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• Algorithm for Source Control System?

  - by Michael Stum

  I need to write a simple source control system and wonder what algorithm I would use for file differences? I don't want to look into existing source code due to license concerns. I need to have it licensed under MPL so I can't look at any of the existing systems like CVS or Mercurial as they are all GPL licensed. Just to give some background, I just need some really simple functions - binary files in a folder. no subfolders and every file behaves like it's own repository. No Metadata except for some permissions. Overall really simple stuff, my single concern really is how to store only the differences of a file from revision to revision without wasting too much space but also without being too inefficient (Maybe store a full version every X changes, a bit like Keyframes in Videos?)

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• NoSQL and meteorological data

  - by christian studer

  So there's this new cool thing, these NoSQL-databases. And so there's my data: Rows of rows of rows of meteorological data: Values, representing certain measurements at a certain station (Identified by a WMO number, not coordinates), at a certain time. Not every station measures every parameter, not every parameter is measured all the time. I store this data (30 years worth of hourly values, resulting in ~1 billion values) currently in MySQL. The continous growth and the forseeable addition of even more data give me a little headache. Reading about the document based NoSQL systems which seem to scale rather easily, I was wondering if NoSQL is a viable data storage concept for meteorological data too. Do you have any experience with this?

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• malloc()/free() behavior differs between Debian and Redhat

  - by StasM

  I have a Linux app (written in C) that allocates large amount of memory (~60M) in small chunks through malloc() and then frees it (the app continues to run then). This memory is not returned to the OS but stays allocated to the process. Now, the interesting thing here is that this behavior happens only on RedHat Linux and clones (Fedora, Centos, etc.) while on Debian systems the memory is returned back to the OS after all freeing is done. Any ideas why there could be the difference between the two or which setting may control it, etc.?

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• kill -9 and production application

  - by valodzka

  Which problem can cause kill -9 in production application (in linux to be exact)? I have application which do some periodical work, stopping these takes long time, and I don't care if some jobs will be aborted - work can be finished by new processes. So can I use kill -9 just to stop it immediately or this can cause serious OS problems? For example, Unicorn, uses it as normal working procedure: When your application goes awry, a BOFH can just "kill -9" the runaway worker process without worrying about tearing all clients down, just one. But this article claims: The -9 (or KILL) argument to kill(1) should never be used on Unix systems

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• How to decouple an app's agile development from a database using BDUF?

  - by Rob Wells

  G'day, I was reading the article "Database as a Fortress" by Dan Chak from the excellent book "97 Things Every Software Architect Should Know" (sanitised Amazon link) which suggests that databases should not be designed using an agile approach. There's an SO question on agile approaches and databases "Agile development and database changes" which has some excellent answers covering agile development approaches. In fact, one of the answers supplies a brilliant idea of what's needed for each update of the DB. ;-) But after reading Dan Chak's article, I am left wondering if an agile approach is really suitable for large scale systems. This of course leads on to the question of how best to decouple an agile approach for the application that is interacting with the BDUF database design without adding complicated translation layers in the final design employed? Any suggestions? cheers,

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• Pros and Cons of Java HTML to XML cleaners

  - by cjavapro

  I am looking to allow HTML emails (and other HTML uploads) without letting in scripts and stuff. I plan to have a white list of safe tags and attributes as well as a whitelist of CSS tags and value regexes (to prevent automatic return receipt). I asked a question: Parse a badly formatted XML document (like an HTML file) I found there are many many ways to do this. Some systems have built in sanitizers (which I don't care so much about). I will post some answers and say Community Wiki. Please post any other options you like and say Community Wiki so they can be voted on. Also any comments or wiki edits on what part of a certain product is better and what is not would be greatly appreciated. This page is a very nice listing page but I get kinda lost http://java-source.net/open-source/html-parsers

