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• Managing Data Prefetching and Dependencies with .NET Typed Datasets

  - by Derek Morrison

  I'm using .NET typed datasets on a project, and I often get into situations where I prefetch data from several tables into a dataset and then pass that dataset to several methods for processing. It seems cleaner to let each method decide exactly which data it needs and then load the data itself. However, several of the methods work with the same data, and I want the performance benefit of loading data in the beginning only once. My problem is that I don't know of a good way or pattern to use for managing dependencies (I want to be sure I load all the data that I'm going to need for each class/method that will use the dataset). Currently, I just end up looking through the code for the various classes that will use the dataset to make sure I'm loading everything appropriately. What are good approaches or patterns to use in this situation? Am I doing something fundamentally wrong? Although I'm using typed datasets, this seems like it would be a common situation where prefetching data is used. Thanks!

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• Best way to code a webservice in weblogic?

  - by John

  I am new to Weblogic and J2ee. I need to build a webservice that simply runs a query on the backend database (DB2 zOS) and returns the results. Being new to this I have a few questions. 1) What is the best way to build the webservice? 2) How do I connect to the database with weblogic. 3) Is there a way to cache the data returned so that the next request for the same data is pulled from cache? If googled for this but there seems to be many way to handle this. I am looking for the best way that can handle a high volume of requests. Any links to sample code would be helpful. - Thanks

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• SSIS - Connection Management Within a Loop

  - by Rob Bowman

  Hi I have the following SSIS package: The problem is that within the Foreach loop a connection is opened and closed for each iteration. On running SQL Profiler I see a series of: Audit Login RPC:Completed Audit Lout The duration for the login and the RPC that actually does the work is minimal. However, the duration for the logout is significant, running into several seconds each. This causes the JOB to run very slowly - taking many hours. I get the same problem when running either on a test server or stand-alone laptop. Could anyone please suggest how I may change the package to improve performance? Also, I have noticed that when running the package from Visual Studio, it looks as though it continues to run with the component blocks going amber then green but actually all the processing has been completed and SQL profiler has dropped silent? Thanks, Rob.

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• parsing/matching string occurrence in C

  - by David

  I have the following string: const char *str = "\"This is just some random text\" 130 28194 \"Some other string\" \"String 3\"" I would like to get the the integer 28194 of course the integer varies, so I can't do strstr("20194"). So I was wondering what would be a good way to get that part of the string? I was thinking to use #include <regex.h> which I already have a procedure to match regexp's but not sure how the regexp in C will look like using the POSIX style notation. [:alpha:]+[:digit:] and if performance will be an issue. Or will it be better using strchr,strstr? Any ideas will be appreciate it

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• Is it really wrong to version documents using CouchDB's behaviour?

  - by Tomas Sedovic

  This is one of those "I know I shouldn't do this but it's oh so convenient." questions. Sorry about that. I plan to use CouchDB for storing a bunch of documents and keeping their entire revision history. CouchDB does the versioning automatically, but it is strongly discouraged for programmer's use: "You cannot rely on document revisions for any other purpose than concurrency control." From what I've found on the CouchDB wiki, the versions can get deleted either during compaction or during replication. As far as I can tell, Compaction must always be triggered manually and Replication occurs only when there's more than one database server. The question is: if I won't run compaction and will use only single database instance for my documents, can I just use CouchDB's document versioning and expect it to work? What other problems I might run into? E.g. does not running compaction hurt the performance or consume significantly more disk space (than if I did handle the versioning manually)?

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• How to update only certain items in a list when using MVC?

  - by Eugen

  I'm building a GUI that includes a list with quite a lot of items. I allow the user to add/delete/edit those items. Up until now my update method called in the controller implied an entire JList reset (with its obvious performance issues). Now that there are hundreds of items available, updating the entire list is not fezable any longer. Does anyone know of a tutorial or can share an example (I haven't found any to suit my needs so far) in which the JList is updated something like JList.update(startIndex, endIndex);? Thanks for taking the time to answer.

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• Is both approach same ?

