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• Dispelling the UIImage imageNamed: FUD

  - by Roger Nolan

  I see a lot of people saying imageNamed is bad but equal numbers of people saying the performance is good - especially when rendering UITableViews. See this SO question for example or this article on iPhoneDeveloperTips.com UIImage's imageNamed method used to leak so it was best avoided but has been fixed in recent releases. I'd like to understand the caching algorithm better in order to make a reasoned decision about where I can trust the system to cache my images and where I need to go the extra mile and do it myself. My current basic understanding is that it's a simple NSMutableDictionary of UIImages referenced by filename. It gets bigger and when memory runs out it gets a lot smaller. For example, does anyone know for sure that the image cache behind imageNamed does not respond to didReceiveMemoryWarning? It seems unlikely that Apple would not do this. If you have any insight into the caching algorithm, please post it here.

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• writing a fast parser in python

  - by panzi

  I've written a hands-on recursive pure python parser for a some file format (ARFF) we use in one lecture. Now running my exercise submission is awfully slow. Turns out by far the most time is spent in my parser. It's consuming a lot of CPU time, the HD is not the bottleneck. I wonder what performant ways are there to write a parser in python? I'd rather not rewrite it in C. I tried to use jython, but that decreased performance a lot! The files I parse are partially huge ( 150 MB) with very long lines. My current parser only needs a look-ahead of one character. I'd post the source here but I don't know if that's such a good idea. After all the submission deadline has not jet ended. But then, the focus in this exercise is not the parser. You can choose whatever language you want to use and there already is a parser for Java.

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• Is it a good idea to create an STL iterator which is noncopyable?

  - by BillyONeal

  Most of the time, STL iterators are CopyConstructable, because several STL algorithms require this to improve performance, such as std::sort. However, I've been working on a pet project to wrap the FindXFile API (previously asked about), but the problem is it's impossible to implement a copyable iterator around this API. A find handle cannot be duplicated by any means -- DuplicateHandle specifically forbids passing handles to it. And if you just maintain a reference count to the find handle, then a single increment by any copy results in an increment of all copies -- clearly that is not what a copy constructed iterator is supposed to do. Since I can't satisfy the traditional copy constructible requirement for iterators here, is it even worth trying to create an "STL style" iterator? On one hand, creating some other enumeration method is going to not fall into normal STL conventions, but on the other, following STL conventions are going to confuse users of this iterator if they try to CopyConstruct it later. Which is the lesser of two evils?

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• Add Core Data Index to certain Attributes via migration

  - by steipete

  For performance reasons, i want to set the Indexed Attribute to some of my entities. I created a new core data model version to perform the changes. Core Data detects the changes and migrates my model to the new version, however, NO INDEXES ARE GENERATED. If I recreate the database from scratch, the indexes are there. I checked with SQLite Browser both on the iPhone and on the Simulator. The problem only occurs if a database in the prior format is already there. Is there a way to manually add the indexes? Write some sql for that? Or am I missing something? I did already some more critical migrations, no problems there. But those missing indexes are bugging me. Thanks for helping!

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• how does NTFS actually work with B-tree ?

  - by bakra

  To improve performance, NTFS directories use a special data management structure called a B-tree. "B-tree" concept here refers to a "tree of storage units" that hold the contents of an individual directory. What I don't understand is where on the disk is this tree stored? Its surely not created every-time we reboot...that would take lots of time. and since its a tree(dynamic Data structure) unlike arrays it will grow. so space needs to be allocated every-time it grows. so how is this "dynamic meta-data" stored ?

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• Tomcat - virtualhosting - name / ip / port - based

  - by lisak

  Hey, what are the usage scenarios for these kinds of virtual hosting ? Name Based - typical tomcat virtual hosting, one HOME instance with many contexts, each as an individual host IP based / port based - multiple instances of tomcat ( how is it with performance and memory consuption?) running on IP aliases (virtual IPs) for one network adapter, usually behind http apache server that can run name based virtual hostings. Otherwise I can't figure out how would I forward requests in iptables/firewall based on IP address, which is just one. How is IP based virtual hosting done as to Tomcat and multiple instances ? I'd like to hear some usage scenarios from your experience. How are you running your applications. Cause there are applications having it's own modified classloader and they are developed in a way to run alone withing a tomcat instance. Then there are trivial applications which can run within one instance without problems. Many thanks

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• Choosing between ExtJS and YUI based on application parameters.