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• graphic error on console

  - by Christian Elsner

  I have Linux on an embedded system. There is no graphic system, but I still have graphic errors. For example, if I type: ifconfig eth2 hw ether 00:0e:8c:d0:59:d2 I see: ifconfig eth hw ether 00:0e:8:2:2 If I type Enter, it accepts the command I typed, so it's just a matter of displaying. Everything is fine, when I log in via SSH. Anyone any ideas, what could be the cause or where to look at? Output of lspci: 00:00.0 Host bridge: Intel Corporation 3100 Chipset Memory I/O Controller Hub 00:00.1 Unassigned class [ff00]: Intel Corporation 3100 DRAM Controller Error Reporting Registers 00:01.0 System peripheral: Intel Corporation 3100 Chipset Enhanced DMA Controller 00:02.0 PCI bridge: Intel Corporation 3100 Chipset PCI Express Port A 00:03.0 PCI bridge: Intel Corporation 3100 Chipset PCI Express Port A1 00:1c.0 PCI bridge: Intel Corporation 631xESB/632xESB/3100 Chipset PCI Express Root Port 1 (rev 01) 00:1c.1 PCI bridge: Intel Corporation 631xESB/632xESB/3100 Chipset PCI Express Root Port 2 (rev 01) 00:1d.0 USB Controller: Intel Corporation 631xESB/632xESB/3100 Chipset UHCI USB Controller #1 (rev 01) 00:1d.1 USB Controller: Intel Corporation 631xESB/632xESB/3100 Chipset UHCI USB Controller #2 (rev 01) 00:1d.7 USB Controller: Intel Corporation 631xESB/632xESB/3100 Chipset EHCI USB2 Controller (rev 01) 00:1e.0 PCI bridge: Intel Corporation 82801 PCI Bridge (rev c9) 00:1f.0 ISA bridge: Intel Corporation 631xESB/632xESB/3100 Chipset LPC Interface Controller (rev 01) 00:1f.2 IDE interface: Intel Corporation 631xESB/632xESB/3100 Chipset SATA IDE Controller (rev 01) 00:1f.3 SMBus: Intel Corporation 631xESB/632xESB/3100 Chipset SMBus Controller (rev 01) 02:00.0 Ethernet controller: Intel Corporation 82574L Gigabit Network Connection 03:01.0 Network controller: Siemens Nixdorf AG Device 4003 (rev 02) 03:01.1 Unassigned class [ff00]: Siemens Nixdorf AG Device 4003 (rev 02) 03:02.0 Ethernet controller: Siemens Nixdorf AG Device 4047 (rev 01) 03:03.0 Ethernet controller: National Semiconductor Corporation DP83815 (MacPhyter) Ethernet Controller 03:04.0 Unassigned class [ff00]: Siemens Nixdorf AG Device 4057 (rev 01) 04:00.0 PCI bridge: Texas Instruments XIO2000(A)/XIO2200(A) PCI Express-to-PCI Bridge (rev 03) 05:00.0 Ethernet controller: Advanced Micro Devices [AMD] 79c970 [PCnet32 LANCE] (rev 44) 06:00.0 PCI bridge: Texas Instruments XIO2000(A)/XIO2200(A) PCI Express-to-PCI Bridge (rev 03) 07:00.0 VGA compatible controller: Silicon Motion, Inc. SM720 Lynx3DM (rev c1) 07:01.0 USB Controller: NEC Corporation USB (rev 43) 07:01.1 USB Controller: NEC Corporation USB (rev 43) 07:01.2 USB Controller: NEC Corporation USB 2.0 (rev 04) The whole thing is running on an Intel Core 2 Duo U2500

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• Building a minimal plugin architecture in Python.

  - by dF

  I have an application, written in Python, which is used by a fairly technical audience (scientists). I'm looking for a good way to make the application extensible by the users, i.e. a scripting/plugin architecture. I am looking for something extremely lightweight. Most scripts, or plugins, are not going to be developed and distributed by a third-party and installed, but are going to be something whipped up by a user in a few minutes to automate a repeating task, add support for a file format, etc. So plugins should have the absolute minimum boilerplate code, and require no 'installation' other than copying to a folder (so something like setuptools entry points, or the Zope plugin architecture seems like too much.) Are there any systems like this already out there, or any projects that implement a similar scheme that I should look at for ideas / inspiration?

