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How to recover deleted tablespace?

Abdel-Mawla Gharieb - Fri, 2014-11-14 22:56

Sometimes, MySQL tablespace file(s) might be deleted by mistake, e.g. delete the shared tablespace (ibdata1) or an individual tablespace (table_name.ibd).

In this post I will show you how to recover those files (on Linux OS) having only one condition, MySQL service should still be running. If MySQL service stopped after deleting that file, this method will not work, so it is extremely important to act as quick as possible to avoid data loss.

The following is a simple table creation (innodb_file_per_table is enabled) and the records count inside that table:

SQL> SHOW CREATE TABLE t\G *************************** 1. row *************************** Table: t Create Table: CREATE TABLE `t` ( `id` int(11) NOT NULL AUTO_INCREMENT, PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=23 DEFAULT CHARSET=latin1 1 row in set (0.00 sec) SQL> SELECT COUNT(*) FROM t; +----------+ | COUNT(*) | +----------+ | 22 | +----------+ 1 row in set (0.02 sec)

Now, lets delete the individual tablespace for that table:

shell> rm -rf /var/lib/mysql/test/t.ibd

At this time, we can still select and modify that table!!

SQL> INSERT INTO t VALUES (NULL); Query OK, 1 row affected (0.00 sec) SQL> SELECT COUNT(*) FROM t; +----------+ | COUNT(*) | +----------+ | 23 | +----------+ 1 row in set (0.00 sec)

To be more accurate, rm does not actually delete the file, rather it removes the directory entry pointing to the file's inode. The inode - and in consequence the file - will be removed only if this is the last reference, but as long as the MySQL server process has the file opened, there is another reference which is the open file handle (that's why the "mysqld" server process must still be running).

To list the opened files we can use the Linux command lsof (we filter the output to get only the deleted tablespace information):

shell> lsof |grep t.ibd COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME mysqld 11401 mysql 25uW REG 7,0 98304 1010691 /var/lib/mysql/test/t.ibd (deleted)

The file has a tag of (deleted) which means that the directory entry pointing to the file's inode was deleted but there is another reference(s) to that inode, otherwise it won't be listed by the above command.
Now the question is, how can we get the on-disk path to that opened file if the directory entry was removed?

We can use the "/proc" interface to the running processes and their file handles by the following formula:

  • File path = /proc/PID/fd/FD-number

According to the above formula and using the output of the "lsof" command, the file we just deleted is located here:

shell> ll /proc/11401/fd/25 lrwx------ 1 mysql mysql 64 Oct 28 16:14 /proc/11401/fd/25 -> /var/lib/mysql/test/t.ibd (deleted)

To make sure that this is the on-disk path for the file we deleted, check the reference: it still points to the original path.

How can we recover that file??
  • First, we should make sure that no other queries are modifying that table: SQL> LOCK TABLE t READ; Query OK, 0 rows affected (0.00 sec)
  • Then we copy the data blocks (/proc/11401/fd/25) to a new file (we use the original file path) and change the ownership to the MySQL system user (mysql): shell> cp /proc/11401/fd/25 /var/lib/mysql/test/t.ibd shell> chown mysql:mysql /var/lib/mysql/test/t.ibd
  • Restart MySQL service (if we didn't restart MySQL service directly after recovering the tablespace all changes on that table will still be redirected to the open file handle not the just recovered copy and thus will be lost after the restart): shell> service mysql restart ..... SUCCESS! ..... SUCCESS!
  • The tablespace is now recovered and we can modify the table normally: SQL> SELECT COUNT(*) FROM t; +----------+ | COUNT(*) | +----------+ | 23 | +----------+ 1 row in set (0.00 sec) SQL> INSERT INTO t VALUES (NULL); Query OK, 1 row affected (0.00 sec) SQL> INSERT INTO t VALUES (NULL); Query OK, 1 row affected (0.00 sec) SQL> select COUNT(*) from t; +----------+ | COUNT(*) | +----------+ | 25 | +----------+ 1 row in set (0.00 sec)

Notes:

  • We can use the same procedures above to recover the shared tablespace (ibdata1) but we should lock all tables before the recovery process by using the SQL command "FLUSH TABLES WITH READ LOCK;"
  • If the MySQL server had to deal with more files (.frm, .ibd, .MYI, .MYD, ...) than its "open_file_limit", it might happen that it will close this handle. In that case, the file will also cease to exist, even though the process is still running and that's why it is extremely important to act as quick as possible.
  • The same procedure can be used to recover MyISAM files (.MYI and .MYD) but note that the file handle will be released if "FLUSH TABLES;" SQL command was executed.
  • The same procedure can be used as well to recover binary logs, general logs, ... etc but note that the file handle will be released if "FLUSH LOGS;" SQL command was executed.
  • This method can be used to recover any deleted file on Linux not only MySQL files but if the inode files have other references (lsof).

Real life case:

One of our customers was enabling the general query log on his production system, he noticed that the file was continuously growing and to not to consume the available free disk space on his server he removed that file by "rm /path/to/general_query.log". However, the available free space was still being consumed while he couldn't see the general log file. The customer thought that the file was deleted but in fact, the file handle was still opened by MySQL server process.
To get the problem solved we only issued the SQL command "FLUSH LOGS;" - which the customer should have issued after removing the file - then the file handle was closed, thus the inode was deleted and the consumed disk space freed back to the system.

Things you should consider before using GTID

Abdel-Mawla Gharieb - Fri, 2014-11-14 16:50

Global Transaction ID (GTID) is one of the major features that were introduced in MySQL 5.6 which provides a lot of benefits (I have talked about the GTID concept, implementation and possible troubleshooting at Percona Live London 2014, you can download the slides from our presentations repository or from my session at Percona Live.
On the other hand, there are some important things you should consider before deploying GTID in production, I'm going to list them here in this blog post.

Table of Content Migration to GTID replication

It is required to shutdown MySQL service on all servers in the replication setup in order to perform the migration from classic replication (based on binary logs information) to the transaction-based (GTID) replication which means that the migration process requires downtime.

The online migration to GTID replication is not yet available.
Facebook and Booking.com provided some MySQL patches for this, but they are not yet contained in Oracle's binaries.
So, if you can't afford a downtime during the migration process, then you might not be able to make the change.

Non transactionally safe statement will raise errors now

It is required to enable the system variable (enforce_gtid_consistency) on all servers inside the GTID replication setup which prevent executing the non transactionally safe statements (check GTID restrictions) like:

  • CREATE TABLE .. SELECT.
  • CREATE TEMPORARY TABLE (inside a transaction).
  • Statements that update non-transactional tables inside a transaction.

So, you will have to fix your application first if it contains any of the above statements before using GTID replication.

MySQL Performance in GTID

It is required to enable the variables (bin_log and log_slave_updates) on - at least - the slave servers which affects the performance on those slaves negatively.

So, the performance should be tested very well before the production migration to GTID replication.

mysql_upgrade script

The mysql_upgrade script's problem when executed on a server having gtid_mode=on has been fixed since MySQL 5.6.7, but it is still not recommended to execute mysql_upgrade when gtid_mode=on as it might change system tables that is using MyISAM, which is non transactional.