  - by Harikrishna

  I have one datatable which is not bindided and records are coming from the file by parsing it in the datatable dynamically every time. Now there is three columns in the datatable Marks1,Marks2 and FinalMarks. And their types is decimal. Now for making addition of columns Marks1 and Marks2 's records and store it into FinalMarks column,For that what I do is : datatableResult.Columns["FinalMarks"].Expression="Marks1+Marks2"; It's works properly. It can be done in other way also is foreach (DataRow r in datatableResult.Rows) { r["FinalMarks"]=Convert.ToDecimal(r["Marks1"])+Convert.ToDecimal(r["Marks2"]); } Now I don't know that which is the best way to do this means performance wise. Is first approach same as second approach in background means is both approach same or what?

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• How can I avoid "Your system is running low on virtual memory" pop-up?

  - by Xavier Nodet

  Our application sometimes uses a lot of memory, and this is expected. But when we test it under high load on Windows XP, we usually get the very annoying "Your system is running low on virtual memory" popup, and this prevents our automated, unattended, tests to run through... Is it possible to prevent this popup to appear, and just have the allocation fail? The app will handle it gracefully, and tests will go on... We are using Windows XP, but if a solution only exists on later versions, I'd be happy to know anyway.

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• Question about varrying top margin when using custom Fonts on the iPhone.

  - by user170030

  I am using FontLabel to display varying lengths of texts in a custom font. I size the FontLabel using the following : CGSize size = [myString sizeWithFont:[UIFont systemFontOfSize:[[[UIApplication sharedApplication] delegate] getFontSize]] constrainedToSize:CGSizeMake(290, 4000) lineBreakMode:UILineBreakModeWordWrap]; For some reason, this always presents a Fontlabel where the text starts at a different space from the top. Sometimes the text begins at the correct location. Other times, it appears either too high or too low. Would appreciate some help in how to solve this issue.

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• Is select() Ok to implement single socket read/write timeout ?

  - by chmike

  I have an application processing network communication with blocking calls. Each thread manages a single connection. I've added a timeout on the read and write operation by using select prior to read or write on the socket. Select is known to be inefficient when dealing with large number of sockets. But is it ok, in term of performance to use it with a single socket or are there more efficient methods to add timeout support on single sockets calls ? The benefit of select is to be portable.

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• Are there any good books on writing commercial quality software?

  - by Andy

  Hey, My background has been generally new technology demonstrators, which, well... demonstrate the latest technology and how it can be of use to a clients company. They use it for internal demos etc. Now my career has shiffed course a bit more into actual products, in particular software which runs in locations like museums as interactive pieces. Clearly, although the technology demonstrators had to be well coded etc, there wasn't as much emphasis as there is on my current work, which has to work, be highly configurable, probably multi-ligual and run constantly, without restarts. So my question is, now that I'm trying to up my coding quality and write more commercial applications, are there any books which discuss issues surrounding high quality commercial software? I currently have a copy of Code Complete 2nd Edition, which is excellent, but just wondering if there's any better, possibly more focused titles out there? Thanks a lot! Andy.

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• What FIX implementation do you recommend for use with .NET

  - by Ajaxx

  I am reviewing implementation choices for FIX when using .NET. A few obvious choices come to mind, but I want to know if there are other options, better choices or if we've made the same decision as a lot of you. QuickFIX - Stable, C++ implementation - so you've got unmanaged code to interop with. FIX4NET - C# implementation - seems to have some gaps in its implementation. DIY - Chime in here if you've made your own FIX engine Let me throw in some caveats here. I'm not looking for sub 100 microsecond processing. Performance is a requirement, but not so much that it's driving my decisions. A solid product that is stable, performs well and is flexible enough to deal with vendor specific dialects is the sweet spot. The more we can do in .NET the better.

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• ExtJS Grid slow with 3000+ records

  - by Oliver Watkins

  I am using ExtJS Grid and its getting pretty slow with 3000+ records. Sorting takes about 4 seconds. Compared to other more Javascript tables, this is pretty slow. I am thinking maybe to use pagination in my table. However after reading the documentation, I am still a bit unsure about how pagination works in extjs. Does this pull data from the server each time u turn a page? I would prefer that wasn't the case. I would prefer the 3000 records are saved in the browser and then what is rendered is just a portion of those rows. Also I am using Extjs version 4.2.1. If I upgrade to version 5. will I get some performance improvements?