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• strategies for learning complex software packages

  - by Tom

  I am a fairly novice Java programmer and I am currently working on a project to extend a piece of software that has been developed over a few years. So it has pretty big code base and the previous developers knew it well, so extending it is not going to be easy without a thorough understanding of the structure and function. 1) I had begun by trying to tackle small parts of the system and document them with mindmap. (particularly I am trying to document the interactions with external systems) 2) I have the book "code complete", which I am working through. 3) I have pointed some tools like "tattletale" at the code to get some diagrams of dependency relationships. What other strategies should I employ, should I focus on one particular aspect?

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• How should I structure my git commits?

  - by int3

  I'm trying to contribute to open source software for the first time, but I'm pretty inexperienced with version control systems. In particular, right now I want to make a number of changes to different parts of the code, but I'm not sure if the maintainer would want to integrate all of them into the master repository. However, the changes I'll be making are independent, i.e. they affect different parts of the file, or parts of different files. How should I go about making the changes? If I make a string of commits on the same branch, will the maintainer be able to pick and choose what he wants from the individual commit? E.g. can he patch in the changes I made in my second commit while ignoring the first one? Or should I make each change in a separate branch?

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• Database storage for high sample rate data in web app

  - by Jim

  I've got multiple sensors feeding data to my web app. Each channel is 5 samples per second and the data gets uploaded bundled together in 1 minute json messages (containing 300 samples). The data will be graphed using flot at multiple zoom levels from 1 day to 1 minute. I'm using Amazon SimpleDB and I'm currently storing the data in the 1 minute chunks that I receive it in. This works well for high zoom levels, but for full days there will be simply be too many rows to retrieve. The idea I've currently got is that every hour I can crawl through the data and collect together 300 samples for the last hour and store them in an hour Domain (table if you like). Does this sound like a reasonable solution? How have others implemented the same sort of systems?

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• Google maps spatial reference system

  - by JavaRocky

  What is Google map's spatial reference system using when you enter a lat, long into the maps search bar? I've found hints that it might be WGS84 but after converting to that coordinate system, nothing shows up when i paste the coordinates into the google maps search box. I am converting from GDA MGA 56. Sample: Input MGA56 coords: 336301, 6253363 Expected WGS86 coords: -33.8473340793201, 151.230631835944 I get: 16834916.928327594 -4008321.1020318186 Spatial coord systems: EPSG:28356 for MGA56 EPSG:900913 for WGS86 (google maps) I am using geotools to do the transform: CoordinateReferenceSystem crsMga56 = CRS.parseWKT(mga56); CoordinateReferenceSystem crsGmaps = CRS.parseWKT(gmaps); Coordinate coordinate = new Coordinate(336301, 6253363); Point point = new GeometryFactory().createPoint(coordinate); MathTransform transform = CRS.findMathTransform(crsMga56, crsGmaps); Geometry geometry = JTS.transform(point, transform); I know the transform is not correct, as when i use an online tool it gives me the correct coords. http://www.environment.gov.au/cgi-bin/transform/mga2geo%5Fgda.pl?east=336301&north=6253363&zone=56

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• Could Grand Central Dispatch (`libdispatch`) ever be made available on Windows?

  - by elliottcable

  I’m looking into multithreading, and GCD seems like a much better option than manually writing a solution using pthread.h and pthreads-win32. However, although it looks like libdispatch is either working on, or soon going to be working on, most newer POSIX-compatible systems… I have to ask, what about Windows? What are the chances of libdispatch being ported to Windows? What are the barriers preventing that from happening? If it came down to it, what would I need to do to preform that portage? Edit: Some things I already know, to get the discussion started: We need a blocks-compatible compiler that will compile on Windows, no? Will PLBlocks handle that? Can we use the LLVM blocks runtime? Can’t we replace all the pthread.h dependencies in userspace libdispatch with APR calls, for portability? Or, alternatively, use pthreads-win32 I suppose…

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• What's the coolest machine you've ever worked on?

  - by mxg

  What's the most exotic, coolest, unique, or interesting machine you've worked on? Most of us work on machines with x86 architectures using some Windows or Linux variant. I'm sure there are those of you out there who are working on or have worked on machines with experimental architecures, or operating systems. Maybe you worked on a machine that has some sigificance in the history of computing. I'd be interested to hear about it. I'm sure others reading SO will as well. EDIT: I appreciate all of you who took some time to talk about their experiences with interesting or unusual machines. I enjoyed reading your answers. Although it wasn't my intent to get nostalgic, I see that theme amongst the responses.

