Archive for March, 2007

Online Vs Offline Applications: Everything old is new again

Released March 28th, 2007

Everyone has probably noticed this already but the old is new again cycle for “online” desktop apps has been shortening at a rapid pace. Everywhere you turn you see people talking about offline and online apps and what should be online vs offline. If you take your time machine back you would see something like the following timeline:

  • 1970s 3270
  • 1980s X terminal
  • 1990s Java applets
  • 2000 Flash
  • 2005 Ajax

Up until about 2000 it was taking 10 years to cycle from “we want everything on our desktop” to “we want everything on the server”. Now the cycle seems to have sped up to every year and then to constant. A couple recent examples of new faces on this old idea are Adobe’s Apollo and Joyent’s Slingshot.

Fundamentally not much has changed from the 1970s. The goal is to centralize computing resources into one place (in the simple view of things) and make issues like software deployment easier.The main difference now is that the industry has come to the point where there isn’t any turning back and everyone has bought on to the need and usefulness of online apps. The main sticking point seems to be finding a way to resolve issues that come up from users being disconnected from time to time. I’ll bet that one won’t be fully resolved until you have connectivity anywhere and everywhere you go.

Posted in Software Development | No Comments »
Tagged:

Tomcat + UTF8 + HTTP Get

Released March 19th, 2007

By default tomcat doesn’t UTF-8 encode get parameters like it does post parameters. This doesn’t seem to be the case with other application servers. So before you get yourself into trouble with your internationalized web application, make sure you make this change.

Posted in Web Development | 1 Comment »
Tagged:

iSeries SQL Performance

Released March 11th, 2007

Our project has entered the stage where we start tuning the data access to improve performance. This project uses Hibernate to access a AS400/iSeries system via the JT400 JDBC driver. My prior experience using the SQL Server
database introduced me to Microsoft’s Query Analyzer, which is a nice tool for identifying where you need to index the database. A bit of searching turned up an IBM tool called Visual Explain that fits the same need. The sysadmin started the profiling tool against my connection, and I ran through a standard usage scenario in our application. Visual Explain showed each query, how long it took, the access strategy, and recommended indexes. This kind of tool is absolutely essential for database performance tuning.

The second important item we learned from this process is the performance difference between a true SQL index on the iSeries and a keyed logical index. From iSeries V4R2 on, SQL indexes have page sizes of 64k. By comparison, a DDS logical will max out at 32k, and will typically be much smaller. The performance is so much better that our customer is converting all all their DDS logical indexes to SQL, even if only their legacy RPG applications use it. This IBM document has a good discussion of this issue.

Posted in System Administration | No Comments »
Tagged:

Hibernate and your Getters and Setters

Released March 11th, 2007

When you’re using Hibernate and are mapping to properties, keep your getters and setters as simple and self-contained as possible. The receiver being initialized may not have any other properties set, and the value being passed may not be fully initialized yet, either.

If you don’t respect these two possibilities, then you will get bit in the butt alot, when you least expect it. To be fair, these situations can happen whether you’re using Hibernate or not, but when we first started using the framework we made lots of assumptions.

Here is a completely ridiculous example that violates the above restrictions:
(more…)

Posted in Software Development | 3 Comments »
Tagged:

Scary apache errors moving from prefork to worker

Released March 7th, 2007

We were helping a client push more data through their apache/tomcat web application running on a Solaris box and decided to switch from the process (prefork) to the threaded(worker) processing model. When we fired up the new apache we started getting errors like these:

[emerg] (45)Deadlock situation detected/avoided: apr_proc_mutex_lock failed. Attempting to shutdown process gracefully.

Not good. After a little digging we found that the default AcceptMutex switched from pthread to fcntl between apache 2.0.49 and 2.0.52.

Adding:

AcceptMutex pthread

to httpd.conf cleared up the errors and we’ve had smooth sailing ever since.

Posted in System Administration | 1 Comment »
Tagged: