ 5400RPM.

Software configurations:

• OS: Ubuntu 12.04
• MySQL Server: 5.6.17
• Sysbench: 0.4.12

Test Information:

• Sysbench command: sysbench --num-threads=1 --max-requests=1000 --db-driver=mysql --test=oltp --mysql-table-engine=InnoDB --mysql-user=root run .
• Table structure which was used by sysbench tests: mysql> show create table sbtest.sbtest\G CREATE TABLE `sbtest` ( `id` int(10) unsigned NOT NULL AUTO_INCREMENT, `k` int(10) unsigned NOT NULL DEFAULT '0', `c` char(120) NOT NULL DEFAULT '', `pad` char(60) NOT NULL DEFAULT '', PRIMARY KEY (`id`), KEY `k` (`k`) ) ENGINE=InnoDB AUTO_INCREMENT=8574 DEFAULT CHARSET=latin1

Note:

The test had been made against 1,2,4,8,16 and 32 threads, each throughput/response time value for each thread's number for each test case is generated by the average of ten (10) times execution.

General log Disabled:

To make sure that the general query log is disabled:

mysql> show global variables like'general_log'; +---------------+-------+ | Variable_name | Value | +---------------+-------+ | general_log | OFF | +---------------+-------+

Testing results:

General log Enabled:

The general query log is a dynamic variable which means that it could be enabled or disabled ONLINE without restarting MySQL (since MySQL 5.1):

mysql> SET GLOBAL general_log=ON;

We can choose the output for this log to be either in a log file (by default) or in a MySQL table (mysql.general_log).

What are the benefits that we might get if we have the log output to be stored in a table not in a file?

• We can use the normal SQL statements to access the log contents to get information about specific criteria (e.g. using WHERE condition) and this is a little harder when dealing with files.
• The log contents could be accessed remotely if someone can connect to the MySQL server.
• Standard format for the log entries.
• If the CSV engine is used for the log table, it will be easy to import the CSV file into spreadsheets.
• It is easy to expire the logs by simply TRUNCATE the log table.
• Log rotation is possible by using RENAME TABLE statement.
• Log entries are not replicated to the slave because they are not written to the binary logs.
• The mysqldump does not include the log tables contents (general_log or slow_log) in the backup even if --all-databases backup option is used.

So, let's check the performance impact then of each log output.

Output is FILE:

To check the output destination of the general log, the following command should be used:

mysql> show global variables like'log_output'; +---------------+-------+ | Variable_name | Value | +---------------+-------+ | log_output | FILE | +---------------+-------+

Testing results:

Output is TABLE (CSV table):

To change the output destination of the general log from file to table (CSV by default), the following command should be used:

mysql> SET GLOBAL log_output='TABLE'; mysql> show global variables like'log_output'; +---------------+-------+ | Variable_name | Value | +---------------+-------+ | log_output | TABLE | +---------------+-------+

Testing results:

Output is TABLE (MyISAM table):

Maybe due to the nature of the CSV storage ENGINE we faced performance issues in the previous case. Is it possible to change the table engine of the general_log table?

The answer is yes, but unfortunately, we are restricted to use only MyISAM storage engine and no engines other than CSV or MyISAM are allowed. Check this link for more information.

To alter the log table, you must first disable the logging:

mysql> alter table mysql.general_log engine=MYISAM; ERROR 1580 (HY000): You cannot 'ALTER' a log table if logging is enabled mysql> SET GLOBAL general_log=OFF; mysql> alter table mysql.general_log engine=MYISAM; mysql> SET GLOBAL general_log=ON;

Testing results:

Output is TABLE (MyISAM table with some structures changes):

In general, to make any SQL query work faster, we might need to optimize the table structure, add indexes, re-write the query, .. etc.

The following is the general log table structure:

mysql> show create table mysql.general_log\G CREATE TABLE `general_log` ( `event_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP, `user_host` mediumtext NOT NULL, `thread_id` bigint(21) unsigned NOT NULL, `server_id` int(10) unsigned NOT NULL, `command_type` varchar(64) NOT NULL, `argument` mediumtext NOT NULL ) ENGINE=MyISAM DEFAULT CHARSET=utf8 COMMENT='General log'

Let's check what can we do to optimize the general_log table structure (other suggestions are welcomed):

• Can we create partitions on that table which might boost our search?
  Although this is a normal MyISAM table but partitioning IS NOT allowed for the log tables (by the way, partitioning is not permitted also for CSV tables).
• Can we change the datatype of the `user_host` column from mediumtext to e.g. varchar(100)? (The max length of this column's data on my machine didn't exceed 50 characters)
  While it is - syntax wise - accepted but no logs will be stored in the table after that and the following error will be printed in the error log file: 2014-03-06 18:44:21 6987 [ERROR] Failed to write to mysql.general_log: 2014-03-06 18:44:23 6987 [ERROR] Incorrect definition of table mysql.general_log: expected column 'user_host' at position 1 to have type mediumtext, found type varchar(100).
  
• What about creating indexes on the columns we will use for most of our searches (`event_time` and `argument`)? lets try that!
  
  • Add index on `event_time` column:
    mysql> SET GLOBAL general_log=OFF; mysql> alter table mysql.general_log add index ev_tm_idx(`event_time`); mysql> show create table mysql.general_log\G CREATE TABLE `general_log` ( `event_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP, `user_host` mediumtext NOT NULL, `thread_id` bigint(21) unsigned NOT NULL, `server_id` int(10) unsigned NOT NULL, `command_type` varchar(64) NOT NULL, `argument` mediumtext NOT NULL, KEY `ev_tm_idx` (`event_time`) ) ENGINE=MyISAM DEFAULT CHARSET=utf8 COMMENT='General log' mysql> SET GLOBAL general_log=ON;
    

    Testing results:

• Add FULLTEXT index on `argument` column:
  mysql> SET GLOBAL general_log=OFF; mysql> alter table mysql.general_log add fulltext index (`argument`); mysql> show create table mysql.general_log\G CREATE TABLE `general_log` ( `event_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP, `user_host` mediumtext NOT NULL, `thread_id` bigint(21) unsigned NOT NULL, `server_id` int(10) unsigned NOT NULL, `command_type` varchar(64) NOT NULL, `argument` mediumtext NOT NULL, KEY `ev_tm_idx` (`event_time`), FULLTEXT KEY `argument` (`argument`) ) ENGINE=MyISAM DEFAULT CHARSET=utf8 COMMENT='General log' mysql> SET GLOBAL general_log=ON;
  

  Testing results:

To make it more clear, the following is the combination of all results in one graph followed by response time comparison:

The raw results in Transactions / Sec might be useful:

Threads12481632General log disabled383.996814.7591421.2881674.7331414.9851071.189General log enabled (File)281.642521.391230.7431406.1271095.896923.986General log enabled (CSV Table)231.659447.173787.578507.846426.324439.992General log enabled (MyISAM Table)249.47536.379933.304532.912476.454454.015General log enabled (MyISAM Table + index)238.508430.05875.209465.464465.464395.063General log enabled (MyISAM Table + Fulltext index)157.436236.156210.968212.273218.617220.701
Conclusion:

• The best MySQL performance - among all above test cases - could be achieved by disabling the general query log, e.g. if we compared the above results for the case 4 concurrent threads (the highest value for most scenarios) we would find that:
  • Using the general log enabled (general_log = ON) and the log destination is file (log_output = FILE) decreased the throughput by 13.4% and increased the response time by 17.5%.
  • Using the general log enabled and the log destination is CSV table decreased the throughput by 44.6% and increased the response time by 90%.
  • Using the general log enabled and the log destination is MyISAM table decreased the throughput by 34.3% and increased the response time by 59%.
  • Using the general log enabled and the log destination is MyISAM having an index added on column `event_time` decreased the throughput by 38.4% and increased the response time by 73%.
  • Using the general log enabled and the log destination is MyISAM having an index added on column `event_time` and FULLTEXT index added on column `argument` decreased the throughput by 85% and increased the response time by 542%.
• Although using table as a log output destination has many benefits - as described above - but it has more negative impact on the MySQL performance as compared to log file.
• Increasing the number of concurrently running threads - in the case of log_output=TABLE - will increase the general_log table contention which is controlled by the table locking level for MyISAM or CSV ENGINES.
• Like any other MySQL table - as many rows inserted in the log table as more negative performance impact.
• Although mysqldump does not include the log tables contents in the backup but this is not the case when having full physical backup using Xtrabackup or any other physical backup based tools.
• Finally, it is preferred to only enable the general query log when it is really needed and it is not recommended to enable it in a production system. It could be enabled (dynamically) for a while then should be disabled again once we have got what we are searching for.

Taxonomy upgrade extras: general query logperformance

Sometimes, it is required to enable the general query log (which is disabled by default). If the general query log is enabled the server writes to this log information when clients connect or disconnect, and each SQL statement received from the client.

The question is, does enabling the general query log affects the MySQL performance ?
Also, it is possible to record the output of this log into either file or table in the mysql database (mysql.general_log), what is the performance impact of each one?

Let's do some simple benchmark for those scenarios to measure the actual impact on the mysql performance.

System Information: HW configurations:

• CPU: Intel® Core™ i7-3520M Processor (4M Cache, up to 3.60 GHz).
• 2 cores, 4 threads, HT enabled.
• Memory: 8GB RAM (1600).
• Storage: HDD 1TB/ 5400RPM.

Software configurations:

• OS: Ubuntu 12.04
• MySQL Server: 5.6.17
• Sysbench: 0.4.12

Test Information:

• Sysbench command: sysbench --num-threads=1 --max-requests=1000 --db-driver=mysql --test=oltp --mysql-table-engine=InnoDB --mysql-user=root run .
• Table structure which was used by sysbench tests: mysql> show create table sbtest.sbtest\G CREATE TABLE `sbtest` ( `id` int(10) unsigned NOT NULL AUTO_INCREMENT, `k` int(10) unsigned NOT NULL DEFAULT '0', `c` char(120) NOT NULL DEFAULT '', `pad` char(60) NOT NULL DEFAULT '', PRIMARY KEY (`id`), KEY `k` (`k`) ) ENGINE=InnoDB AUTO_INCREMENT=8574 DEFAULT CHARSET=latin1

Note:

The test had been made against 1,2,4,8,16 and 32 threads, each throughput/response time value for each thread's number for each test case is generated by the average of ten (10) times execution.

General log Disabled:

To make sure that the general query log is disabled:

mysql> show global variables like'general_log'; +---------------+-------+ | Variable_name | Value | +---------------+-------+ | general_log | OFF | +---------------+-------+

Testing results:

General log Enabled:

The general query log is a dynamic variable which means that it could be enabled or disabled ONLINE without restarting MySQL (since MySQL 5.1):

mysql> SET GLOBAL general_log=ON;

We can choose the output for this log to be either in a log file (by default) or in a MySQL table (mysql.general_log).

What are the benefits that we might get if we have the log output to be stored in a table not in a file?

