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• Why is changing displays slow?

  - by Josh Bronson

  I've had many laptops over the course of many years, and while many things have sped up, one thing remains as slow today as it was years ago: (dis)connecting an external display. What's taking it so long to detect the new display and update the pixel buffers? I use Macs primarily, but I think this is equally slow on other platforms.

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• Whats faster in Javascript a bunch of small setInterval loops, or one big one?

  - by RobertWHurst

  Just wondering if its worth it to make a monolithic loop function or just add loops were they're needed. The big loop option would just be a loop of callbacks that are added dynamically with an add function. adding a function would look like this setLoop(function(){ alert('hahaha! I\'m a really annoying loop that bugs you every tenth of a second'); }); setLoop would add the function to the monolithic loop. so is the is worth anything in performance or should I just stick to lots of little loops using setInterval?

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• Distributed Message Ordering

  - by sbanwart

  I have an architectural question on handling message ordering. For purposes of this question, the transport is irrelevant, so I'm not going to specify one. Say we have three systems, a website, a CRM and an ERP. For this example, the ERP will be the "master" system in terms of data ownership. The website and the CRM can both send a new customer message to the ERP system. The ERP system then adds a customer and publishes the customer with the newly assigned account number so that the website and CRM can add the account number to their local customer records. This is a pretty straight forward process. Next we move on to placing orders. The account number is required in order for the CRM or website to place an order with the ERP system. However the CRM will permit the user to place an order even if the customer lacks an account number. (For this example assume we can't modify the CRM behavior) This creates the possibility that a user could create a new customer, and place an order before the account number gets updated in the CRM. What is the best way to handle this scenario? Would it be best to send the order message sans account number and let it go to an error queue? Would it be better to have the CRM endpoint hold the message and wait until the account number is updated in the CRM? Maybe something completely different that I haven't thought of? Thanks in advance for any help.

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• faster alternative to memcpy?

  - by hatorade

  I have a function that is doing memcpy, but it's taking up an enormous amount of cycles. Is there a faster alternative/approach than using memcpy to move a piece of memory?

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• Fastest way to check array items existence in mySQL table

  - by Enrique

  User writes a series of tags (, separated) and posts the form. I build an array containing the tags and delete dupes with array_unique() php function. I'm thinking of doing: go through the array with foreach($newarray as $item) { ... } check each $item for existence in the tags mySQL table if item does not exists, insert into tags table Is there a FASTER or MORE OPTIMUM way for doing this?

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• .NET values lookup

  - by Maciej

  Hi, I have a feeling of missing something obvious. UDP receiver application. It holds a collection of valid UDP sender IPs - only guys with IP on that list will be considered. Since that list must be looked at on every packet and UDPs are so volatile, that operation must be maximum fast. Good choice is Dictionary but it is a key-value structure and what I actually need here is a dictionary-like (hash lookup) key only structure. Is there something like that? Small annoyance rather than a bug but still. I can still use Dictionary Thanks, M.

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• cloud and existing enterprise applications technologies

  - by maxxxee

  What is the significance of new cloud platforms and databases like Microsoft Azure and Amazon EC2? Is it a replacement for enterprise application platforms like .net or JEE in a cloud environment? Is it neccessary to use these or other cloud specific platforms, or can we implement .net or JEE on a cloud based environment?

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• Should I invest time in learning about OR\M or LINQ?

  - by Peter Smith

  I'm a .NET web developer primarily who occasionally writes console applications to mine data, cleanup tasks, etc. Most of what I do winds up involving a database which I currently design via sql server management studio, using stored procedures, and query analyzer. I also create a lot of web services which are consumed via AJAX applications. Do these technologies really help you in speeding up development times? Do you still have to build the database or object code first?

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• Are any of these quad-tree libraries any good?

  - by Noctis Skytower

  It appears that a certain project of mine will require the use of quad-trees, something that I have never worked with before. From what I have read they should allow substantial performance enhancements than a brute-force attempt at the problem would yield. Are any of these python modules any good? Quadtree 0.1.2 <= No: unable to execute in Python 3.1 QuadTree <= Yes: simple while working with rectangles quadtree.py <= No: no support for needed operations EDIT: Does anyone know of a better implementation that the one presented on the pygame wiki article?

