Setting Up Master-Master Replication With MySQL 5 On Debian Etch

Version 1.0
Author: Falko Timme <ft [at] falkotimme [dot] com>
Last edited 10/15/2007

Since version 5, MySQL comes with built-in support for master-master replication, solving the problem that can happen with self-generated keys. In former MySQL versions, the problem with master-master replication was that conflicts arose immediately if node A and node B both inserted an auto-incrementing key on the same table. The advantages of master-master replication over the traditional master-slave replication are that you don't have to modify your applications to make write accesses only to the master, and that it is easier to provide high-availability because if the master fails, you still have the other master.

I do not issue any guarantee that this will work for you!

1 Preliminary Note

In this tutorial I will show how to replicate the database exampledb from the server server1.example.com with the IP address 192.168.0.100 to the server server2.example.com with the IP address 192.168.0.101 and vice versa. Each system is the slave of the other master and the master of the other slave at the same time. Both systems are running Debian Etch; however, the configuration should apply to almost all distributions with little or no modifications.

2 Installing MySQL 5.0

If MySQL 5.0 isn't already installed on server1 and server2, install it now:

server1/server2:

apt-get install mysql-server-5.0 mysql-client-5.0

To make sure that the replication can work, we must make MySQL listen on all interfaces, therefore we comment out the line bind-address = 127.0.0.1 in /etc/mysql/my.cnf:

server1/server2:

vi /etc/mysql/my.cnf

[...]
# Instead of skip-networking the default is now to listen only on
# localhost which is more compatible and is not less secure.
#bind-address           = 127.0.0.1
[...]

Restart MySQL afterwards:

server1/server2:

/etc/init.d/mysql restart

Then check with

server1/server2:

netstat -tap | grep mysql

that MySQL is really listening on all interfaces:

server1:~# netstat -tap | grep mysql
tcp        0      0 *:mysql                 *:*                     LISTEN     2671/mysqld
server1:~#

Afterwards, set a MySQL password for the user root@localhost:

server1/server2:

mysqladmin -u root password yourrootsqlpassword

Next we create a MySQL password for root@server1.example.com:

server1:

mysqladmin -h server1.example.com -u root password yourrootsqlpassword

Now we set up a replication user slave2_user that can be used by server2 to access the MySQL database on server1:

server1:

mysql -u root -p

On the MySQL shell, run the following commands:

server1:

GRANT REPLICATION SLAVE ON *.* TO 'slave2_user'@'%' IDENTIFIED BY 'slave2_password';
FLUSH PRIVILEGES;
quit;

Now we do the last two steps again on server2:

server2:

mysqladmin -h server2.example.com -u root password yourrootsqlpassword

mysql -u root -p

GRANT REPLICATION SLAVE ON *.* TO 'slave1_user'@'%' IDENTIFIED BY 'slave1_password';
FLUSH PRIVILEGES;
quit;

3 Some Notes

In the following I will assume that the database exampledb is already existing on server1, and that there are tables with records in it. We will set up replication of exampledb to server2, and afterwards we set up replication of exampledb from server2 to server1.

Before we start setting up the replication, we create an empty database exampledb on server2:

server2:

mysql -u root -p

CREATE DATABASE exampledb;
quit;

4 Setting Up Replication

Now we set up master-master replication in /etc/mysql/my.cnf. The crucial configuration options for master-master replication are auto_increment_increment and auto_increment_offset:

• auto_increment_increment controls the increment between successive AUTO_INCREMENT values.
• auto_increment_offset determines the starting point for AUTO_INCREMENT column values.

Let's assume we have N MySQL nodes (N=2 in this example), then auto_increment_increment has the value N on all nodes, and each node must have a different value for auto_increment_offset (1, 2, ..., N).

Now let's configure our two MySQL nodes:

server1:

vi /etc/mysql/my.cnf

Search for the section that starts with [mysqld], and put the following options into it (commenting out all existing conflicting options):

[...]
[mysqld]
server-id = 1
replicate-same-server-id = 0
auto-increment-increment = 2
auto-increment-offset = 1

master-host = 192.168.0.101
master-user = slave1_user
master-password = slave1_password
master-connect-retry = 60
replicate-do-db = exampledb

log-bin = /var/log/mysql/mysql-bin.log
binlog-do-db = exampledb

relay-log = /var/lib/mysql/slave-relay.log
relay-log-index = /var/lib/mysql/slave-relay-log.index

expire_logs_days        = 10
max_binlog_size         = 500M
[...]