  - by Kabeer

  Hello. I need help in taking call to choose between Ext JS and YUI libraries. Here are the key factors I have derived from my application requirements & development process: Complex, windows forms like controls Widgets, Layouts, Utilities Inter widget communication Easy to extend Easy to learn Intuitive & concise coding Strong exception handling Active support / community To update with upcoming technologies (HTML5, etc.) Skins & Themes to be easy to change Skins & Themes to support variety (a text box for different context to appear differently) Support & Utilities for standard protocols (XmlHttp, JSON) Good performance (responsive) Cost is not crucial, but I don't mind saving :)

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• Best way to store large dataset in SQL Server?

  - by gary

  I have a dataset which contains a string key field and up to 50 keywords associated with that information. Once the data has been inserted into the database there will be very few writes (INSERTS) but mostly queries for one or more keywords. I have read "Tagsystems: performance tests" which is MySQL based and it seems 2NF appears to be a good method for implementing this, however I was wondering if anyone had experience with doing this with SQL Server 2008 and very large datasets. I am likely to initially have 1 million key fields which could have up to 50 keywords each. Would a structure of keyfield, keyword1, keyword2, ... , keyword50 be the best solution or two tables keyid keyfield | 1 | | M keyid keyword Be a better idea if my queries are mostly going to be looking for results that have one or more keywords?

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• Struct in C, are they efficient?

  - by pygabriel

  I'm reading some C code like that: double function( int lena,double xa,double ya, double za, double *acoefs, ..., int lenb,double xb,double yb, double zb, double *bcoefs, ..., same for c, same for d ) This function is called in the code mor than 100.000 times so it's performance-critical. I'm trying to extend this code but I want to know if it's efficient or not (and how much this influences the speed) to encapsulate all the parameters in a struct like this struct PGTO { int len; double x,y,z ; double *acoefs } and then access the parameters in the function.

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• Using Windows media foundation

  - by Martin Beckett

  Ok so my new gig is high performance video (think Google streetview but movies) - the hard work is all embedded capture and image processing but: I was looking at the new MS video offerings to display content = Windows Media Foundation. Is anyone actually using this ? There are no books on the topic. The only documentation is a developer team blog with a single entry 9 months old. I thought we had got past having to learn an MS api by spying on the com control messages! Is it just another wrapper around the same old activeX control?

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• How to achieve a palette effect on iPhone using OpenGL

  - by Joe

  I'm porting a 2d retro game to iPhone that has the following properties: targets OpenGL ES 1.1 entire screen is filled with tiles (textured triangle strip tile textured using a single 256x256 RGBA texture image the texture is passed to OpenGL once at the start of the game only 4 displayed colours are used one of the displayed colours is black The original game flashed the screen when time starts to run out by toggling the black pixels to white using an indexed palette. What is the best (i.e. most efficient) way to achieve this in OpenGL ES 1.1? My thoughts so far: Generate an alternative texture with white instead of black pixels, and pass to OpenGL when the screen is flashing Render a white poly underneath the background and render the texture with alpha on to display it Try and render a poly on top with some blending that achieves the effect (not sure this is possible) I'm fairly new to OpenGL so I'm not sure what the performance drawbacks of each of these are, or if there's a better way of doing this.

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• Can I get the stack traces of all threads in my c# app?

  - by Drew Shafer

  I'm debugging an apparent concurrency issue in a largish app that I hack on at work. The bug in question only manifests on certain lower-performance machines after running for many (12+) hours, and I have never reproduced it in the debugger. Because of this, my debugging tools are basically limited to analyzing log files. C# makes it easy to get the stack trace of the thread throwing the exception, but I'd like to additionally get the stack traces of every other thread currently executing in my AppDomain at the time the exception was thrown. Is this possible?