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• Is there table with timing(cost) of C functions?

  - by DSblizzard

  Preferable for x86-32 gcc implementation

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• Cloud Database Service Latency/Performance

  - by Gcoop

  Hi All, I am running a heavy traffic site and our server is beginning to get to its limits, at the moment the entire LAMP stack is on one box (not ideal). I would like to move the database onto it's own box or onto a cloud service, but from my previous experience moving the database off the same box as the webserver increases the latency of reads quite dramatically slowing down the site. Is using a cloud service for this going to overcome this problem, because as far as I can tell its essentially the same situation (as moving it onto a separate box in my control)? In which case why is there so much popularity around cloud based database services at the moment? Are cloud based database services so quick that the latency of reads is so low that its almost like having it on the same box in the same datacentre?

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• Should one use PHP to print all of a page's HTML?

  - by Mala

  Hi So I've always developed PHP pages like this: <?php goes at the top, ?> goes at the bottom, and all the HTML gets either print()ed or echo()ed out. Is that slower than having non-dynamic html outputted outside of <?php ?> tags? I can't seem to find any info about this. Thanks! --Mala UPDATE: the consesus seems to be on doing it my old way being hard to read. This is not the case if you break your strings up line by line as in: print("\n". "first line goes here\n". "second line goes here\n". "third line"); etc. It actually makes it a lot easier to read than having html outside of php structures, as this way everything is properly indented. That being said, it involves a lot of string concatenation.

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• How to hand-over a TCP listening socket with minimal downtime?

  - by Shtééf

  While this question is tagged EventMachine, generic BSD-socket solutions in any language are much appreciated too. Some background: I have an application listening on a TCP socket. It is started and shut down with a regular System V style init script. My problem is that it needs some time to start up before it is ready to service the TCP socket. It's not too long, perhaps only 5 seconds, but that's 5 seconds too long when a restart needs to be performed during a workday. It's also crucial that existing connections remain open and are finished normally. Reasons for a restart of the application are patches, upgrades, and the like. I unfortunately find myself in the position that, every once in a while, I need to do this kind of thing in production. The question: I'm looking for a way to do a neat hand-over of the TCP listening socket, from one process to another, and as a result get only a split second of downtime. I'd like existing connections / sockets to remain open and finish processing in the old process, while the new process starts servicing new connectinos. Is there some proven method of doing this using BSD-sockets? (Bonus points for an EventMachine solution.) Are there perhaps open-source libraries out there implementing this, that I can use as is, or use as a reference? (Again, non-Ruby and non-EventMachine solutions are appreciated too!)

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• cheap way to scale a rails application

  - by VP

  I have an application, that is becoming big, but until now, its not giving me a good revenue. That means, short money to re-invest on that. In this scenario, i found a way to make a "cheap distributed rails" deployment. I've got 4 VPS. All of them are in the same physical server. I added a load balance server running HAproxy in one dedicated VPS. There i pointed my virtual ip address where my domain name is associated. Behind this HAproxy i have more two VPS running my rails APP, passenger and memcache. Both apps servers are looking to the same database server, my 4th VPS. So with $44/month, i mounted a distributed environment. It won't be my final choice, but now, that the budget is short, is that a good way to deploy a rails application? Any pros or cons? It worth my $44/month?

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• How do you save the state of a computation in while using SNOW (or Multicore or ...)

  - by James

  From hard experience I've found it useful to occasionally save the state of my long computations to disk to start them up later if something fails. Can I do this in a distributed computation package in R (like SNOW or multicore)? It does not seem clear how this could be done since the master is collecting things from the slaves in a non-transparent way.

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• Quickly retrieve the subset of properties used in a huge collection in C#

  - by ccornet

  I have a huge Collection (which I can cast as an enumerable using OfType<()) of objects. Each of these objects has a Category property, which is drawn from a list somewhere else in the application. This Collection can reach sizes of hundreds of items, but it is possible that only, say, 6/30 of the possible Categories are actually used. What is the fastest method to find these 6 Categories? The size of the huge Collection discourages me from just iterating across the entire thing and returning all unique values, so is there a faster method of accomplishing this? Ideally I'd collect the categories into a List.

