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• mongodb read/write performance and mongo hosting in the cloud

  - by z3cko

  we are currently developing a high traffic rails application with facebooker (facebook game). since amazon simpledb (aws-sdb) is really slow, we are thinking of using a dedicated mongodb server as offered by mongoHQ for example. questions: what is the read/writes peak value for a mongodb server running on a amazon ec2 instance? what would be a recommended setup for a ec2 hosted app with mongodb - a master on amazon EBS and replicas on the ec2 instances? any examples or experiences? is there a company that offers mongodb hosting in the cloud? thanks, mz

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• Specification: Use cases for CRUD

  - by Mario Ortegón

  I am writing a Product requirements specification. In this document I must describe the ways that the user can interact with the system in a very high level. Several of these operations are "Create-Read-Update-Delete" on some objects. The question is, when writing use cases for these operations, what is the right way to do so? Can I write only one Use Case called "Manage Object x" and then have these operations as included Use Cases? Or do I have to create one use case per operation, per object? The problem I see with the last approach is that I would be writing quite a few pages that I feel do not really contribute to the understanding of the problem. What is the best practice?

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• [C#] Async threaded tcp server

  - by mark_dj

  I want to create a high performance server in C# which could take about ~10k clients. Now i started writing a TcpServer with C# and for each client-connection i open a new thread. I also use one thread to accept the connections. So far so good, works fine. The server has to deserialize AMF incoming objects do some logic ( like saving the position of a player ) and send some object back ( serializing objects ). I am not worried about the serializing/deserializing part atm. My main concern is that I will have a lot of threads with 10k clients and i've read somewhere that an OS can only hold like a few hunderd threads. Are there any sources/articles available on writing a decent async threaded server ? Are there other possibilties or will 10k threads work fine ? I've looked on google, but i couldn't find much info about design patterns or ways which explain it clearly

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• Testing perceived performance

  - by Josh Kelley

  I recently got a shiny new development workstation. The only disadvantage of this is that the desktop apps I'm developing now run very, very fast, and so I fear that parts of the code that would be annoyingly slow on end users' machines will go unnoticed during my testing. Is there a good way to slow down an application for testing? I've tried searching around, but all of the results I've been able to find seem pretty fiddly to set up (e.g., manually setting up a high-priority CPU-bound task on the same CPU core as the target app, or running a background process that rapidly interrupts and resumes the target app), and I don't know if the end result is actually a good representation of running on a slower computer (with its slower CPU, slower RAM, slower disk I/O...). I don't think that this is a job for a profiler; I'm interested in the user's perception of end-to-end performance rather than in where the time goes for particular operations.

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• How to estimate the thread context switching overhead?

  - by Ignas Limanauskas

  I am trying to improve the performance of the threaded application with real-time deadlines. It is running on Windows Mobile and written in C / C++. I have a suspicion that high frequency of thread switching might be causing tangible overhead, but can neither prove it or disprove it. As everybody knows, lack of proof is not a proof of opposite :). Thus my question is twofold: If exists at all, where can I find any actual measurements of the cost of switching thread context? Without spending time writing a test application, what are the ways to estimate the thread switching overhead in the existing application? Does anyone know a way to find out the number of context switches (on / off) for a given thread?

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• Socket server stops accepting connections after a period of time

  - by Rob

  We have an async socket server written in C#. (running on Windows Web Server 2008) It works flawlessly up until it stop accepting new connections for an unknown reason. We have about 200 concurrent connections on average, however we keep a count of both connections created and connections dropped. These figures can reach as high as 10,000 or as low as only 1000 before it just stops! It can run for up to around 8 hours sometimes before it stops or it can run for about half hour, at the moment it's running for about an hour before we have another application bring it back up automatically when that can't connect (not exactly ideal). It doesn't appear like we're running out of sockets as we're closing them properly, we're also logging all errors and nothing is happening immediately before it stops. We can figure this out. Does anyone have any ideas what might be going on? I can paste code, but it generally just the same old async beginaccept/send code you see everywhere.