Then restart MySQL:

server1:

/etc/init.d/mysql restart

Now do the same on server2:

server2:

vi /etc/mysql/my.cnf

[...]
server-id = 2
replicate-same-server-id = 0
auto-increment-increment = 2
auto-increment-offset = 2

master-host = 192.168.0.100
master-user = slave2_user
master-password = slave2_password
master-connect-retry = 60
replicate-do-db = exampledb

log-bin= /var/log/mysql/mysql-bin.log
binlog-do-db = exampledb

relay-log = /var/lib/mysql/slave-relay.log
relay-log-index = /var/lib/mysql/slave-relay-log.index

expire_logs_days        = 10
max_binlog_size         = 500M
[...]

server2:

/etc/init.d/mysql restart

Next we lock the exampledb database on server1, find out about the master status of server1, create an SQL dump of exampledb (that we will import into exampledb on server2 so that both databases contain the same data), and unlock the database so that it can be used again:

server1:

mysql -u root -p

On the MySQL shell, run the following commands:

server1:

USE exampledb;
FLUSH TABLES WITH READ LOCK;
SHOW MASTER STATUS;

The last command should show something like this (please write it down, we'll need it later on):

mysql> SHOW MASTER STATUS;
+------------------+----------+--------------+------------------+
| File             | Position | Binlog_Do_DB | Binlog_Ignore_DB |
+------------------+----------+--------------+------------------+
| mysql-bin.000009 |       98 | exampledb    |                  |
+------------------+----------+--------------+------------------+
1 row in set (0.00 sec)

mysql>

Now don't leave the MySQL shell, because if you leave it, the database lock will be removed, and this is not what we want right now because we must create a database dump now. While the MySQL shell is still open, we open a second command line window where we create the SQL dump snapshot.sql and transfer it to server2 (using scp):

server1:

cd /tmp
mysqldump -u root -pyourrootsqlpassword --opt exampledb > snapshot.sql
scp snapshot.sql root@192.168.0.101:/tmp

Afterwards, you can close the second command line window. On the first command line window, we can now unlock the database and leave the MySQL shell:

server1:

UNLOCK TABLES;
quit;

On server2, we can now import the SQL dump snapshot.sql like this:

server2:

/usr/bin/mysqladmin --user=root --password=yourrootsqlpassword stop-slave
cd /tmp
mysql -u root -pyourrootsqlpassword exampledb < snapshot.sql

Afterwards, we must find out about the master status of server2 as well and write it down:

server2:

mysql -u root -p

USE exampledb;
FLUSH TABLES WITH READ LOCK;

SHOW MASTER STATUS;

mysql> SHOW MASTER STATUS;
+------------------+----------+--------------+------------------+
| File             | Position | Binlog_Do_DB | Binlog_Ignore_DB |
+------------------+----------+--------------+------------------+
| mysql-bin.000009 |      783 | exampledb    |                  |
+------------------+----------+--------------+------------------+
1 row in set (0.00 sec)

mysql>

Then unlock the tables:

server2:

UNLOCK TABLES;

and run the following command to make server2 a slave of server1 (it is important that you replace the values in the following command with the values you got from the SHOW MASTER STATUS; command that we ran on server1!):

CHANGE MASTER TO MASTER_HOST='192.168.0.100', MASTER_USER='slave2_user', MASTER_PASSWORD='slave2_password', MASTER_LOG_FILE='mysql-bin.000009', MASTER_LOG_POS=98;

Finally start the slave:

server2:

START SLAVE;

Then check the slave status:

server2:

SHOW SLAVE STATUS;

It is important that both Slave_IO_Running and Slave_SQL_Running have the value Yes in the output (otherwise something went wrong, and you should check your setup again and take a look at /var/log/syslog to find out about any errors):

mysql> SHOW SLAVE STATUS;
+----------------------------------+---------------+-------------+-------------+---------------+------------------+---------------------+--------------------+---------------+-----------------------+------------------+-------------------+-----------------+---------------------+--------------------+------------------------+-------------------------+-----------------------------+------------+------------+--------------+---------------------+-----------------+-----------------+----------------+---------------+--------------------+--------------------+--------------------+-----------------+-------------------+----------------+-----------------------+
| Slave_IO_State                   | Master_Host   | Master_User | Master_Port | Connect_Retry | Master_Log_File  | Read_Master_Log_Pos | Relay_Log_File     | Relay_Log_Pos | Relay_Master_Log_File | Slave_IO_Running | Slave_SQL_Running | Replicate_Do_DB | Replicate_Ignore_DB | Replicate_Do_Table | Replicate_Ignore_Table | Replicate_Wild_Do_Table | Replicate_Wild_Ignore_Table | Last_Errno | Last_Error | Skip_Counter | Exec_Master_Log_Pos | Relay_Log_Space | Until_Condition | Until_Log_File | Until_Log_Pos | Master_SSL_Allowed | Master_SSL_CA_File | Master_SSL_CA_Path | Master_SSL_Cert | Master_SSL_Cipher | Master_SSL_Key | Seconds_Behind_Master |
+----------------------------------+---------------+-------------+-------------+---------------+------------------+---------------------+--------------------+---------------+-----------------------+------------------+-------------------+-----------------+---------------------+--------------------+------------------------+-------------------------+-----------------------------+------------+------------+--------------+---------------------+-----------------+-----------------+----------------+---------------+--------------------+--------------------+--------------------+-----------------+-------------------+----------------+-----------------------+
| Waiting for master to send event | 192.168.0.100 | slave2_user |        3306 |            60 | mysql-bin.000009 |                  98 | slave-relay.000002 |           235 | mysql-bin.000009      | Yes              | Yes               | exampledb       |                     |                    |                        |                         |                             |          0 |            |            0 |                  98 |             235 | None            |                |             0 | No                 |                    |                    |                 |                   |                |                     0 |
+----------------------------------+---------------+-------------+-------------+---------------+------------------+---------------------+--------------------+---------------+-----------------------+------------------+-------------------+-----------------+---------------------+--------------------+------------------------+-------------------------+-----------------------------+------------+------------+--------------+---------------------+-----------------+-----------------+----------------+---------------+--------------------+--------------------+--------------------+-----------------+-------------------+----------------+-----------------------+
1 row in set (0.00 sec)

