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mmattax
Asked: 2010-05-26 09:32:44 +0800 CST

Can a MySQL slave be a master at the same time?

  • 772

I am in the process of migrating 2 DB servers (Master & Slave) to two new DB Servers (Master and Slave)

DB1 - Master (production)

DB2 - Slave (production)

DB3 - New Master

DB4 - New Slave

Currently I have the replication set up as:

DB1 -> DB2
DB3 -> DB4

To get the production data replicated to the new servers, I'd like to get it "daisy chained" so that it looks like this:

DB1 -> DB2 -> DB3 -> DB4

Is this possible? When I run show master status; on DB2 (the production slave) the binlog possition never seems to change:

+------------------+----------+--------------+------------------+
| File             | Position | Binlog_Do_DB | Binlog_Ignore_DB |
+------------------+----------+--------------+------------------+
| mysql-bin.000020 |       98 |              |                  | 
+------------------+----------+--------------+------------------+

I'm a bit confused as to why the binlog position is not changing on DB2, Ideally it will be the master to DB3.

mysql mysql-replication

5 Answers

  1. Best Answer

    The binlog on DB2 wasn't updating the slave updates. To daisy chain the replication, one must set log-slave-updates in my.conf.

    http://dev.mysql.com/doc/refman/5.1/en/replication-options-slave.html#option_mysqld_log-slave-updates

    • 19

  2. Yes, it is possible :) This is called "Master with Relay Slave" replication and there a lot of documents about it on the net.

    I'd recommend you to take a look at the official documentation here.

    Btw, also take a look at these slides. They've some hints about replication topologies.

    Hope this helps.

    • 11

  3. yes - you can daisy-chain mysql servers, you can even make a circular replication with two or more machines in it. just remember to enable binloging on slave that also acts as master.

    • 3

  4. Yes, it is possible. Realistically, you need a new snapshot of DB2 to build DB3. At that point, if you have a good position, you can either use than for DB4 or take another snapshot of DB3.

    Don't forget to set unique server_id for each server.

    High Performance MySQL is a great book for referencing more advanced MySQL administration.

    • 0

  5. Why not just add DB3 as a new slave, and then promote it to master when you're ready to make the switch? This would give you the temporary added benefit of having multiple slaves, and reduce or eliminate your downtime.

    • 0