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  • Random server lag, no CPU/mem/pagefile usage

    - by Kev
    We have a fairly new server running Windows 2003 SP2, and the past few days we've noticed random slowdowns. When I'm logged into the server over remote desktop while this is happening, or if I'm physically sitting at the server logged in, suddenly everything becomes extremely laggy. Any UI element I try to interact with takes upwards of ten seconds to react, and then responds very slowly. Then a minute later everything is quite snappy again. During this, I have Task Manager minimized to the tray, and there's no CPU usage. I open it up right after this happens, and there's very little CPU usage on the graph, and no memory or pagefile usage above normal. (Normal being 1.5 GB free in the case of memory.) This is what I see logged into the server, and then users start calling saying things are slow, timing out, and failing--anything to do with our server. No events in the Event Viewer around the times this happens. The context I'm working in (last thing I clicked, etc.) seems different every time--different programs active, different combinations of programs open. Never anything particularly stressful (like adding an event entry to a Cobian Backup configuration, or editing text in TextPad, which has been exceptionally stable in my extensive usage of it.) I would've thought it was just the server, but a family member's home PC (entirely separate) running WinXPSP3 had the same thing happen to it last night a few times. Is this some new behaviour introduced by the latest Windows Updates? Either way, where do I even start to look when nothing seems to be chewing up resources?

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  • Measuring performance indicators on a cluster

    - by Aditya Singh
    My architecture is based on Amazon. A ELB load balancer balances POST requests among m1.large instances. Every instance has a nginx server on port 80 which distributes the requests to 4 python-tornado servers on backend which handle the request. These tornado servers are taking about 5 - 10ms to respond to one request but this is the internal compute time of every request. I want to put this thing on test and i want to measure the response time from ELB to upstream and back and how does it vary when the QPS throughput is increased and plot a graph of Time vs. QPS vs. Latency and other factors like CPU and Memory. Is there a software to do that or should i log everything somewhere with latency checks and then analyze the whole log to get the stuff out. I would also need to write a self-monitor which keeps checking the whole response time. Is it possible to do it with a script from within the server. If so, will it be accurate ?

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  • Auto-organized / smart inventory system?

    - by VeXe
    for the past week I've been working on an inventory system with Unity3D. At first I got help from the guys at Design3 but it wasn't too long till we split path, because I really didn't like the way they did their code, it didn't have any smell of OOP whatsoever. I took it further steps ahead - items take more than one slot, advanced placement system (items tries their best to find the best close fit), local mouse system (mouse gets trapped in active bag area), etc. Here's a demo of my work. What we would like to have in our game, is an auto-organizing feature - not auto-sort. We want this feature because our inventory's going to be in 'real-time' - not like in Resident Evil 1,2,3 etc where you would pause the game and do things in your inventory. Now imagine your self in a sticky situation surrounded by zombies, and you don't have bullets, you look around, you see that there are bullets nearby on the ground, so you go for them and try to pick them up, but they don't fit! you look at your inventory and find out that if you reorganize some of the items, it will fit! - now the player - in that situation doesn't have time to reorganize because he's surrounded with zombies and will die if he stops and organizes the inventory to make space (remember inventory in real-time, no pausing) - wouldn't it be nice for that to happen automatically? - Yes! (I believe this has been implemented in some games like Dungeon siege or something, so sure it's doable) take a look at this picture for example: Yes, so if you auto-sort the issue you will get your spaces but it's bad because: 1- Expensive: it doesn't need a whole sort operation to free those spaces, in the first picture, just slide the red item at the bottom to the very left, and you get the same spaces that you got from the auto-sort. 2- It's annoying to the player: "Who the F told you to re-order my stuff?" I'm not asking for "How to write the code" for this, I'm just asking for some guidance, where to look, what algorithms are involved? Is this something related to graphs and shortest path stuff? I hope not cuz I didn't manage to continue my college studies :/ But even if it is, just tell me and I will learn the stuff related. Notice there could be more than just one solution. So I guess the first thing I have to do is figure out if the situation is 'solvable' - if I know how to determine if a situation is solvable or not, then I can 'solve' it. I just need to know the conditions that makes it 'solvable'. And I believe there must be some algorithm/data structure for this. Here's a pic for more than one solution of trying to fit a 1x3 item: The arrows show just one of the solutions, but if you look you will find more than one. This is what I ultimately not auto-sorting but find a solution and applying it. Note that if I spend time on it I will come up with a way to solve it, but it wouldn't be the best way, it's like, holding a car wheel with your feet instead of your hands! XD Or just like trying to solve an issue that requires arrays, but you're not yet aware of their existence! So what is the right approach to this? Hope somebody helps, thanks a lot in advance :)

