Working on my recent projects I once again cursed about the flat structure of my source code file. In modern source code editors it is quite common to be able to “fold” block of coding to enhance readability and overview, but nobody seemed to have cared about comments here: In almost all cases, source code editors just allow to collapse the comment block itself. Thinking about this I came up to the point that source code is not that “flat” as the plain text file might suggest. The same way as you collapse a block in the source code editor, you often do it when browsing through the content of an XML file. That brought me to the idea of structuring source code with the help of XML. Continue reading ‘Structured Source Code as the Truth’ »
Repotting Fedora Core 12 on Software RAID
Last weekend I had to change the size of the root partition of a Fedora Core 12 system. Reason for it was a) the size of the partition where the root file system is located is too large and b) the remaining free space shall be used in another partition (for a different purpose). Due to the circumstances it was not an option to use the disk space within the same partition. Continue reading ‘Repotting Fedora Core 12 on Software RAID’ »
Testing Hotswapping on Java with Apache Felix’ OSGi Tutorial
About half a year ago I stumbled over the problem that Java does not allow certain types of changes on compiled coding on the fly (for good reason BTW). It is even not possible when using the debugger interface (see also JDPA for more details on this). On the other hand, however, I know from the ABAP/4 world that generating coding might be a very good idea sometimes, because in most cases it impacts performance less compared to writing generic coding (for example by using introspection or reflection). In this situation you often want to automize the generation thus immediately having to struggle with the problem that you need to reload changed compiled codes “on the fly” (during the runtime of the virtual machine) for example to correct errors or to deploy a new version. Since that time I was searching for some alternative which could work around many restrictions Java currently poses here. Looking around with Google I found that already some people before me had thought about this problem. I stumbled – for example – over the following papers:
- Overcoming JVM HotSwap constraints via binary rewriting
- Towards Unanticipated Runtime Adaptation of Java Applications
Finally, I read in a forum that the OSGi standard (besides some other things) would provide such a feature. Reading a bit more at their website I figured out that this is not just about hotswapping Java Byte Code, but an entire approach of implementing a certain component model coming from the embedded device world. I was quite eager getting to know more about it and planned to conduct a more thorough practical look at an implementation of the standard some time.
First Steps with Felix
Within the last weeks I found this opportunity and had a closer look at Apache Felix, one of the major implementations of the OSGi standard. Continue reading ‘Testing Hotswapping on Java with Apache Felix’ OSGi Tutorial’ »
Using Subversion+Apache Webserver as Backup Storage
For more than two years I am furious about what standard backup programs deliver today. Yes, they provide you safety by making copies of your data reoccuringly ensuring that you can copy it back upon necessity. But when you have a closer look at what they really do especially in the sense of versioning it suddently turns into a surprise. I stumbled over that when I investigated the following scenario more thoroughly:
Scenario
For several years now I administer a local network with some workstations and two servers. For historical reasons one of the server is a Linux box (LinS) which is mainly responsible for doing the internet-related routing and similar stuff whilst the Windows Server (WinS) acts as simple file share server for the core application. Safety of the data is considered key in this situation – especially concerning the Windows Server (loosing the internet access for a day or two is also not eligible, but survivable). Still both servers feature a RAID1 system. Previously, backup of data for the Windows Server was done via DVD+RW with a simple commercial backup software. As the RAID1 array in the WinS already ensured that ongoing failures did not cause an unrevokable data loss, still “pushing the DEL button” on the keyboard could cause an entire data loss (this is also the reason why “only backing up your data on a RAID array” is never a good idea alone). Consequently, the major task in this situation for this commercial software was to provide differential backups such that – if required – it would be possible to restore a previous state (to be also immune against data that was garbled some days before).
Continue reading ‘Using Subversion+Apache Webserver as Backup Storage’ »
Preview: Apache Felix Tutorial Additions
The last few days I am playing around with Apache Felix, an implementation of the OSGi standard after having stumbled over the problem that it is not so trivial to exchange Java coding while the Java Virtual Machine still is running. At their documentation’s page the implementors of Felix have a very nice tutorial which I had a walk-through the last few days. On addition to this I did some enhanced tests with it which I would like to report on in the next couple of posts.
Stay tuned!