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• Can I replicate some of the optimisations done by the JVM by hand?

  - by Subb

  I'm working on a Sudoku solver at school and we're having a little performance contest. Right now, my algorithm is pretty fast on the first run (about 2.5ms), but even faster when I solve the same puzzle 10 000 times (about 0.5ms for each run). Those timing are, of course, depend of the puzzle being solved. I know the JVM do some optimization when a method is called multiple time, and this is what I suspect is happening. I don't think I can further optimize the algorithm itself (though I'll keep looking), so I was wondering if I could replicate some of the optimizations done by the JVM. Note : compiling to native code is not an option Thanks!

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• Simple cdd (custom debian distribution) problem

  - by Daniel G. R.

  Hi everyone, Im trying to make my own debian distribution but I have a problem. simple-cdd works fine but when I try to install my generated .iso, everything goes right since a message apears: " No installable kernel was found in the defined APT sources You may try to continue without a kernel. and manually install your kernel later. This is only recommended for experts, otheriwse you will likely end with a machine that dosent boot. COntinue Without installing a kernel? " And if y say yes, it continues... When is time to install grub it says: " Installation step failed An installation step failed. You can try to run the failing item again from the menu, or skip it and choose something else. The failing step is: Install the GRUB boot loader on a hard disk " HELP!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

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• Endless saving of CoreData Context

  - by Robert

  Sometimes I noticed that a 'save:' operation an a ManagedObjectContext never returns and consumes 100% CPU. I'm using an SQL Store in a GarbageCollected environment (Mac OS X 10.6.3). The disk activity shows about 700 KB/s writing. While having a look at the folder that contains the sqlite database file the "-journal" file appears and disappears, appears and disappears, ... This is part of the call graph from the process analysis: 2203 -[NSManagedObjectContext save:] 1899 -[NSPersistentStoreCoordinator(_NSInternalMethods) executeRequest:withContext:] 1836 -[NSSQLCore executeRequest:withContext:] 1836 -[NSSQLCore saveChanges:] 1479 -[NSSQLCore performChanges] ... 335 -[NSSQLCore recordChangesInContext:] ... 20 -[NSSQLCore rollbackChanges] ... 2 -[NSSQLCore prepareForSave:] ... 62 -[NSPersistentStoreCoordinator(_NSInternalMethods) _checkRequestForStore:originalRequest:andOptimisticLocking:] ... 1 -[NSPersistentStore(_NSInternalMethods) _preflightCrossCheck] ... 184 -[NSMergePolicy resolveConflicts:] ... 120 -[NSManagedObjectContext(_NSInternalChangeProcessing) _prepareForPushChanges:] ... Everything a happening in the main GUI thread. Any ideas what I can to do to resolve the problem?

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• C# asp.net MVC: When to update LastActivityDate?

  - by Oskar Kjellin

  I'm using asp.net mvc and creating a public website. I need to keep track of users that are online. I see that the standard way in asp.net of doing this is to keep track of LastActivityDate. My question is when should I update this? If I update it every time the users clicks somewhere, I will feel a performance draw back. However if I do not do that, people that only surf arround will be listed as offline. What is the best way to do this in asp.net MVC?

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• Which are the current/emerging desktop development technologies worth looking into?

  - by heeboir

  Greetings, With all the existing development towards web development and emerging technologies in that area, I'm left wondering; what is a state of the art way to implement desktop applications in this day and age? If you were to start a new application of considerable size from scratch what technology would you invest your efforts in (focusing on cross platform portability, decent performance and interoperability with existing standards)? I've looked into the Adobe Air platform which appears quite impressive but seems rather limited to support a large application. Would something like Java/SWT still be the sensible choice? Do things like GWT fit the bill? Thanks P.S. I'm leaving my question a bit open-ended in an effort to gather diverse answers. Surely this a subjective matter and there is no right and wrong answer.

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• Why SQL functions are faster than UDF

  - by Zerotoinfinite

  Though it's a quite subjective question but I feel it necessary to share on this forum. I have personally experienced that when I create a UDF (even if that is not complex) and use it into my SQL it drastically decrease the performance. But when I use SQL inbuild function they happen to work pretty faster. Conversion , logical & string functions are clear example of that. So, my question is "Why SQL in build functions are faster than UDF"? and it would be an advantage if someone can guide me how can I judge/manipulate function cost either mathematically or logically.