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• Avoiding problem of overwriting files which are in use

  - by zaf

  For example on a high traffic web server. To reduce problems when switching a file I usually rename the old file out and then rename in the new file. I was told some time ago that renaming a file does not change the 'inode data' so that processes reading the file can keep doing so without glitches. And, of course, rather than copying in the new file it is faster and safer to rename a temp copy. Is this still best practice and if not what do you do?

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• How to prevent Artificial Intelligence from escaping into the internet?

  - by Jason

  I have an interest in artificial intelligence from a evolutionary standpoint. I want to experiment with it somewhat with a high level language like C#, however, I'm stuck on one of the most elementary problems with artificial life -- how to contain it? The best thing I can think of is a virtual machine. Where would I start to create a VM for my budding digital organisms in C#? How could I be sure they couldn't escape into the 'wild'? (I understand this unlikely, by the way.)

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• how to create a particle system on iphone and retain the created particles?

  - by lukya

  Hi all, I need to create a particle system and retain the created particles. I need to shake / move the created particles with the iphone accelerometer. Also, the number of particles needs to be very high (I need to show sand!). I do not have any OpenGLES programming experience. After initial search, I found Cocos2D can be used for particle generation. But there is no way of retaining the particles in the CCParticle system. As a work around, I tried creating many sprites at the end of particle generation and shown them as particles. But moving few number of sprites with accelerometer drops the frame rate considerably. Please suggest how this can be achieved and whether I should look for some other framework or if some kind of similar demo code is available. Thanks, Swapnil

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• What is the correct way to unit test areas around exceptions

  - by Codek

  Hi, Looking at our code coverage of our unit tests we're quite high. But the last few % is tricky because a lot of them are catching things like database exceptions - which in normal circumstances just dont happen. For example the code prevents fields being too long etc, so the only possible database exceptions are if the DB is broken/down, or if the schema is changed under our feet. So is the only way to Mock the objects such that the exception can be thrown? That seems a little bit pointless. Perhaps it's better to just accept not getting 100% code coverage? Thanks, Dan

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• Agile Approach for WCM

  - by cameron.f.logan

  Can anyone provide me with advice, opinions, or experience with using an agile methodology to delivery an enterprise-scale Web Content Management system (e.g., Interwoven TeamSite, Tridion)? My current opinion is that to implement a CM system there is a certain--relatively high--amount of upfront work that needs to happen to make sure the system is going to be scalable and efficient for future projects for the multi-year lifespan an WCM is expected to have. This suggests a hybrid approach at best, if not a more waterfall-like approach. I'm really interested to learn what approaches others have taken. Thanks.

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• What database works well with 200+GB of data?

  - by taw

  I've been using mysql (with innodb; on Amazon rds) because it's sort of universal default, but it's been ridiculously under-performing, and tweaking it only delays the inevitable. The data is mostly relatively short (<1kB of bytes each) blobs information about 100Ms of urls. There is (or should be, mysql cannot seem to handle it) very high amount of insert / update / retrieve but few complex queries - not that complex queries wouldn't be useful, but because mysql is so slow that it's far faster to get the data out, process it locally, and cache the results somewhere. I can keep tweaking mysql and throwing more hardware at it, but it seems increasingly futile. So what are the options? SQL/relational model/etc. optional - anything will do as long as it's fast, networked, and language-independent.

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• Starting a cocos2d game with initial gameplay as background

  - by boz

  Hi All, Id like to start my game, with the initial game play layout as the background, with a buttons layer over the top with maybe 'Tap to start' and a high score etc. and similarly, when the game finishes, id like to just 'pause' the final game play layout and overlay a game over menu of sorts. I tried calling [[CCDirector sharedDirector] pause] as the last line of the appDidFinishLaunching which didnt seem to have any effect. Is there a better way trying to do this? I dont really like my initial approach.