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• How to split movie and play parts to look as a whole?

  - by luksow

  I'm writing software which is demonstraiting video on demand service. One of the feature is something similiar to IIS Smooth Streaming - I want to adjust quality to the bandwith of the client. My idea is, to split single movie into many, let's say - 2 seconds parts, in different qualities and then send it to the client and play them. The point is that for example first part can be in very high quality, and second in really poor (if the bandwith seems to be poor). The question is - do you know any software that allows me to cut movies precisly? For example ffmpeg splits movies in a way that join is visible and really annoying (seconds are the measure of precision). I use qt + phonon as a player if it matters. Or maybe you know any better way to provide such feature, without splitting movie into parts?

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• Conceptually, how does replay work in a game?

  - by SnOrfus

  I was kind of curious as to how replay might be implemented in a game. Initially, I thought that there would be just a command list of every player/ai action that was taken in the game, and it then 're-plays' the game and lets the engine render as usual. However, I have looked at replays in FPS/RTS games, and upon careful inspection even things like the particles and graphical/audible glitches are consistent (and those glitches are generally *in*consistent). So How does this happen. In fixed camera angle games I though it might just write every frame of the whole scene to a stream that gets stored and then just replays the stream back, but that doesn't seem like enough for games that allow you to pause and move the camera around. You'd have to store the locations of everything in the scene at all points in time (No?). So for things like particles, that's a lot of data to push which seems like a significant draw on the game's performance whilst playing.

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• Writing custom Django form fields and widgets

  - by hekevintran

  Django has very good documentation that describes how to write custom database fields and custom template tags and filters. I cannot find the document that describes how to write custom form fields and widgets. Does this document exist? The way I've been able to write custom form fields and widgets is by reading the Django source code and imitating what I see there. I know that there are still things about implementing fields and widgets that I do not completely understand because I have not read any high level document that describes their interfaces.

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• How can I configure different worker pools using celery?

  - by Chris R

  I need to deploy a queued execution service with (generally) the following three classes of worker: A periodic, low-priority job class that takes a long time and can be processed serially; these jobs should only use 0..2 workers in the system at most. A periodic, deadline-sensitive job class that take a short to medium amount of time (say, topping out at 5 minutes) An ad-hoc job class, that is higher priority than #1, but can interleave with #2. Any workers from class #2 that are inactive when this type of job comes in should handle it, without ever starving the pool of workers for #2 All three job classes are the same task, the only difference between them is how they're requested; they'll take the same input and generate the same output, but each one has different performance guarantees. How can I implement this using celery?

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• OpenGL and layouts

  - by Hnefi

  I'm using OpenGL to render a game view in my android application. The game is turn based and I wish to add some buttons to the interface. I'd prefer to use standard Android widgets, structured in an XML-generated layout (or, if I have to, a hardcoded layout) and put the OpenGL view in its own window as part of that layout. So in regards to this, I have 3 questions: 1: Is such a thing possible? I've done a few half-hearted tries, but have had no luck so far. 2: Is such a thing advisable? Does it carry a significant performance penalty, for example, over using OpenGL-based homebrew widgetry? 3: Is it possible to pass particular arguments to instances created in XML layouts? For example, my current OpenGL view has three arguments in its constructor; is it somehow possible for me to invoke that particular constructor with particular parameters when it's part of a layout?

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• What is the best method of assessment for computer science students?

  - by Gavimoss

  This question is a bit more philosophical so feel free to remove if you like but it's been bugging me for the last 4 years! As a final year student I find that exams can be often be passed with a couple of days of cramming, without necessarily retaining or understanding the content i.e. a regurgitation of lecture notes is often enough to gain high marks. A friend of mine is about to graduate with an honours degree whose final year evaluation was based solely on practical work (a project, assignment marks and the creation of a poster) yet all of this work could have been completed by a third party. Personally I don't think either of these methods of assessment is sufficient as I am currently on track for a 1st class honours in artificial intelligence and computer science and believe this is mostly due to my skill in passing exams not my skill as a programmer or my vast in depth knowledge of any of the subjects I have "studied". Surely there is a better way to assess our skills - isn't there?