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• how do I download a large file (via HTTP) in .NET

  - by nickcartwright

  I need to download a LARGE file (2GB) over HTTP in a C# console app. Problem is, after about 1.2GB, the app runs out of memory. Here's the code I'm using: WebClient request = new WebClient(); request.Credentials = new NetworkCredential(username, password); byte[] fileData = request.DownloadData(baseURL + fName); As you can see... I'm reading the file directly into memory. I'm pretty sure I could solve this if I were to read the data back from HTTP in chunks and write it to a file on disk. Does anyone know how I could do this?

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• C#. Struct design. Why 16 byte is recommended size?

  - by maxima120

  I read Cwalina book (recommendations on development and design of .NET apps). He says that good designed struct has to be less than 16 bytes in size (for performance purpose). My questions is - why exactly is this? And (more important) can I have larger struct with same efficiency if I run my .NET 3.5 (soon to be .NET 4.0) 64-bit application on i7 under Win7 x64 (is this limitation CPU / OS based)? Just to stress again - I need as efficient struct as it is possible. I try to keep it in stack all the time, the application is heavily multi-threaded and runs on sub-millisecond intervals, the current size of the struct is 64 byte.

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• Password protect web pages on Windows CE 6

  - by Chris

  I am using the default web server for WinCE 6 and wish to password protect certain folders. The default VROOT /remoteadmin/ is password protected, and this works but my configuration doesn't work. I have tried mimicking these settings on my own folders but to little success. Here is how one looks: In the HKLM\Comm\HTTPD\VROOTS key I have created a subkey called /web/configuration (this folder actually exists on the box). The following values are in this key A = 1 DefaultPage = config.html Path = /hard disk/webroot/web/configuration/ UserList = ADMIN This is nigh on identical to the settings in /RemoteAdmin/ but /RemoteAdmin/ requests a password and /web/configuration doesn't (even after reboot).

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• Oracle spatial search within distance

  - by KA_lin

  I have the following table Cities: ID(int),City(char),latitude(float),longitude(float). Now based on a user`s longitude(ex:44.8) and latitude(ex:46.3) I want to search for all the cities near him within 100 miles/KM. I have found some examples but don`t know how to adapt them to my case select * from GEO.Cities a where SDO_WITHIN_DISTANCE([I don`t know], MDSYS.SDO_GEOMETRY(2001, 8307, MDSYS.SDO_POINT_TYPE(44.8,46.3, NULL) ,NULL, NULL), 'distance = 1000') = 'TRUE'; Any help would be appreciated. P.S: If it is possible to have the distance and to be sorted P.P.S: I want to do it in this way due to performance issues, I have done this in this way http://www.scribd.com/doc/2569355/Geo-Distance-Search-with-MySQL but it takes too long...

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• Django: common template subsections

  - by Parand

  What's a good way to handle commonly occurring subsections of templates? For example, there is a sub-header section that's used across 4 different pages. The pages are different enough to not work well with template inheritance (ie. "extends" doesn't fit well). Is "include" the recommended method here? It feels a bit heavyweight, requiring each subsection or snippet to be in its own file. Are there any performance issues in using include or is it smart about forming template from the subsections (ie. if I make extensive use of it, do I pay any penalties)? I think what I'm looking for is something like template tags, but without the programming - a simple way to create a library of html template tags I can sprinkle in other templates.

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• Using pthread condition variable with rwlock

  - by Doomsday

  Hello, I'm looking for a way to use pthread rwlock structure with conditions routines in C++. I have two questions: First: How is it possible and if we can't, why ? Second: Why current POSIX pthread have not implemented this behaviour ? To understand my purpose, I explain what will be my use: I've a producer-consumer model dealing with one shared array. The consumer will cond_wait when the array is empty, but rdlock when reading some elems. The producer will wrlock when adding(+signal) or removing elems from the array. The benefit of using rdlock instead of mutex_lock is to improve performance: when using mutex_lock, several readers would block, whereas using rdlock several readers would not block.

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• Is a selector like *+* safe to use?