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  • Could 0x800CCC0E in Outlook be caused by bad wireless connection?

    - by AndrejaKo
    I have a computer connected to a WiFi access point/router/modem. Sometimes, I get page not found errors and similar when opening a browser window, sometimes pings fail and it looks like the router's signal isn't very good. On the other hand, I get around 4 bars of signal strength in windows and graph looks good in Inssider. I also never get dropped connection to the router. My main problem is that I often get errors (such as 0x800CCC0E) in Outlook 2010 that after some searching appear to be connected to bad server connection. I'm using GMail over IMAP and all settings are correct. I didn't have similar errors on my previous router, but I'm not 100% sure that they appeared after switching to current one. It may have worked for some time without errors. There are also around 3000 messages on the server and the size of mailbox is around 12 GiB, which may contribute to the problems. On the other hand, there are at least 24 other networks in the 2.4 GHz range which I'm using and the number may have increased since I switched routers. Should I try solving this by getting a router with stronger signal?

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  • Creating dynamic map graphs

    - by Mehper C. Palavuzlar
    I need a software (or softwares) to achieve the following. I'm not sure if it could be done, but I'd like to hear the suggestions from super users. The data I want to use for graphing purposes include sales figures of magazines by provinces. There are 81 provinces of Turkiye, and I want the computer to automatically paint / write on a graph according to the sales magnitude of the provinces. Since there are loads of magazines with loads of issues, the process must be executed automatically just after selecting the related magazine and issue. So there will be graphs showing the sales weight of the whole country with some nice illustrations. Those graphs might be used as part of some decision support mechanism to help field teams. Is it possible? I have all the data and base maps of Turkiye to be filled/painted. I'm sure this is not easy. If there is a way to do that, it might probably include more than one software. Thanks in advance for any valuable comments and answers.

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  • quad sli with gtx 690 not working

    - by Moaadh
    I have two cards GTX 690 (dual core). I did the Sli successfully. Nvidia control panel acknowledges the two cards as quad Sli. However, the problem is that Windows 7 64-bit Ultimate is showing me the graph memory size as 4 GB while it is supposed to be 8 GB because of the Sli. Also the benchmark from all software is giving me a very low score compared to some other guy's benchmark on YouTube. It gives me a big headache. Does anyone know why this is happening? If so, how can I get Windows 7 to recognize all 8 GB of memory? Thanks for your help in advance. My computer specifications: (Processor: Intel Core i7-3930k @3.2GHz(12CPUs))--- (Memory: 65536 MB Ram 1866 MHz)-- (OS: Windows 7 Ultimate 64-bit)-- (OCZ 240GB as SSD PCIe drive for booting and storage disk)-- (DirextX version: DirectX 11)-- (VGA Card: 2 X EVGA GTX 690 Dual GPU. Each GPU is 2 GB, so total memory should be 8 GB.)-- (MotherBoard: ASUS Rampage IV Extreme)-- Others with lesser specifications get a 2500 score in heaven benchmark while I get 1501 as if it is one card.

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  • vSphere education - What are the downsides of configuring virtual machines with *too* much RAM?

