So far, I've never blogged about the work I've been doing for the MySQL Certification Team. Time to change that: I'd like to tell you a little bit more about the things I've been doing since I joined MySQL AB.

I started in July 2006 and from the on, I've been almost exclusively occupied with activities to develop certification for MySQL 5.1 Cluster.
A summary of the things I have done so far:

• 
  
• Working with the training department to design an outline for the cluster exam
  
• Interviewing MySQL Cluster developers to check all kinds of facts and details of the behaviour of MySQL 5.1 Cluster
  
• Creating, reviewing …

Alfresco, the leader in open source document management, has now made a subtle but significant change in their licensing.  Effective immediately, Alfresco is being released under the GPL rather than their previous Mozilla-derived license. 

While there's nothing wrong with the Mozilla license they used, my take is, it had two things that were slowing things down.  First of all, it's yet-another-license, even if it is based on a reasonably well-known and accepted license.  So inevitably that means that lawyers start asking lots of questions, at least compared to the GPL which is fairly well understood.  (The GPL is not perfect, but in my view, it's the best going.  And partly because it's widely used by Linux, MySQL and others, it's understood.)  The second issue is that …

Changing hats

I have put on the hat of a MySQL user, a customer, as opposed to a developer (Federated Storage Engine, DBD::mysql) these last couple months with my new employer, Grazr. One of the things we need is a whole replication set-up, with read-only slaves, and write masters. Thats master(s), with an 's', plural. We need a set-up where we have two data centers. In each of the data centers, there is a master and it's slaves, all on the same network. That master needs to replicate to another slave, which is also a master, in its own data center, where it has its own slaves. The idea is that the web servers running mod_perl applications in each data center send all their read-only queries to slaves running on the same server, and all write-only queries to the master in that data center.

How does one go about setting up a multi-master replication scheme, also having slaves in the mix? There are several articles …

Solid has released 5.0.27-0059. It is primarily a bug fixing release. You can get it from the usual place (http://dev.soliddb.com/download/).

Today Alfresco announced that it has gone 100% GPL. As you might imagine, I'm ecstatic about the move (and have been working toward this since I joined Alfresco in 2005). Actually, I think it would be fair to say that everyone in the company is ecstatic about the move. It makes things easier for marketing, for engineering, and for sales. (Gasp! Did he really say "GPL" and "sales" in the same paragraph? :-)

As CNET has covered, this move is in part designed to help expand our already healthy community. But it's also about driving a stake into the heart of our outdated, expensive, proprietary competitors, as John Powell, Alfresco's CEO …

I recently found a great article on mysql performance blog giving you a short and precise description of what to tune in the first place.

This is a must!

[Note: Most of this comes from the standard job description... More from me at the bottom.]

Do you prefer to work on a wide variety of projects in a challenging environment? Have you ever felt that your job was monotonous or repetitive? Are you a builder, not a maintainer? Do you enjoy change? If so, Yahoo's platform engineering may have the job for you. Come be a part of our Tiger team.

The Tiger team at Yahoo is dedicated to providing highly skilled, senior engineers to a variety of projects. Tigers perform as an internal "consulting" team, providing short term resourcing to dedicated product engineering teams that have critical or time sensitive problems. In the past Tigers have contributed to highly visible products such as Y! Mail and anti-spam, Y! Messenger and Y! Alerts.

The ideal Tiger is a technically strong engineer who likes a dynamic environment and assignments that change every 6-8 months. As a member of the …

In a previous post I mentioned about patches needed to accomadate the new DST changes for Sql Server. (I know, this is one of Dannyman’s favorite subjects ;))

For MySQL, obviously you need to patch the host server first. Then you need to find out if MySQL needs separate work. Here is a note I gathered. Let me know if I am wrong on this or if there is a better way.

1. Get into mysql and do \s to find out the version of your MySQL.

If it is prior to 4.1.3, don’t worry about it.

Else

2. Do select @@global.time_zone;

If the result is SYSTEM, don’t worry about it.

Else

You need to load time zone info, usually at /usr/share/zoneinfo into your mysql database, by running something like:

# …

Here is MySQL's nested outer joins optimization cheat sheet:

• Conversions:
  
  • RIGHT JOIN is converted to LEFT JOIN. FULL JOIN is not supported.
  • Outer joins are converted to inner joins when possible
• Constraints on join order:
  • "Outer tables go first"
  • "No interleaving"
• Table access rules:
  • "Inner" table access methods are constructed from parts of the ON condition. WHERE condition can't be used to construct table accesses.
  • Parts of ON condition are checked as soon as possible
  • Parts of the WHERE condition
    - are not checked until we've found a row combination that matches the ON clause
    - are checked as soon as possible after that.

Or, in more detail:

…

When you ask someone how to optimize SQL queries you will always get the answer

• enable the slow query log
• set the long-query-time to 1-2 seconds
• enable the logging of query which aren't using an index
• run EXPLAIN on the queries that are shown and optimize them with proper indexes

But how to understand what the EXPLAIN is telling you ?

I picked a query from the ORDER BY RAND article as they became interesting enough to show the different aspects of of a query. They contain:

• Sub-Queries
• Unions
• Special cases
• JOINs
• ORDER BY + LIMIT

If you want to understand how this query was developed, check the original article about …