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• URL encoded POST bad practice?

  - by StackedCrooked

  I am (just for fun) trying to implement a High Score web-service. I would like it be compatible with REST principles. I want to be able to add a new highscore using url parameters like this http://mydomain.com/hs/add&name=John&score=987. According to REST this must be done using a POST request. Which leads to empty POST request with all data contained in the URL parameters. Would this be considered a bad practice? Update Security is currently not a big concern.

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• feature extraction from acoustic signals

  - by Dolphin

  Hi everyone, It's been a while. I found APIs in Java for extracting features from acoustic audio files and symbolic files separately. But now I have a problem in mapping from low level wav audio features to high level midi features. i.e. I need to write the extracted wav audio features on to midi format. But I cannot think of anything even close to it. Can someone pls provide me some insight as in how I can approach this. Greatly appreciate your responses. Advance thanks

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• Taking Responsibilites too early - danger or boon?

  - by narresh

  Just I am only six months experienced guy in software industry.Due to recession season,a large volume of employees from our company are asked to leave.This impact affects the new inexperienced guys. The problem is We have to interact with the client directly to gather the requirement We have to design all HLD and LLD ,use cases and DB Diagrams ,that should staisfy the customers who keeping the high software insdutry standards In this do or die situation (Client gives us narrow dead line),we spend most of time with interacting client (only less time is available for development and testing,even sit out for 24 X 7 won't help us to finish our task) If task will not be finished with in the expected time frame ,that will trigger poor performance ration to our profile There are two important questions flashing in our mind : (1) Quit the job and do other business (2) Face the challenge : (if the option is to face the challenge ,What are all the tools should we follow to automate requirement gathering,testing,DB diagram,Code review and the rest.(We are working on ASP.NET 3.5 with SQL Server 2005).

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• XmlDocument caching memory usage

  - by mdsharpe

  We are seeing very high memory usage in .NET web applications which use XmlDocument. A small (~5MB) XML document is loaded into an XmlDocument object and stored in HttpContext.Cache for easy querying and XSLT transformation on each page load. The XML is modified on disk periodically so a cache has a dependency on the file. Such an application appears to be using hundreds of megabytes of RAM. I have experimented with requesting garbage collection on each request start, and this keeps the RAM usage far lower but I cannot imagine this is good practise. Does anyone have any suggestions as to how we can achieve the same goal but with lower RAM usage?

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• How To Make Moving News Bar in Windows Forms Application without Timer

  - by Ehab Sutan

  I'm making a desktop application in C# which contains a moving News Bar labels. I'm using a timer to move these labels but the problem is that when i make the interval of this timer low (1-10 for example) the application takes very high percentage of CPU Usage, And when i make it higher(200 -500 ) the movement of the labels becomes intermittent or not smooth movement even that the user may not be able to read the news in Comfortable way. ((More Information)) it is Windows form application. the way i move the labels is as follows : the news items from RSS feeds are represented in a group of linklabels. All these linklabels are added to a flowlayout container. The timer moves the whole flowlayout container. I found this way according to my knowledge the best way to making the news bar. If you have better idea or solution please help

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• RoR - Paperclip - How to set minimal width of an attachement

  - by sNiCKY

  Hi, my layout's requirement is to keep all thumbnails at 80px height, not higher, not smaller. In my model I set the style to :thumb= "500x80", so basically almost every picture which is not too wide gets its perfect miniature with 80px height. Sometimes, however, my pictures are narrow and high, so the thumb can have unclickable dimensions of like 5x80. So I dont want to crop pictures as long as thumbnails are not getting crazy narrow, but I think I can make a little sacrifice and crop them if thumb's width is getting smaller than 25px. So my questions is - is it possible in paperclip to set minimal proportions of a picture by which the style will be "500x80" and beyond that it will turn to sth like "25x80#"?

