June 2007

I am invited to participate in the Java Certification Day on 21 June in Hong Kong. The talk mainly introduces some new technologies in the Java World, but I think they are not quite useful.

The first talk I attended is “Java Programming with no Java *code*”. The name is so attracting but the content is rubbish. It just introduces how Netbeans creates a BPEL project. It is not really about JAVA programming, it’s a construction of SOA projects.

The second talk is about non-intrusive monitoring using JMX. Other than the introduction of two softwares, JConsole and JFluid, I don’t think the talk is worth attending. And the last talk is on “High Performance Java Technology in a Multi-core World”, it did state how hardward can help to improve the performance of Java applications, but that’s not my knowledge field. That’s why I leave earlier (actually it overruns a lot).

After that, I went outside and proceeded to the promotional counter. After discussion with an Education Manager, I am much clear about my certification path. Personally, I want to take the SCEA exam as a long-term objective. Before that, I will take SCWCD and SCBCD which I did set as objective this year. Thus, I bought two discounted exam coupons and two corresponding ePractice exams. Totally, it costs me HKD2000. The price is acceptable and I hope this is worth and get me to a good career in the next job.

It is so surprised to me that MySQL Database does not support well in the use of subquery, which is the very basic syntax that we used in SQL.

These days, I received a performance report from my user and saying that one of our operations is very slow. A single SQL needs 1.5 minute to run on recent Dual Core server. After some investigations, I locked the target to one particular SQL during the execution of the operation. This SQL makes use of subquery which is in this syntax: WHERE…IN.

Google tells me that this issue has been reported since 2004 in early version of MySQL like 4.x. The problem was not focused in any of the updates afterward. After that, I read the article on the topic
How to optimize subqueries and joins in MySQL

This article not only shows the workaround to the issue, it also explains why the performance is so bad. It is briefly due to the reason that MySQL runs in an outside-inside manner, which means it first executes the main query and run the subquery later.

I am happy that there is a workaround to the issue, but I just don’t understand why MySQL does not fix the internal logic using this approach and need us, application developers, to do the workaround.  Perhaps, that’s the problem of open-source project.