• We can use the normal SQL statements to access the log contents to get information about specific criteria (e.g. using WHERE condition) and this is a little harder when dealing with files.
• The log contents could be accessed remotely if someone can connect to the MySQL server.
• Standard format for the log entries.
• If the CSV engine is used for the log table, it will be easy to import the CSV file into spreadsheets.
• It is easy to expire the logs by simply TRUNCATE the log table.
• Log rotation is possible by using RENAME TABLE statement.
• Log entries are not replicated to the slave because they are not written to the binary logs.
• The mysqldump does not include the log tables contents (general_log or slow_log) in the backup even if --all-databases backup option is used.

So, let's check the performance impact then of each log output.

Output is FILE:

To check the output destination of the general log, the following command should be used:

mysql> show global variables like'log_output'; +---------------+-------+ | Variable_name | Value | +---------------+-------+ | log_output | FILE | +---------------+-------+

Testing results:

Output is TABLE (CSV table):

To change the output destination of the general log from file to table (CSV by default), the following command should be used:

mysql> SET GLOBAL log_output='TABLE'; mysql> show global variables like'log_output'; +---------------+-------+ | Variable_name | Value | +---------------+-------+ | log_output | TABLE | +---------------+-------+

Testing results:

Output is TABLE (MyISAM table):

Maybe due to the nature of the CSV storage ENGINE we faced performance issues in the previous case. Is it possible to change the table engine of the general_log table?

The answer is yes, but unfortunately, we are restricted to use only MyISAM storage engine and no engines other than CSV or MyISAM are allowed. Check this link for more information.

To alter the log table, you must first disable the logging:

mysql> alter table mysql.general_log engine=MYISAM; ERROR 1580 (HY000): You cannot 'ALTER' a log table if logging is enabled mysql> SET GLOBAL general_log=OFF; mysql> alter table mysql.general_log engine=MYISAM; mysql> SET GLOBAL general_log=ON;

Testing results:

Output is TABLE (MyISAM table with some structures changes):

In general, to make any SQL query work faster, we might need to optimize the table structure, add indexes, re-write the query, .. etc.

The following is the general log table structure:

mysql> show create table mysql.general_log\G CREATE TABLE `general_log` ( `event_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP, `user_host` mediumtext NOT NULL, `thread_id` bigint(21) unsigned NOT NULL, `server_id` int(10) unsigned NOT NULL, `command_type` varchar(64) NOT NULL, `argument` mediumtext NOT NULL ) ENGINE=MyISAM DEFAULT CHARSET=utf8 COMMENT='General log'

Let's check what can we do to optimize the general_log table structure (other suggestions are welcomed):

• Can we create partitions on that table which might boost our search?
  Although this is a normal MyISAM table but partitioning IS NOT allowed for the log tables (by the way, partitioning is not permitted also for CSV tables).
• Can we change the datatype of the `user_host` column from mediumtext to e.g. varchar(100)? (The max length of this column's data on my machine didn't exceed 50 characters)
  While it is - syntax wise - accepted but no logs will be stored in the table after that and the following error will be printed in the error log file: 2014-03-06 18:44:21 6987 [ERROR] Failed to write to mysql.general_log: 2014-03-06 18:44:23 6987 [ERROR] Incorrect definition of table mysql.general_log: expected column 'user_host' at position 1 to have type mediumtext, found type varchar(100).
  
• What about creating indexes on the columns we will use for most of our searches (`event_time` and `argument`)? lets try that!
  
  • Add index on `event_time` column:
    mysql> SET GLOBAL general_log=OFF; mysql> alter table mysql.general_log add index ev_tm_idx(`event_time`); mysql> show create table mysql.general_log\G CREATE TABLE `general_log` ( `event_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP, `user_host` mediumtext NOT NULL, `thread_id` bigint(21) unsigned NOT NULL, `server_id` int(10) unsigned NOT NULL, `command_type` varchar(64) NOT NULL, `argument` mediumtext NOT NULL, KEY `ev_tm_idx` (`event_time`) ) ENGINE=MyISAM DEFAULT CHARSET=utf8 COMMENT='General log' mysql> SET GLOBAL general_log=ON;
    

    Testing results:

• Add FULLTEXT index on `argument` column:
  mysql> SET GLOBAL general_log=OFF; mysql> alter table mysql.general_log add fulltext index (`argument`); mysql> show create table mysql.general_log\G CREATE TABLE `general_log` ( `event_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP, `user_host` mediumtext NOT NULL, `thread_id` bigint(21) unsigned NOT NULL, `server_id` int(10) unsigned NOT NULL, `command_type` varchar(64) NOT NULL, `argument` mediumtext NOT NULL, KEY `ev_tm_idx` (`event_time`), FULLTEXT KEY `argument` (`argument`) ) ENGINE=MyISAM DEFAULT CHARSET=utf8 COMMENT='General log' mysql> SET GLOBAL general_log=ON;
  

  Testing results:

To make it more clear, the following is the combination of all results in one graph followed by response time comparison:

The raw results in Transactions / Sec might be useful:

Threads12481632General log disabled383.996814.7591421.2881674.7331414.9851071.189General log enabled (File)281.642521.391230.7431406.1271095.896923.986General log enabled (CSV Table)231.659447.173787.578507.846426.324439.992General log enabled (MyISAM Table)249.47536.379933.304532.912476.454454.015General log enabled (MyISAM Table + index)238.508430.05875.209465.464465.464395.063General log enabled (MyISAM Table + Fulltext index)157.436236.156210.968212.273218.617220.701
Conclusion:

• The best MySQL performance - among all above test cases - could be achieved by disabling the general query log, e.g. if we compared the above results for the case 4 concurrent threads (the highest value for most scenarios) we would find that:
  • Using the general log enabled (general_log = ON) and the log destination is file (log_output = FILE) decreased the throughput by 13.4% and increased the response time by 17.5%.
  • Using the general log enabled and the log destination is CSV table decreased the throughput by 44.6% and increased the response time by 90%.
  • Using the general log enabled and the log destination is MyISAM table decreased the throughput by 34.3% and increased the response time by 59%.
  • Using the general log enabled and the log destination is MyISAM having an index added on column `event_time` decreased the throughput by 38.4% and increased the response time by 73%.
  • Using the general log enabled and the log destination is MyISAM having an index added on column `event_time` and FULLTEXT index added on column `argument` decreased the throughput by 85% and increased the response time by 542%.
• Although using table as a log output destination has many benefits - as described above - but it has more negative impact on the MySQL performance as compared to log file.
• Increasing the number of concurrently running threads - in the case of log_output=TABLE - will increase the general_log table contention which is controlled by the table locking level for MyISAM or CSV ENGINES.
• Like any other MySQL table - as many rows inserted in the log table as more negative performance impact.
• Although mysqldump does not include the log tables contents in the backup but this is not the case when having full physical backup using Xtrabackup or any other physical backup based tools.
• Finally, it is preferred to only enable the general query log when it is really needed and it is not recommended to enable it in a production system. It could be enabled (dynamically) for a while then should be disabled again once we have got what we are searching for.

Sometimes, it is required to enable the general query log (which is disabled by default). If the general query log is enabled the server writes to this log information when clients connect or disconnect, and each SQL statement received from the client.

The question is, does enabling the general query log affects the MySQL performance ?
Also, it is possible to record the output of this log into either file or table in the mysql database (mysql.general_log), what is the performance impact of each one?

Let's do some simple benchmark for those scenarios to measure the actual impact on the mysql performance.

System Information: HW configurations:

• CPU: Intel® Core™ i7-3520M Processor (4M Cache, up to 3.60 GHz).
• 2 cores, 4 threads, HT enabled.
• Memory: 8GB RAM (1600).
• Storage: HDD 1TB/ 5400RPM.

Software configurations:

• OS: Ubuntu 12.04
• MySQL Server: 5.6.17
• Sysbench: 0.4.12

Test Information:

• Sysbench command: sysbench --num-threads=1 --max-requests=1000 --db-driver=mysql --test=oltp --mysql-table-engine=InnoDB --mysql-user=root run .
• Table structure which was used by sysbench tests: mysql> show create table sbtest.sbtest\G CREATE TABLE `sbtest` ( `id` int(10) unsigned NOT NULL AUTO_INCREMENT, `k` int(10) unsigned NOT NULL DEFAULT '0', `c` char(120) NOT NULL DEFAULT '', `pad` char(60) NOT NULL DEFAULT '', PRIMARY KEY (`id`), KEY `k` (`k`) ) ENGINE=InnoDB AUTO_INCREMENT=8574 DEFAULT CHARSET=latin1

Note:

The test had been made against 1,2,4,8,16 and 32 threads, each throughput/response time value for each thread's number for each test case is generated by the average of ten (10) times execution.

General log Disabled:

To make sure that the general query log is disabled:

mysql> show global variables like'general_log'; +---------------+-------+ | Variable_name | Value | +---------------+-------+ | general_log | OFF | +---------------+-------+

Testing results:

General log Enabled:

The general query log is a dynamic variable which means that it could be enabled or disabled ONLINE without restarting MySQL (since MySQL 5.1):

mysql> SET GLOBAL general_log=ON;

We can choose the output for this log to be either in a log file (by default) or in a MySQL table (mysql.general_log).

What are the benefits that we might get if we have the log output to be stored in a table not in a file?

• We can use the normal SQL statements to access the log contents to get information about specific criteria (e.g. using WHERE condition) and this is a little harder when dealing with files.
• The log contents could be accessed remotely if someone can connect to the MySQL server.
• Standard format for the log entries.
• If the CSV engine is used for the log table, it will be easy to import the CSV file into spreadsheets.
• It is easy to expire the logs by simply TRUNCATE the log table.
• Log rotation is possible by using RENAME TABLE statement.
• Log entries are not replicated to the slave because they are not written to the binary logs.
• The mysqldump does not include the log tables contents (general_log or slow_log) in the backup even if --all-databases backup option is used.

So, let's check the performance impact then of each log output.

Output is FILE:

To check the output destination of the general log, the following command should be used:

mysql> show global variables like'log_output'; +---------------+-------+ | Variable_name | Value | +---------------+-------+ | log_output | FILE | +---------------+-------+

Testing results:

Output is TABLE (CSV table):

To change the output destination of the general log from file to table (CSV by default), the following command should be used:

mysql> SET GLOBAL log_output='TABLE'; mysql> show global variables like'log_output'; +---------------+-------+ | Variable_name | Value | +---------------+-------+ | log_output | TABLE | +---------------+-------+

Testing results:

Output is TABLE (MyISAM table):

Maybe due to the nature of the CSV storage ENGINE we faced performance issues in the previous case. Is it possible to change the table engine of the general_log table?

The answer is yes, but unfortunately, we are restricted to use only MyISAM storage engine and no engines other than CSV or MyISAM are allowed. Check this link for more information.