    - by ewwhite
    VMware memory management seems to be a tricky balancing act. With cluster RAM, Resource Pools, VMware's management techniques (TPS, ballooning, host swapping), in-guest RAM utilization, swapping, reservations, shares and limits, there are a lot of variables. I'm in a situation where clients are using dedicated vSphere cluster resources. However, they are configuring the virtual machines as though they were on physical hardware. In turn, this means a standard VM build may have 4 vCPUs and 16GB or more of RAM. I come from the school of starting small (1 vCPU, minimal RAM), checking real-world use and adjusting up as necessary. Some examples from a "problem" cluster. Resource pool summary - Looks almost 4:1 overcommitted. Note the high amount of ballooned RAM. Resource allocation - The Worst Case Allocation column shows that these VMs would have access to less than 50% of their configured RAM under constrained conditions. The real-time memory utilization graph of the top VM in the listing above. 4 vCPU and 64GB RAM allocated. It averages under 9GB use. Summary of the same VM What are the downsides of overcommitting and overconfiguring resources (specifically RAM) in vSphere environments? Assuming that the VMs can run in less RAM, is it fair to say that there's overhead to configuring virtual machines with more RAM than they need? What is the counter-argument to: "if a VM has 16GB of RAM allocated, but only uses 4GB, what's the problem??"? E.g. do customers need to be educated? What specific metric should be used to meter RAM usage. Tracking the peaks of "Active" versus time?

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  • Debian 100% cpu every 30 minutes but not loggable?

    - by user654123
    I have a Debian 7 x64 machine running with Digital Ocean that has every 30 Minutes a 100% cpu usage for about 1 minute. A couple of days ago it stayed there for a couple of hours so the server finally crashed and I had to repair my Mysql databases. The server is a pure webserver running apache2 and Mysql. I tried tracing which processes use the cpu but with no luck. The script I used: #!/bin/sh while true; do ps -A -eo pcpu,pid,user,args | sort -k 1 -r | head -3 >> proclog.txt; echo "\n" >> proclog.txt; sleep 2; done I was monitoring htop as well while this was happening, but the top processess' cpu usage didn't add up to ~15% even though htop's cpu meter showed constant 100%. htop was configured to show all users' processess, user- and kernel-threads. Edit: By stopping Apache2 & Mysql prior to the expected 100% usage I can tell both are not responsible for it. The 100% usage occurred anyway. This is what the graph looked like the past hours:

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  • Can I select which folders the Photos live tile chooses from?

    - by nhinkle
    The built-in Photos app in Windows 8 has a live tile on the start screen that shows photos from your pictures library. It's a cool little visual, even if it's not particularly useful. The problem is that a lot of image files on my computer are not really photos per se -- I have a lot of screenshots, PNGs of technical drawings, graph images, etc. Those all look pretty awkward on the start screen. I look pretty awkward on the start screen too... sometimes photos like resume profile shots show up that I don't want to delete, but they're not really what I want to be staring at when I start my computer up. I'm looking for some way to configure which folders the Photos app should look in for images to display on the live tile. That way, I could point it to some directories of pretty scenic pictures I've taken, and not have to see graphs and my own mug. For the time being, I've just disabled the live tile (right click - disable live tile), but I would ultimately like to have this functionality, just with more control over it.

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  • How do you go from a so so programmer to a great one? [closed]

    - by Cervo
    How do you go from being an okay programmer to being able to write maintainable clean code? For example David Hansson was writing Basecamp when in the process he created Rails as part of writing Basecamp in a clean/maintainable way. But how do you know when there is value in a side project like that? I have a bachelors in computer science, and I am about to get a masters and I will say that colleges teach you to write code to solve problems, not neatly or anything. Basically you think of a problem, come up with a solution, and write it down...not necessarily the most maintainable way in the world. Also my first job was in a startup, and now my third is in a small team in a large company where the attitude was/is get it done yesterday (also most of my jobs are mainly database development with SQL with a few ASP.NET web pages/.NET apps on the side). So of course cut/paste is more favored than making things more cleanly. And they would rather have something yesterday even if you have to rewrite it next month rather than to have something in a week that lasts for a year. Also spaghetti code turns up all over the place, and it takes very smart people to write/understand/maintain spaghetti code...However it would be better to do things so simple/clean that even a caveman/woman could do maintenance. Also I get very bored/unmotivated having to go modify the same things cut/pasted in a few locations. Is this the type of skill that you need to learn by working with a serious software organization that has an emphasis on maintenance and maybe even an architect who designs a system architecture and reviews code? Could you really learn it by volunteering on an open source project (it seems to me that a full time programmer job is way more practice than a few hours a week on an open source project)? Is there some course where you can learn this? I can attest that graduate school and undergraduate school do not really emphasize clean software at all. They just teach the structures/algorithms and then send you off into the world to solve problems. Overall I think the first thing is learning to write clean/maintainable code within the bounds of the project in order to become a good programmer. Then the next thing is learning when you need to do a side project (like a framework) to make things more maintainable/clean even while you still deliver things for the deadline in order to become a great programmer. For example, you are making an SQL report and someone gives you 100 calculations for individual columns. At what point does it make sense to construct a domain specific language to encode the rules in simply and then generate all the SQL as opposed to cut/pasting the query from the table a bunch of times and then adjusting each query to do the appropriate calculations. This is the type of thing I would say a great programmer would know. He/she would maybe even know ways to avoid the domain specific language and to still do all the calculations without creating an unmaintainable mess or a ton of repetitive code to cut/paste everywhere.