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• Whats the difference between Paxos and W+R>=N in Cassandra?

  - by user1128016

  Dynamo-like databases (e.g. Cassandra) provide ability to enforce consistency by means of quorum, i.e. a number of synchronously written replicas (W) and a number of replicas to read (R) should be chosen in such a way that W+RN where N is a replication factor. On the other hand, PAXOS-based systems like Zookeeper are also used as a consistent fault-tolerant storage. What is the difference between these two approaches? Does PAXOS provide guarantees that are not provided by W+RN schema?

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• How can I get read-ahead bytes?

  - by Bruno Martinez

  Operating systems read from disk more than what a program actually requests, because a program is likely to need nearby information in the future. In my application, when I fetch an item from disk, I would like to show an interval of information around the element. There's a trade off between how much information I request and show, and speed. However, since the OS already reads more than what I requested, accessing these bytes already in memory is free. What API can I use to find out what's in the OS caches? Alternatively, I could use memory mapped files. In that case, the problem reduces to finding out whether a page is swapped to disk or not. Can this be done in any common OS?

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• Service Layer Patter - Could we avoid the service layer on a specific case?

  - by lidermin

  Hi, we are trying to implement an application using the Service Layer Pattern cause our application needs to connect to other multiple applications too, and googling on the web, we found this link of a demostrative graphic for the "right" way of apply the pattern: martinfowler.com - Service Layer Pattern But now we have a question: what if our system needs to implement some business logic, only for our application (like some maintenance data for the system itself) that we don't need to share with other systems. Based on this graphic: As it seems, it will be unnecesary to implement a service layer just for that; it will be more practical to avoid the service layer, and just go from User Interface to the Business Layer (for example). What should be the right way in this case to implement the Service Layer Pattern? What do you suggest us for a scenario like the one I told you? Thanks in advance.

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• Service Layer Patter - Could we avoid the service layer on a specific case?

  - by lidermin

  Hi, we are trying to implement an application using the Service Layer Pattern cause our application needs to connect to other multiple applications too, and googling on the web, we found this link of a demostrative graphic for the "right" way of apply the pattern: martinfowler.com - Service Layer Pattern But now we have a question: what if our system needs to implement some business logic, only for our application (like some maintenance data for the system itself) that we don't need to share with other systems. Based on this graphic: As it seems, it will be unnecesary to implement a service layer just for that; it will be more practical to avoid the service layer, and just go from User Interface to the Business Layer (for example). What should be the right way in this case to implement the Service Layer Pattern? What do you suggest us for a scenario like the one I told you? Thanks in advance.

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• Why do Java/C# edge out C++ as the recommended language to learn OOP on S.O?

  - by viksit

  I noticed after reading the answers/discussion to this question (What is the best language to learn OOP on?) - that more and more people are recommending C# or Java over C++ to learn OOP on. A simple term search on that answer page results in 10 hits for C++, 21 for C# and 27 for Java. Now, I understand that these 2 languages fix a lot of quirks and issues with C++, and looked up these resources that relate mostly to performance, JVM vs native implementation, systems focus vs applications, manual memory management vs automated et al. My question is - are there any fundamental differences in the OO capabilities of Java/C# vs C++? Or are the former recommended purely due to their generic ease of use/improvements over the latter? Thanks. PS, I'm aware of Java interface inheritance vs C++ multiple inheritance as a difference. I would consider that an implementational one rather than functional.

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• Performance statistics hooks

  - by tinny

  Lets be honest, most software that developers produce has quite modest performance requirements. E.g. Systems perhaps serving 100's of requests per second, if that. But lets assume for a moment (or even dream) that you where perhaps involved in the "next big thing" (whatever that means) and you wanted to put some sort of performance statistics logging in place to help you out when all those users come flying in. Performance statistics logging, how would you approach this requirement? Perhaps you would use some sort of generic framework for this? Or roll your own solution? What would you log? How granular? Or would you not even bother putting anything in place and rather deal with this issue when it actually became an issue? It would be really interesting to hear your thoughts on this topic.

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• How to allow for modular development while still running in same JVM?