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• How to make active services highly available?

  - by Jader Dias

  I know that with Network Load Balancing and Failover Clusteringwe can make passive services highly available. But what about active apps? Example: One of my apps retrieves some content from a external resource in a fixed interval. I have imagined the following scenarios: Run it in a single machine. Problem: if this instance falls, the content won't be retrieved Run it in each machine of the cluster. Problem: the content will be retrieved multiple times Have it in each machine of the cluster, but run it only in one of them. Each instance will have to check some sort of common resource to decide whether it its turn to do the task or not. When I was thinking about the solution #3 I have wondered what should be the common resource. I have thought of creating a table in the database, where we could use it to get a global lock. Is this the best solution? How does people usually do this? By the way it's a C# .NET WCF app running on Windows Server 2008

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• RackSpace Cloud Strips $_SESSION if URL Has Certain File Extensions

  - by macinjosh

  The Situation I am creating a video training site for a client on the RackSpace Cloud using the traditional LAMP stack (RackSpace's cloud has both Windows and LAMP stacks). The videos and other media files I'm serving on this site need to be protected as my client charges money for access to them. There is no DRM or funny business like that, essentially we store the files outside of the web root and use PHP to authenticate user's before they are able to access the files by using mod_rewrite to run the request through PHP. So let's say the user requests a file at this URL: http://www.example.com/uploads/preview_image/29.jpg I am using mod_rewrite to rewrite that url to: http://www.example.com/files.php?path=%2Fuploads%2Fpreview_image%2F29.jpg Here is a simplified version of the files.php script: <?php // Setups the environment and sets $logged_in // This part requires $_SESSION require_once('../../includes/user_config.php'); if (!$logged_in) { // Redirect non-authenticated users header('Location: login.php'); } // This user is authenticated, continue $content_type = "image/jpeg"; // getAbsolutePathForRequestedResource() takes // a Query Parameter called path and uses DB // lookups and some string manipulation to get // an absolute path. This part doesn't have // any bearing on the problem at hand $file_path = getAbsolutePathForRequestedResource($_GET['path']); // At this point $file_path looks something like // this: "/path/to/a/place/outside/the/webroot" if (file_exists($file_path) && !is_dir($file_path)) { header("Content-Type: $content_type"); header('Content-Length: ' . filesize($file_path)); echo file_get_contents($file_path); } else { header('HTTP/1.0 404 Not Found'); header('Status: 404 Not Found'); echo '404 Not Found'; } exit(); ?> The Problem Let me start by saying this works perfectly for me. On local test machines it works like a charm. However once deployed to the cloud it stops working. After some debugging it turns out that if a request to the cloud has certain file extensions like .JPG, .PNG, or .SWF (i.e. extensions of typically static media files.) the request is routed to a cache system called Varnish. The end result of this routing is that by the time this whole process makes it to my PHP script the session is not present. If I change the extension in the URL to .PHP or if I even add a query parameter Varnish is bypassed and the PHP script can get the session. No problem right? I'll just add a meaningless query parameter to my requests! Here is the rub: The media files I am serving through this system are being requested through compiled SWF files that I have zero control over. They are generated by third-party software and I have no hope of adding or changing the URLs that they request. Are there any other options I have on this? Update: I should note that I have verified this behavior with RackSpace support and they have said there is nothing they can do about it.

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• Are functional programming languages good for practical tasks?