mysql>

Afterwards, you can leave the MySQL shell on server2:

server2:

quit

Now the replication from server1 to server2 is set up. Next we must configure replication from server2 to server1.

To do this, we stop the slave on server1 and make it a slave of server2:

server1:

mysql -u root -p

STOP SLAVE;

Make sure that you use the values of the SHOW MASTER STATUS; command that you ran on server2 in the following command:

server1:

CHANGE MASTER TO MASTER_HOST='192.168.0.101', MASTER_USER='slave1_user', MASTER_PASSWORD='slave1_password', MASTER_LOG_FILE='mysql-bin.000009', MASTER_LOG_POS=783;

Then start the slave on server1:

server1:

START SLAVE;

Then check the slave status:

server1:

SHOW SLAVE STATUS;

It is important that both Slave_IO_Running and Slave_SQL_Running have the value Yes in the output (otherwise something went wrong, and you should check your setup again and take a look at /var/log/syslog to find out about any errors):

mysql> SHOW SLAVE STATUS;
+----------------------------------+---------------+-------------+-------------+---------------+------------------+---------------------+--------------------+---------------+-----------------------+------------------+-------------------+-----------------+---------------------+--------------------+------------------------+-------------------------+-----------------------------+------------+------------+--------------+---------------------+-----------------+-----------------+----------------+---------------+--------------------+--------------------+--------------------+-----------------+-------------------+----------------+-----------------------+
| Slave_IO_State                   | Master_Host   | Master_User | Master_Port | Connect_Retry | Master_Log_File  | Read_Master_Log_Pos | Relay_Log_File     | Relay_Log_Pos | Relay_Master_Log_File | Slave_IO_Running | Slave_SQL_Running | Replicate_Do_DB | Replicate_Ignore_DB | Replicate_Do_Table | Replicate_Ignore_Table | Replicate_Wild_Do_Table | Replicate_Wild_Ignore_Table | Last_Errno | Last_Error | Skip_Counter | Exec_Master_Log_Pos | Relay_Log_Space | Until_Condition | Until_Log_File | Until_Log_Pos | Master_SSL_Allowed | Master_SSL_CA_File | Master_SSL_CA_Path | Master_SSL_Cert | Master_SSL_Cipher | Master_SSL_Key | Seconds_Behind_Master |
+----------------------------------+---------------+-------------+-------------+---------------+------------------+---------------------+--------------------+---------------+-----------------------+------------------+-------------------+-----------------+---------------------+--------------------+------------------------+-------------------------+-----------------------------+------------+------------+--------------+---------------------+-----------------+-----------------+----------------+---------------+--------------------+--------------------+--------------------+-----------------+-------------------+----------------+-----------------------+
| Waiting for master to send event | 192.168.0.101 | slave1_user |        3306 |            60 | mysql-bin.000009 |                 783 | slave-relay.000002 |           235 | mysql-bin.000009      | Yes              | Yes               | exampledb       |                     |                    |                        |                         |                             |          0 |            |            0 |                 783 |             235 | None            |                |             0 | No                 |                    |                    |                 |                   |                |                     0 |
+----------------------------------+---------------+-------------+-------------+---------------+------------------+---------------------+--------------------+---------------+-----------------------+------------------+-------------------+-----------------+---------------------+--------------------+------------------------+-------------------------+-----------------------------+------------+------------+--------------+---------------------+-----------------+-----------------+----------------+---------------+--------------------+--------------------+--------------------+-----------------+-------------------+----------------+-----------------------+
1 row in set (0.00 sec)

mysql>

Afterwards you can leave the MySQL shell:

quit

If nothing went wrong, MySQL master-master replication should now be working. If it isn't, please check /var/log/syslog for MySQL errors on server1 and server2.

5 Links

• MySQL: http://www.mysql.com
• Debian: http://www.debian.org