  - by mcmullins

  I recently came across this CSS selector while trying to find a way to easily space out major blog elements such as paragraphs and images. An example of its use would be something like this: .post *+* {margin-top: 15px;} /* or... */ .post > *+* {margin-top: 15px;} /* if you don't want the margin to apply to nested elements */ At first glance, it seemed pretty useful. So my question is: What downsides are there to using these selectors? Specifically: What's the browser support like for this? Are there any cases you wouldn't want an even margin spacing between elements in an article and if not, is it easier to declare this first and then overwrite or simply declare each element individually? Does this have performance issues since you're selecting everything twice?

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• When configuring daily backups, which files should I include to be sure I have the MySQL db's

  - by user575599

  I have a dedicated LAMP server with cpanel hosting 100 websites (some of them have MySQL db's). I am currently using the Jungle Disk Server Edition to backup our files from our LAMP server to Amazon S3. Once a week were are backing up the entire cpanel which is an enormous strain on resources but that is a separate issue. Now, what I want to do is to set up a daily job to backup just the HTML files and the MySQL db's. If I just backup the "public_html" folder will my MySQL database info be stored in that directory? Would backing up the public_html folder be enough to recover the db? I can find plenty of resources online about how to manually backup MySQL db's but with a 100 sites, I need it automated. I'm hoping for an easy solution where I can just grab a folder to backup each day.

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• Worried about spiders repeatedly hitting high-demand page

  - by Matt Thrower

  Due to some rather bizarre architectural considerations I've had to set up something that really ought to run as a console application as a web page. It does the job of writing a large variety of text files and xml feeds from our site data for various other services to pick up so obviously it takes a little while to run and is pretty processor intensive. However, before I deploy it I'm rather worried that it might get hit repeatedly by spiders and the like. It's fine for the data to be re-written but continual hits on this page are going to trigger performance issues for obvious reasons. Is this something I ought to worry about? Or in reality is spider traffic unlikely to be intensive enough to cause problems?

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• A non-blocking server with java.io

  - by Jon

  Everybody knows that java IO is blocking, and java NIO is non-blocking. In IO you will have to use the thread per client pattern, in NIO you can use one thread for all clients. Now my question follows: is it possible to make a non-blocking design using only the Java IO api. (not NIO) I was thinking about a pattern like this (obviously very simplified); List<Socket> li; for (Socket s : li) { InputStream in = s.getInputStream(); byte[] data = in.available(); in.read(data); // processData(data); (decoding packets, encoding outgoing packets } Also note that the client will always be ready for reading data. What are your opinions on this? Will this be suitable for a server that should at least hold a few hundred of clients without major performance issues?

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• How do search engines see dynamic profiles?

  - by Lumpy

  Recently search engines have been able to page dynamic content on social networking sites. I would like to understand how this is done. Are there static pages created by a site like Facebook that update semi frequently. Does Google attempt to store every possible user name? As I understand it, a page like www.facebook.com/username, is not an actual file stored on disk but is shorthand for a query like: select username from users and display the information on the page. How does Google know about every user, this gets even more complicated when things like tweets are involved.

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• C++ Vector at/[] operator speed

  - by sub

  In order to give functions the option to modify the vector I can't do curr = myvec.at( i ); doThis( curr ); doThat( curr ); doStuffWith( curr ); But I have to do: doThis( myvec.at( i ) ); doThat( myvec.at( i ) ); doStuffWith( myvec.at( i ) ); (as the answers of my other question pointed out) I'm going to make a hell lot of calls to myvec.at() then. How fast is it, compared to the first example using a variable to store the result? Is there a different option for me? Can I somehow use pointers? When it's getting serious there will be thousands of calls to myvec.at() per second. So every little performance-eater is important.

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• c++ Sorting a vector based on values of other vector, or what's faster?

  - by pollux

  Hi, There are a couple of other posts about sorting a vector A based on values in another vector B. Most of the other answers tell to create a struct or a class to combine the values into one object and use std::sort. Though I'm curious about the performance of such solutions as I need to optimize code which implements bubble sort to sort these two vectors. I'm thinking to use a vector<pair<int,int>> and sort that. I'm working on a blob-tracking application (image analysis) where I try to match previously tracked blobs against newly detected blobs in video frames where I check each of the frames against a couple of previously tracked frames and of course the blobs I found in previous frames. I'm doing this at 60 times per second (speed of my webcam). Any advice on optimizing this is appreciated. The code I'm trying to optimize can be shown here: http://code.google.com/p/projectknave/source/browse/trunk/knaveAddons/ofxBlobTracker/ofCvBlobTracker.cpp?spec=svn313&r=313 Thanks