Errant transactions! Transactions which are executed on a slave apart from the replication transactions (i.e. not executed on the master) are called "Errant transactions", those transactions cause trouble if that slave later is promoted to be a new master in the a fail-over process.
Once the other slaves connect to the new master, they send the value of gtid_executed and the master in turn checks those values, compares it with its own gtid_executed set and sends back all missing transactions (the errant transactions) to the slaves which leads to one of the following problems:
  • If those transactions still exist in the new master's binary log files, they will be replicated to the other slave which was not intentional when those were executed only on the slave (new master).
  • If those transactions do no longer exist in the new master's binary log file, the replication will break on all slaves.
How to avoid such problem?
  • Choose some slaves to be possible candidates for promotion in case of fail-over. Thus, stand alone transactions (which are not coming from the master) should NOT be executed there.
  • Use one of the MySQL utilities (mysqlfailover or mysqlrpladmin) to find out if there are any errant transactions on the slave before the promotion or not.
Filtration on the slave

In some cases we might need to make filtration to the replication on the slave(s) i.e. not all tables' or databases' changes are propagated to the slave by using the system variables (replicate_ignore_db or replicate_ignore_table). When the slave receives transactions from the master which modify those ignored tables or databases, it simply skips executing them and when the slave restarted it sends the gtid_excuted to the master and the master finds the missing transactions (those for the ignored tables or databases) and sends them back to the slave.

Again, that leads to one of the following two conditions:

  • If those transactions still exist in the master's binary log files, then no problem as the slave will skip executing them again!!
  • If those transactions are no longer there in the master's binary log files, the replication will break on the slave.

Well, the above problem is supposed to be fixed in MySQL 5.6.18 (Bug #70048) The fix is injecting empty transactions on the slave for those ones modifying ignored tables or databases instead of just skipping them, and when the slave restarted they won't be sent back again from the master.

I listed the above problem although it should be fixed now because I want to mention that having MySQL always updated to the recent release is a good practice to avoid such problems and to get the most bug fixes.

Conclusion:

The following are the main things which should be considered before using GTID:

  • Migration from classic replication to transaction-based (GTID) replication requires downtime.
  • Non-transactionally safe statements will not be executed in GTID replication.
  • MySQL performance is a little bit slower in GTID replication, especially, on the slaves.
  • mysql_upgrade script might cause troubles on a server having GTID_MODE=ON and it should be tested first.
  • Errant transactions might break the replication in the fail-over process, thus, planning slaves for promotion will avoid falling in such cases.
  • Some GTID bugs are fixed now (like slave filtration issue), thus MySQL server should be updated to the latest version once there is a new release.
  • New bugs are expected to be discovered, so the application should be tested very well with GTID before performing the migration on production.

Galera Cluster and XA Transactions

Abdel-Mawla Gharieb - Thu, 2014-10-23 23:47

A few weeks ago, we received an interesting Galera Cluster support case from one of our customers that the application is not working well and they face a lot of troubles in their Galera Cluster setup.

After some investigations, we found a lot of insert queries in state "query end" and lasting for long time without being completed. Also some other queries which were sleeping for long time having the info of "XA COMMIT":

SQL> SHOW PROCESSLIST; 27 user host:33214 foodmart Query 14440 sleeping XA COMMIT 0x31302e31312e31332e34372e746d30303336383030303031,0x31302e31312e31332e34372e746d333638,0x SQL> SHOW ENGINE INNODB STATUS; TRANSACTIONS ============ ---TRANSACTION 2DE71D, ACTIVE 14459 sec 9 lock struct(s), heap size 1248, 1 row lock(s), undo log entries 115 MySQL thread id 27, OS thread handle 0x7fc21a42c700, query id 96187 host host-ip foodmart sleeping XA COMMIT 0x31302e31312e31332e34372e746d30303336383030303031,0x31302e31312e31332e34372e746d333638,0x41544f4d ONE PHASE

XA means eXtended Architecture and "XA COMMIT" statement is one of the distributed transactions (XA Transactions) commands which are clearly NOT supported in Galera Cluster and one of its limitations because of possible rollback on commit.

The following command can be used to check if XA Transactions are being used by your application or not:

SQL> SHOW GLOBAL STATUS LIKE 'Com_xa%'; +-------------------+---------+ | Variable_name | Value | +-------------------+---------+ | Com_xa_commit | 2828094 | | Com_xa_end | 2828221 | | Com_xa_prepare | 0 | | Com_xa_recover | 2205697 | | Com_xa_rollback | 42 | | Com_xa_start | 2828305 | +-------------------+---------+ 6 rows in set (0.00 sec)

There are only two possible solutions for this problem:

  • Get rid of all XA transactions in the application to get the Galera Cluster work.
  • Use another HA solution (Active/passive, Master/Slave, ... etc) but not Galera Cluster.
Conclusion
  • XA transactions can not be supported in Galera Cluster and that is already stated clearly in the Galera Cluster Limitations.
  • Before Moving to Galera Cluster, it is preferred to go through all its limitations and check whether your application can cope with them or not.

Get rid of wrongly deleted InnoDB tables

Shinguz - Wed, 2014-10-22 22:10
Taxonomy upgrade extras: BackupRestoreRecoveryinnodbtable

Precaution: Before you try this out on your production system do a BACKUP first! FromDual Backup Manager can help you with this.

Situation

A MySQL user has delete its InnoDB table files for example like this:

shell> rm -f $datadir/test/test.* Analysis

We do some analysis first:

mysql> DROP TABLE test; ERROR 1051 (42S02): Unknown table 'test' mysql> CREATE TABLE test (id INT) ENGINE = InnoDB; ERROR 1050 (42S01): Table '`test`.`test`' already exists

The MySQL error log shows us the following information:

141022 17:09:04 InnoDB: Operating system error number 2 in a file operation. InnoDB: The error means the system cannot find the path specified. InnoDB: If you are installing InnoDB, remember that you must create InnoDB: directories yourself, InnoDB does not create them. 141022 17:09:04 InnoDB: Error: trying to open a table, but could not InnoDB: open the tablespace file './test/test.ibd'! InnoDB: Have you moved InnoDB .ibd files around without using the InnoDB: commands DISCARD TABLESPACE and IMPORT TABLESPACE? InnoDB: It is also possible that this is a temporary table #sql..., InnoDB: and MySQL removed the .ibd file for this. InnoDB: Please refer to InnoDB: http://dev.mysql.com/doc/refman/5.5/en/innodb-troubleshooting-datadict.html InnoDB: for how to resolve the issue.
Fix

User claims that he does NOT need the table and/or the data any more but wants to get rid of the error messages and/or create a new table with the same name.

mysql> CREATE SCHEMA recovery; mysql> use recovery mysql> CREATE TABLE test (id INT) ENGINE = InnoDB; mysql> \! cp $datadir/recovery/test.frm $datadir/test/ mysql> DROP SCHEMA recovery; mysql> use test mysql> DROP TABLE test; Prove

To prove it works we create a new table and fill in some records:

mysql> CREATE TABLE test (id int UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY, data VARCHAR(64), ts TIMESTAMP) ENGINE = InnoDB; mysql> INSERT INTO test VALUES (NULL, 'Test data', NULL); Literature

GTID Replication talk at Percona Live London 2014

Abdel-Mawla Gharieb - Tue, 2014-10-21 14:58

In a few weeks, I'll be speaking at Percona Live London 2014 (November 3-4) about "Transaction-based REPLICATION (GTID) - IMPLEMENTATION AND TROUBLESHOOTING". I'll talk about how to implement GTID replication in different scenarios and how to troubleshoot most of the common issues in GTID replication.

Anyone interested in learning more about GTID replication or planing to go with GTID replication in production should attend this talk.

Face-to-face meetings are very welcome, please let me know (abdel-mawla.gharieb@fromdual.com) if you are interested so we can schedule a meeting.

Looking forward to seeing you there!!