To alter the log table, you must first disable the logging:

mysql> alter table mysql.general_log engine=MYISAM; ERROR 1580 (HY000): You cannot 'ALTER' a log table if logging is enabled mysql> SET GLOBAL general_log=OFF; mysql> alter table mysql.general_log engine=MYISAM; mysql> SET GLOBAL general_log=ON;

Testing results:

Output is TABLE (MyISAM table with some structures changes):

In general, to make any SQL query work faster, we might need to optimize the table structure, add indexes, re-write the query, .. etc.

The following is the general log table structure:

mysql> show create table mysql.general_log\G CREATE TABLE `general_log` ( `event_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP, `user_host` mediumtext NOT NULL, `thread_id` bigint(21) unsigned NOT NULL, `server_id` int(10) unsigned NOT NULL, `command_type` varchar(64) NOT NULL, `argument` mediumtext NOT NULL ) ENGINE=MyISAM DEFAULT CHARSET=utf8 COMMENT='General log'

Let's check what can we do to optimize the general_log table structure (other suggestions are welcomed):

• Can we create partitions on that table which might boost our search?
  Although this is a normal MyISAM table but partitioning IS NOT allowed for the log tables (by the way, partitioning is not permitted also for CSV tables).
• Can we change the datatype of the `user_host` column from mediumtext to e.g. varchar(100)? (The max length of this column's data on my machine didn't exceed 50 characters)
  While it is - syntax wise - accepted but no logs will be stored in the table after that and the following error will be printed in the error log file: 2014-03-06 18:44:21 6987 [ERROR] Failed to write to mysql.general_log: 2014-03-06 18:44:23 6987 [ERROR] Incorrect definition of table mysql.general_log: expected column 'user_host' at position 1 to have type mediumtext, found type varchar(100).
  
• What about creating indexes on the columns we will use for most of our searches (`event_time` and `argument`)? lets try that!
  
  • Add index on `event_time` column:
    mysql> SET GLOBAL general_log=OFF; mysql> alter table mysql.general_log add index ev_tm_idx(`event_time`); mysql> show create table mysql.general_log\G CREATE TABLE `general_log` ( `event_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP, `user_host` mediumtext NOT NULL, `thread_id` bigint(21) unsigned NOT NULL, `server_id` int(10) unsigned NOT NULL, `command_type` varchar(64) NOT NULL, `argument` mediumtext NOT NULL, KEY `ev_tm_idx` (`event_time`) ) ENGINE=MyISAM DEFAULT CHARSET=utf8 COMMENT='General log' mysql> SET GLOBAL general_log=ON;
    

    Testing results:

• Add FULLTEXT index on `argument` column:
  mysql> SET GLOBAL general_log=OFF; mysql> alter table mysql.general_log add fulltext index (`argument`); mysql> show create table mysql.general_log\G CREATE TABLE `general_log` ( `event_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP, `user_host` mediumtext NOT NULL, `thread_id` bigint(21) unsigned NOT NULL, `server_id` int(10) unsigned NOT NULL, `command_type` varchar(64) NOT NULL, `argument` mediumtext NOT NULL, KEY `ev_tm_idx` (`event_time`), FULLTEXT KEY `argument` (`argument`) ) ENGINE=MyISAM DEFAULT CHARSET=utf8 COMMENT='General log' mysql> SET GLOBAL general_log=ON;
  

  Testing results:

To make it more clear, the following is the combination of all results in one graph followed by response time comparison:

The raw results in Transactions / Sec might be useful:

Threads12481632General log disabled383.996814.7591421.2881674.7331414.9851071.189General log enabled (File)281.642521.391230.7431406.1271095.896923.986General log enabled (CSV Table)231.659447.173787.578507.846426.324439.992General log enabled (MyISAM Table)249.47536.379933.304532.912476.454454.015General log enabled (MyISAM Table + index)238.508430.05875.209465.464465.464395.063General log enabled (MyISAM Table + Fulltext index)157.436236.156210.968212.273218.617220.701
Conclusion:

• The best MySQL performance - among all above test cases - could be achieved by disabling the general query log, e.g. if we compared the above results for the case 4 concurrent threads (the highest value for most scenarios) we would find that:
  • Using the general log enabled (general_log = ON) and the log destination is file (log_output = FILE) decreased the throughput by 13.4% and increased the response time by 17.5%.
  • Using the general log enabled and the log destination is CSV table decreased the throughput by 44.6% and increased the response time by 90%.
  • Using the general log enabled and the log destination is MyISAM table decreased the throughput by 34.3% and increased the response time by 59%.
  • Using the general log enabled and the log destination is MyISAM having an index added on column `event_time` decreased the throughput by 38.4% and increased the response time by 73%.
  • Using the general log enabled and the log destination is MyISAM having an index added on column `event_time` and FULLTEXT index added on column `argument` decreased the throughput by 85% and increased the response time by 542%.
• Although using table as a log output destination has many benefits - as described above - but it has more negative impact on the MySQL performance as compared to log file.
• Increasing the number of concurrently running threads - in the case of log_output=TABLE - will increase the general_log table contention which is controlled by the table locking level for MyISAM or CSV ENGINES.
• Like any other MySQL table - as many rows inserted in the log table as more negative performance impact.
• Although mysqldump does not include the log tables contents in the backup but this is not the case when having full physical backup using Xtrabackup or any other physical backup based tools.
• Finally, it is preferred to only enable the general query log when it is really needed and it is not recommended to enable it in a production system. It could be enabled (dynamically) for a while then should be disabled again once we have got what we are searching for.

One of the most expensive database operations is performing Data Definition Language (DDL, e.g. CREATE, DROP, ALTER, etc.) statements, specially, the ALTER statements because MySQL blocks the entire table for both reads and writes while modifying the table.

For the huge tables, this might take hours to get the table changed which affects the application, so that, a good planning is required for such operations in order to avoid doing these changes during the peak times. For those people who have 24/7 services or limited maintenance window, DDL on huge tables is a really nightmare.

Percona developed a very good tool called pt-online-schema-change (version 2.2.6 at the time of writing this article) to perform such operations online without blocking/affecting the application and read/write operations to the table being changed is available.
Also MySQL made some enhancements for DDL statements and introduced the Online DDL feature in MySQL 5.6.

In this article, I will talk about an overview of both ways (Online DDL & pt-online-schema-change) alongside with an example and which one of them should be used in different scenarios.

pt-online-schema-change Overview

This tool is developed by Percona to alter tables without locking them during the ALTER operation.
Simply, this tool creates a new empty table like the original table with the needed structure change, copy the data from the original table in small chunks to the new table, drop the original table and then rename the new table to the original name. During the copy process all new changes to the original table are being applied to the new one because a trigger is created on the original table which ensure that all new changes will be applied on the new table.

For more information about pt-online-schema-change tool, check out the manual documentation.

Example

Altering a table called "test.test1" by adding an index (name_idx) on column "name":

[root@gcservera ~]# pt-online-schema-change --execute --alter "add index name_idx (name)" D=test,t=test1,h=localhost Operation, tries, wait: copy_rows, 10, 0.25 create_triggers, 10, 1 drop_triggers, 10, 1 swap_tables, 10, 1 update_foreign_keys, 10, 1 Altering `test`.`test1`... Creating new table... Created new table test._test1_new OK. Altering new table... Altered `test`.`_test1_new` OK. 2014-02-09T15:33:27 Creating triggers... 2014-02-09T15:33:27 Created triggers OK. 2014-02-09T15:33:27 Copying approximately 1 rows... 2014-02-09T15:33:27 Copied rows OK. 2014-02-09T15:33:27 Swapping tables... 2014-02-09T15:33:27 Swapped original and new tables OK. 2014-02-09T15:33:27 Dropping old table... 2014-02-09T15:33:27 Dropped old table `test`.`_test1_old` OK. 2014-02-09T15:33:27 Dropping triggers... 2014-02-09T15:33:27 Dropped triggers OK. Successfully altered `test`.`test1`.

Note:

The output is perfectly describing all steps that the tool is doing in the background.

Limitations of pt-online-schema-change

• A PRIMARY KEY or a unique index should be defined for the table before using this tool because it is required for the DELETE trigger.
• Not supported if the table has already triggers defined.
• The tool become complicate a little if the table has a foreign key constraint and an additional option --alter-foreign-keys-method should be used.
• Also because of the foreign keys, the object names might be changed (indexes names , .. etc).
• In Galera Cluster environment, altering MyISAM tables is not supported and the system variable "wsrep_OSU_method" must be set to "TOI" (total order isolation).

Online DDL Overview

In MySQL 5.5 and 5.1 with the InnoDB plugin, a new feature known as Fast Index Creation was introduced to avoid copying the tables data - when adding or removing secondary indexes - using the optimized CREATE INDEX and DROP INDEX statements.

In MySQL 5.6, the Online DDL method was introduced to allow more changes to be made on the table while accessing and writing to the table being changed is available.

The Online DDL syntax is exactly the same like the normal alter statement after specifying two parameters:

ALGORITHM:

• INPLACE: the table change will be made in-place without rebuilding the entire table (in most cases, no copying data to temporary table is required).
• COPY: copying data to a temporary table, rebuilding the table and reconstructing the secondary indexes will be made (equivalent to the traditional method).

LOCK:

• NONE: Read and write operations are allowed during the altering process.
• SHARED: Only read operations are allowed during the altering operations (DML is not allowed).
• EXCLUSIVE: The entire table will be locked for both reading and writing (neither select nor DML are allowed).

The Online DDL is perfectly explained in the online manual documentation, you can check it out here for more information.

Example

Altering a table called "test.test2" by adding an index (name_idx) on column "name":

mysql> alter table test2 -> add index name_idx (name),algorithm=inplace, lock=none; Query OK, 0 rows affected (0.03 sec) Records: 0 Duplicates: 0 Warnings: 0 Limitations of Online DDL

• Works only with InnoDB (syntax wise it could be used with other storage engines "like MyISAM" but only "algorithm=copy" is allowed which is equivalent to the traditional method).
• Regardless of the locking used (none,shared or exclusive) a brief period at the beginning and at the end of the process is requiring an exclusive lock on the table.
• foreign_key_checks should be disabled when adding/dropping foreign keys to avoid table copying behavior.
• Still some alter operations require table copying or table locking in order to make the change (the old behavior). For more details on which table change require table-copying or table locking, check out this manual page.
• LOCK=NONE is not allowed in the alter table statement if there are ON...CASCADE or ON...SET NULL constraints on the table.
• While the Online DDL will be replicated on the slaves the same like the master (if LOCK=NONE no table-locking will take place on the slaves during the alter execution) but the replication itself will be blocked as the replay process executes in a single thread on the replicas which will cause slave lagging problem.

