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• Is it a good idea to close and open hibernate sessions frequently?

  - by Gaurav

  Hi, I'm developing an application which requires that state of entities be read from a database at frequent intervals or triggers. However, once hibernate reads the state, it doesn't re-read it unless I explicitly close the session and read the entity in a new session. Is it a good idea to open a session everytime I want to read the entity and then close it afterwards? How much of an overhead does this put on the application and the database (we use a c3p0 connection pool also)? Will it be enough to simply evict the entity from the session before reading it again?

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• Secure password transmission over unencrypted tcp/ip

  - by academicRobot

  I'm in the designing stages of a custom tcp/ip protocol for mobile client-server communication. When not required (data is not sensitive), I'd like to avoid using SSL for overhead reasons (both in handshake latency and conserving cycles). My question is, what is the best practices way of transmitting authentication information over an unencrypted connection? Currently, I'm liking SRP or J-PAKE (they generate secure session tokens, are hash/salt friendly, and allow kicking into TLS when necessary), which I believe are both implemented in OpenSSL. However, I am a bit wary since I don't see many people using these algorithms for this purpose. Would also appreciate pointers to any materials discussing this topic in general, since I had trouble finding any.

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• Using LocationManager from another class than Main

  - by iphonePom

  Hi, i'm new here, i'm new in iphone development, i'm new in Objective-c and i'm new in engligh speaking, so don't hate me :P I'm creating an application that will use the location manager to display the distance between the own position and the positions of a list of shops, like AroundME. Now, i give the locationManager property to my main class and in the .m of that class, precisely in the viewDidLoad method, i make: [locationManager startUpdatingLocation]. It all works fine, but the problem is: i need to know my position in other classes than the main, but i don't think that is a good idea making [locationManager startUpdatingLocation] every time i need it, is not time overhead? The view of my main class is always below the others, so can i retrieve the updated location in my other classes? In what way? Creating another instance of my main class is not useful, i think, but the locationManager, once started, doesn't stop until my main class is released, isn't true? So i think that it is accessible in some way. Thanks for your attention and sorry for my awful english : )

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• All things equal what is the fastest way to output data to disk in C++?

  - by user260197

  I am running simulation code that is largely bound by CPU speed. I am not interested in pushing data in/out to a user interface, simply saving it to disk as it is computed. What would be the fastest solution that would reduce overhead? iostreams? printf? I have previously read that printf is faster. Will this depend on my code and is it impossible to get an answer without profiling? Edit: Output data needs to be in text format, whether tab or comma separated. This will require formatting, precision, etc. Running in Windows.

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• Performance of jquery visible

  - by Mark Steudel

  I have a bunch of checkboxes on a page, and I only show a subset of those checkboxes at a time. I then perform some action which loops through all of the checkboxes and sees if they are checked or not: e.g. $(".delete_items").click( function() { $('.checkboxes' ).each(function(){ //do stuff } } Then I was thinking, well since the user can never interact with the hidden checkboxes, that adding :visible to checkboxes would speed up the loop e.g. $(".delete_items").click( function() { $('.checkboxes :visible' ).each(function(){ //do stuff } } But I don't know if adding :visible adds more overhead. Any thoughts?

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• Best Practice for creating Web Services

  - by Holograham

  To preface I am new to web development. I am looking at creating a core set of RESTful web services around a valuable document library of sorts (initial CRUD abilities). In doing so I am theoretically creating a perfectly re-usable and scalable back-end to be used by unanticipated applications in the future. My question centers around the best practice for doing this. My initial requirement has me also creating a unique front end. Would I make the front end and back end completely separate projects to enhance the re-usability. It would increase overhead. Looking at using GWT, Restlet, and JEE technology stack if this influences the setup at all.