How to install multiple MySQL instances on a single host using MyEnv?

Abdel-Mawla Gharieb - Thu, 2014-10-16 16:36

We have been asked several times by MySQL users about how to install multiple MySQL instances on a single host.
Typically, this is required when testing different MySQL versions or MySQL servers (MySQL server, Percona server and MariaDB server) while no available resources are available.
Sometimes, it is even required to install multiple MySQL instances on a single production server.

In this article, I'll go through the steps needed to install multiple MySQL instances on a single host (using the tar balls binaries) and how our popular tool MyEnv can make such process so easy.

Prepare MySQL environment [root@centos-temp ~]# groupadd mysql [root@centos-temp ~]# useradd -g mysql mysql [root@centos-temp ~]# su - mysql [mysql@centos-temp:~]$ mkdir ~/product [mysql@centos-temp:~]$ mkdir ~/data [mysql@centos-temp ~]$ cd /downloads [mysql@centos-temp ~]$ wget http://dev.mysql.com/get/Downloads/MySQL-5.6/mysql-5.6.21-linux-glibc2.5-x86_64.tar.gz [mysql@centos-temp ~]$ cd ~/product [mysql@centos-temp ~]$ tar xf /downloads/mysql-5.6.21-linux-glibc2.5-x86_64.tar.gz [mysql@centos-temp ~]$ ln -s mysql-5.6.21-linux-glibc2.5-x86_64 mysql-5.6.21 Install MyEnv

MyEnv can be downloaded from here and the installation steps are listed here.

Install the first instance (named master)
  • Prepare the first instance: [mysql@centos-temp ~]$ mkdir ~/data/master [mysql@centos-temp ~]$ vi ~/data/master/my.cnf [mysqld] port = 3306 basedir = /home/mysql/product/mysql-5.6.21 datadir = /home/mysql/data/master socket = /home/mysql/data/master/master.sock user = mysql
  • Launch the myenv installer: [mysql@centos-temp ~]$ ~/product/myenv/bin/installMyEnv.sh PHP is installed on /usr/bin/php Starting MyEnv installer: /home/mysql/product/myenv-1.1.2/bin/installMyEnv.php Configuration file /etc/myenv/myenv.conf does NOT exist. Copy from template or abort (T, a):
  • Since this is the first instance, the myenv config file does not exist yet, we take the template (t): Copy from template or abort (T, a): t Copy /home/mysql/product/myenv-1.1.2/etc/myenv.conf.template to /etc/myenv/myenv.conf
  • Then MyEnv will detect that no instances are there, we choose the first option (a) to add a new instance: No instance exists yet. An instance is the same as a mysqld process. What do you want to do next? o Add a new instance, o change an existing instance, o delete an existing instance, o save configuration and exit or o quit without saving (A/c/d/s/q)? a
  • MyEnv will ask for the new instance name (master): You have to enter a new instance name. An instance name can consist of 0-9, a-z, A-Z, - and _. Examples: test, prod, dev, [mysqld1] mysqld-3306 Enter a new instance name: master
  • MyEnv will ask for the MySQL basedir and datadir: Changing instance master: Set basedir. The basedir is the directory where your MySQL binaries are located. Example: /home/mysql/product/myenv /home/mysql/product/myenv-1.1.2 /home/mysql/product/mysql-5.6.21 /home/mysql/product/mysql-5.6.21-linux-glibc2.5-x86_64 /usr/local/mysql /opt/mysql [/usr] basedir = /home/mysql/product/mysql-5.6.21 /home/mysql/product/mysql-5.6.21 seems to exist and has already some files in it . Omitting installation of binary tar ball. Set datadir. The datadir is the directory where your MySQL data are located. Example: /usr/local/mysql/data, /opt/mysql/data or /var/lib/mysql or /home/mysql/product/mysql-5.6.21/data or [/home/mysql/data/master] or /home/mysql/data/master datadir = /home/mysql/data/master WARNING: directory /home/mysql/data/master already exist.
  • MyEnv will detect that no mysql database is created yet in the datadir and ask if it should install it for us or not (using the normal mysql_install_db script) Shall I install a mysql database under /home/mysql/data/master (Y/n)? y Installing MySQL instance. Please be patient, this can take a while... /home/mysql/product/mysql-5.6.21/scripts/mysql_install_db --datadir=/home/mysql/data/master --basedir=/home/mysql/product/mysql-5.6.21
  • For the new instance, we should specify the port, the socket, and the location of my.cnf (all these must be specific per instance): Set port. Example: 3307 or [3306] port = 3306 Set socket. Example: /tmp/mysql-3306.sock /tmp/mysql-master.sock [/tmp/mysql.sock] /var/run/mysqld/mysql.sock socket = /home/mysql/data/master/master.sock Choose location of my.cnf: Example: /etc/my.cnf /etc/mysql/my.cnf /home/mysql/data/master/my-3306.cnf [/home/mysql/data/master/my.cnf] my.cnf = /home/mysql/data/master/my.cnf
  • MyEnv will list the just added instance and ask what should be the next step, we should save and exit (s): The following instances are available: master An instance is the same as a mysqld process. What do you want to do next? o Add a new instance, o change an existing instance, o delete an existing instance, o save configuration and exit or o quit without saving (a/c/d/S/q)? s Writing the configuration file... Rename /etc/myenv/myenv.conf to /etc/myenv/myenv.conf.2014-10-15-05-50-12 Write /etc/myenv/myenv.conf
  • MyEnv will propose to add the following lines to the .bash_profile file, we should confirm (y): Do you want to add the following code to your ~/.bash_profile file? . /etc/myenv/MYENV_BASE MYENV_PWD=`pwd` cd $MYENV_BASE/bin . myenv.profile cd $MYENV_BASE; $MYENV_BASE/bin/showMyEnvStatus.php; cd - > /dev/null cd $MYENV_PWD (Y/n)? y Writing /etc/myenv/MYENV_BASE
  • We should add the myenv startup script as shown here into the appropriate path (the provided commands should be executed manually from the root/privileged-user after that): Please copy yourself manually the MyEnv start/stop script to the following location: shell> sudo cp /home/mysql/product/myenv-1.1.2/bin/myenv.server /etc/init.d/myenv done (Y)? y and link it to your O/S runlevels: RedHat/CentOS: shell> sudo chkconfig --add myenv; chkconfig myenv on Ubuntu/Debian: shell> sudo update-rc.d myenv defaults SLES/OpenSuSE: shell> sudo chkconfig --add myenv done (Y)? y Now source your profile as follows: . ~/.bash_profile
  • Now, we should logout and login so that the .bash_profile code will be executed (we can copy the startup script in the meantime): [mysql@centos-temp ~]$> exit [root@centos-temp ~]# cp /home/mysql/product/myenv-1.1.2/bin/myenv.server /etc/init.d/myenv [root@centos-temp ~]# chkconfig --add myenv [root@centos-temp ~]# su - mysql Up : Down : master (5.6.21) master ( 3306) : test mysql@centos-temp:~ [master, 3306]>
  • Now, we can start the just installed instance and check if it is started correctly or not: mysql@centos-temp:~ [master, 3306]> start . SUCCESS! mysql@centos-temp:~ [master, 3306]> up Up : master (5.6.21) Down : master ( 3306) : test mysql@centos-temp:~/data/master [master, 3306]>

Cool! We have got the first instance installed. let's install the second one ...