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  • Ubuntu's garbage collection cron job for PHP sessions takes 25 minutes to run, why?

    - by Lamah
    Ubuntu has a cron job set up which looks for and deletes old PHP sessions: # Look for and purge old sessions every 30 minutes 09,39 * * * * root [ -x /usr/lib/php5/maxlifetime ] \ && [ -d /var/lib/php5 ] && find /var/lib/php5/ -depth -mindepth 1 \ -maxdepth 1 -type f -cmin +$(/usr/lib/php5/maxlifetime) ! -execdir \ fuser -s {} 2> /dev/null \; -delete My problem is that this process is taking a very long time to run, with lots of disk IO. Here's my CPU usage graph: The cleanup running is represented by the teal spikes. At the beginning of the period, PHP's cleanup jobs were scheduled at the default 09 and 39 minutes times. At 15:00 I removed the 39 minute time from cron, so a cleanup job twice the size runs half as often (you can see the peaks get twice as wide and half as frequent). Here are the corresponding graphs for IO time: And disk operations: At the peak where there were about 14,000 sessions active, the cleanup can be seen to run for a full 25 minutes, apparently using 100% of one core of the CPU and what seems to be 100% of the disk IO for the entire period. Why is it so resource intensive? An ls of the session directory /var/lib/php5 takes just a fraction of a second. So why does it take a full 25 minutes to trim old sessions? Is there anything I can do to speed this up? The filesystem for this device is currently ext4, running on Ubuntu Precise 12.04 64-bit. EDIT: I suspect that the load is due to the unusual process "fuser" (since I expect a simple rm to be a damn sight faster than the performance I'm seeing). I'm going to remove the use of fuser and see what happens.

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  • Perfmon % Processor Time vs. task manager's CPU usage

    - by nat
    I'm new to using Perfmon and performance monitoring in general (so go easy on me please ;) I know that Perfmon doesn't have anything exactly like Task Manager's CPU usage display, but I'm trying to figure out how to monitor user's CPU usage via Perfmon in a similar way, and trying to understand the measurements (or how to convert the numbers to get a similar understanding) For example, if in Task Manager, a particular user is consistently using more than 5% CPU, I would want to contact the user about it. I learn best by example, so here is exactly what I'm trying to do, with a specific example: This is for a 32-bit Dual Quad Core Windows 2003 web server (8 CPUs), there are many web sites on the server, each running within their own application pool/worker process ID. Through other research here I learned of a registry change that I made so that the PID shows up with the w3wp process so I can easily identify the site later by cross-referencing it. I set up a counter with the following settings: Process -> % Processor Time -> all instances Here is an example. Say I'm interested in "black line" user in this graph below, as his process is spiking quite high compared to all the other users: (I wasn't allowed to post the image as I'm a new user on this site.. I've uploaded the image to:) http://i35.tinypic.com/106yn8k.jpg So... using this as an example, I see that they have an AVERAGE % PROCESSOR TIME of 23.264 , and have spiked as high as 103.124 So what exactly does this 23.264 number mean to me? Is it similar to an average of Task Manager's CPU reading for this user? Or, since this server has 8 CPUs, should I divide this number by 8? (23.264/8 = 2.9% AVERAGE CPU LOAD?) Thanks in advance.

