We don’t often see this option configured (default: unlimited) but it might be a good idea to set it. What it does is limit the amount of disk space the combined relay logs are allowed to take up.

A slave’s IO_Thread reads from the master and puts the events into the relay log; the slave’s SQL_Thread reads from the relay log and executes the query. If/when replication “breaks”, unless it’s connection related it tends to be during execution of a query. In that case the IO_Thread will keep running (receiving master events and storing in the relay log). Beyond some point, that doesn’t make sense.

The reason for having two separate replication threads (introduced in MySQL 4.0) is that long-running queries don’t delay receiving more data. That’s good. But receiving data is generally pretty fast, so as long as that basic issue is handled, it’s not necessary (for performance) to have the IO_Thread run ahead that far. …

Since the time that I’ve been using MySQL I have filed quite a few bug reports. Some of these have been fixed and many of the bug reports are actually new feature requests. While working with MySQL Enterprise Monitor I’ve probably filed more feature requests than bug reports.

That’s fine of course and my opinion of what is needed in MySQL or Merlin is one thing,  yours or the MySQL developers is something else. We all have our own needs and find things missing which would solve our specific problems.

If I have ten feature requests open and only one could be added to the software I’d also like to be able to say: this feature is the most important one for me.

However, it seems to me that there is no easy way in the mysql bug tracker at the moment to group together different types of new feature requests into groups of related features and then see the different types of …

Database replication is still interesting after all these years.  Two of my talks focused on replication technology were accepted for the upcoming MySQL 2010 Conference.  Here are the summaries.

• Clustering for the Masses - A Gentle Introduction to Tungsten for MySQL 

• Not Your Grandpa’s Replication-The New Wave of MySQL Replication and How It Helps Your Applications

The first talk is a solo presentation covering Tungsten, which creates highly available and scalable database clusters using vanilla MySQL databases linked by flexible …

I have been talking about this for a while, now at last I have found the time to get started! Below is a picture from my 2008 MySQL User Conference presentation. It illustrates how engine level replication works, and also shows how this can be ramped up to provide a multi-master HA setup.


What I now have running is the first phase: asynchronous replication, in a master/slave configuration. The way it works is simple. For every slave in the configuration the master PBXT engine starts a thread which reads the transaction log, and transfers modifications to a thread which applies the changes to PBXT tables on the slave.

Where to get it

I have pushed the changes that do this trick to PBXT 2.0 on Launchpad. The branch to try out is …

As I've been doing the last couple of years, I will be going to the O'Reilly MySQL Conference & Expo. In addition to the tutorial and the replication sessions that I will be holding together with Lars, I will be holding a session about the binary log together with Chuck from the Backup team which the Replication team normally works very close with.

This year, O'Reilly also have a Friend of the Speaker discount of 25% that you can use when you register using the code mys10fsp.

The sessions that we are going to hold are listed below. Note that I am using Microformats, which will allow …

I have recently been trying out semisynchronous replication. This is a new feature added in MySQL 5.5 based on the original google patch.

Installing was very simple and has been covered elsewhere in detail. Suffice to say it was relatively simple to do.

While test I was a bit surprised by some behavior I saw that turned out correct. What I wanted to examine what was semi-synchronous actually does and use cases for it.

The manual defines this feature correctly in very careful language:
If semisynchronous replication is enabled on the master side and there is at least one semisynchronous slave, a thread …

This Thursday (February 11th, 14:00 UTC), Seppo Jaakola & Alex Yurchenko will talk about MySQL Galera Multi-Master Replication. Galera provides synchronous multi-master replication and uses a certification-based replication method for replicating transaction write sets in a DBMS cluster. The replication method requires close co-operation with database transaction processing and DMBS must support a specific replication API to be compatible with Galera. Codership has integrated Galera replication in the InnoDB storage engine, and the resulting MySQL/Galera cluster product has been published as a production-ready GA release in December 2009. The MySQL/Galera release 0.7 is available on the Codership and …

This Thursday (February 11th, 14:00 UTC), Seppo Jaakola & Alex Yurchenko will talk about MySQL Galera Multi-Master Replication. Galera provides synchronous multi-master replication and uses a certification-based replication method for replicating transaction write sets in a DBMS cluster. The replication method requires close co-operation with database transaction processing and DMBS must support a specific replication API to be compatible with Galera. Codership has integrated Galera replication in the InnoDB storage engine, and the resulting MySQL/Galera cluster product has been published as a production-ready GA release in December 2009. The MySQL/Galera release 0.7 is available on the Codership and …

This Thursday (February 11th, 14:00 UTC), Seppo Jaakola & Alex Yurchenko will talk about MySQL Galera Multi-Master Replication. Galera provides synchronous multi-master replication and uses a certification-based replication method for replicating transaction write sets in a DBMS cluster. The replication method requires close co-operation with database transaction processing and DMBS must support a specific replication API to be compatible with Galera. Codership has integrated Galera replication in the InnoDB storage engine, and the resulting MySQL/Galera cluster product has been published as a production-ready GA release in December 2009. The MySQL/Galera release 0.7 is available on the Codership and …

In case you have not noticed, MariaDB is joining the list of projects thinking about how to improve MySQL replication.   The discussion thread starts here on the maria-developers mailing list.

This discussion was jointly started by Monty Program, Codership, and Continuent (my employer) in an effort to push the state of the art beyond features offered by the current MySQL replication.  Now that things are starting to die down with the Oracle acquisition, we can get back to the job of making the MySQL code base …