Install the second instance (named slave1)
  • Prepare the second instance: mysql@centos-temp:~ [master, 3306]> mkdir ~/data/slave1 mysql@centos-temp:~ [master, 3306]> vi ~/data/slave1/my.cnf [mysqld] port = 3307 basedir = /home/mysql/product/mysql-5.6.21 datadir = /home/mysql/data/slave1 socket = /home/mysql/data/slave1/slave1.sock user = mysql
  • Launch the MyEnv installer and add the new instance: mysql@centos-temp:~ [master, 3306]> product/myenv/bin/installMyEnv.sh PHP is installed on /usr/bin/php Starting MyEnv installer: /home/mysql/product/myenv-1.1.2/bin/installMyEnv.php Configuration file /etc/myenv/myenv.conf already exists. Use this, overwrite with template or abort (U,t,a): u The following instances are available: master An instance is the same as a mysqld process. What do you want to do next? o Add a new instance, o change an existing instance, o delete an existing instance, o save configuration and exit or o quit without saving (A/c/d/s/q)? a You have to enter a new instance name. An instance name can consist of 0-9, a-z, A-Z, - and _. Examples: test, prod, dev, [mysqld1] mysqld-3306 Enter a new instance name: slave1 Changing instance slave1: Set basedir. The basedir is the directory where your MySQL binaries are located. Example: /home/mysql/product/myenv /home/mysql/product/myenv-1.1.2 /home/mysql/product/mysql-5.6.21 /home/mysql/product/mysql-5.6.21-linux-glibc2.5-x86_64 /usr/local/mysql /opt/mysql [/usr] basedir = /home/mysql/product/mysql-5.6.21 /home/mysql/product/mysql-5.6.21 seems to exist and has already some files in it. Omitting installation of binary tar ball. Set datadir. The datadir is the directory where your MySQL data are located. Example: /usr/local/mysql/data, /opt/mysql/data or /var/lib/mysql or /home/mysql/product/mysql-5.6.21/data or [/home/mysql/data/slave1] or /home/mysql/data/slave1 datadir = /home/mysql/data/slave1 WARNING: directory /home/mysql/data/slave1 already exist. Shall I install a mysql database under /home/mysql/data/slav1 (Y/n)? y Installing MySQL instance. Please be patient, this can take a while... /home/mysql/product/mysql-5.6.21/scripts/mysql_install_db --datadir=/home/mysql/data/slave1 --basedir=/home/mysql/product/mysql-5.6.21 Set port. Example: 3307 or [3306] port = 3307 Set socket. Example: /tmp/mysql-3307.sock /tmp/mysql-slave1.sock [/tmp/mysql.sock] /var/run/mysqld/mysql.sock socket = /home/mysql/data/slave1/slave1.sock Choose location of my.cnf: Example: /etc/my.cnf /etc/mysql/my.cnf /home/mysql/data/slave1/my-3307.cnf [/home/mysql/data/slave1/my.cnf] my.cnf = /home/mysql/data/slave1/my.cnf The following instances are available: master slave1 An instance is the same as a mysqld process. What do you want to do next? o Add a new instance, o change an existing instance, o delete an existing instance, o save configuration and exit or o quit without saving (a/c/d/S/q)? s Writing the configuration file... Rename /etc/myenv/myenv.conf to /etc/myenv/myenv.conf.2014-10-15-06-44-04 Write /etc/myenv/myenv.conf Now source your profile as follows: . ~/.bash_profile
  • Then we logout and login again to load the new configs: mysql@centos-temp:~ [master, 3306]> exit logout [root@centos-temp product]# su - mysql Up : master (5.6.21) Down : slave1 (5.6.21) master ( 3306) : test slave1 ( 3307) : test mysql@centos-temp:~ [master, 3306]>

MyEnv says that we have two instances (master and slave1), master is up and running while slave1 is stopped. Let's start it then ..

  • First, all commands we execute are sent to the master instance, we should change to the slave1 instance: mysql@centos-temp:~ [master, 3306]> slave1 mysql@centos-temp:~ [slave1, 3307]> start . SUCCESS! mysql@centos-temp:~ [slave1, 3307]>
  • Both instances are now up and running ... mysql@centos-temp:~ [slave1, 3307]> up Up : master (5.6.21) slave1 (5.6.21) Down : master ( 3306) : test slave1 ( 3307) : test mysql@centos-temp:~ [slave1, 3307]>
Instances navigation and MySQL connection

After we installed the two instances we need to know how can we navigate between them to open MySQL connections.

  • Open a MySQL connection to the master instance: mysql@centos-temp:~ [master, 3306]> mysql -u root Welcome to the MySQL monitor. Commands end with ; or \g. Your MySQL connection id is 7 Server version: 5.6.21 MySQL Community Server (GPL) Copyright (c) 2000, 2014, Oracle and/or its affiliates. All rights reserved. Oracle is a registered trademark of Oracle Corporation and/or its affiliates. Other names may be trademarks of their respective owners. Type 'help;' or '\h' for help. Type '\c' to clear the current input statement. root@localhost master [(none)] SQL>
  • While the instance name is already printed in the terminal we need to double check that by a MySQL command (the used port) and exit after that: root@localhost master [(none)] SQL> SHOW GLOBAL VARIABLES LIKE 'port'; +---------------+-------+ | Variable_name | Value | +---------------+-------+ | port | 3306 | +---------------+-------+ 1 row in set (0.00 sec) root@localhost master [(none)] SQL> exit Bye mysql@centos-temp:~ [master, 3306]>
  • Open a MySQL connection to the slave1 instance and check the used port: mysql@centos-temp:~ [master, 3306]> slave1 mysql@centos-temp:~ [slave1, 3307]> mysql -u root Welcome to the MySQL monitor. Commands end with ; or \g. Your MySQL connection id is 5 Server version: 5.6.21 MySQL Community Server (GPL) Copyright (c) 2000, 2014, Oracle and/or its affiliates. All rights reserved. Oracle is a registered trademark of Oracle Corporation and/or its affiliates. Other names may be trademarks of their respective owners. Type 'help;' or '\h' for help. Type '\c' to clear the current input statement. root@localhost slave1 [(none)] SQL> SHOW GLOBAL VARIABLES LIKE 'port'; +---------------+-------+ | Variable_name | Value | +---------------+-------+ | port | 3307 | +---------------+-------+ 1 row in set (0.00 sec) root@localhost slave1 [(none)] SQL>
  • Navigate back to the master instance: mysql@centos-temp:~ [slave1, 3307]> master mysql@centos-temp:~ [master, 3306]>

More information about MyEnv commands can be checked here.

Notes:
  • Using the same procedures above we can add several instances using either the same binaries or some others.
  • We used the smallest configurations in the my.cnf file, you are free to make your own changes.

Migration between MySQL/Percona Server and MariaDB

Shinguz - Wed, 2014-10-08 21:40
Taxonomy upgrade extras: migrationsidegradeupgrademysqlmariadbpercona serverconversioncompatibility

This week we did some migrations from MariaDB 10.0 to Percona Server 5.6 at the IT department of a big German bank.

We were perfectly aware that since version 10.0 the MariaDB code base started to diverge slightly away from the MySQL and Percona Server code base which are still pretty close to each other.

Because of the Percona Server option enforce_storage_engine we wanted to do this migration.

