Hi MMM users.
On this post I just want to let you know that I will speak up at Froscon in Cologne, Germany next week (21st, August).
My speech will cover an architecture what I have used to "keep your mysql backend online, no matter what", what is the title of the presentation too.
This architecture includes MMM as a very important part of it.
Please visit the conference's website and join us there if you can.
There is a nagios plugin available on the MMM's google-code page, but if you didn't find it yet, here it is:
You can call this plugin over nrpe. I'm already working on to fork a version which more useful with passive checks.
This plugin was developed by Ryan Lowe (Percona).
There is no centralized authentication for mysql. You have to set up your user accounts individually for each of your mysql servers. You can use replication, but that would mean, your master servers must have the same authentication privileges as your slaves have. What about security?
So, here is a little workaround that I did and I can't find the same anywhere.
We all knew that we are risking with MMM. Risking, and placing availability as a more important like consistency. But non of us can risk loosing data forever but we show using it, regarding to our conversations think: "I can fix my data later on, but I can’t turn back time and prevent the downtime. (Pascal Hofmann@xaprb.com)".
As I wrote before about staying online, now let me write about how to stay consistent.
We all know, mmm is not like a key of salvation, but its getting close to it . While MySQL doesn't support multi-master-slave environments from it's source code, we will sleep badly wondering on the safety of our precious databases.
But its not just about MMM, a few days ago we ran in to a well known InnoDB "feature". Its about the auto increment counter determination on restart. InnoDB try to count the next auto increment value on MySQL restart what can screw up things in the replication as in your data integrity too (http://dev.mysql.com/doc/refman/5.1/en/innodb-auto-increment-handling.html) what could be risky when you are about to use mmm, because you can restart your masters whenever you just want to.
In this post I'm using maatkit to verify and restore the rows without locking or downtime.