What's it all about, Alfie?

This morning I had a Java HotSpot error in one of the components of a production system of mine, and I have to say, it's not been very helpful. I've looked at the HotSpot file and the problem seems to be in java.util.zip.ZipFile.getEntry() and Google tells me this is because of a possibly corrupt jar file, or someone has written to the jar file and made it so that the reading get very confused.

Unfortunately, all the jars have been stable for quite a while, but maybe the filesystem was the issue. We might have had some NFS issues which might have lead to this. Unfortunately, I can't do a lot about where the jars are stored, they need to be centrally located and there's only the one filer. Bummer.

I've sent a few emails the the guys who wrote this component to see if they have any ideas about what might be done to increase stability. I'm on JDK 1.5.0_10, but would 1.5.0_15 be better? 1.6.0? I'm searching for anything because there's no way the files were corrupted. I restarted the app and it all came back. Odd.

I just wish there were more information or a clear explanation of other possible causes so I might find the real culprit of this crash.

UPDATE: when it looks like the chips are down, sometimes you get a break. While digging into this with the developer that wrote the component having the problem, he noticed that the crash occurred when a script was being run through the system. I noticed that the last two crashes occurred at 8:00 am for the last two Friday mornings - just when cron launches these jobs. BINGO! While he was going to track down if the problem was in the bsh jar I was using, I decided to take a completely different track - forego the bsh script and write it in perl. Then, I'm not calling the system to do the work for me, I can do it outside the system and it's much safer and cleaner. Not to mention faster. I recoded this and it works like a champ. It's going to make things so much easier. Whew!

A friend of mine that wanted to get up to speed on matrix math asked me what I thought he should do. I told him I'd look at iTunes U and if I found some good class on Linear Algebra I'd tell him about it. Well, I have to say I'm amazed at what's available in the iTunes U selection.

I looked around a bit - it could be a little better organized, but I can say it's not bad - just time-consuming to find what you might be looking for. What I found was a pretty nice course called Linear Algebra, Spring 2005 from MIT Open Courseware. Thirty-five 40 minute lectures that start at a pretty basic level and seem to cover all the basics. It'll give him a really solid understanding of the matrix manipulations he's doing in his work, and hopefully some understanding as to why he's doing them.

I have to say that the first time I took Linear Algebra I got the mechanics down pretty well, but the level of understanding was just too thin. Maybe it was the guy teaching it, after all, it was a night-school class at a local campus, so it's not like he was a renowned lecturer, but still, I have to accept a good chunk of the blame.

Later, in grad school when I really learned it, I really enjoyed it as well. I told my friend that if he watched the course and had any questions I'd be glad to meet him for lunch and help him through the issues. I doubt he'll have a lot of questions - he's a smart guy, but it's always nice to know you have a safety net, and that's what I really gave him. Should be interesting to see how he does.