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• Tips for improving performance of DB that is above size 40 GB (Sql Server 2005) and growing monthly

  - by HotTester

  The current DB or our project has crossed over 40 GB this month and on an average it is growing monthly by around 3 GB. Now all the tables are best normalized and proper indexing has been used. But still as the size is growing it is taking more time to fire even basic queries like 'select count(1) from table'. So can u share some more points that will help in this front. Database is Sql Server 2005. Further if we implement Partitioning wouldn't it create a overhead ? Thanks in advance.

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• Why do debug symbols so adversely affect the performance of threaded applications on Linux?

  - by fluffels

  Hi. I'm writing a ray tracer. Recently, I added threading to the program to exploit the additional cores on my i5 Quad Core. In a weird turn of events the debug version of the application is now running slower, but the optimized build is running faster than before I added threading. I'm passing the "-g -pg" flags to gcc for the debug build and the "-O3" flag for the optimized build. Host system: Ubuntu Linux 10.4 AMD64. I know that debug symbols add significant overhead to the program, but the relative performance has always been maintained. I.e. a faster algorithm will always run faster in both debug and optimization builds. Any idea why I'm seeing this behavior?

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• Converting delimited string to multiple values in mysql

  - by epo

  I have a mysql legacy table which contains an client identifier and a list of items, the latter as a comma-delimited string. E.g. "xyz001", "foo,bar,baz". This is legacy stuff and the user insists on being able to edit a comma delimited string. They now have a requirement for a report table with the above broken into separate rows, e.g. "xyz001", "foo" "xyz001", "bar" "xyz001", "baz" Breaking the string into substrings is easily doable and I have written a procedure to do this by creating a separate table, but that requires triggers to deal with deletes, updates and inserts. This query is required rarely (say once a month) but has to be absolutely up to date when it is run, so e.g. the overhead of triggers is not warranted and scheduled tasks to create the table might not be timely enough. Is there any way to write a function to return a table or a set so that I can join the identifier with the individual items on demand?

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• What should I tell kids about how great it is to be a programmer?

  - by Sara Chipps

  I am putting a presentation together. I thought about illustrating with websites like Facebook, and MySpace. Does anyone have children around that age that could tell me what they are into? How to hold their attention? Ways to illustrate what we do? Get them interested? Your ideas are greatly appreciated, I really want to be able to convey how fun this is :). I don't have access to a digital projector... which really stinks. I do have access to an old transparency overhead, though. http://stackoverflow.com/questions/207278/career-day-how-do-i-make-computer-programmer-sound-cool-to-8-year-olds

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• What is the best way to embed controls in a list/grid

  - by Brad

  I have a table of about 450 rows that I would like to display in a graphical list for users to view or modify the line items. The users would be selection options from comboboxes and selecting check boxes etc. I have found a listview class that extends the basic listview to allow for embeding objects but it seems kind of slugish when I load all the rows into it. I have used a datagridview in the past for comboboxes and checkboxes, but there was a lot of time invested in getting that up and running...not a big fav of mine. I am looking for sugestions how I can do this with minimal overhead. thanks c#, vs2008, .net 2.0, system.windows.forms

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• static images aren't caching with php-generated page

  - by scootklein

  Our website was just converted to being generated by mod_rewrite and php scripts. Images aren't caching in browsers when they seemingly should be. All images follow format: <img src="/images/header.png" /> I must avoid the script completely caching because the PHP parser needs to handle each page dynamically on each request; however, the download overhead of the large images is cumbersome on every single page load. I would ideally provide headers for "Cache-Control: no-cache, must-revalidate" and "Expires: some_date_in_the_past" to force revalidation of the PHP script. Why isn't the browser caching static images with consistent href values across all pages?