Comparison results

The following is a comparison results between Online DDL and pt-online-schema-change for some alter operations applied on a table contains 1,078,880 rows:

Online DDLpt-online-schema-changeChange OperationRow(s) affectedIs table locked?Time (sec)Row(s) affectedIs table locked?Time (sec)Add Index0No3.76All rowsNo38.12Drop Index0No0.34All rowsNo36.04Add Column0No27.61All rowsNo37.21Rename Column0No0.06All rowsNo34.16Rename Column + change its data typeAll rowsYes30.21All rowsNo34.23Drop Column0No22.41All rowsNo31.57Change table ENGINEAll rowsYes25.30All rowsNo35.54Which method should be used?

Now the question is, which method should we use to perform alter table statements?

While pt-online-schema-change allows read and write operations to the table being altered, it still copies the tables data to a temporary table in the background which adds overhead on the MySQL server. So basically, we should use pt-online-schema-change if the Online DDL will not work efficiently. In other words, if the Online DDL will require copying data to a temporary table (algorithm=copy) and the table will be blocked for long time (lock=exclusive) or when altering huge tables in a replication environment then we should use pt-online-schema-change tool.

One of the most expensive database operations is performing Data Definition Language (DDL, e.g. CREATE, DROP, ALTER, etc.) statements, specially, the ALTER statements because MySQL blocks the entire table for both reads and writes while modifying the table.

For the huge tables, this might take hours to get the table changed which affects the application, so that, a good planning is required for such operations in order to avoid doing these changes during the peak times. For those people who have 24/7 services or limited maintenance window, DDL on huge tables is a really nightmare.

Percona developed a very good tool called pt-online-schema-change (version 2.2.6 at the time of writing this article) to perform such operations online without blocking/affecting the application and read/write operations to the table being changed is available.
Also MySQL made some enhancements for DDL statements and introduced the Online DDL feature in MySQL 5.6.

In this article, I will talk about an overview of both ways (Online DDL & pt-online-schema-change) alongside with an example and which one of them should be used in different scenarios.

pt-online-schema-change Overview

This tool is developed by Percona to alter tables without locking them during the ALTER operation.
Simply, this tool creates a new empty table like the original table with the needed structure change, copy the data from the original table in small chunks to the new table, drop the original table and then rename the new table to the original name. During the copy process all new changes to the original table are being applied to the new one because a trigger is created on the original table which ensure that all new changes will be applied on the new table.

For more information about pt-online-schema-change tool, check out the manual documentation.

Example

Altering a table called "test.test1" by adding an index (name_idx) on column "name":

[root@gcservera ~]# pt-online-schema-change --execute --alter "add index name_idx (name)" D=test,t=test1,h=localhost Operation, tries, wait: copy_rows, 10, 0.25 create_triggers, 10, 1 drop_triggers, 10, 1 swap_tables, 10, 1 update_foreign_keys, 10, 1 Altering `test`.`test1`... Creating new table... Created new table test._test1_new OK. Altering new table... Altered `test`.`_test1_new` OK. 2014-02-09T15:33:27 Creating triggers... 2014-02-09T15:33:27 Created triggers OK. 2014-02-09T15:33:27 Copying approximately 1 rows... 2014-02-09T15:33:27 Copied rows OK. 2014-02-09T15:33:27 Swapping tables... 2014-02-09T15:33:27 Swapped original and new tables OK. 2014-02-09T15:33:27 Dropping old table... 2014-02-09T15:33:27 Dropped old table `test`.`_test1_old` OK. 2014-02-09T15:33:27 Dropping triggers... 2014-02-09T15:33:27 Dropped triggers OK. Successfully altered `test`.`test1`.

Note:

The output is perfectly describing all steps that the tool is doing in the background.

Limitations of pt-online-schema-change

• A PRIMARY KEY or a unique index should be defined for the table before using this tool because it is required for the DELETE trigger.
• Not supported if the table has already triggers defined.
• The tool become complicate a little if the table has a foreign key constraint and an additional option --alter-foreign-keys-method should be used.
• Also because of the foreign keys, the object names might be changed (indexes names , .. etc).
• In Galera Cluster environment, altering MyISAM tables is not supported and the system variable "wsrep_OSU_method" must be set to "TOI" (total order isolation).

Online DDL Overview

In MySQL 5.5 and 5.1 with the InnoDB plugin, a new feature known as Fast Index Creation was introduced to avoid copying the tables data - when adding or removing secondary indexes - using the optimized CREATE INDEX and DROP INDEX statements.

In MySQL 5.6, the Online DDL method was introduced to allow more changes to be made on the table while accessing and writing to the table being changed is available.

The Online DDL syntax is exactly the same like the normal alter statement after specifying two parameters:

ALGORITHM:

• INPLACE: the table change will be made in-place without rebuilding the entire table (in most cases, no copying data to temporary table is required).
• COPY: copying data to a temporary table, rebuilding the table and reconstructing the secondary indexes will be made (equivalent to the traditional method).

LOCK:

• NONE: Read and write operations are allowed during the altering process.
• SHARED: Only read operations are allowed during the altering operations (DML is not allowed).
• EXCLUSIVE: The entire table will be locked for both reading and writing (neither select nor DML are allowed).

The Online DDL is perfectly explained in the online manual documentation, you can check it out here for more information.

Example

Altering a table called "test.test2" by adding an index (name_idx) on column "name":

mysql> alter table test2 -> add index name_idx (name),algorithm=inplace, lock=none; Query OK, 0 rows affected (0.03 sec) Records: 0 Duplicates: 0 Warnings: 0 Limitations of Online DDL

• Works only with InnoDB (syntax wise it could be used with other storage engines "like MyISAM" but only "algorithm=copy" is allowed which is equivalent to the traditional method).
• Regardless of the locking used (none,shared or exclusive) a brief period at the beginning and at the end of the process is requiring an exclusive lock on the table.
• foreign_key_checks should be disabled when adding/dropping foreign keys to avoid table copying behavior.
• Still some alter operations require table copying or table locking in order to make the change (the old behavior). For more details on which table change require table-copying or table locking, check out this manual page.
• LOCK=NONE is not allowed in the alter table statement if there are ON...CASCADE or ON...SET NULL constraints on the table.
• While the Online DDL will be replicated on the slaves the same like the master (if LOCK=NONE no table-locking will take place on the slaves during the alter execution) but the replication itself will be blocked as the replay process executes in a single thread on the replicas which will cause slave lagging problem.

Comparison results

The following is a comparison results between Online DDL and pt-online-schema-change for some alter operations applied on a table contains 1,078,880 rows:

Online DDLpt-online-schema-changeChange OperationRow(s) affectedIs table locked?Time (sec)Row(s) affectedIs table locked?Time (sec)Add Index0No3.76All rowsNo38.12Drop Index0No0.34All rowsNo36.04Add Column0No27.61All rowsNo37.21Rename Column0No0.06All rowsNo34.16Rename Column + change its data typeAll rowsYes30.21All rowsNo34.23Drop Column0No22.41All rowsNo31.57Change table ENGINEAll rowsYes25.30All rowsNo35.54Which method should be used?

Now the question is, which method should we use to perform alter table statements?

While pt-online-schema-change allows read and write operations to the table being altered, it still copies the tables data to a temporary table in the background which adds overhead on the MySQL server. So basically, we should use pt-online-schema-change if the Online DDL will not work efficiently. In other words, if the Online DDL will require copying data to a temporary table (algorithm=copy) and the table will be blocked for long time (lock=exclusive) or when altering huge tables in a replication environment then we should use pt-online-schema-change tool.

One of the most expensive database operations is performing Data Definition Language (DDL, e.g. CREATE, DROP, ALTER, etc.) statements, specially, the ALTER statements because MySQL blocks the entire table for both reads and writes while modifying the table.

For the huge tables, this might take hours to get the table changed which affects the application, so that, a good planning is required for such operations in order to avoid doing these changes during the peak times. For those people who have 24/7 services or limited maintenance window, DDL on huge tables is a really nightmare.

Percona developed a very good tool called pt-online-schema-change (version 2.2.6 at the time of writing this article) to perform such operations online without blocking/affecting the application and read/write operations to the table being changed is available.
Also MySQL made some enhancements for DDL statements and introduced the Online DDL feature in MySQL 5.6.

In this article, I will talk about an overview of both ways (Online DDL & pt-online-schema-change) alongside with an example and which one of them should be used in different scenarios.

pt-online-schema-change Overview

This tool is developed by Percona to alter tables without locking them during the ALTER operation.
Simply, this tool creates a new empty table like the original table with the needed structure change, copy the data from the original table in small chunks to the new table, drop the original table and then rename the new table to the original name. During the copy process all new changes to the original table are being applied to the new one because a trigger is created on the original table which ensure that all new changes will be applied on the new table.

For more information about pt-online-schema-change tool, check out the manual documentation.

Example

Altering a table called "test.test1" by adding an index (name_idx) on column "name":

[root@gcservera ~]# pt-online-schema-change --execute --alter "add index name_idx (name)" D=test,t=test1,h=localhost Operation, tries, wait: copy_rows, 10, 0.25 create_triggers, 10, 1 drop_triggers, 10, 1 swap_tables, 10, 1 update_foreign_keys, 10, 1 Altering `test`.`test1`... Creating new table... Created new table test._test1_new OK. Altering new table... Altered `test`.`_test1_new` OK. 2014-02-09T15:33:27 Creating triggers... 2014-02-09T15:33:27 Created triggers OK. 2014-02-09T15:33:27 Copying approximately 1 rows... 2014-02-09T15:33:27 Copied rows OK. 2014-02-09T15:33:27 Swapping tables... 2014-02-09T15:33:27 Swapped original and new tables OK. 2014-02-09T15:33:27 Dropping old table... 2014-02-09T15:33:27 Dropped old table `test`.`_test1_old` OK. 2014-02-09T15:33:27 Dropping triggers... 2014-02-09T15:33:27 Dropped triggers OK. Successfully altered `test`.`test1`.

Note:

The output is perfectly describing all steps that the tool is doing in the background.

Limitations of pt-online-schema-change

• A PRIMARY KEY or a unique index should be defined for the table before using this tool because it is required for the DELETE trigger.
• Not supported if the table has already triggers defined.
• The tool become complicate a little if the table has a foreign key constraint and an additional option --alter-foreign-keys-method should be used.
• Also because of the foreign keys, the object names might be changed (indexes names , .. etc).
• In Galera Cluster environment, altering MyISAM tables is not supported and the system variable "wsrep_OSU_method" must be set to "TOI" (total order isolation).

Online DDL Overview

In MySQL 5.5 and 5.1 with the InnoDB plugin, a new feature known as Fast Index Creation was introduced to avoid copying the tables data - when adding or removing secondary indexes - using the optimized CREATE INDEX and DROP INDEX statements.

In MySQL 5.6, the Online DDL method was introduced to allow more changes to be made on the table while accessing and writing to the table being changed is available.

The Online DDL syntax is exactly the same like the normal alter statement after specifying two parameters:

ALGORITHM:

• INPLACE: the table change will be made in-place without rebuilding the entire table (in most cases, no copying data to temporary table is required).
• COPY: copying data to a temporary table, rebuilding the table and reconstructing the secondary indexes will be made (equivalent to the traditional method).