  - by Marcus

  Our current app runs in a single JVM. We are now splitting up the app into separate logical services where each service runs in its own JVM. The split is being done to allow a single service to be modified and deployed without impacting the entire system. This reduces the need to QA the entire system - just need to QA the interaction with the service being changed. For interservice communication we use a combination of REST, an MQ system bus, and database views. What I don't like about this: REST means we have to marshal data to/from XML DB views couple the systems together which defeats the whole concept of separate services MQ / system bus is added complexity There is inevitably some code duplication between services You have set up n JBoss server configurations, we have to do n number of deployments, n number of set up scripts, etc, etc. Is there a better way to structure an internal application to allow modular development and deployment while allowing the app to run in a single JVM (and achieving the associated benefits)?

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• How do i get out of the habit of procedural programming and into object oriented programming?

  - by Shadi Almosri

  Hiya all, I'm hoping to get some tips to kinda help me break out of what i consider after all these years a bad habit of procedural programming. Every time i attempt to do a project in OOP i end up eventually reverting to procedural. I guess i'm not completely convinced with OOP (even though i think i've heard everything good about it!). So i guess any good practical examples of common programming tasks that i often carry out such as user authentication/management, data parsing, CMS/Blogging/eComs are the kinda of things i do often, yet i haven't been able to get my head around how to do them in OOP and away from procedural, especially as the systems i build tend to work and work well. One thing i can see as a downfall to my development, is that i do reuse my code often, and it often needs more rewrites and improvement, but i sometimes consider this as a natural evolution of my software development. Yet i want to change! to my fellow programmers, help :) any tips on how i can break out of this nasty habbit?

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• How can I integrate graphs and JPEG images with RAVE Reports?

  - by JonDave of the Philippines

  I really love RAVE Reports in creating multiple reports especially with formulas and accounting systems... but recently I am having problems with integrating JPEG Pictures and Graphs with my newly Delphi Language developed Little ERP System. I bought some JPEG Components but it seems problematic. I also experienced some irregularities with my RAVE Reports now. When I run my program then try to preview some reports, it seems to be running fine, but when I close the program, the EXE file is still in the taskbar. I need to ctrl-alt-delete first for me to use Report Previews normally. If I don't, RAVE REPORT ERROR message will appear everytime I click the PRINT button; it says "STREAM READ ERROR" even though I used to "FreeAndNil" to free the memory stream when Report Preview Form closes. When I tried to run the My Applications without previewing RAVE reports, the program closes perfectly. Any suggestions and recommendations will be an enormous help. Thank you.

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• List available languages for PyGTK UI strings

  - by detly

  I'm cleaning up some localisation and translation settings in our PyGTK application. The app is only intended to be used under GNU/Linux systems. One of the features we want is for users to select the language used for the applications (some prefer their native language, some prefer English for consistency, some like French because it sounds romantic, etc). For this to work, I need to actually show a combo box with the various languages available. How can I get this list? In fact, I need a list of pairs of the language code ("en", "ru", etc) and the language name in the native language ("English (US)", "???????"). If I had to implement a brute force method, I'd do something like: look in the system locale dir (eg. "/usr/share/locale") for all language code dirs (eg. "en/") containing the relative path "LC_MESSAGES/OurAppName.mo". Is there a more programmatic way?

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• Email form isn't sending

  - by Jonathan

  Hi I have an email form that isn't sending out an email to the recipient or a copy to the client. The form can be found at www.kelcos.co.uk/contact and the files associated with this are: /index.php /jquery.js /sendemail.php /submitform.php /thanks.php /verify.php I have used this form on other websites http://www.bowlesgreen.co.uk/contact/ and http://www.arbortectreecare.co.uk/contact/ and it works fine - the only difference is that these other sites use my usual hosting provider and for the one that won't send I'm working through the clients hosting provider, which I can only presume is what is causing the problem. I have contacted the hosting and so far we have eliminated a few things such as: 'The limitation to our systems is that the emails sent using scripts will be blocked if they are not going to or coming from an email address setup on the web hosting account. - so I am now sending the form to an a kelcos.co.uk address, but still no joy. PHP/ASP was originally disabled, but now has been activated the mail() script is enabled I would really appreciated any advise any of you could offer. Thanks

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