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• Is AsParallel() good practice in a web environment?

  - by Bjorn Bailleul

  I have no doubt that for client applications, AsParallel() will bring some out-of-the-box performance gains. But what if I would use it in a web environment. Let's say I have a widget framework that loops over all widgets to get their data and render output. This would parallelize great no? I do have my doubts on using AsParallel() in this scenario. What if I have a large number of visitors for my site, isn't IIS going to use multiple threads to handle all requests? Aren't there going to be locking issues presented after a while, or threads dying because all processors are in use? It's just a thought, what do you think about this?

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• How to SET ARITHABORT ON for connections in Linq To SQL

  - by Laurence

  By default, the SQL connection option ARITHABORT is OFF for OLEDB connections, which I assume Linq To SQL is using. However I need it to be ON. The reason is that my DB contains some indexed views, and any insert/update/delete operations against tables that are part of an indexed view fail if the connection does not have ARITHABORT ON. Even selects against the indexed view itself fail if the WITH(NOEXPAND) hint is used (which you have to use in SQL Standard Edition to get the performance benefit of the indexed view). Is there somewhere in the data context I can specify I want this option ON? Or somewhere in code I can do it?? I have managed a clumsy workaround, but I don't like it .... I have to create a stored procedure for every select/insert/update/delete operation, and in this proc first run SET ARITHABORT ON, then exec another proc which contains the actual select/insert/update/delete. In other words the first proc is just a wrapper for the second. It doesn't work to just put SET ARITHABORT ON above the select/insert/update/delete code.

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• Are C++ meta-templates required knowledge for programmers?

  - by Robert Gould

  In my experience Meta-templates are really fun (when your compilers are compliant), and can give good performance boosts, and luckily I'm surrounded by seasoned C++ programmers that also grok meta-templates, however occasionally a new developer arrives and can't make heads or tails of some of the meta-template tricks we use (mostly Andrei Alenxandrescu stuff), for a few weeks until he gets initiated appropriately. So I was wondering what's the situation for other C++ programmers out there? Should meta-template programming be something C++ programmers should be "required" to know (excluding entry level students of course), or not? Edit: Note my question is related to production code and not little samples or prototypes

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• Flexible argument list in LibreOffice Calc Macro

  - by Patru

  I want to write a function that geometrically links performance data which is usually provided as percentages, so the function will basically return (1+a)*(1+b)*(1+c)* … *(1+x)-1 This should be done using LibreOffice-calc and it should behave similarly to the regular sum function. As you may throw any number of arguments at sum I would like to be able to do the same with my alternative geoSum function but I am unable to find suitable documentation on handling a variable number of arguments with variable types (i.e. an arbitrary mix of numbers, cells and ranges). How would I have to specify the arguments to my LibreOffice-Basic function and how would I have to interpret it?

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• Are IoC containers about configuration files?

  - by Jader Dias

  Recently I developed a performance tester console application, with no UI, with the help of a IoC containter (Castle-Windsor-Microkernel). This library enabled me to let the user choose which test(s) to run, simply by changing the configuration file. Have I realized what IoC containers are about? I'm not sure. Even Joel said here on SO that IoC are difficult to understand. From my example, what do you conclude? Am I using IoC container for exactly what they were designed for? Or I am just using one of its secondary features?

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• NHibernate transaction management in ASP.NET MVC - how should it be done?

  - by adrin

  I am writing a simple ASP.NET MVC using session per request and transaction per request patterns (custom HttpModule). It seems to work properly, but.. the performance is terrible (a simple page loads ~7 seconds). For every http request, graphical resources incuding (all images on the site) a transaction is created and that seems to delay the loading times (without the transactions loading times per one image are ~1-10 ms with transactions they are over 1 second). What is the proper way to manage transactions in ASP.NET MVC + NH stack? When i've put all transactions into my repository methods, for some obscure reasons I got 'implicit transactions' warning in NHProf (the SQL statements were executed outside transaction, even that in code session.Save()/Update()/etc methods were invoked within transaction 'using' scope and before transaction.Commit() call) BTW are implicit transactions really bad?