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• Enumerating combinations in a distributed manner

  - by Reyzooti

  I have a problem where I must analyse 500C5 combinations (255244687600) of something. Distributing it over a 10 node cluster where each cluster processes roughly 10^6 combinations per second means the job will be complete in about 7hours. The problem I have is distributing the 255244687600 combinations over the 10 nodes. I'd like to present each node with 25524468760, however the algorithms I'm using can only produce the combinations sequentially, I'd like to be able to pass the set of elements and a range of combination indicies eg: [0-10^7) or [10^7,2.0 10^7) etc and have the nodes themselves figure out the combinations. The algorithms I'm using at the moment are from the following: http://home.roadrunner.com/~hinnant/combinations.html A logical question I've considered using a master node, that enumerates each of the combinations and sends work to each of the nodes, however the overhead incurred in iterating the combinations from a single node and communicating back and forth work is enormous, and will subsequently lead to the master node becoming the bottleneck. Are there any good combination iterating algorithms geared up for efficient/optimal distributed enumeration?

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• In C, is it possible do free only an array first or last position?

  - by user354959

  Hi there! I've an array, but I don't need its first (or last) position. So I point a new variable to the rest of the array, but I should free the array first/last position. For instance: p = read_csv_file(); q = p + 1; // I don't need the first CSV file field // Here I'd like to free only the first position of p return q; Otherwise I've to memcpy the array to other variable, excluding the first position, and then free the original array. Like this: p = read_csv_file(); q = (int*) malloc(sizeof(int) * (SOME_SIZE - 1)); memcpy(q, p+1, sizeof(int) * (SOME_SIZE - 1)); free(p); return q; But then I'll have the overhead of copying all the array. Is this possible to only free a single position of an array?

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• Can layouts be chosen by Grails controllers?

  - by maerics

  I'm building a CMS as a learning exercise in Grails and would like to give content managers the ability to choose between different HTML page structures (e.g. 2 column, 3 column, etc). Grails Layouts seem like a logical choice but is it possible for a Grails controller to explicitly name which layout will be used for rendering? Ideally there would be a layout option to the render method, per Ruby on Rails but I don't see anything like it. It seems like it might be possible using the applyLayout method by passing the name of the layout but this requires each GSP page to explicitly request layout (annoying overhead per-page) rather than using Layout by Convention. Any ideas?

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• Are there any way to link my program with Wine-compiled part?

  - by seas

  I am trying to use windows dll functionality in Linux. My current solution is a compilation of a separate wine application, that uses dll and transfer requests/responses between dll and main application over IPC. This works, but is a real overhead comparing to a simple dll calls. I see that wine-compiled program usually is a bootstrapping-script and some .so, which (according to file utility) is normal linux dynamically linked library. Are there any way to link that .so directly to my application? Are there any manual?

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• Function calls in virtual machine killing performance

  - by GenTiradentes

  I wrote a virtual machine in C, which has a call table populated by pointers to functions that provide the functionality of the VM's opcodes. When the virtual machine is run, it first interprets a program, creating an array of indexes corresponding to the appropriate function in the call table for the opcode provided. It then loops through the array, calling each function until it reaches the end. Each instruction is extremely small, typically one line. Perfect for inlining. The problem is that the compiler doesn't know when any of the virtual machine's instructions are going to be called, as it's decided at runtime, so it can't inline them. The overhead of function calls and argument passing is killing the performance of my VM. Any ideas on how to get around this?

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• when to use StringBuilder in java

  - by kostja

  It is supposed to be generally preferable to use a StringBuilder for String concatenation in Java. Is it always the case? What i mean is : Is the overhead of creating a StringBuilder object, calling the append() method and finally toString() smaller then concatenating existing Strings with + for 2 Strings already or is it only advisable for more Strings? If there is such a threshold, what does it depend on (the String length i suppose, but in which way)? And finally - would you trade the readability and conciseness of the + concatenation for the performance of the StringBuilder in smaller cases like 2, 3, 4 Strings?

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• How to convert value of Generic Type Argument to a concrete type?

