On Wednesday May 16th, we ran a webinar to provide an overview of all of the new replication features and enhancements that are previewed in the MySQL 5.6 Development Release – including Global Transaction IDs, auto-failover and self-healing, multi-threaded, crash-safe slaves and more.

Collectively, these new capabilities enable MySQL users to scale for next generation web and cloud applications.

Attendees posted a number of great questions to the MySQL developers, serving to provide additional insights into how these new features are implemented. So I thought it would be useful to post those below, for the benefit of those unable to attend the live webinar (note, you can listen to the On-Demand replay which is available now).

Before getting to the Q&A, there are a couple of other resources that maybe useful to …

High availability is about more than just making sure that applications can get to your data, even if there is a failure:

How about when you are upgrading your database schema What if you need to add memory to a database server or reconfigure/restart MySQL If your apps want to read data from a MySQL slave, how can you be sure they are not reading stale data without re-coding your apps What

An increasing number of organizations run applications that depend on MySQL multi-master replication between remote sites.   I have worked on several such implementations recently.  This article summarizes the lessons from those experiences that seem most useful when deploying multi-master on existing as well as new applications.

Let's start by defining terms.  Multi-master replication means that applications update the same tables on different masters, and the changes replicate automatically between those masters.  Remote sites mean that the masters are separated by a wide area network (WAN), which implies high average network latency of 100ms or more.  WAN network latency is also characterized by a long tail, ranging from seconds due to congestion to hours or even days if a ship runs over the wrong undersea cable.
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New versions of MySQL are always interesting to try out. Often they have features which I may have asked for myself so it’s satisfying to see them eventually appear on a system I use. Often other new features make life easier for the DBA. Finally we hope overall performance will improve and managing the server(s) will be come easier.

So I had a system which needs to make heavy writes, and performance was a problem, even when writing to SSDs. Checkpointing seemed to be the big issue and the ib_logfile size in MySQL 5.5 is limited to 4 GB. That seems a lot, but once MySQL starts to fill these files (and this happens at ~70% of the total I believe),  checkpointing kicks in heavily, and slows things down.  So the main reason for trying out MySQL 5.6 was to see how things performed with larger ib_logfiles. (Yes, MariaDB 5.5 can do this too.)

Things improved a lot for my specific workload which was great news, but one thing …

Experienced MySQL DBAs know that temp tables cause major problems for MySQL replication.  It turns out the converse is also true:  replication can cause major problems for temporary tables.

In a recent customer engagement we enabled Tungsten Replicator with a MySQL application that originally ran on a server that did not use replication.  QA promptly discovered reports that previously ran in 10 seconds were now running in as many minutes.  It turned out that the reports used temp tables to assemble data, and these were being written into the master binlog.  This created bloated binlogs and extremely slow reports.  We fixed the problem by enabling row replication (i.e., binlog-format=row in my.cnf).

A common DBA response to temp table problems is to try to eliminate them completely, as suggested in the excellent …

Thanks to all of those who came by our booth and to see Leif’s presentation on Read Optimization, and to my Lightning Talk on OLTP and OLAP at the Percona MySQL Conference and Expo. It was an incredible week and a great place to launch TokuDB v6.0 from! A big thanks to Percona for a great event, to …

MySQL 5.1 or newer can sometimes start throwing a strange message into an error log. The message states that a query was unsafe for binary logging along with some additional information. What does it mean? Is it a problem?

From time to time you might spot MySQL error log filling with the following warning:

“[Warning] Unsafe statement written to the binary log using statement format since BINLOG_FORMAT = STATEMENT. The statement is unsafe because it uses a LIMIT clause. This is unsafe because the set of rows included cannot be predicted. Statement: DELETE FROM score WHERE user_id = 12345 AND created = ’2012-04-15′ LIMIT 1″

If binary logging is enabled and the log format is set to STATEMENT, MySQL generates such message when it considers that a query is ambiguous and could behave differently each time it executes against the same data set. Such situation could happen, for example, on a …

Lets see what HA solutions can be designed in mysql and where are they suited.

1. Single master - single slave.

M(RW)|S(R) A simple master slave solution can be used for a small site - where all the inserts go into the master and some (non-critical) requests are served from the slave. In case if the master crashes, the slave can be simply promoted as the master - once it has replicated the "

The new MySQL 5.6 Development Milestone Release (DMR) includes many new enhancements. One of the most impressive is the use of Global Transaction Identifiers (GTIDs) for replication. With GTIDs enabled, administrators no longer need to keep track of binary log files and positions. In a nutshell, GTIDs simplify the setup and maintenance of replication.

MySQL Utilities has taken this a step further by providing two new utilities that automate two of the most complex replication administration tasks - switchover and failover. Switchover is changing the role of an active, healthy master to one of its slaves whereas failover is the act of promoting a candidate slave to become the new master. Clearly, switchover is an elective operation and failover is performed when there are issues with the master.

The GTID utilities are included in release-1.0.5 of MySQL Utilities. They are included as a plugin for MySQL Workbench or via …

As the Product Manager for the MySQL database it is always great to announce when the MySQL Engineering team delivers another great product release.  As a field DBA and developer it is even better when that release contains improvements and innovation that I know will help those currently using MySQL for apps that range from modest intranet sites to the most highly trafficked web sites on the web.  That said, it is my pleasure to take my hat off to MySQL Engineering for today's release of the MySQL 5.6.5 Development Milestone Release ("DMR"). The new highlighted features in MySQL 5.6.5 are discussed here:

New Self-Healing Replication Clusters
The 5.6.5 DMR improves MySQL Replication by adding Global Transaction Ids and automated utilities for self-healing Replication clusters.  Prior to 5.6.5 this has been somewhat of a pain point for MySQL users with most developing custom solutions or looking to costly, …