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• ASP.Net Web Site Project vs. Web Application Project

  - by user144612

  I'm trying to convince my co-workers to switch from a web site project to a web application project, because I want the use of the project file. However I can't diffuse this argument against: The web site project allows each page to be compiled into a single dll. Their argument is this enables easy fixing of errors found after publishing. This is contrast to how the web application project compiles all code behind into a single dll. Is updating a single page's dll essentially different to updating the entire site's dll? Is there some way to compile each page's code behind into a seperate dll in the web application project? Are there some prohibitive (performance,memory?) costs to compiling each page's code behind into seperate dll's that we are unaware of? Why is the feature(?) to compile each page to separate dlls in web site projects and not web app projects?

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• Using different languages in one project

  - by Tarbal

  I recently heard about the use of several different languages in a (big) project, I also read about famous services such as Twitter using Rails as frontend, mixed with some other languages, and Scala I think it was as backend. Is this common practice? Who does that? I'm sure there are disadvantages to this. I think that you will have problems with the different interpreters/compilers and seamlessly connecting the different languages. Is this true? Why is this actually done? For performance?

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• arbitrary typed data in django model

  - by Dmitry Shevchenko

  I have a model, say, Item. I want to store arbitrary amount of attributes on it, like title, description, release_date. And i want them to be not just strings but have python type, so string, boolean, datetime etc. What are my options here? EAV pattern with separate name-value table won't work because of the same DB type across all values. JSONField can probably help, but it doesn't know about datetime, for example. Also i was looking at PickeField, it fits perfectly, but i'm a bit concerned about performance.

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• Tokenizer for full-text

  - by user72185

  This should be an ideal case of not re-inventing the wheel, but so far my search has been in vain. Instead of writing one myself, I would like to use an existing C++ tokenizer. The tokens are to be used in an index for full text searching. Performance is very important, I will parse many gigabytes of text. Edit: Please note that the tokens are to be used in a search index. Creating such tokens is not an exact science (afaik) and requires some heuristics. This has been done a thousand time before, and probably in a thousand different ways, but I can't even find one of them :) Any good pointers? Thanks!

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• How to re-use a thread in Java ?

  - by David

  I am a building a console Sudoku Solver where the main objective is raw speed. I now have a ManagerThread that starts WorkerThreads to compute the neibhbors of each cell. So one WorkerThread is started for each cell right now. How can I re-use an existing thread that has completed its work? The Thread Pool Pattern seems to be the solution, but I don't understand what to do to prevent the thread from dying once its job has been completed. ps : I do not expect to gain much performance for this particular task, just want to experiment how multi-threading works before applying it to the more complex parts of the code. Thanks

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• C#, WinForms: Which view type for periodically updated list?

  - by rdoubleui

  I'm having an application, that periodically polls a web service (about every 10 seconds). In my application logic I'm having a List<Message> holding the messages. All messages have an id, and might be received out of order. Therefore the class implements the Comparable Interface. What WinForm control would fit to be regurarly updated (with the items in order). I plan to hold the last 500 messages. Should I sort the list and then update the whole form? Or is data binding approriate (concerning performance)?

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• Precompile Lambda Expression Tree conversions as constants?

  - by Nathan

  It is fairly common to take an Expression tree, and convert it to some other form, such as a string representation (for example this question and this question, and I suspect Linq2Sql does something similar). In many cases, perhaps even most cases, the Expression tree conversion will always be the same, i.e. if I have a function public string GenerateSomeSql(Expression<Func<TResult, TProperty>> expression) then any call with the same argument will always return the same result for example: GenerateSomeSql(x => x.Age) //suppose this will always return "select Age from Person" GenerateSomeSql(x => x.Ssn) //suppose this will always return "select Ssn from Person" So, in essence, the function call with a particular argument is really just a constant, except time is wasted at runtime re-computing it continuously. Assuming, for the sake of argument, that the conversion was sufficiently complex to cause a noticeable performance hit, is there any way to pre-compile the function call into an actual constant?

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