Matthias Merz

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since Oct 31, 2008
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Recent posts by Matthias Merz


Thanks Wiliam!

This is by far the most useful I have heard yet.

I guess most of my problems do indeed come from a thread that is waiting for messages in an oracle queue. I'm currently refactoring it.
14 years ago
Hello Bauke!

Sorry, but I am looking for CAUSES of memory leaks

A profiler is just a tool.

Of course I need it to check if my memory usage is okay. But if a timed out session keeps 800 objects (120 classes) in memory, then it's hard to find the cause.

Maybe you can help me now that I have clearified my question.
14 years ago
Hello Mohammed!

Thanks for your reply. These are all important issues when dealing with too much memory consumption.

I am currently focussing on uncleaned sessions. Objects that remain in memory, even though the servlet is quitted and the session invalidated.

Those object never become cleaned up (you have to restart Tomcat).

One issue I have come across is the usage of String concatenation. As far as I've understood, those are never removed from memory. So if you do a lot of string concatening (e.g. for logging or sql statements), than by the time you'll get an OutOfMemoryException.

Is this right?
14 years ago
Hi everyone!

I am currently hunting down memory leaks in a Tomcat servlet. One I haven't developed myself I must add.

I tried to take an analytical approach to where the leaks might come from, as the application ist about 2000 classes and I have only an architectural overview.

So I asked myself, where memory leaks could general ly come from. Maybe you've got some more causes or are willing to discuss mine.


Memory Leak Causes
-------------------------
1. Unfinshed Threads
2. Static Attributes
3. Open Connections
3.1 Databases
3.2 Queues
4. References from outside systems


Any suggestions?

Matthias
14 years ago
Hi!

I just passed the OCUP Fundamental Exam and wanted to share my experiences.

At first, I took the exam at a testing center in Munich, Germany. As a non-native english speaker I got additional 30 minutes, alltogether 120 minutes.

There was more than enough time to answer and review twice. Nevertheless I found the exam quite frustrating. I worked through Tim Weilkens book and the spec but many of the questions I could not answer at once.

Most of the times when I was unsure, I thought no answer really fitted. I studied the definitions from Tim Weilkens, but none of the answers matched to the possible answers in the exam.

But enough of the downsides. I passed with 69 out of 80 questions and here are my hints for you:

-Study the Use Case section really hard. Interpret diagrams: Which use cases in a diagram could be abstract, extended, included, deleted? How many actors are involved at least? And so on

-Know all about Pins, Input/OutputParameters and ObjectFlows in Activity Diagrams

-Know the meaning of each diagram type and how they relate to another: e.g. Communication Diagrams are more general than Sequence Diagrams


Good Luck

Hi!

I am currently preparing for the OMG UML Foundation Exam an took the sample test form oose.de (http://www.oose.de/seminare/zertifizierungen/ocup/testfragen.html). There are some answers that appear wrong to me, but maybe I haven't understood the concept. Could you help me?

1.The test answer says, that Boolean, Integer, UnlimitedNatural and String are PrimititveTypes. I disagree with the String. At least the UML2 Certification Guide from Weilkiens and Ösetreich doesn't mention it. (Number 5)

2. The test states that it is not possible to define an alias for package imports. (Number 7) This also differs from the Certification Guide, doesn't it?

3.In Number 31, I thought the correct answers would be b,d and f but the result says f is wrong. Any idea why?

Thanks a lot for your help!

Matthias
Yes!

Would you agree with this statement (Agile Testing = Test first in Agile Projects)?

If not, then what is your idea of Agile Testing?
I thought that in an agile aproach it would be very straight forward to use test first if you care about testing at all :-)

You need test for each sprint to check if the sprint was successful and everything has been implemented in a sufficent quality. No need to wait. Just write the tests at the beginning of the sprint. That way, the developers think before they implement and a "tester" or quality manager can confirm the effectiveness of the test suite.
Hi!

I have a design question.

I am currently wotking on a project that manages stocks.

Bank information like the adress can be retrieved through a webservice via the ISIN.

The problem is, that I need to store additional information to the bank, so i have a bank entity.

My first thougt was: Take the creation lifecycle method and get the informatione out of the service when the entity is fetched into the persistence context. Put them into transient fields and everything will be ok. But sometimes, i need lists of banks and the webservice was too slow.

Next thought was: Take some kind of Factory/Creator/Builder to fill the transient fields with the webservice information when needed. But when I discussed this with a friend, he said: Neither of this patterns matches your design. So I thougt, maybe this is not such a good solution.

He said: looks like a proxy. So my next idea is: Create a proxy, that inherits from bank. Forward the webservice calls to the webservice when needed (with lazy loading of the data) and forward the rest to the bank bean.

Does this look like a sound solution?