LOCK:

• NONE: Read and write operations are allowed during the altering process.
• SHARED: Only read operations are allowed during the altering operations (DML is not allowed).
• EXCLUSIVE: The entire table will be locked for both reading and writing (neither select nor DML are allowed).

The Online DDL is perfectly explained in the online manual documentation, you can check it out here for more information.

Example

Altering a table called "test.test2" by adding an index (name_idx) on column "name":

mysql> alter table test2 -> add index name_idx (name),algorithm=inplace, lock=none; Query OK, 0 rows affected (0.03 sec) Records: 0 Duplicates: 0 Warnings: 0 Limitations of Online DDL

• Works only with InnoDB (syntax wise it could be used with other storage engines "like MyISAM" but only "algorithm=copy" is allowed which is equivalent to the traditional method).
• Regardless of the locking used (none,shared or exclusive) a brief period at the beginning and at the end of the process is requiring an exclusive lock on the table.
• foreign_key_checks should be disabled when adding/dropping foreign keys to avoid table copying behavior.
• Still some alter operations require table copying or table locking in order to make the change (the old behavior). For more details on which table change require table-copying or table locking, check out this manual page.
• LOCK=NONE is not allowed in the alter table statement if there are ON...CASCADE or ON...SET NULL constraints on the table.
• While the Online DDL will be replicated on the slaves the same like the master (if LOCK=NONE no table-locking will take place on the slaves during the alter execution) but the replication itself will be blocked as the replay process executes in a single thread on the replicas which will cause slave lagging problem.

Comparison results

The following is a comparison results between Online DDL and pt-online-schema-change for some alter operations applied on a table contains 1,078,880 rows:

Online DDLpt-online-schema-changeChange OperationRow(s) affectedIs table locked?Time (sec)Row(s) affectedIs table locked?Time (sec)Add Index0No3.76All rowsNo38.12Drop Index0No0.34All rowsNo36.04Add Column0No27.61All rowsNo37.21Rename Column0No0.06All rowsNo34.16Rename Column + change its data typeAll rowsYes30.21All rowsNo34.23Drop Column0No22.41All rowsNo31.57Change table ENGINEAll rowsYes25.30All rowsNo35.54Which method should be used?

Now the question is, which method should we use to perform alter table statements?

While pt-online-schema-change allows read and write operations to the table being altered, it still copies the tables data to a temporary table in the background which adds overhead on the MySQL server. So basically, we should use pt-online-schema-change if the Online DDL will not work efficiently. In other words, if the Online DDL will require copying data to a temporary table (algorithm=copy) and the table will be blocked for long time (lock=exclusive) or when altering huge tables in a replication environment then we should use pt-online-schema-change tool.

Taxonomy upgrade extras: mysqlperformancePerformance Tuningqueryquery tuningtuningMySQL single query performance - the truth!

As suggested by morgo I did a little test for the same query and the same data-set mentioned in Impact of column types on MySQL JOIN performance but looking into an other dimension: the time (aka MySQL versions).

The answer

To make it short. As a good consultant the answer must be: "It depends!" :-)

The test

The query was again the following:

SELECT * FROM a JOIN b ON b.a_id = a.id WHERE a.id BETWEEN 10000 AND 15000 ;

The Query Execution Plan was the same for all tested releases.

The relevant MySQL variables where used as follows where possible. Should I have considered join buffer, or any other of those local per session buffers (read_buffer_size, read_rnd_buffer_size, join_buffer_size)?

innodb_buffer_pool_size = 768M innodb_buffer_pool_instances = 1 innodb_file_per_table = 1
The results mysql-4.0.30mysql-4.1.25mysql-5.0.96mysql-5.1.73mysql-5.5.35mysql-5.6.15mysql-5.7.3AVG40.8638.683.714.694.647.226.05MEDIAN41.0738.133.694.464.656.326.05STDEV1.512.260.060.340.032.210.03MIN39.2736.993.674.404.596.266.02MAX44.1144.453.865.234.6713.166.10COUNT10.0010.0010.0010.0010.0010.0010.00
mariadb-5.1.44mariadb-5.2.10mariadb-5.3.3mariadb-5.5.34mariadb-10.0.6AVG4.588.638.345.026.12MEDIAN4.587.978.015.026.01STDEV0.011.451.100.020.25MIN4.557.867.904.995.97MAX4.6011.3811.465.066.75COUNT10.0010.0010.0010.0010.00
percona-5.0.92-23.85percona-5.1.72-14.10percona-5.5.34-32.0percona-5.6.14-62.0AVG3.794.704.9410.53MEDIAN3.794.704.8912.41STDEV0.020.030.143.35MIN3.764.674.865.68MAX3.834.755.3412.93COUNT10.0010.0010.0010.00
galera-5.5.33-23.7.6 / 2.7AVG4.31MEDIAN3.98STDEV1.18MIN3.76MAX8.54COUNT30.00
The Graph

Conclusion

Do not trust benchmarks. They are mostly worthless for your specific workload and pure marketing buzz... Including the one above! ;-)

Database vendors (Oracle/MySQL, Percona, MariaDB) are primarily focussing on throughput and features. In general this is at the costs of single query performance.
MySQL users like Facebook, LinkedIn, Google, Wikpedia, Booking.com, Yahoo! etc. are more interested in throughput than single query performance (so I assume). But most of the MySQL users (95%) do not have a troughput problem but a single query performance problem (I assume here that this is true also for Oracle, MS-SQL Server, DB2, PostgreSQL, etc.).

So database vendors are not primarily producing for the masses but for some specific users/customers (which possibly pay a hell of money for this).

Back to the data:

My first hypothesis: "The old times were always better" is definitely not true. MySQL 4.0 and 4.1 sucked with this specific query. But since MySQL 5.0 the rough trend is: single query performance becomes worse over time (newer versions). I assume this also true for other databases...

Some claims like: "We have the fastest MySQL" or "We have hired the whole optimizer team" does not necessary reflect in better single query performance. At least not for this specific query.

So in short: If you upgrade or side-grade (MySQL <-> Percona <-> MariaDB), test always very carefully! It is not predictable where the traps are. Newer MySQL release can increase performance of your application or not. Do not trust marketing buzz!

Artefacts

Some artefacts we have already found during this tiny test:

• In MySQL 5.0 an optimization was introduced (not in the Optimizer!?!) to speed up this specific query dramatically.
• MariaDB 5.2 and 5.3 were bad for this specific query.
• I have no clue why Galera Cluster has shown the best results for 5.5. It is no intention or manipulation! It is poor luck. But I like it! :-)
• MySQL 5.6 seems to have some problems with this query. To much improvement done by Oracle/MySQL?
• Percona 5.6 sometimes behaves much better with this query than normal MySQL but from time to time something kicks in which makes Percona dramatically slower. Thus the bad results. I have no clue why. I first though about an external influence. But I was capable to reproduce this behaviour (once). So I assume it must be something Percona internally (AHI for example?).

Finally

Do not shoot the messenger!

If you want to reproduce the results most information about are already published. If something is missing please let me know.

Please let me know when you do not agree with the results. So I can expand my universe a bit...

It was fun doing this tests today! And MyEnv was a great assistance doing this kind of tests!

If you want us to do such test for you, please let us know. Our consulting team would be happy to assist you with upgrading or side-grading problems.

Taxonomy upgrade extras: sqlquerytuningmysql

In our MySQL trainings and consulting engagements we tell our customers always to use the smallest possible data type to get better query performance. Especially for the JOIN columns. This advice is supported as well by the MySQL documentation in the chapter Optimizing Data Types:

Use the most efficient (smallest) data types possible. MySQL has many specialized types that save disk space and memory. For example, use the smaller integer types if possible to get smaller tables. MEDIUMINT is often a better choice than INT because a MEDIUMINT column uses 25% less space.

I remember somewhere the JOIN columns where explicitly mentioned but I cannot find it any more.

Test set-up

To get numbers we have created a little test set-up:

CREATE TABLE `a` ( `id` int(10) unsigned NOT NULL AUTO_INCREMENT , `data` varchar(64) DEFAULT NULL , `ts` timestamp NOT NULL , PRIMARY KEY (`id`) ) ENGINE=InnoDB CHARSET=latin1  
CREATE TABLE `b` ( `id` int(10) unsigned NOT NULL AUTO_INCREMENT , `data` varchar(64) DEFAULT NULL , `ts` timestamp NOT NULL , `a_id` int(10) unsigned DEFAULT NULL , PRIMARY KEY (`id`) ) ENGINE=InnoDB DEFAULT CHARSET=latin1
1048576 rows 16777216 rows

The following query was used for the test:

EXPLAIN SELECT * FROM a JOIN b ON b.a_id = a.id WHERE a.id BETWEEN 10000 AND 15000; +----+-------------+-------+--------+---------------+---------+---------+-------------+----------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+--------+---------------+---------+---------+-------------+----------+-------------+ | 1 | SIMPLE | b | ALL | NULL | NULL | NULL | NULL | 16322446 | Using where | | 1 | SIMPLE | a | eq_ref | PRIMARY | PRIMARY | 4 | test.b.a_id | 1 | NULL | +----+-------------+-------+--------+---------------+---------+---------+-------------+----------+-------------+

And yes: I know this query could be more optimal by setting an index on b.a_id.

Results

The whole workload was executed completely in memory and thus CPU bound (we did not want to measure the speed of our I/O system).

SEJOIN columnbytesquery timeGainSpaceCharacter setInnoDBMEDIUMINT35.28 s96%4% faster75%InnoDBINT45.48 s100%100%100%InnoDBBIGINT85.65 s107%7% slower200%InnoDBNUMERIC(7, 2)~46.77 s124%24% slower~100%InnoDBVARCHAR(7)7-86.44 s118%18% slower~200%latin1InnoDBVARCHAR(16)7-86.44 s118%18% slower~200%latin1InnoDBVARCHAR(32)7-86.42 s118%18% slower~200%latin1InnoDBVARCHAR(128)7-86.46 s118%18% slower~200%latin1InnoDBVARCHAR(256)8-96.17 s114%14% slower~225%latin1InnoDBVARCHAR(16)7-86.96 s127%27% slower~200%utf8InnoDBVARCHAR(128)7-86.82 s124%24% slower~200%utf8InnoDBCHAR(16)166.85 s125%25% slower400%latin1InnoDBCHAR(128)1289.68 s177%77% slower3200%latin1InnoDBTEXT8-910.7 s195%95% slower~225%latin1MyISAMINT43.16 s58%42% fasterTokuDBINT44.52 s82%18% faster

Some comments to the tests:

• MySQL 5.6.13 was used for most of the tests.
• TokuDB v7.1.0 was tested with MySQL 5.5.30.
• As results the optimistic cases were taken. In reality the results can be slightly worse.
• We did not take into consideration that bigger data types will eventually cause more I/O which is very slow!

