You mentioned a future post would cover setting up multimaster replication using an already active cluster…is that still in the works? We’re considering doing that and I would love to read your thoughts on it.

thanks for your response. If you set this same configuration on each server, would they not still have clashing auto-increment values? Wouldn’t it be better to set the increment to 2 on each server but the offset to 1 on one and 2 on the other? That way one server would generate odd values and the other even.

Regards, Andrew.

Consider we’ve already set a master-master replication.
Now create following table on Server1:

CREATE TABLE `temp` (
`id` int(10) NOT NULL auto_increment,
PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=12 DEFAULT CHARSET=latin1;

The table will will get replicated on Mysql Server2 in the master-master setup.

Now insert value on Mysql Server1 as follows:
insert into temp values(null);

On Mysql Server2 in replication you will see single row inserted.
Now insert one row from Mysql Server2 as follows:
insert into temp values(null);

You should see an error:
Error ‘Duplicate entry ’1′ for key ‘PRIMARY” on query…

The obvious problem of maintaining auto increments in sync will persist on both mysql servers as AUTO_INCREMENT’s value.

The solution is to use the variables auto_increment_increment and auto_increment_offset as explained below.

- Stop both master-master replication servers.
- Add variables to my.[ini|cnf] file.
Eg. On both the Server’s my.[ini|cnf] add following lines:
auto_increment_increment=1
auto_increment_offset=2
- Restart mysql servers.
- Start slave.

BR
johan

When doing cross-geographical replication, don’t forget to set up replication over SSL, or your data is unencrypted across the network.

Regards