We stopped the MariaDB 10.0 server replaced the binaries by the Percona Server 5.6 binaries and started the Percona 5.6 server again. After successfully starting the instance we found some error messages in the MySQL error log. By running the mysql_upgrade command some of the problems were fixed but not all of them. Still left problems were:

  • The MariaDB binary logs provoked some error messages for the Percona Server: [ERROR] Error in Log_event::read_log_event(): 'Found invalid event in binary log', data_len: 25, event_type: -93 [Warning] Error reading GTIDs from binary log: -1 [ERROR] Incorrect definition of table mysql.db: expected column 'User' at position 2 to have type char(16), found type char(80). [ERROR] Incorrect definition of table mysql.event: expected column 'definer' at position 3 to have type char(77), found type char(141). [ERROR] Incorrect definition of table mysql.event: expected column 'sql_mode' at position 14 to have type set... A purge of the binary logs solved this issue.
  • The tables mysql.event, mysql.innodb_table_stats and mysql.innodb_index_stats where not fixed by mysql_upgrade (a bug to fix for Percona and MySQL/Oracle?). We had to replace those tables manually by copying from an other already working Percona 5.6 Server.

Later in the FromDual technology labs we investigated further and tried the other way from Percona Server 5.6 to MariaDB 10.0. In this direction we found some other errors in the MySQL error log which also where not completely resolved by the mysql_upgrade utility:

  • The mysql.innodb_table_stats and mysql.innodb_index_stats tables where recreated manually (here a bug to fix for the MariaDB people?).
  • All error messages from tables affected by the following message: InnoDB: in InnoDB data dictionary has unknown flags 40/50/52. could be silenced by a run of the OPTIMIZE TABLE command (which can become quite expensive for very big tables).

Sidegrades from MySQL 5.6 to Percona Server 5.6 and back did not provoke any error message written to the MySQL log files. Sidegrades from MariaDB 10.0 to MySQL 5.6 and vice versa behaved exactly the same as MariaDB 10.0 to Percona Server 5.6 and back.

from/to: MySQL 5.6 MariaDB 10.0 Percona Server 5.6 MySQL 5.6 - 2 tables, OPTIMIZE OK MariaDB 10.0 binlog, 3 tables - binlog, 3 tables Percona Server 5.6 OK 2 tables, OPTIMIZE -

During our tests we got rid of the error messages. If they caused any technical harm to the tables or the data we cannot say so far. Further testing and experience from real life is needed. Any feedback is welcome!

Observations

It looks like MariaDB 10.0 understands MySQL/Percona Server replication but not the other way around. So replication from MariaDB 10.0 to MySQL 5.6 does probably not work (different implementation of GTID)?

Recommendation

To make sure a sigdegrade between these 3 MySQL branches/forks is seamlessly possible the best method seems to be to dump/restore (NOT xtrabackup!) the data. This can be an issue with huge databases (hundreds of Gbyte).

Further aid

Also have a look at our MySQL compatibility matrix and our MySQL upgrade check-list.

If you need any help to convert MySQL to MariaDB to Percona Server or the other way do not hesitate to contact the FromDual consultancy team. We will be pleased to assist you as a neutral and vendor independent consulting company.

Galera Cluster VS PXC VS MariaDB Galera Cluster - Benchmarking

Abdel-Mawla Gharieb - Thu, 2014-08-07 15:36

It is not clear for many MySQL users that Percona XtraDB Cluster (PXC) and MariaDB Galera Cluster depend on the same Galera library i.e used in Galera Cluster for MySQL which is provided by Codership team:

  • Galera Cluster: MySQL Server (by Oracle) + Galera library.
  • Percona XtraDB Cluster: Percona Server + Galera library.
  • MariaDB Galera Cluster: MariaDB Server + Galera library.

But the question is, are there any performance differences between the three of them ?

Let's discover that by doing some simple benchmark to test MySQL write performance in Galera Cluster, PXC and MariaDB Galera Cluster installations.

System Information: HW configurations (AWS Servers): Nodes Servers HW configurations:
  • CPU: Intel(R) Xeon(R) CPU E5-2680 v2 @ 2.80GHz (# of cores 8, # of threads 16, HT enabled).
  • Memory: 16GB RAM.
  • Storage: HDD 120GB/ 5400RPM.
Load balancer Server HW configurations:
  • CPU: Intel(R) Xeon(R) CPU E5-2651 v2 @ 1.80GHz (# of cores 4, # of threads 8, HT enabled).
  • Memory: 16GB RAM.
  • Storage: HDD 10GB/ 5400RPM.
Load generator Server HW configurations:
  • CPU: Intel(R) Xeon(R) CPU E5-2680 v2 @ 2.80GHz (# of cores 16, # of threads 32, HT enabled).
  • Memory: 32GB RAM.
  • Storage: HDD 10GB/ 5400RPM.
Software configurations:
  • OS : Red Hat Enterprise Linux Server release 6.5 (Santiago)
  • Sysbench : 0.5.3
  • GLB : 1.0.0
  • Galera Cluster : 5.5.34 and 5.6.16
  • Percona XtraDB Cluster : 5.5.37 and 5.6.19
  • MariaDB Galera Cluster : 5.5.38 and 10.0.12
  • Galera Library : 3.5
Test Information:
  • The testing environment consists of 5 AWS servers, three servers for a three-node cluster (each node is installed on a single server), one server for the load balancer and the final server for the load generator in which sysbench is installed to send requests to the load balancer from.
  • Sysbench command: sysbench --num-threads=64 --max-requests=1000 --db-driver=mysql --test=/usr/share/doc/sysbench/tests/db/oltp.lua --mysql-table-engine=InnoDB --mysql-user=dev --mysql-password='test' --mysql-host=load_balancer_ip 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
  • The my.cnf used is something like: [mysqld] key_buffer_size = 16M max_allowed_packet = 16M thread_stack = 192K thread_cache_size = 8 innodb_buffer_pool_size = 8G innodb_flush_log_at_trx_commit = 0 expire_logs_days = 10 max_binlog_size = 100M server-id = 1 log-bin = mysql-bin binlog_format = ROW auto_increment_increment = 3 auto_increment_offset = 1 log_slave_updates default_storage_engine = InnoDB # Path to Galera library wsrep_provider = /usr/lib64/galera/libgalera_smm.so # Cluster connection URL contains the IPs of node#1, node#2 and node#3 wsrep_cluster_address = gcomm://nodeB-IP,nodeC-IP innodb_autoinc_lock_mode = 2 # Node #1 address wsrep_node_address = nodeA-IP # Cluster name wsrep_cluster_name = test_cluster # SST method wsrep_sst_method = rsync # Authentication for SST method wsrep_sst_auth = "sst:password"

Notes:

  • The number of threads used in this test is 64 as it generated the highest throughput on all cluster installations.
  • Each throughput value for each test case is generated by the average of ten (10) times execution.
Testing Results:









The raw results in Transactions / Sec might be useful:


sync_binlog=0innodb_flush_log_ at_trx_commitGalera Cluster 5.5.34PXC 5.5.37MariaDB Galera Cluster 5.5.38Galera Cluster 5.6.16PXC 5.6.15MariaDB Galera Cluster 10.0.120525.119534.022534.249519.575532.19520.7361125.615131.748341.384157.001162.783174.972526.761528.858524.039511.817526.06521.024sync_binlog=10242.201249.622262.516220.313229.807220.97196.82996.759148.815111.995114.8113.0562224.476210.904217.142209.139201.596214.311
Conclusion

According to the above results:

  • innodb_flush_log_at_trx_commit = 1 significantly slows down Galera.
  • sync_binlog also cuts in half the throughput.
  • All other are more or less equal in throughput.

Replication Troubleshooting - Classic VS GTID

Abdel-Mawla Gharieb - Fri, 2014-07-04 15:05

In previous posts, I was talking about how to set up MySQL replication, Classic Replication (based on binary logs information) and Transaction-based Replication (based on GTID). In this article I'll summarize how to troubleshoot MySQL replication for the most common issues we might face with a simple comparison how can we get them solved in the different replication methods (Classic VS GTID).