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  • Do SEO-friendly URLs really affect a page's ranking?

    - by Lee Harold
    SEO-friendly URLs are all the rage these days. But do they actually have a meaningful impact on a page's ranking in Google and other search engines? If so, why? If not, why not? (Note that I would absolutely agree that SEO-friendly URLs are nicer to use for human beings. My question is whether they actually make a difference to the ranking algorithms.) Update: As it turns out, the Google post that endorphine points to here has caused tremendous confusion in the SEO community. For a sampling of the discussion, see here, here, and here. Part of the problem is that the Google post is addressing the worst case where URL rewriting is done poorly and so you'd be better off sticking with a dynamic URL rather than a mangled static "SEO-friendly" URL. There's no question dynamic URLs can be crawled by Google and can achieve high rankings. Maybe it would be easier to reframe the question more concretely: given 2 otherwise equivalent pages, which will rank higher for the search "do seo friendly urls really affect page ranking"? A) http://stackoverflow.com/questions/505793/do-seo-friendly-urls-really-affect-a-pages-ranking or B) http://stackoverflow.com?question=505793 (a fake URL for comparison only)

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  • Algorithm design, "randomising" timetable schedule in Python although open to other languages.

    - by S1syphus
    Before I start I should add I am a musician and not a native programmer, this was undertook to make my life easier. Here is the situation, at work I'm given a new csv file each which contains a list of sound files, their length, and the minimum total amount of time they must be played. I create a playlist of exactly 60 minutes, from this excel file. Each sample played the by the minimum number of instances, but spread out from each other; so there will never be a period where for where one sound is played twice in a row or in close proximity to itself. Secondly, if the minimum instances of each song has been used, and there is still time with in the 60 min, it needs to fill the remaining time using sounds till 60 minutes is reached, while adhering to above. The smallest duration possible is 15 seconds, and then multiples of 15 seconds. Here is what I came up with in python and the problems I'm having with it, and as one user said its buggy due to the random library used in it. So I'm guessing a total rethink is on the table, here is where I need your help. Whats is the best way to solve the issue, I have had a brief look at things like knapsack and bin packing algorithms, while both are relevant neither are appropriate and maybe a bit beyond me.

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  • Most useful free .NET libraries?

    - by Binoj Antony
    I have used a lot of free .NET libraries, some from Microsoft itself! Which ones have you found the most useful? Dependency Injection/Inversion of Control Unity Framework - Microsoft StructureMap - Jeremy Miller Castle Windsor NInject Spring Framework Autofac Managed Extensibility Framework Logging Logging Application Block - Microsoft Log4Net - Apache Error Logging Modules and Handlers(ELMAH) NLog Compression SharpZipLib DotNetZip YUI Compressor (CSS and JS compression/minification) AjaxMinifier (in other downloads) (JS compression. Also includes MSBuild task) Ajax Ajax Control Toolkit - Microsoft AJAXNet Pro Data Mapper XmlDataMapper AutoMapper ORM NHibernate Castle ActiveRecord Subsonic XmlDataMapper Charting/Graphics Microsoft Chart Controls for ASP.NET 3.5 SP1 Microsoft Chart Controls for Winforms ZedGraph Charting NPlot - Charting for ASP.NET and WinForms PDF Creators/Generators PDFsharp iTextSharp Unit Testing/Mocking NUnit Rhino Mocks Moq TypeMock.Net xUnit.net mbUnit Machine.Specifications Automated Web Testing Selenium Watin URL Rewriting url rewriter UrlRewriting.Net Url Rewriter and Reverse Proxy - Managed Fusion Controls Krypton - Free winform controls Source Grid - A Grid control Devexpress - free controls Unclassified CSLA Framework - Business Objects Framework AForge.net - AI, computer vision, genetic algorithms, machine learning Enterprise Library 4.1 - Logging, Exception Management, Validation, Policy Injection File helpers library C5 Collections - Collections for .NET Quartz.NET - Enterprise Job Scheduler for .NET Platform MiscUtil - Utilities by Jon Skeet Lucene.net - Text indexing and searching Json.NET - Linq over JSON Flee - expression evaluator PostSharp - AOP IKVM - brings the extensive world of Java libraries to .NET. Title of the question taken from here. [EDIT] Please provide links to these free libraries as well. Once we have a huge list of this, it can be arranged in categories! Please do not mention .NET Applications/EXEs here.