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• Single SingOn - Best practice

  - by halfdan

  Hi Guys, I need to build a scalable single sign-on mechanism for multiple sites. Scenario: Central web application to register/manage account (Server in Europe) Several web applications that need to authenticate against my user database (Servers in US/Europe/Pacific region) I am using MySQL as database backend. The options I came up with are either replicating the user database across all servers (data security?) or allowing the servers to directly connect to my MySQL instance by explicitly allowing connections from their IPs in my.cnf (high load? single point of failure?). What would be the best way to provide a scalable and low-latency single sign-on for all web applications? In terms of data security would it be a good idea to replicate the user database across all web applications? Note: All web applications provide an API which users can use to embed widgets into their own websites. These widgets work through a token auth mechanism which will again need to authenticate against my user database.

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• Most efficient algorithm for mesh-level, optimal occlusion culling?

  - by Fredriku73

  I am new to culling. On a first glance, it seems that most occlusion culling algorithms are object-level, not examining single meshes, which would be practical for game rendering. What I am looking for is an algorithm that culls all meshes within a single object that are occluded for a given viewpoint, with high accuracy. It needs to be at least O(n log n), a naive mesh-by-mesh comparison (O(n^2)) is too slow. I notice that the Blender GUI identifies the occluded meshes for you in real-time, even if you work with large objects of 10,000+ meshes. What algorithm is used there, pray tell?

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• Why isn't Hadoop implemented using MPI?

  - by artif

  Correct me if I'm wrong, but my understanding is that Hadoop does not use MPI for communication between different nodes. What are the technical reasons for this? I could hazard a few guesses, but I do not know enough of how MPI is implemented "under the hood" to know whether or not I'm right. Come to think of it, I'm not entirely familiar with Hadoop's internals either. I understand the framework at a conceptual level (map/combine/shuffle/reduce and how that works at a high level) but I don't know the nitty gritty implementation details. I've always assumed Hadoop was transmitting serialized data structures (perhaps GPBs) over a TCP connection, eg during the shuffle phase. Let me know if that's not true.

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• Audio processing in C# or C++

  - by melculetz

  Hi, I would like to create an application that uses AI techniques and allows the user to record a part of a song and then tries to find that song in a database of wav files. I would have liked to use some already existing libraries for the audio processing part. So, could you recommend any libraries in C# which can read a wav file, get input from microphone, have some audio filters (low pass, high pass, FFT etc) and maybe have the ability to plot the audio signal as well. I would prefer to develop in C#, but if there aren't good libraries for audio processing, I guess I could work in C++ as well. As far as I know, Mathlab already has the above mentioned functionalities, but I can't use it in my application.

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• Trying to Unit Test A Class That Makes DB Queries Using Hibernate And Can't Get Session Created...

  - by Jared Michaels

  I am trying to implement JUnit tests for a class that performs DB queries using Hibernate. When I create the class under test, I get access to the session through the factory by doing the following: InitialContext context = new InitialContext(); sessionFactory = (SessionFactory) context.lookup(hibernateContext); This works fine when I deploy this to JBoss 5.1. I am trying to figure out how to get this to work with my JUnit test. I keep getting an exception stating that I "Need to specify class name in environment or system property, or as an applet parameter, or in an application resource file: java.naming.factory.initial". I've searched high and low but haven't been able to find any information about what specifically I need to do to get this to work. I am not using Spring or any frameworks, just plain old Java and JUnit.

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• How change column names randomly in gridview?

  - by James123

  I am struggling to show different views of gridview with database values. Here is my requirement. Database Table: I need to show one drop downlist with three values 1,2,3. If user selects 3 i Need to show a grid like below Age,AnnualSales and Assortment are names which are coming dynamically from database. High,Medium and Core all are values Here my question is I need to show same attribute names. Like If the name changes from "Assortment" to "Location" I need to show it in different page index . In page index 2 i need to show like below. Please help with solution

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