Commands ALTER TABLE a CONVERT TO CHARACTER SET latin1; ALTER TABLE b CONVERT TO CHARACTER SET latin1; ALTER TABLE a MODIFY COLUMN id INT UNSIGNED NOT NULL; ALTER TABLE b MODIFY COLUMN a_id INT UNSIGNED NOT NULL;

Table of Content

• Introduction
• Prerequisites
• What is MyEnv?
• MySQL Workbench configuration.
  • Add MySQL connections to MySQL Workbench.
  • Start/Stop instance configurations.

Introduction

MySQL Workbench is a very good and free GUI tool provided by Oracle to manage MySQL administration and development tasks. Opening many MySQL connections (same or different instances, remote or local MySQL servers) at the same time is one of its main features. While it's working fine to perform SQL statements on the different connections opened for multiple instances, but some people are asking if it is available as well to start and stop multiple MySQL instances using MySQL Workbench? if yes, how to configure it to perform such task? and also does that make any conflict with MyEnv tool - if it's installed - or not?
Yes, MySQL Workbench could be configured to start and stop multiple MySQL instances (local or remote) and it does not make any conflict with MyEnv tool.

In this article, I will describe how to configure MySQL Workbench to start and stop multiple MySQL instances and getting benefits from MyEnv scripts in this purpose.

Prerequisites

System information and installed packages:

• Operating System: Ubuntu 12.04 (64 bit) .
• MySQL Server: Any mysql version (I used MySQL 5.5 tarballs).
• Number of MySQL Instances: Two instances are installed (mysql1 & mysql2).
• MySQL Workbench: Version 6.0 .
• MyEnv: Version 1.0.1.

What is MyEnv?

MyEnv is a set of scripts to run comfortably multiple MySQL, Percona Server or MariaDB database instances on the same server. You can even run multiple database instances with different binary versions. If you have MySQL multiple instance setups, you really should try out MyEnv.

I will not talk more about MyEnv features and its benefits rather, I'd like to mention that if you're using MyEnv and want to use MySQL Workbench at the same time, you will not face any conflict between them both and you can manage your MySQL instances by either MyEnv or MySQL Workbench. More over, you can use MyEnv scripts to configure MySQL Workbench starting/stopping multiple instances in an easy way!

For more information about MyEnv tool , you can check it out on our website myenv.

MySQL Workbench configuration
Add MySQL connections to MySQL Workbench

• Choose a connection name for the 1st instance "mysql1" and specify the connection string:
  
  

  If you didn't adjust the "Configure Server Management" in this step - at the left bottom of the previous screen - you can open MySQL connections and perform SQL queries normally to this instance but you can neither edit the instance configuration parameters nor start/stop it.
  BTW, you can adjust it at anytime later and that what I did already in this example.

• Add another connection for the 2nd instance "mysql2" the same like "mysql1".

Start/Stop instance configurations

To configure MySQL Workbench to start/stop instance, we need to have relevant start and stop commands because it just execute them as they would be execute in the system shell. In this case, we may get benefit of MyEnv scripts for that purpose using the following command:

$MYENV_BASE/bin/database.php $MYENV_DATABASE start|stop
Where $MYENV_BASE is the MyEnv basedir ("/opt/myenv" in this ex.) and $MYENV_DATABASE is the instance name in MyEnv (mysqld1 & mysqld2 for mysql1 & mysql2 respectively in this ex.)

Now, we can use the following window to modify System type,Configuration file path, start , stop and status commands to match each instance configurations:

Now MySQL Workbench should be able to start and stop the configured MySQL instances.

Notes:

• MyEnv doesn't allow any user to start a mysql instance except mysql user (even if it's the root user), so that mysql OS user should be used to execute those commands and you might need to assign it SUDO permissions.
• Start/Stop Server button in MySQL Workbench depends on the output of the status command used ("cat /opt/mysql1/data/*.pid 2>/dev/null" for checking mysql1 instance status), and the button label will be changed to execute the appropriate command accordingly (for ex. if the instance is not running, the label should be changed to "Start Server" and the start command will be executed if the button clicked and vise verse), so you should make sure that this command is returning the expected results, otherwise, Workbench wont be able to manage the instance.
• It doesn't matter how MySQL was installed (RPM, tarballs or from source), it's the same concept, you just need to provide MyEnv start and stop commands along with the status command and then MySQL Workbench will work.
• If MyEnv is not installed, you can also configure MySQL Workbench to start/stop multiple instances by providing normal start|stop instance commands in the "Manage Server Connections" window but those need to be prepared first.

Taxonomy upgrade extras: MyEnv

Table of Content

• Introduction
• Prerequisites
• What is MyEnv?
• MySQL Workbench configuration.
  • Add MySQL connections to MySQL Workbench.
  • Start/Stop instance configurations.

Introduction

MySQL Workbench is a very good and free GUI tool provided by Oracle to manage MySQL administration and development tasks. Opening many MySQL connections (same or different instances, remote or local MySQL servers) at the same time is one of its main features. While it's working fine to perform SQL statements on the different connections opened for multiple instances, but some people are asking if it is available as well to start and stop multiple MySQL instances using MySQL Workbench? if yes, how to configure it to perform such task? and also does that make any conflict with MyEnv tool - if it's installed - or not?
Yes, MySQL Workbench could be configured to start and stop multiple MySQL instances (local or remote) and it does not make any conflict with MyEnv tool.

In this article, I will describe how to configure MySQL Workbench to start and stop multiple MySQL instances and getting benefits from MyEnv scripts in this purpose.

Prerequisites

System information and installed packages:

• Operating System: Ubuntu 12.04 (64 bit) .
• MySQL Server: Any mysql version (I used MySQL 5.5 tarballs).
• Number of MySQL Instances: Two instances are installed (mysql1 & mysql2).
• MySQL Workbench: Version 6.0 .
• MyEnv: Version 1.0.1.

What is MyEnv?

MyEnv is a set of scripts to run comfortably multiple MySQL, Percona Server or MariaDB database instances on the same server. You can even run multiple database instances with different binary versions. If you have MySQL multiple instance setups, you really should try out MyEnv.

I will not talk more about MyEnv features and its benefits rather, I'd like to mention that if you're using MyEnv and want to use MySQL Workbench at the same time, you will not face any conflict between them both and you can manage your MySQL instances by either MyEnv or MySQL Workbench. More over, you can use MyEnv scripts to configure MySQL Workbench starting/stopping multiple instances in an easy way!

For more information about MyEnv tool , you can check it out on our website myenv.

MySQL Workbench configuration
Add MySQL connections to MySQL Workbench

• Choose a connection name for the 1st instance "mysql1" and specify the connection string:
  
  

  If you didn't adjust the "Configure Server Management" in this step - at the left bottom of the previous screen - you can open MySQL connections and perform SQL queries normally to this instance but you can neither edit the instance configuration parameters nor start/stop it.
  BTW, you can adjust it at anytime later and that what I did already in this example.

• Add another connection for the 2nd instance "mysql2" the same like "mysql1".

Start/Stop instance configurations

To configure MySQL Workbench to start/stop instance, we need to have relevant start and stop commands because it just execute them as they would be execute in the system shell. In this case, we may get benefit of MyEnv scripts for that purpose using the following command:

$MYENV_BASE/bin/database.php $MYENV_DATABASE start|stop
Where $MYENV_BASE is the MyEnv basedir ("/opt/myenv" in this ex.) and $MYENV_DATABASE is the instance name in MyEnv (mysqld1 & mysqld2 for mysql1 & mysql2 respectively in this ex.)

Now, we can use the following window to modify System type,Configuration file path, start , stop and status commands to match each instance configurations:

Now MySQL Workbench should be able to start and stop the configured MySQL instances.

Notes:

• MyEnv doesn't allow any user to start a mysql instance except mysql user (even if it's the root user), so that mysql OS user should be used to execute those commands and you might need to assign it SUDO permissions.
• Start/Stop Server button in MySQL Workbench depends on the output of the status command used ("cat /opt/mysql1/data/*.pid 2>/dev/null" for checking mysql1 instance status), and the button label will be changed to execute the appropriate command accordingly (for ex. if the instance is not running, the label should be changed to "Start Server" and the start command will be executed if the button clicked and vise verse), so you should make sure that this command is returning the expected results, otherwise, Workbench wont be able to manage the instance.
• It doesn't matter how MySQL was installed (RPM, tarballs or from source), it's the same concept, you just need to provide MyEnv start and stop commands along with the status command and then MySQL Workbench will work.
• If MyEnv is not installed, you can also configure MySQL Workbench to start/stop multiple instances by providing normal start|stop instance commands in the "Manage Server Connections" window but those need to be prepared first.

Taxonomy upgrade extras: MyEnv

Table of Content

• Introduction
• Prerequisites
• What is MyEnv?
• MySQL Workbench configuration.
  • Add MySQL connections to MySQL Workbench.
  • Start/Stop instance configurations.

Introduction

MySQL Workbench is a very good and free GUI tool provided by Oracle to manage MySQL administration and development tasks. Opening many MySQL connections (same or different instances, remote or local MySQL servers) at the same time is one of its main features. While it's working fine to perform SQL statements on the different connections opened for multiple instances, but some people are asking if it is available as well to start and stop multiple MySQL instances using MySQL Workbench? if yes, how to configure it to perform such task? and also does that make any conflict with MyEnv tool - if it's installed - or not?
Yes, MySQL Workbench could be configured to start and stop multiple MySQL instances (local or remote) and it does not make any conflict with MyEnv tool.

In this article, I will describe how to configure MySQL Workbench to start and stop multiple MySQL instances and getting benefits from MyEnv scripts in this purpose.

Prerequisites

System information and installed packages:

• Operating System: Ubuntu 12.04 (64 bit) .
• MySQL Server: Any mysql version (I used MySQL 5.5 tarballs).
• Number of MySQL Instances: Two instances are installed (mysql1 & mysql2).
• MySQL Workbench: Version 6.0 .
• MyEnv: Version 1.0.1.

What is MyEnv?

MyEnv is a set of scripts to run comfortably multiple MySQL, Percona Server or MariaDB database instances on the same server. You can even run multiple database instances with different binary versions. If you have MySQL multiple instance setups, you really should try out MyEnv.

I will not talk more about MyEnv features and its benefits rather, I'd like to mention that if you're using MyEnv and want to use MySQL Workbench at the same time, you will not face any conflict between them both and you can manage your MySQL instances by either MyEnv or MySQL Workbench. More over, you can use MyEnv scripts to configure MySQL Workbench starting/stopping multiple instances in an easy way!

For more information about MyEnv tool , you can check it out on our website myenv.

MySQL Workbench configuration
Add MySQL connections to MySQL Workbench

• Choose a connection name for the 1st instance "mysql1" and specify the connection string:
  
  

  If you didn't adjust the "Configure Server Management" in this step - at the left bottom of the previous screen - you can open MySQL connections and perform SQL queries normally to this instance but you can neither edit the instance configuration parameters nor start/stop it.
  BTW, you can adjust it at anytime later and that what I did already in this example.