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  • how to tackle this combinatorial algorithm problem

    - by Andrew Bullock
    I have N people who must each take T exams. Each exam takes "some" time, e.g. 30 min (no such thing as finishing early). Exams must be performed in front of an examiner. I need to schedule each person to take each exam in front of an examiner within an overall time period, using the minimum number of examiners for the minimum amount of time (i.e. no examiners idle) There are the following restrictions: No person can be in 2 places at once each person must take each exam once noone should be examined by the same examiner twice I realise that an optimal solution is probably NP-Complete, and that I'm probably best off using a genetic algorithm to obtain a best estimate (similar to this? http://stackoverflow.com/questions/184195/seating-plan-software-recommendations-does-such-a-beast-even-exist). I'm comfortable with how genetic algorithms work, what i'm struggling with is how to model the problem programatically such that i CAN manipulate the parameters genetically.. If each exam took the same amount of time, then i'd divide the time period up into these lengths, and simply create a matrix of time slots vs examiners and drop the candidates in. However because the times of each test are not necessarily the same, i'm a bit lost on how to approach this. currently im doing this: make a list of all "tests" which need to take place, between every candidate and exam start with as many examiners as there are tests repeatedly loop over all examiners, for each one: find an unscheduled test which is eligible for the examiner (based on the restrictions) continue until all tests that can be scheduled, are if there are any unscheduled tests, increment the number of examiners and start again. i'm looking for better suggestions on how to approach this, as it feels rather crude currently.

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  • Merge method in MergeSort Algorithm .

    - by Tony
    I've seen many mergeSort implementations .Here is the version in Data Structures and Algorithms in Java (2nd Edition) by Robert Lafore : private void recMergeSort(long[] workSpace, int lowerBound,int upperBound) { if(lowerBound == upperBound) // if range is 1, return; // no use sorting else { // find midpoint int mid = (lowerBound+upperBound) / 2; // sort low half recMergeSort(workSpace, lowerBound, mid); // sort high half recMergeSort(workSpace, mid+1, upperBound); // merge them merge(workSpace, lowerBound, mid+1, upperBound); } // end else } // end recMergeSort() private void merge(long[] workSpace, int lowPtr, int highPtr, int upperBound) { int j = 0; // workspace index int lowerBound = lowPtr; int mid = highPtr-1; int n = upperBound-lowerBound+1; // # of items while(lowPtr <= mid && highPtr <= upperBound) if( theArray[lowPtr] < theArray[highPtr] ) workSpace[j++] = theArray[lowPtr++]; else workSpace[j++] = theArray[highPtr++]; while(lowPtr <= mid) workSpace[j++] = theArray[lowPtr++]; while(highPtr <= upperBound) workSpace[j++] = theArray[highPtr++]; for(j=0; j<n; j++) theArray[lowerBound+j] = workSpace[j]; } // end merge() One interesting thing about merge method is that , almost all the implementations didn't pass the lowerBound parameter to merge method . lowerBound is calculated in the merge . This is strange , since lowerPtr = mid + 1 ; lowerBound = lowerPtr -1 ; that means lowerBound = mid ; Why the author didn't pass mid to merge like merge(workSpace, lowerBound,mid, mid+1, upperBound); ? I think there must be a reason , otherwise I can't understand why an algorithm older than half a center ,and have all coincident in the such little detail.