There are two main operations we might need to do in a replication setup:

  • Skip or ignore a statement that causes the replication to stop.
  • Re-initialize a slave when the Replication is broke and could not be started anymore.
Skip or Ignore statement

Basically, the slave should be always synchronized with its master having the same copy of data, but for some reasons there might be inconsistency between both of them (unsafe statement in SBR, Slave is not read_only and was modified apart of replication queries, .. etc) which causes errors and stops the replication, e.g. if the master inserted a record which was already inserted on the slave (Duplicate entry) or updated/deleted a row which was not exist on the slave, ... etc.

To solve this issue, we have to either reverse what we have done on the slave (e.g. delete the inserted rows) if that was made by mistake and is known or we can skip executing those statements on the slave and continue the replication again (I'll focus on skipping a statement in this post as it needs different interaction in Classic and GTID replication).

Sample error messages (from SHOW SLAVE STATUS output): Last_SQL_Error: Could not execute Write_rows event on table test.t1; Duplicate entry '4' for key 'PRIMARY', Error_code: 1062; handler error HA_ERR_FOUND_DUPP_KEY; the event's master log mysql-bin.000304, end_log_pos 285 Last_SQL_Error: Could not execute Update_rows event on table test.t1; Can't find record in 't1', Error_code: 1032; handler error HA_ERR_KEY_NOT_FOUND; the event's master log mysql-bin.000304, end_log_pos 492 Last_SQL_Error: Could not execute Delete_rows event on table test.t1; Can't find record in 't1', Error_code: 1032; handler error HA_ERR_KEY_NOT_FOUND; the event's master log mysql-bin.000304, end_log_pos 688 How to solve that issue ?
CLASSIC REPLICATION

Solving this problem is a straight forward process in the classic replication setup, what only we need is to issue the following SQL commands on the slave's:

SQL> SET GLOBAL SQL_SLAVE_SKIP_COUNTER=1; SQL> START SLAVE;
GTID REPLICATION

Solving this problem is not a straight forward in GTID replication like it is in the Classic replication and the variable SQL_SLAVE_SKIP_COUNTER wont be useful in this area anymore.

To get this problem solved in a GTID replication we will need to inject an empty transaction as follows:

  • Check which transaction is causing the problem: SQL> SHOW SLAVE STATUS\G . . Retrieved_Gtid_Set: b9b4712a-df64-11e3-b391-60672090eb04:1-7 Executed_Gtid_Set: 4f6d62ed-df65-11e3-b395-60672090eb04:1, b9b4712a-df64-11e3-b391-60672090eb04:1-6 Auto_Position: 1

    Retrieved_Gtid_Set means the retrieved GTIDs from the master

    Executed_Gtid_Set means the executed GTIDs on the slave.

    According to the above output, the slave retrieved GTIDs from 1:7 (b9b4712a-df64-11e3-b391-60672090eb04:1-7) and executed only from 1:6 (b9b4712a-df64-11e3-b391-60672090eb04:1-6), so the problem is in transaction number 7.

  • Inject an empty transaction: SQL> SET GTID_NEXT='b9b4712a-df64-11e3-b391-60672090eb04:7'; SQL> BEGIN;COMMIT; SQL> SET GTID_NEXT='AUTOMATIC'; SQL> START SLAVE;

    BE CAUTIOUS: The first part of Executed_Gtid_Set (4f6d62ed-df65-11e3-b395-60672090eb04:1) is the local executed GTIDs (not received from the master) while the second part (b9b4712a-df64-11e3-b391-60672090eb04:1-6) is the executed GTIDs which retrieved from the master (check the master's UUID by either checking the UUID value in "Retrieved_Gtid_Set" which is basically for the master's UUID or by issuing SHOW GLOBAL VARIABLES LIKE 'server_uuid'; on the master server). So we should make sure that we are using the master's UUID when injecting an empty transaction, otherwise, the problem will still remain and the slave wont be started.

Note:

After starting the slave successfully in either classic or GTID replication we might need to use a combination of Percona tools pt-table-checksum and pt-table-sync to fix the inconsistency problem.

Re-initialize/ re-build a slave

For many reasons, we might end up with only re-build a slave to get the replication working, e.g. if we stopped a slave for a while where the master purged the binary log file that is needed by that slave or there are many duplicate entry errors so that pt-table-checksum and pt-table-sync could not be used then we have to re-initialize the slave from the beginning by having a fresh backup from the master server and restore it on the slave. Lets check how can we do that in both replication methods.

How to solve that issue ?
CLASSIC REPLICATION
Sample error message:
Last_IO_Errno: 1236 Last_IO_Error: Got fatal error 1236 from master when reading data from binary log: 'Could not find first log file name in binary log index file'

Fix steps:

  • Backup the master server by the following command: 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-$TIMESTAMP.sql
  • Restore the backup file on the slave: shell> mysql -u root -p < /path/to/backupdir/full_backup-$TIMESTAMP.sql
  • Get the binary logs information when the backup was taken: shell> head -n 50 /path/to/backupdir/full_backup-$TIMESTAMP.sql|grep "CHANGE MASTER TO" CHANGE MASTER TO MASTER_LOG_FILE='mysql-bin.000011', MASTER_LOG_POS=120;
  • Issue the "CHANGE MASTER TO" command using the new information: SQL> CHANGE MASTER TO MASTER_LOG_FILE='mysql-bin.000011', MASTER_LOG_POS=120;
  • Start the slave: SQL> START SLAVE;

NOTE:

Xtrabackup tool could be used instead of mysqldump,especially, if the database size is big. Check out this link for more information.

GTID REPLICATION
Sample error message:
Last_IO_Errno: 1236 Last_IO_Error: Got fatal error 1236 from master when reading data from binary log: 'The slave is connecting using CHANGE MASTER TO MASTER_AUTO_POSITION = 1, but the master has purged binary logs containing GTIDs that the slave requires.'

Fix steps:

  • Backup the master server by the following command: shell> mysqldump -u root -p --all-databases --flush-privileges --single-transaction --flush-logs --triggers --routines --events --hex-blob >/path/to/backupdir/full_backup-$TIMESTAMP.sql
  • Check the GTID value when the backup was taken: shell> head -n 50 /path/to/backupdir/full_backup-$TIMESTAMP.sql|grep PURGED SET @@GLOBAL.GTID_PURGED='b9b4712a-df64-11e3-b391-60672090eb04:1-8';
  • Reset the GTID_EXECUTED and GTID_PURGED values on the slave: SQL> RESET MASTER;
  • Restore the backup file on the slave: shell> mysql -u root -p < /path/to/backupdir/full_backup-$TIMESTAMP.sql
  • Make sure that the values of GTID_EXEUCTED and GTID_PURGED are the correct ones: SQL> SHOW GLOBAL VARIABLES LIKE 'gtid_executed'; +---------------+------------------------------------------+ | Variable_name | Value | +---------------+------------------------------------------+ | gtid_executed | b9b4712a-df64-11e3-b391-60672090eb04:1-8 | +---------------+------------------------------------------+ 1 row in set (0.00 sec) SHOW GLOBAL VARIABLES LIKE 'gtid_purged'; +---------------+------------------------------------------+ | Variable_name | Value | +---------------+------------------------------------------+ | gtid_purged | b9b4712a-df64-11e3-b391-60672090eb04:1-8 | +---------------+------------------------------------------+ 1 row in set (0.01 sec)
  • Start the slave: SQL> START SLAVE;

NOTES:

  • If we didn't reset the GTID_EXECUTED and GTID_PURGED values on the slave before restoring the backup file, the following error will be appeared:
    shell> mysql -u root -p < /path/to/backupdir/full_backup-$TIMESTAMP.sql. ERROR 1840 (HY000): @@GLOBAL.GTID_PURGED can only be set when @@GLOBAL.GTID_EXECUTED is empty.