  - by Clueless

  It seems to me from my experimenting with Haskell, Erlang and Scheme that functional programming languages are a fantastic way to answer scientific questions. For example, taking a small set of data and performing some extensive analysis on it to return a significant answer. It's great for working through some tough Project Euler questions or trying out the Google Code Jam in an original way. At the same time it seems that by their very nature, they are more suited to finding analytical solutions than actually performing practical tasks. I noticed this most strongly in Haskell, where everything is evaluated lazily and your whole program boils down to one giant analytical solution for some given data that you either hard-code into the program or tack on messily through Haskell's limited IO capabilities. Basically, the tasks I would call 'practical' such as Aceept a request, find and process requested data, and return it formatted as needed seem to translate much more directly into procedural languages. The most luck I have had finding a functional language that works like this is Factor, which I would liken to a reverse-polish-notation version of Python. So I am just curious whether I have missed something in these languages or I am just way off the ball in how I ask this question. Does anyone have examples of functional languages that are great at performing practical tasks or practical tasks that are best performed by functional languages?

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• C++ Numerical truncation error

  - by Andrew

  Hello everyone, sorry if dumb but could not find an answer. #include <iostream> using namespace std; int main() { double a(0); double b(0.001); cout << a - 0.0 << endl; for (;a<1.0;a+=b); cout << a - 1.0 << endl; for (;a<10.0;a+=b); cout << a - 10.0 << endl; cout << a - 10.0-b << endl; return 0; } Output: 0 6.66134e-16 0.001 -1.03583e-13 Tried compiling it with MSVC9, MSVC10, Borland C++ 2010. All of them arrive in the end to the error of about 1e-13. Is it normal to have such a significant error accumulation over only a 1000, 10000 increments?

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• PVM terminates after Adding Host

  - by Tyug

  On Ubuntu 9.10 using PVM 3.4.5-12 (the PVM package when you use apt-get) The program terminates after adding a host. laptop> pvm pvm> add bowtie-slave add bowtie-slave terminated laptop> Current Configuration only $PVM_RSH = bin/usr/ssh I can ssh perfectly fine into the slave without a password, and run commands on it. Any ideas? Thanks in advance! Here are the sample logs: Laptop log [t80040000] 02/11 10:23:32 laptop (127.0.1.1:xxxxx) LINUX 3.4.5 [t80040000] 02/11 10:23:32 ready Thu Feb 11 10:23:32 2010 [t80040000] 02/11 10:23:32 netoutput() sendto: errno=22 [t80040000] 02/11 10:23:32 em=0x2c24f0 [t80040000] 02/11 10:23:32 [49/à][6e/à][76/à][61/à][6c/à][69/à][64/à][20/à][61/à][72/à] [t80040000] 02/11 10:23:32 netoutput() sendto: Invalid argument [t80040000] 02/11 10:23:32 pvmbailout(0) bowtie-log [t80080000] 02/11 10:23:25 bowtie-slave (xxx.x.x.xxx:xxxxx) LINUX64 3.4.5 [t80080000] 02/11 10:23:25 ready Thu Feb 11 10:23:25 2010 [t80080000] 02/11 10:28:26 work() run = STARTUP, timed out waiting for master [t80080000] 02/11 10:28:26 pvmbailout(0)

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• median of a billion numbers

  - by anony

  If you have one billion numbers and one hundred computers, what is the best way to locate the median of the numbers?

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• Reproducibility in scientific programming

  - by Andrew Grimm

  Along with producing incorrect results, one of the worst fears in scientific programming is not being able to reproduce the results you've generated. What best practices help ensure your analysis is reproducible?

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• open source gossip-based membership protocol?

  - by Aaron

  I am looking for a library which I can plug into a distributed application which implements any gossip-based membership protocol. Such a library would allow me to send/receive membership lists, merge received membership lists, etc... Even better would be if the library implemented a protocol with performance O(logn) performance guarantees. Does anyone know of any open source library like this? It doesn't need to meet all of the aforementioned requirements; even something partially implemented would be helpful.

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• generic async loading method for page web scripts?

  - by boomhauer

  The google analytics code went to an async load model some time back. I've noticed that a lot of the other scripts I use on many sites are causing slow load times - specifically the addthis script and the facebook like button. I'm noticing that the slow load times of these scripts is causing the google bot to calc my page loadtimes as being much slower than previously. I'd like to know if there is a standard/generic way of causing these scripts to load async as well, or perhaps a pointer to someone who has done the work for this already. Seems this would be a popular thing to do, but not much luck searching around.

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