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• Capture IP packets on Dialup connection - Windows 7

  - by Assaf Levy

  Our product utilizes (the wonderful) Winpcap to capture ip packets from all devices with an IP address and analyze them in real time. Unfortunately, we discovered that it does NOT capture any packets on dialup (e.g. PPP) connections on Windows 7, and that there are no near-term plans for enabling this (1). So we need something else. Microsoft Network Monitor and Windows Packet Filter are two options that surfaced during a bit of googling, but before delving into research I wanted to ask the experienced: what are out options, given the following requirements: Capture all in/outbound IP packets on the machine. Complete background processing - no UI should be involved. Support Windows Vista / 7. Performance (user should not feel the difference). Thanks in advance.

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• Can Silverlight be linked with a C++ static library ?

  - by Niklaos

  Hi, I'm currently doing research to start a new project. This project will be in 2 parts a light Client (probably console) and an heavy one using silverlight. The light client must be cross-platform. However, they will both use the same Core (by the way, the core will need to use the sockets). I'd like to use C++ to build the light client but given that the core is common to both applications, it would be much appreciated if it's could be the same code. So the question is quite simple : Can Silverlight be compilated with a C++ static library ? And if it's possible, what about cross-platform issues (with moonlight) ? If it's not possible. Which language can i use to work with silverlight while being cross-platform ? Because of performance, a compilated language will be better ! Thanks for your expertise :)

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• Is Android (read typical devices) fast enough for a game that requires plotting pixel by pixel rather than blitting

  - by mP

  i have an idea for an Android game which is a little different from the typical game that usually moves sprites(bitmaps) around the screen. Id want to plot lots of little pixels to create my visuals. PROS no bitmaps required pixel plotting of stuff like "fire" can react to wind. no need to scale bitmaps, works w/ any screen res (lets pretend device can handle more drawing because its got a bigger screen). CONS slower to plot pixels than blit bitmaps need lot of animation frames. WISHES id like to update my game in real time, more is better 30fps is good but not essential, 15fps is enough. PERFORMANCE Q... Is the typical Android device fast enough to plot say half a screenful of pixels w/ a default background ? if full screen is not practical what window size should be able to handle such refreshes

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• select subquery cause mysql server to be unresponsive

  - by Xiao

  DELETE FROM item_measurement WHERE measurement_id IN ( SELECT (-id) AS measurement_id FROM invoice_item WHERE invoice_id = 'A3722' ) I've really tried hard to find what's wrong with the code. I tried to run this in a php page, which doesn't respond. I also tried the same line in phpmyadmin, infinite spinning circle and I had to restart the server(MAMP on Mac 10.9). No error was given in browser/ If I run the delete and select separately, they both finish very quickly. I don't think it's a performance issue because the separate run took < 0.1 sec each. Thanks for any help in advance. Edit: I also found that a simple select statement will also suspend mysql: select * from item_measurement where measurement_id in (select -id from invoice_item where invoice_id='A3722')

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• java-maven2: How to include the a jar as depedency in pom so that I will be able to access test clas

  - by flavour-of-bru

  Hi, I have a set of functional jars(more than 3) that tests my source code. These jars just contains test classes and assisting asserter classes. I am creating a new performance jar that would import all the functional tests from these jars so that all can be run simultaneously. But when I include them as test dependencies in pom of current jar, what all I get to see is the classes in src/main/java. How can I include these functional jars as dependent jars so that I can also reference classes in src/test/java. In other words, how do I reference the test classes in other jars. In what way should I include the dependency as. Thanks for your support.

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• WPF databind in memory image to Image control

  - by Ready Cent

  I am using a DataGrid and trying to do the following Databinding <DataTemplate> <Grid> <Image> <Image.Source> <BitmapImage UriSource="{Binding Data.CustomImage}" CacheOption="OnLoad" /> </Image.Source> </Image> </Grid> </DataTemplate> CustomImage is of type BitmapImage. When I run I get the error: Initialization of 'System.Windows.Media.Imaging.BitmapImage' threw an exception. The thing is that these images are stored as resources in a different assembly so I can't just point to a location on disk

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