MySQL replication is fast, easy to use, and reliable, but once it breaks, it can be very hard to figure out what the problem is. One of the concerns often raised is that events are corrupted, either through failing hardware, network failure, or software bugs. Even though it is possible to handle errors during transfer over the network using an SSL connection, errors here is rarely the problem. A more common problem (relatively) is that the events are corrupted either due to a software bug, or hardware error.

To be able to better handle corrupted events, the replication team has added replication event checksums to MySQL 5.6 Milestone Development Release.

The replication event checksums are added to each event as it is written to the binary log and are used to check that nothing happened with the event on the way to the slave. Since the checksums are added to …

I saw that both Haidong Ji and Geert VanderKelen have proposed a Python monitor for MySQL replication, calling it the "poor man's version".
See Poor man’s MySQL replication monitoring and Geert's Refactored: Poor man’s MySQL replication monitoring.
Having Python in your server doesn't really qualify as "poor man". In many cases it's a luxury, and thus, here's my shot at the problem, using a Bash shell script.
Unlike its Python-based competition, this version also checks that the slave is replicating from the intended master, and that it is not lagging behind.

#!/bin/bash

USERNAME=msandbox
PASSWORD=msandbox
EXPECTED_MASTER_HOST=127.0.0.1
EXPECTED_MASTER_PORT=27371

SLAVE_HOST=127.0.0.1 …

Version 1.2 of Slave Readahead is now available for download here. If you don't know what this little project is about, it is used to pre-warm the MySQL Cache for the Replication thread on MySQL slaves.

It is built to support MySQL 5.5 and up only, as it uses some new commands in MySQL (like the SHOW RELAYLOG EVENTS admin command). For more information regarding this little project, either read this blogpost or download the documentation for the project.

/Karlsson

Isolation is an important part of ACID properties that guarantee that transactions are processed in a reliable manner. But there are four different levels of isolation available and you have to understand each one of them to be able to select the correct one for your needs. This post intends on explaining the four levels together with their effects on locking and performance.

The O'Reilly MySQL 2011 conference is coming up fast.  It should be a good conference as it covers the increasingly diverse MySQL community and MySQL alternatives very well.   As usual, there are some painful choices about which talks to attend.  I'm doing two talks myself that I hope you have on your list:

• Curing Replication Deprivation with Tungsten -- A tutorial together with my colleague Ed Archibald.  It covers everything you ever wanted to know about how to use parallel replication, handle multi-master/multi-source, replication to PostgreSQL/Oracle, etc.  We will have a short section at the end about how to build full clusters with Tungsten Enterprise.   Giuseppe Maxia is threatening to join and do some of his famous …

Many people have a master/slave MySQL environment of various different topologies, and many use the slave as a backup.
Is your slave schema identical to your production schema? As long as an SQL statements completes without an error, your slave schema can differ. Common examples are different indexes or storage engines for example. However if you use the slave as backup, you want to ensure when you recover, you are recovering a production environment, not a slave environment.

While the changes may be small, the can lead to different results. For a client I found that the default value of a price field was 10.00 in one schema and 0.00 in another. Not withstanding using defaults for important fields and not defining in an INSERT is a different issue, it highlighted the different schemas can easily exist.

My tool of choice is SchemaSync. The reason why I like this command is …

I have been working with MySQL replication for quite a while. I have dealt with simple replication setups and I have experimented with complex ones. Five years ago I wrote an article about advanced MySQL replication, which was mostly a dream on what you could do with imagination and skill, but the matter from that article is still not even remotely ready for production. Yet, since that article, I have been approached by dozens of people who wanted to know how to make the multiple master dream become reality. To all of them, I had to say, "sorry, this is just a proof of concept.Come back in a few years, it may become possible". It still isn't.
Despite its latest great technological advance, MySQL native replication is is very poor of topologies. What you can do with MySQL native replication is master-to-slave (which also includes relayed …

This title is not nearly as snappy as Yeats' line from "The Second Coming," but it will have to do.  Conflict resolution has been a holy grail for us on Tungsten--we had people asking for it when MySQL was still MySQL AB, lo these many years ago.   Well, it's finally starting to happen after about a year of work.  

Let's start with a simple multi-master configuration.  To replicate bi-directionally between two masters, you typically run Tungsten replicator on each master with two replication services on each master.  The first local service reads the master log.  The second remote service is a slave of the other master.  It looks like the following picture:

…

A user on a linux user group mailing list asked about this, and I was one of the people replying. Re-posting here as I reckon it’s of wider interest.

> [...] tens of gigs of data in MySQL databases. > Some in memory tables, some MyISAM, a fair bit InnoDB. According to my > understanding, when one doesn’t have several hours to take a DB > offline and do dbbackup, there was/is ibbackup from InnoBase.. but now > that MySQL and InnoBase have both been ‘Oracle Enterprised’, said > product is now restricted to MySQL Enterprise customers.. > > Some quick searching has suggested Percona XtraBackup as a potential > FOSS alternative. > What backup techniques do people employ around these parts for backups > of large mixed MySQL data sets where downtime *must* be minimised? > > Has your backup plan ever been put to the test?

You should put it to the test regularly, not just when it’s needed. …

So, back when we released our first beta in September, one of the many responses was this

The comments about the reliability / durability of the log definitely struck me as testing we needed.

It’s taken a while (we had this GA thing we were working on…), but we finally have crash and recover testing of the innodb transaction log and the slave plugin.

Here is what happens for the innodb-based log:

• Set up the test servers and start the randgen with the trx_log grammars.  I’ll point you …