    The above error indicates that the statement at the beginning of the backup file - which is "SET @@GLOBAL.GTID_PURGED='b9b4712a-df64-11e3-b391-60672090eb04:1-8';" - failed because GTID_PURGED cannot be set unless GTID_EXECUTED is empty. Since GTID_EXECUTED is a read only variable, the only way to empty its value is to issue "RESET MASTER" on the slave server before restoring the backup file.

  • Xtrabackup tool could be used as well instead of mysqldump to get this problem solved and without the need to reset GTID_EXECUTED and GTID_PURGED values . Check out this link for more information.
Conclusion

While GTID provides many benefits over the classic replication but it has different troubleshooting and fix strategies which must be known first before deploying GTID in production systems.

Replication channel fail-over with Galera Cluster for MySQL

Shinguz - Thu, 2014-06-19 07:05
Taxonomy upgrade extras: channelgaleraclusterfail-overreplicationmasterslave

Sometimes it could be desirable to replicate from a Galera Cluster to a single MySQL slave or to an other Galera Cluster. Reasons for this measure could be:

  • An unstable network between two Galera Cluster locations.
  • A separation of a reporting slave and the Galera Cluster so that heavy reports on the slave do not affect the Galera Cluster performance.
  • Mixing different sources in a slave or a Galera Cluster (fan-in replication).

This article is based on earlier research work (see MySQL Cluster - Cluster circular replication with 2 replication channels) and uses the old MySQL replication style (without MySQL GTID).

Preconditions
  • Enable the binary logs on 2 nodes of a Galera Cluster (we call them channel masters) with the log_bin variable.
  • Set log_slave_updates = 1 on ALL Galera nodes.
  • It is recommended to have small binary logs and relay logs in such a situation to reduce overhead of scanning the files (max_binlog_size = 100M).
Scenarios

   

Let us assume that for some reason the actual channel master of channel 1 breaks. As a consequence the slave of channel 1 does not receive any replication events any more. But we have to keep the replication stream up and running. So we have to switch the replication channel to channel master 2.

Switching replication channel

First for security reasons we should stop the slave of replication channel 1 first:

mysql> STOP SLAVE;

Then we have to find the actual relay log on the slave:

mysql> pager grep Relay_Log_File mysql> SHOW SLAVE STATUS\G mysql> nopager Relay_Log_File: slave-relay-bin.000019

Next we have to find the last applied transaction on the slave:

mysql> SHOW RELAYLOG EVENTS IN 'slave-relay-bin.000019'; | slave-relay-bin.000019 | 3386717 | Query | 5201 | 53745015 | BEGIN | | slave-relay-bin.000019 | 3386794 | Table_map | 5201 | 53745067 | table_id: 72 (test.test) | | slave-relay-bin.000019 | 3386846 | Write_rows | 5201 | 53745142 | table_id: 72 flags: STMT_END_F | | slave-relay-bin.000019 | 3386921 | Xid | 5201 | 53745173 | COMMIT /* xid=1457451 */ | +------------------------+---------+-------------+-----------+-------------+--------------------------------+

This is transaction 1457451 which is the same on all Galera nodes.

On the new channel master of channel 2 we have to find now the matching binary log. This can be done best by matching times between the relay log and the binary log of master of channel 2.

On slave:

shell> ll *relay-bin* -rw-rw---- 1 mysql mysql 336 Mai 22 20:32 slave-relay-bin.000018 -rw-rw---- 1 mysql mysql 3387029 Mai 22 20:37 slave-relay-bin.000019

On master of channel 2:

shell> ll *bin-log* -rw-rw---- 1 mysql mysql 2518737 Mai 22 19:57 bin-log.000072 -rw-rw---- 1 mysql mysql 143 Mai 22 19:57 bin-log.000073 -rw-rw---- 1 mysql mysql 165 Mai 22 20:01 bin-log.000074 -rw-rw---- 1 mysql mysql 62953648 Mai 22 20:40 bin-log.000075

It looks like binary log 75 of master 2 matches to relay log of our slave.

Now we have to find the same transaction on the master of channel 2:

mysql> pager grep -B 6 1457451 mysql> SHOW BINLOG EVENTS IN 'bin-log.000075'; mysql> nopager | bin-log.000075 | 53744832 | Write_rows | 5201 | 53744907 | table_id: 72 flags: STMT_END_F | | bin-log.000075 | 53744907 | Xid | 5201 | 53744938 | COMMIT /* xid=1457450 */ | | bin-log.000075 | 53744938 | Query | 5201 | 53745015 | BEGIN | | bin-log.000075 | 53745015 | Table_map | 5201 | 53745067 | table_id: 72 (test.test) | | bin-log.000075 | 53745067 | Write_rows | 5201 | 53745142 | table_id: 72 flags: STMT_END_F | | bin-log.000075 | 53745142 | Xid | 5201 | 53745173 | COMMIT /* xid=1457451 */ | +----------------+----------+-------------+-----------+-------------+---------------------------------------+

We successfully found the transaction and want the position of the next transaction 53745173 where we should continue replicating.

As a last step we have to set the slave to the master of replication channel 2:

mysql> CHANGE MASTER TO master_host='master2', master_port=3306, master_log_file='bin-log.000075', master_log_pos=53745173; mysql> START SLAVE;

After a while the slave has caught up and is ready for the next fail-over back.

Discussion

We found during our experiments that an IST of a channel master does not lead to a gap or loss of events in the replication stream. So restarting a channel master does not require a channel fail-over as long as an IST can be used for resyncing the channel master with the Galera Cluster.

The increase of wsrep_cluster_conf_id is NOT an indication that a channel fail-over is required.

A SST resets the binary logs so after the SST a slave will not replicate any more. So using this method should be safe to use. If you find any situation where you experience troubles with channel fail-over please let us know.

GTID In Action

Abdel-Mawla Gharieb - Thu, 2014-06-12 14:09

In a previous post I was talking about How to Setup MySQL Replication using the classic method (based on binary logs information). In this article I'll go through the transaction-based replication implementation using GTID in different scenarios.

The following topics will be covered in this blog:

What is the concept of GTID protocol?

GTID is a Global Transaction IDentifier which introduced in MySQL 5.6.5. It's not only unique on the server it was originated but it's unique among all servers in a replication setup.
GTID also guarantee consistency because once a transaction is committed on a server, any other transaction having the same GTID will be ignored, i.e. a committed transaction on a master will be applied only once on the slaves.

GTID consists of two parts separated by a column {source_id:transactions_id}.

WHERE

  • source_id: Normally the server's UUID on which the transaction originates. e.g. "b9b4712a-df64-11e3-b391-60672090eb04" .
  • transaction_id: A sequence number determining the order of the committed transaction.