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  • Dealing with huge SQL resultset

    - by Dave McClelland
    I am working with a rather large mysql database (several million rows) with a column storing blob images. The application attempts to grab a subset of the images and runs some processing algorithms on them. The problem I'm running into is that, due to the rather large dataset that I have, the dataset that my query is returning is too large to store in memory. For the time being, I have changed the query to not return the images. While iterating over the resultset, I run another select which grabs the individual image that relates to the current record. This works, but the tens of thousands of extra queries have resulted in a performance decrease that is unacceptable. My next idea is to limit the original query to 10,000 results or so, and then keep querying over spans of 10,000 rows. This seems like the middle of the road compromise between the two approaches. I feel that there is probably a better solution that I am not aware of. Is there another way to only have portions of a gigantic resultset in memory at a time? Cheers, Dave McClelland

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  • SHA512 vs. Blowfish and Bcrypt

    - by Chris
    I'm looking at hashing algorithms, but couldn't find an answer. Bcrypt uses Blowfish Blowfish is better than MD5 Q: but is Blowfish better than SHA512? Thanks.. Update: I want to clarify that I understand the difference between hashing and encryption. What prompted me to ask the question this way is this article, where the author refers to bcrypt as "adaptive hashing" http://chargen.matasano.com/chargen/2007/9/7/enough-with-the-rainbow-tables-what-you-need-to-know-about-s.html Since bcrypt is based on Blowfish, I was led to think that Blowfish is a hashing algorithm. If it's encryption as answers have pointed out, then seems to me like it shouldn't have a place in this article. What's worse is that he's concluding that bcrypt is the best. What's also confusing me now is that the phpass class (used for password hashing I believe) uses bcrypt (i.e. blowfish, i.e. encryption). Based on this new info you guys are telling me (blowfish is encryption), this class sounds wrong. Am I missing something?

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  • Schliemann's method of programming language learning

    - by DVK
    Background: 19th-century German archeologist Heinrich Schliemann was of course famous for his successful quest to find and excavate the city of Troy (an actual archeological site for the Troy of Homer's Iliad). However, he is just as famous for being an astonishing learner of languages - within the space of two years, he taught himself fluent Dutch, English, French, Spanish, Italian and Portuguese, and later went on to learn seven more, including both modern and ancient Greek. One of the methods he famously used was comparison of a known text, e.g. take a book in a language one is fluent in, take a good translation of a book in a language you wish to learn, and go over them in parallel. (various sources cited the book used by Schliemann to be the Bible, or, as the link above states, a novel). Now, for the actual question. Has anyone used (or heard of) an equivalent of Schliemann's method for learning a new programming language? E.g. instead of basing the leaning on references and tutorials, take a somewhat comprehensive set of programs known to have high-quality code in both languages implementing similar/identical algorithms and learn by comparing them? I'm curious about either personal experiences of applying such an approach, or references to something published, or existance of codebases which could be used for such an approach? What got me thinking about the idea was Project Euler and some code snippets I saw on SO, in C++, Perl and Lisp.

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  • Sample uniformly at random from an n-dimensional unit simplex.

    - by dreeves
    Sampling uniformly at random from an n-dimensional unit simplex is the fancy way to say that you want n random numbers such that they are all non-negative, they sum to one, and every possible vector of n non-negative numbers that sum to one are equally likely. In the n=2 case you want to sample uniformly from the segment of the line x+y=1 (ie, y=1-x) that is in the positive quadrant. In the n=3 case you're sampling from the triangle-shaped part of the plane x+y+z=1 that is in the positive octant of R3: (Image from http://en.wikipedia.org/wiki/Simplex.) Note that picking n uniform random numbers and then normalizing them so they sum to one does not work. You end up with a bias towards less extreme numbers. Similarly, picking n-1 uniform random numbers and then taking the nth to be one minus the sum of them also introduces bias. Wikipedia gives two algorithms to do this correctly: http://en.wikipedia.org/wiki/Simplex#Random_sampling (Though the second one currently claims to only be correct in practice, not in theory. I'm hoping to clean that up or clarify it when I understand this better. I initially stuck in a "WARNING: such-and-such paper claims the following is wrong" on that Wikipedia page and someone else turned it into the "works only in practice" caveat.) Finally, the question: What do you consider the best implementation of simplex sampling in Mathematica (preferably with empirical confirmation that it's correct)? Related questions http://stackoverflow.com/questions/2171074/generating-a-probability-distribution http://stackoverflow.com/questions/3007975/java-random-percentages