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• Slow Client connection blocks Mongrel

  - by Sanjay

  I have a Apache + Haproxy + Mongrel setup for my rails application. When I hit a particular server page, mongrel takes around 100ms to process the request and I get the page in around 5 secs due to data transmission time on my slow home connection. Now I see that during these 5 secs of data transmission, mongrel does not serve any other request. I am surprised as that means mongrel is serving the response html to the client and is blocked till the client receives it. Shouldn't serving response be the job of Apache? This puts serious bottleneck in the no of requests Mongrel can serve as that would depend on the speed of the client connection. Is there any way that html generated by mongrel is served by apache/haproxy or any other web server like nginx? I wonder how the other high traffic sites are managing it?

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• How does Core Data determine if an NSObjects data can be dropped?

  - by Kevin

  In the app I am working on now I was storing about 500 images in Core Data. I have since pulled those images out and store them in the file system now, but in the process I found that the app would crash on the device if I had an array of 500 objects with image data in them. An array with 500 object ids with the image data in those objects worked fine. The 500 objects without the image data also worked fine. I found that I got the best performance with both an array of object ids and image data stored on the filesystem instead of in core data. The conclusion I came to was that if I had an object in an array that told Core Data I was "using" that object and Core Data would hold on to the data. Is this correct?

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• In a virtual machine monitor such as VMware's ESXi Server, how are shadow page tables implemented?

  - by ali01

  My understanding is that VMMs such as VMware's ESXi Server maintain shadow page tables to map virtual page addresses of guest operating systems directly to machine (hardware) addresses. I've been told that shadow page tables are then used directly by the processor's paging hardware to allow memory access in the VM to execute without translation overhead. I would like to understand a bit more about how the shadow page table mechanism works in a VMM. Is my high level understanding above correct? What kind of data structures are used in the implementation of shadow page tables? What is the flow of control from the guest operating system all the way to the hardware? How are memory access translations made for a guest operating system before its shadow page table is populated? How is page sharing supported? Short of straight up reading the source code of an open source VMM, what resources can I look into to learn more about hardware virtualization?

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• [Symfony] Admin generator and i18n

  - by David

  I have read lots of questions about i18n, but I haven't found any about performance. I have a simple backend app listing the contents of an ads table. These ads have a category, that is translated in some languages (it's defined as i18n in the Doctrine schema). So, when I add a "table_method" in my generator.yml to include de Category table, it reduces the number of queries, but there are yet some of them referencing i18n translation tables. So, if I add the category Translation table to the query, it reduces even more the queries BUT it increases the processing time considerably. Why this time penalty? Just because of the translation table? And why isn't the filter using this method to avoid so many translation queries as well? I mean, if I want to filter by category, it is making one query per category to include the translation table. Why??

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• Examples of fast .NET WPF/WinForms apps?

  - by mythz

  I am currently investigating whether to build a windows application using unmanaged C/C++ or in .NET and would like to know of the kind of performance and responsiveness that is capable with a managed C#/.NET GUI app? Not surprisingly it looks like the fastest most responsive applications (e.g. chrome, spotify, etc) are written in unmanaged C/C++. I've had a hard time finding examples of really good .NET applications and so I would like some help. What's the best example of a fast and responsive .NET windows application?

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• Detect numbers and process them ?

  - by Madhup

  Hi, I am trying to detect the numbers written on a grid and then process them using the iPhone camera. What i have found till yet are some good examples like: http://blog.damiles.com/?p=93 http://cmgresearch.blogspot.com/2010/01/augmented-reality-on-iphone-how-to_01.html Although I am able to draw the numbers on the overlay view to a good extent but still not able to detect what these numbers are. What I don't wanna do is to go through the whole AI process: training the system, providing the system whole set of values and then process them, because this is so much troublesome for me as well for the performance of my application. So guys having any idea or work arround for this please help. Thanks, Madhup

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