The following is the GTID for the third transaction on a server having the uuid "b9b4712a-df64-11e3-b391-60672090eb04":
b9b4712a-df64-11e3-b391-60672090eb04:3

As a new protocol in MySQL there is a set of new related variables, the following are the most important ones (IMHO):

  • gtid-mode: ON|OFF to enable or disable GTID, this is not a Boolean variable (0 and 1 are not acceptable).
  • enforce-gtid-consistency: prevent executing the non transactionally safe statements, like:
    • CREATE TABLE .. SELECT.
    • CREATE TEMPORARY TABLE (inside a transaction).
    • Statements that update nontransactional tables inside a transaction.
  • gtid_purged: The set of transactions that have been purged from the binary logs.
  • gtid_executed: The set of transactions which already executed on that server.
  • gtid_next: The GTID which will be used for the next transaction.
GTID Replication Implementation Fresh Installations

Fresh installation means that there's no data yet in the master or in other words, we are building a replication setup from scratch.

The implementation process is divided into two parts:

MASTER'S SIDE CONFIGURATION:
  • Add the following variables to the MySQL configuration file (my.cnf): [mysqld] server-id=1 log-bin=mysql-bin binlog_format=ROW gtid-mode=on enforce-gtid-consistency log-slave-updates
  • Restart MySQL so that configuration changes take place: shell> service 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';

SLAVE'S SIDE CONFIGURATION:
  • Add the following variables to the my.cnf file: [mysqld] server-id=2 log-bin=mysql-bin binlog_format=ROW relay_log=relay-log skip-slave-start gtid-mode=on enforce-gtid-consistency log-slave-updates
  • Restart MySQL so that configuration changes take place: shell> service mysql restart
  • Set the master information on the slave's:

    Unlike the classic method, we don't need the master's binary log information and only what we need is to specify MASTER_AUTO_POSITION=1 instead:

    SQL> CHANGE MASTER TO -> MASTER_HOST='master_ip', -> MASTER_PORT=3306, -> MASTER_USER='slave_user_name', -> MASTER_PASSWORD='s3cret', -> MASTER_AUTO_POSITION=1;
  • Start replication: SQL> START SLAVE;
  • Check the replication status: SQL> show slave status\G Slave_IO_State: Waiting for master to send event Master_Host: 127.0.0.1 Master_User: gtid_repl Master_Port: 3320 Connect_Retry: 60 Master_Log_File: mysql-bin.000007 Read_Master_Log_Pos: 191 Relay_Log_File: relay-log.000004 Relay_Log_Pos: 401 Relay_Master_Log_File: mysql-bin.000007 Slave_IO_Running: Yes Slave_SQL_Running: Yes Replicate_Do_DB: . . . . Retrieved_Gtid_Set: b9b4712a-df64-11e3-b391-60672090eb04:1-2 Executed_Gtid_Set: b9b4712a-df64-11e3-b391-60672090eb04:1-2 Auto_Position: 1
Adding New Slave

It's a very simple process to add a new slave to a running replication (or setup replication with existing data) where GTID is being used:

  • Backup the master server shell> mysqldump -u root -p --all-databases --flush-privileges --single-transaction --flush-logs --triggers --routines --events --hex-blob >/path/to/backupdir/full_backup-$TIMESTAMP.sql
  • On the new slave, use the same MySQL configuration as described above (except the server id which should be unique) and restart it.
  • Restore the backup file taken from the master.
  • Use change master to with MASTER_AUTO_POSITION=1
  • Start the slave.

Is it so simple like that!! How did the slave know the backup position? What if some transactions were executed on the master after that backup?

Actually, when GTID is enabled, mysqldump includes the last transaction ID (GTID) at the time of taking the backup:

-- -- GTID state at the beginning of the backup -- SET @@GLOBAL.GTID_PURGED='b9b4712a-df64-11e3-b391-60672090eb04:1-7';

After restoring the backup the variable GTID_EXECUTED will be equal to GTID_PURGED (the above value) and when the slave starts it first sends the range of GTIDs it has executed (GTID_EXECUTED) to the master so that the master can sends back every missing transaction which was not applied yet on the slave.

Migration from classic replication to GTID replication How to perform the migration?

To migrate an already running replication using the classical method to GTID replication, the following steps should be done:

  • Ensure that all servers (master and slaves) are in the same point by setting the master server as read only (SET GLOBAL read_only=ON;) and wait until all slaves catch up the master's data.
  • Shutdown MySQL on all servers and add the GTID variables to the configuration files.
  • Beside the GTID variables, add read-only to the master's configuration and skip-slave-start to the slaves configurations.
  • Start MySQL service on all servers.
  • Issue the change master command with MASTER_AUTO_POSITION=1 on all slaves and then start them.
  • Make the master writable again by SET GLOBAL read_only=OFF; (don't forget to remove/hash it from the master's my.cnf file as well).
Is online migration from classic to GTID replication available?

At the time of writing this article, the online migration is not applicable - as you can see from the above steps - we have to shutdown ALL servers at the same time and that is because of two reasons:

  • GTID can NOT be enabled online because GTID_MODE is a read only variable (having this variable to be dynamic is already in Oracle's plan).
  • Replication can NOT be established between two or more servers having different values for GTID_MODE, i.e. either GTID is enabled on ALL servers or disabled on ALL servers.
Workaround ??

There's a feature request (by MySQL Devs team at Booking.com) to have an extra GTID mode (ANONYMOUS_IN-GTID_OUT) which allows a slave to receives anonymous transactions (transactions from master having GTID_MODE = OFF which do not have GTIDs) and assigns GTIDs for those transactions. In this case, this slave could be used as an intermediate server between master having GTID disabled and slaves having GTID enabled (it will be slave for the master and master for the other slaves)

The online migration steps would be:

  • Restart a slave (lets name it slaveA) using the GTID_MODE = ANONYMOUS_IN-GTID_OUT.
  • Rolling restart to the other slaves to use the normal GTID_MODE=ON and pointing them to slaveA as a new master.
  • Point the application to write to slaveA instead of the old master.
  • Restart the old master to use GTID_MODE=ON and having slaveA as a master.

Note: This is not yet available in Oracle binaries

More information on this could be find here.

GTID Benefits
  • Simplifies the setup of MySQL replication as master's binary logs information is not needed anymore (binary log file name and position).
  • Consistency is guaranteed between master and slave as the committed transaction on the master will be applied only once on the slave.
  • Simple to determine whether masters and slaves are consistent or not.
  • Fail-over process is much easier. When the master fail to operate, no need to calculate a slave's binary logs information before promoting it to be new master. MASTER_AUTO_POSITION=1 will do the job as all transactions in all servers inside the replication have the same GTID.
  • Automatic fail-over scripts is now much easier to implement.

In a future post, I will write about how to troubleshoot GTID replication.

Backup Manager for MySQL, MariaDB and Percona Server (mysql_bman)

Shinguz - Tue, 2014-05-06 17:28
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

How to Setup MySQL Master/Slave Replication ?

Abdel-Mawla Gharieb - Thu, 2014-04-24 15:53

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 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.

Setting the right GCache size in Galera Cluster

Abdel-Mawla Gharieb - Thu, 2014-04-17 13:52

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.

Impact of General Query Log on MySQL Performance

Abdel-Mawla Gharieb - Tue, 2014-04-08 11:19

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: 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.

Online DDL vs pt-online-schema-change

Abdel-Mawla Gharieb - Wed, 2014-02-12 18:14

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.

MySQL single query performance - the truth!

Shinguz - Fri, 2013-12-13 17:33
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.

Impact of column types on MySQL JOIN performance

Shinguz - Wed, 2013-12-11 20:12
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;

Workbench starting/stopping multiple instance set-ups with myenv

Abdel-Mawla Gharieb - Sat, 2013-11-23 16:03
Table of Content
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.

Galera Cluster 3.1 GA is out!

Shinguz - Wed, 2013-11-13 11:14

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:


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...

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