• Add another connection for the 2nd instance "mysql2" the same like "mysql1".

Start/Stop instance configurations

To configure MySQL Workbench to start/stop instance, we need to have relevant start and stop commands because it just execute them as they would be execute in the system shell. In this case, we may get benefit of MyEnv scripts for that purpose using the following command:

$MYENV_BASE/bin/database.php $MYENV_DATABASE start|stop
Where $MYENV_BASE is the MyEnv basedir ("/opt/myenv" in this ex.) and $MYENV_DATABASE is the instance name in MyEnv (mysqld1 & mysqld2 for mysql1 & mysql2 respectively in this ex.)

Now, we can use the following window to modify System type,Configuration file path, start , stop and status commands to match each instance configurations:

Now MySQL Workbench should be able to start and stop the configured MySQL instances.

Notes:

• MyEnv doesn't allow any user to start a mysql instance except mysql user (even if it's the root user), so that mysql OS user should be used to execute those commands and you might need to assign it SUDO permissions.
• Start/Stop Server button in MySQL Workbench depends on the output of the status command used ("cat /opt/mysql1/data/*.pid 2>/dev/null" for checking mysql1 instance status), and the button label will be changed to execute the appropriate command accordingly (for ex. if the instance is not running, the label should be changed to "Start Server" and the start command will be executed if the button clicked and vise verse), so you should make sure that this command is returning the expected results, otherwise, Workbench wont be able to manage the instance.
• It doesn't matter how MySQL was installed (RPM, tarballs or from source), it's the same concept, you just need to provide MyEnv start and stop commands along with the status command and then MySQL Workbench will work.
• If MyEnv is not installed, you can also configure MySQL Workbench to start/stop multiple instances by providing normal start|stop instance commands in the "Manage Server Connections" window but those need to be prepared first.

Great News: Galera Cluster v3.1 GA for MySQL 5.6 was released at Percona Live London (PLUK) 2013. The information is still a bit hidden...

You can find it here:

• The Plug-in: https://launchpad.net/galera/3.x/25.3.1
• The MySQL: https://launchpad.net/codership-mysql/5.6/5.6.14-25.1

Or directly on our download page.

Careful: Online-Upgrade from 5.5 to 5.6 will not work yet. We have to find a work-around...

Table of Content

• Introduction
• Prerequisites
• Full Backup
  • Create Full Backup
  • Prepare Full Backup
  • Restore Full Backup
  • Prepare slave from full backup
  • Prepare GTID slave from full backup
  • Advantages / Disadvantages
  • Important Hints
• Incremental Backup
  • Create Incremental Backup
  • Prepare Incremental Backup
  • Restore Incremental Backup
  • Advantages / Disadvantages
  • Important Hints
  • Differential Backup
• Partial Backup
  • Create Partial Backup
  • Prepare Partial Backup
  • Restore Partial Backup
  • Advantages / Disadvantages
  • Important Hints

Introduction

No one can deny that one of the most important and daily tasks for DBAs is performing backup and restore operations, we're not required to perform backup and restore operations only when we want to add new replication slave, when we want to implement disaster recovery procedures or when we want to prepare testing or staging server for the running production system, but even if we're going to make any changes to the database schema in order to enhance the database performance, it's recommended to have fresh backup copy before making any live changes, so if backup and restore operations cannot be handled smoothly, we're going to face many troubles in our daily work. If we're going to talk about backup and restore operations, Xtrabackup tool will be strongly appeared.

Xtrabackup tool is a free open source tool developed by Percona to perform physical backup and restore operations which is much faster than performing logical backup and restore using the MySQL utilities (mysqldump and mysql), and many other advantages.

Xtrabackup tool has many options and features which are very useful, but in this article, I'll go through only on how to use this tool to perform simple full, incremental and partial backups and restores, advantages and disadvantages of each method and some important tips.

For more information about Xtrabackup tool, you can browse the manual document from here.

Prerequisites

• MySQL server installed.
• Download the xtrabackup tool.
• Install it as explained in the manual document.

Full Backup

If you want to have a full backup from your entire database system with the shortest/fastest backup and restore time, this method will be very useful for you. As compared to the full logical database backup using mysqldump and mysql utilities (very long time to backup and more than the doubled time to restore), taking a full physical backup using Xtrabackup tool will make your life much easier.

Below is the needed steps to make a full physical database backup using XtraBackup tool:

Create Backup

A simple Xtrabackup command to backup the full databases should be something like:

[root@ ~]# innobackupex --user=db_user –-password='db_password' --no-timestamp /backup/dir/path/full-backup . . . innobackupex: completed OK!

A timestamped folder (for ex. "2013-11-06_00-00-00") would be created to contain all backup files if we didn't use the option "--no-timestamp" in the above command (I didn't use the timestamped folders here to just simplify the names for the reader, otherwise, it's very useful when using automated backup scripts).

Xtrabackup tool now created the backup files under the folder "full-backup" plus some extra files like "xtrabackup-checkpoints" file which contains some information (useful in the incremental backups) like:

• backup_type = full-backuped : which indicates the backup type "full backup".
• from_lsn = 0 : which indicates the log sequence number where the backup process started from (0 means from the beginning).
• to_lsn = 3768762 : which indicates the log sequence number where the backup process ended at.

Another important file is "xtrabackup_binlog_info" which is very useful in replication setups:

[root@ ~]# cat xtrabackup_binlog_info mysql-bin.000027 191

WHERE:

• mysql-bin.000027: is the binary log file name of the master when the backup created.
• 191: is the binary log position of the backup.

Prepare Full Backup

The backed up files are not ready at the moment to be restored, we must prepare the backup files first as follows:

[root@ ~]# innobackupex --user=db_user –-password='db_password' --apply-log /backup/dir/path/full-backup . . . innobackupex: completed OK!

Now, the full backup is ready to be restored ...

Restore Full Backup

To get the full backup restored, the MySQL instance should be stopped first and then one of the following two procedures should be done:

• Using the copy back option: [root@ ~]# innobackupex --user=db_user –-password='db_password' --copy-back /backup/dir/path/full-backup . . . innobackupex: completed OK!
  

  Xtrabackup tool - in this method - will copy all files under the backup folder (full-backup) to the MySQL datadir which must be indicated in the my.cnf file, otherwise, it wouldn't know where the datadir should be placed.

• Using the operating system copy or move commands:
  

  If you don't want to keep the backup files on your local system (you have another copy in an external server), the move command will be very fast to get your backup restored:

  [root@ ~]# mv /backup/dir/path/full-backup /var/lib/mysql
  

As the user who moves/copies the files into MySQL datadir is not "mysql" user, you should make sure that mysql user has the right permissions on its datadir and also the path "/var/lib/mysql" should be replaced with the MySQL datadir if it's set to a different path.

[root@ ~]# chown -R mysql:mysql /var/lib/mysql

After moving/copying the backup files into MySQL datadir, you are free to start the MySQL instance again.

Prepare slave from full backup

Preparing a slave using Xtrabackup is pretty easy and a straight forward process:

• Restore the full backup as explained above.
• Check the binary logs information of the backup:
  [root@ ~]# cat xtrabackup_binlog_info mysql-bin.000027 191
  
• Execute the CHANGE MASTER TO command using the above info and start the slave:
  SQL> CHANGE MASTER TO -> MASTER_HOST='master_ip', -> MASTER_PORT=master_port, -> MASTER_USER='slave_user_name', -> MASTER_PASSWORD='slave_password', -> MASTER_LOG_FILE='mysql-bin.000027', ## taken from xtrabackup_binlog_info -> MASTER_LOG_POS=191; ## taken from xtrabackup_binlog_info SQL> START SLAVE;
  

For more information on how to set up MySQL Replication, check out this nice manual link.

Prepare GTID slave from full backup

GTID is supported in Xtrabackup starting from version 2.1.0. To restore a GTID slave server, the GTID_MODE should be enabled on the master server before creating its backup, otherwise, no GTID values will be included in the "xtrabackup_binlog_info" file under the backup directory. However, the following steps should be done:

• Restore the full backup normally as explained above.
• Check the GTID value of the backup:
  [root@ ~]# cat xtrabackup_binlog_info mysql-bin.000027 191 b9b4712a-df64-11e3-b391-60672090eb04:1-12
  
• Set the variable GTID_PURGED with the GTID value of the backup:
  SQL> SET GLOBAL GTID_PURGED="b9b4712a-df64-11e3-b391-60672090eb04:1-12";
  
• Execute the auto position CHANGE MASTER TO command and start the slave:
  SQL> CHANGE MASTER TO -> MASTER_HOST='master_ip', -> MASTER_PORT=master_port, -> MASTER_USER='slave_user_name', -> MASTER_PASSWORD='slave_password', -> MASTER_AUTO_POSITION = 1; SQL> START SLAVE;
  

For more information on how to set up Transaction-based Replication in MySQL, check out this link.

Advantages / Disadvantages

• Advantages:
  • Fast, simple and easy way to get your full database backed up and restored.
  • All Xtrabackup tool features (like streaming: move the backed up files directly to a remote server) are supported in the full backup method.
  • Simple way to introduce a new slave to the master.
• Disadvantages:
  • We have to replace the entire MySQL datadir with the new one (In other words, the datadir folder should be empty/removed before the restore process).
  • We can't extract one single database or single table from the whole backup (Unless it's MyISAM table), which means that you have to take it all or leave it all.

Important Hints

• The message innobackupex: completed OK! should be printed at the end of every xtrabackup command , otherwise, it would be failed to make a successful command (backup, prepare or restore).
• The ib_logfile files size should be the same in both source and destination servers, if not, you have to either remove them from the backup folder (which will be restored) before starting the MySQL instance and MySQL will create new ones for you OR change those files size in the destination server's configuration file to match the same size in the backup before starting the MySQL instance
• The MySQL user used in the Xtrabackup tool, should have at least the following privileges (RELOAD, LOCK TABLES and REPLICATION CLIENT).
• To prepare a new slave from another slave, just add the two options (“--slave-info" & --safe-slave-backup”) to the backup command and use the information in the file "xtrabackup_slave_info" under the backup folder to issue the "CHANGE MASTER TO" command in the new slave after finishing the restore.
• To Accelerate the preparation process of your backup, just add the option "--use-memory" in the prepare command in order to allocate more used memory (Xtrabackup will use the specified memory as an internal innodb_buffer_pool_size for the prepare process), for ex: [root@ ~]# innobackupex --user=db_user –-password='db_password' --apply-log --use-memory=512M /backup/dir/path/full-backup . . . innobackupex: completed OK!
• The preparation process consists of two steps, replaying the committed transactions and rolling back the uncommitted transactions, using the --apply-log option only in the preparation command will do both steps for you.
• The backup folder "/backup/dir/path/full-backup" SHOULD NOT be created before executing the backup command, because Xtrabackup will create that folder for you, and it will fail to continue processing if that folder was already exist.