  - by Aleksey Bieneman

  I am trying to convert the value of the generic type parameter T value into integer after making sure that T is in fact integer: public class Test { void DoSomething<T>(T value) { var type = typeof(T); if (type == typeof(int)) { int x = (int)value; // Error 167 Cannot convert type 'T' to 'int' int y = (int)(object)value; // works though boxing and unboxing } } } Although it works through boxing and unboxing, this is an additional performance overhead and i was wandering if there's a way to do it directly. Thank you!

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• C++ Virtual keyword as away to avoid including code units.

  - by user394663

  Currently we have a body of code that allows service plugins which offer forms of communication to the core e.g tcp/ip, udp/ip, usb, etc... These service plugins feedback notifier class instances to the core for further processing. In the current implementation a service project (which is a separate dynamically linked library brought in at runtime by the core via dlopen and friends) will compile against the notifier.cpp file that resides in the core source code (a separate project). This gives access to the notifiers method implementations. This works perfectly no complaints. Two alternative options: 1. put the notifier method implementations in the header file. 2. declare the notifier methods virtual and delay binding until runtime. Avoiding the issues of computational overhead what are the impacts of option 2? Are there any other options available to us? Thanks

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• Securing input of private / protected methods?

  - by ts

  Hello, normally, all sane developers are trying to secure input of all public methods (casting to proper types, validating, sanitizing etc.) My question is: are you in your code validating also parameters passed to protected / private methods? In my opinion it is not necessary, if you securize properly parameters of public methods and return values from outside (other classes, db, user input etc...). But I am constantly facing frameworks and apps (ie. prestashop to name one) where validation is often repeated in method call, in method body and once again for securize returned value - which, I think, is creating performace overhead and is also a sign of bad design.

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• Random numbers from binomial distribution

  - by Sarah

  I need to generate quickly lots of random numbers from binomial distributions for dramatically different trial sizes (most, however, will be small). I was hoping not to have to code an algorithm by hand (see, e.g., this related discussion from November), because I'm a novice programmer and don't like reinventing wheels. It appears Boost does not supply a generator for binomially distributed variates, but TR1 and GSL do. Is there a good reason to choose one over the other, or is it better that I write something customized to my situation? I don't know if this makes sense, but I'll alternate between generating numbers from uniform distributions and binomial distributions throughout the program, and I'd like for them to share the same seed and to minimize overhead. I'd love some advice or examples for what I should be considering.

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• Java: Reflection against casting when you know superclass

  - by Ema

  I don't know exactly how to define my doubt so please be patient if the question has already been asked. Let's say I have to dinamically instantiate an object. This object will surely be instance of a subclass of a known, immutable class A. I can obtain dinamically the specific implementation class. Would it be better to use reflection exactly as if I didn't know anything about the target class, or would it be preferrable/possible to do something like: A obj = (Class.forName("com.package.Sub-A")) new A(); where Sub-A extends A ? The purpose would be to avoid reflection overhead times... Thank you in advance.

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• C# type safe and developer friendly list/collection technique

  - by Agile Noob

  I am populating a "Dictionary" with the results of an sp call. The key is the field name and the value is whatever value the sp returns for the field. This is all well and good but I'd like developers to have a predefined list of keys to access this list, for safety and documentation reasons. What I'd like to do is have something like an enum as a key for the dictionary so developers can safely access the list, but still have the ability to access the dictionary with a string key value. I am hoping to have a list of string values that I can access with an enum key AND a string key. Please make sure any suggestions are simple to implement, this is not the kind of thing I'm willing to build a lot of overhead to implement.

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• Silverlight PRISM and 'loose' style files

  - by Suiva

  Hi, We are looking at starting a new Silverlight project using the PRISM framework (to benefit from modules etc) and I am still a little unclear about the best styling approach. What I'd ideally like is to have editable XAML files (maybe even just 1 for the whole project) containing the application's style so that they can be edited to change the look and feel of the application without having to recompile everything. Is this approach something people use? I guess it would need to load the file in at startup and apply the style which I assume wouldn't be a massive overhead. Just wondering what approaches people use Thanks for your time

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