Incremental Backup

When you have a very large database system, you will need large enough storage to store your database backups in, and if you want to perform a daily backup then your mission will be more difficult. In such cases, the incremental database backup method will be very useful. It allows you to have only the database changes (delta) - after the physical full backup – with the minimum storage space required in a fast way, and hence, you can perform the daily backup operations to your database system without the need to having large storage available.

The following steps describe a simple way to perform your physical incremental database backup using XtraBackup tool:

Create Incremental Backup

To perform an incremental backup, we should first perform a full backup - the same like we did in the previous section - to be the base backup of the upcoming incremental backups.

Creating the full backup (Base Backup):

[root@ ~]# innobackupex --user=db_user –-password='db_password' --no-timestamp /backup/dir/path/full-backup . . . innobackupex: completed OK!

The "xtrabackup-checkpoints" file contents will be something like:

• backup_type = full-backuped : which indicates the backup type "full backup".
• from_lsn = 0 : which indicates the log sequence number where the backup process started from (0 means from the beginning).
• to_lsn = 3768762 : which indicates the log sequence number where the backup process ended at.

Creating the first incremental backup:

[root@ ~]# innobackupex --user=db_user –-password='db_password' --no-timestamp --incremental /backup/dir/path/inc1 --incremental-basedir=/backup/dir/path/full-backup . . . innobackupex: completed OK!

We informed the Xtrabackup tool to perform an incremental backup by adding the command "--incremental", and by specifying the full-backup path as the basedir, we informed it from which backup it should start tracking the database changes.

The "xtrabackup-checkpoints" file contents will be something like:

• backup_type = incremental : which indicates the backup type "incremental backup".
• from_lsn = 3768762 : which indicates the log sequence number where the backup process started from (the same LSN as the previous full backup ended at).
• to_lsn = 4908762 : which indicates the log sequence number where the backup process ended at.

Creating the second incremental backup:

[root@ ~]# innobackupex --user=db_user –-password='db_password' --no-timestamp --incremental /backup/dir/path/inc2 --incremental-basedir=/backup/dir/path/inc1 . . . innobackupex: completed OK!

We informed the Xtrabackup tool to perform an incremental backup by adding the command "--incremental", and by specifying the 1st incremental backup path as the basedir, we informed it to start tracking the database changes since the last incremental (not the full backup).

The "xtrabackup-checkpoints" file contents will be something like:

• backup_type = incremental : which indicates the backup type "incremental backup".
• from_lsn = 4908762 : which indicates the log sequence number where the backup process started from (the same LSN as the 1st incremental backup ended at).
• to_lsn = 6508762 : which indicates the log sequence number where the backup process ended at.

Note: We can create as many incremental backups as we want by using the same procedure above.

Prepare Incremental Backup

As mentioned earlier in the article, the preparation process consists of two steps (replaying the committed transactions and rolling back the uncommitted transactions) and using the --apply-log option only will do both of them (like we did in the full backup) but in the incremental backups, we MUST do them separately as follows:

• Replay the committed transactions on the base backup (by adding the option "--redo-only"): [root@ ~]# innobackupex --user=db_user –-password='db_password' --apply-log --redo-only /backup/dir/path/full-backup . . . innobackupex: completed OK!
• Replay the committed transactions on the 1st incremental backup: [root@ ~]# innobackupex --user=db_user –-password='db_password' --apply-log --redo-only /backup/dir/path/full-backup --incremental-dir=/backup/dir/path/inc1 . . . innobackupex: completed OK!
  

  Note: we specified the full backup folder here, because replaying the committed transactions steps, appends all changes from the incremental backup to the full backup.

• Replay the committed transactions on the 2nd incremental backup: [root@ ~]# innobackupex --user=db_user –-password='db_password' --apply-log --redo-only /backup/dir/path/full-backup --incremental-dir=/backup/dir/path/inc2 . . . innobackupex: completed OK!
  

  Note: here, we didn't use the 1st incremental backup folder, because all changes in the 1st incremental was already appended to the full backup in the previous step.

• Finally, roll back all uncommitted transactions: [root@ ~]# innobackupex --user=db_user –-password='db_password' --apply-log /backup/dir/path/full-backup . . . innobackupex: completed OK!
  

  Note: as the full backup folder contains all data now (full + 1st & 2nd incremental), there's no need to do this step on the incremental backup folders.

Now, the incremental backup is ready to be restored ...

Restore Incremental Backup

The full backup folder will be the only folder to be restored (there's no need to the incremental backup folders) as it contains all data after appending the changes from all incremental backup. We can restore it the same way we did in the full backup restore.

Advantages / Disadvantages

• Advantages:
  • Less storage resources needed.
  • Faster than the full backup.
• Disadvantages:

  In addition to the disadvantages of the full backup, there are other ones:

  • Complicate and hard process to implement as compared to the full backup.
  • The incremental backup strategy, based on Log Sequence Number which affects only XtraDB and InnoDB storage engines while the others (like MyISAM) will be backed up completely (changed + unchanged data) in each incremental backup process.
  • If we have many incremental backups, appending all of them might consume time and might be confusing as well.
  • If one of the incremental backups become corrupted or not available for any reason, we will not be able to add all incremental backups after that to the full backup.

Important Hints

• The backup preparation sequence steps above, MUST be followed using the same order.
• If the "--redo-only" option was not be used in any of the preparation steps (except the final step), all up coming incremental backups will be useless as we won't be able to add them to the base backup anymore.
• Replaying the committed transactions steps bring all incremental data and append it to the full backup, so that, the rolling back of the uncommitted transactions step should be execute only on the full backup (as it contains already the whole data).).
• In the incremental backups, Xtrabackup generates two files for every table ".delta" & ".meta"(for ex. test.ibd.delta & test.ibd.meta), the delta file size reflects the changes which was applied on that table since the last incremental backup.
• The preparation time of the individual incremental backup will depend on how much data changed there since the last incremental.
• The preparation time for the full backup - in most cases - is really small as compared to the incremental ones because full backups apply the redo logs only while the incremental backups apply the deltas plus the redo logs. So if the delta files are big, the preparation process will take longer.
• Full backups is recommended against Incremental backups if there are many changes applied on the DB, while the incremental backups are recommended when there are few changes applied on the DB.

Differential backup

We can use the incremental backup strategy in order to perform differential backups, but we should consider the following points:

• We always specify the full backup folder as the base backup (in the incremental we specify the previous incremental folder as a base backup)
• All incremental backups between differential and full backups MUST BE ignored when preparing the backup files because the differential backup contains already all changes since the last full backup.
• In the backup preparation process, we should consider the last differential backup as the first incremental backup and all incremental backups after that could be applied normally.

Note: Having differnetial backups in the middle of incremental backups will be useful for many reasons, such as:

• Differential backups reduce the backup preparation steps/time needed because differential backp will replace all its previous incremental backups.
• Differential backups reduce the chances of loosing the incremental backups if we have corrupted incremental backup in the middle, because in this case, differential backup will act as a backup of the previous incremental backups.

Partial Backup

Unlike MyISAM, having physical database backup for a single database or table is not possible if the table engine type is InnoDB. But by using the partial database backup method in the XtraBackup tool, it will be possible to have physical InnoDB tables backup the same like MyISAM ones (but with some restrictions).

The following steps describing how to perform partial database backup using XtraBackup tool:

Create Partial Backup

A simple Xtrabackup command to backup some databases (or tables) should be something like:

[root@ ~]# innobackupex --user=db_user –-password='db_password' --no-timestamp --databases=”db1 db2 db3.tbl1” /backup/dir/path/partial-backup . . . innobackupex: completed OK!
Prepare Partial Backup

The same like the other backup methods, the backed up files are not ready until we get them prepared by adding the "--export" option as follows:

[root@ ~]# innobackupex --user=db_user –-password='db_password' --apply-log --export /backup/dir/path/partial-backup . . . innobackupex: completed OK!

Some errors regarding those not included InnoDB tables from the backup may be appeared, but that's fine. Also there will be a notification of creating the ".exp" file for each table which will be used in the import (restore) process.

Now, the partial backup is ready to be restored ...

Restore Partial Backup

The restore process of the partial backup is quite different than the full and incremental backups.

To restore a partial backup, the following steps should be made:

• Unlike the other methods (Full and Incremental backups), MySQL instance on the destination server shouldn't be stopped because we will have to execute some SQL commands.
• On the destination server, we should create new tables (as many as we have in the partial backup or as we will restore) with the same structure like the one in the partial backup and then discard its table space: mysql> CREATE TABLE db.tbl1 (...)ENGINE=INNODB; mysql> ALTER TABLE db.tbl1 DISCARD TABLESPACE;
• Copy “.ibd” and “.exp” files for each table into the corresponding DB directory then assign the right permissions to mysql user: [root@ ~]# cp /backup/dir/path/partial-backup/db/tbl1.ibd /var/lib/mysql/db [root@ ~]# cp /backup/dir/path/partial-backup/db/tbl1.exp /var/lib/mysql/db [root@ ~]# chown -R mysql:mysql /var/lib/mysql/db
• Now we should tell MySQL to use the new table spaces: mysql> ALTER TABLE db.tbl1 IMPORT TABLESPACE;

Advantages / Disadvantages

• Advantages:
  • Although it's a complicated process, but it allows us to backup and restore individual InnoDB tables the same like MyISAM.
  • Useful when having huge InnoDB tables and we want to backup/restore them only.
• Disadvantages:
  • The streaming feature is not available in the partial backup.
  • Restoring/importing individual tables or databases from a partial backup is not applicable unless the destination server is Percona Server.
  • In addition to restoring the files(copy back), three SQL statements should be executed for each table (table creation + two ALTER statements) in order to get them ready for use, which means that we might do a very boring job (or we have to create a special script) to get the partial backup restored if it contains many tables.

Important Hints

• Although we didn't remove the MySQL datadir before the restore process (like full and incremental backups) as well as having the MySQL instance running, but we can restore the partial backup using the same way (remove the datadir contents and copy/move the backup files to the datadir), but we should take into our consideration that we'll have only the backed up databases/tables and all other databases/tables (which are not included in the partial backup) will be missed.
• “innodb_file_per_table” server option must be enabled (in both source and destination servers).
• "innodb_expand_import" option must be enabled in the destination server which is available only in Percona server (and that explain why we can restore partial backup on Percona server only).
• Beside the "--databases" option, other two alternative options to perform the same needs could be used but we must provide each table with the fully qualified naming format:
  • --include='db.tbl'.
  • --tables-file=/path/to/file.txt ==> in that file, we can add multiple tables one per line in the fully qualified naming format.

Now, you can use the Xtrabackup tool to perform full, incremental and partial database backups, you can decide which method(s) of them are suitable for you according to the advantages and disadvantages of each one, and by considering the important hints for each method you can perform your backup efficiently.

I hope you found this article useful for you and to be familiar with such wonderful tool.

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