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  • Perf: Viewing thousands of images in Silverlight 3 on a 3D Wall

    - by Bob Holland
    I currently work on a very cool Silverlight app that displays photos in a 3D wall space like the Wall3D demo that is thrown in with Blend 3. The problem I am currently facing is performance. The app works like this: As you scroll right or left the 3d photo wall rotates As each movement is made, the next column of photos are downloaded, decoded into a BitmapImage and thrown into a 3D Wall Node. As you can imagine users (if you let them) will want to flip through the photos really quickly, but the problem I have is I cannot display the photos quick enough. In most cases it's a beautiful app that works really well, but when an album contains over 300 photos, you can imagine the sort of memory taken up by all the BitmapImage classes and how moving the slider can jump from photo 20 to photo 120 in a second. Of course we have algorithms in place to not download every photo in between, but I still can't work out a fast way to get the photos displayed. It may be a case that we need to throw away the 'great for show' 3D wall and go to a flat DeepZoom like wall like the Playboy archive one that Vertigo did. Still not sure, let me know your thoughts. P.S. We are using Kit3D for all the 3D work, it's using PerspectiveCamera, Model3DGroup, ModelVisual3D, RotateTransform3D & TranslateTransform3D. Cheers, Bob.

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  • Instantiating a list of parameterized types, making beter use of Generics and Linq

    - by DanO
    I'm hashing a file with one or more hash algorithms. When I tried to parametrize which hash types I want, it got a lot messier than I was hoping. I think I'm missing a chance to make better use of generics or LINQ. I also don't like that I have to use a Type[] as the parameter instead of limiting it to a more specific set of type (HashAlgorithm descendants), I'd like to specify types as the parameter and let this method do the constructing, but maybe this would look better if I had the caller new-up instances of HashAlgorithm to pass in? public List<string> ComputeMultipleHashesOnFile(string filename, Type[] hashClassTypes) { var hashClassInstances = new List<HashAlgorithm>(); var cryptoStreams = new List<CryptoStream>(); FileStream fs = File.OpenRead(filename); Stream cryptoStream = fs; foreach (var hashClassType in hashClassTypes) { object obj = Activator.CreateInstance(hashClassType); var cs = new CryptoStream(cryptoStream, (HashAlgorithm)obj, CryptoStreamMode.Read); hashClassInstances.Add((HashAlgorithm)obj); cryptoStreams.Add(cs); cryptoStream = cs; } CryptoStream cs1 = cryptoStreams.Last(); byte[] scratch = new byte[1 << 16]; int bytesRead; do { bytesRead = cs1.Read(scratch, 0, scratch.Length); } while (bytesRead > 0); foreach (var stream in cryptoStreams) { stream.Close(); } foreach (var hashClassInstance in hashClassInstances) { Console.WriteLine("{0} hash = {1}", hashClassInstance.ToString(), HexStr(hashClassInstance.Hash).ToLower()); } }

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  • Reinforcement learning toy project

    - by Betamoo
    My toy project to learn & apply Reinforcement Learning is: - An agent tries to reach a goal state "safely" & "quickly".... - But there are projectiles and rockets that are launched upon the agent in the way. - The agent can determine rockets position -with some noise- only if they are "near" - The agent then must learn to avoid crashing into these rockets.. - The agent has -rechargable with time- fuel which is consumed in agent motion - Continuous Actions: Accelerating forward - Turning with angle I need some hints and names of RL algorithms that suit that case.. - I think it is POMDP , but can I model it as MDP and just ignore noise? - In case POMDP, What is the recommended way for evaluating probability? - Which is better to use in this case: Value functions or Policy Iterations? - Can I use NN to model environment dynamics instead of using explicit equations? - If yes, Is there a specific type/model of NN to be recommended? - I think Actions must be discretized, right? I know it will take time and effort to learn such a topic, but I am eager to.. You may answer some of the questions if you can not answer all... Thanks

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  • Language+IDE for teaching high school students?

    - by daveagp
    I'm investigating languages and IDEs for a project involving teaching high-school students (around grade 11). It will teach basics of programming as an introduction to computer science (e.g., including how numbers/strings/characters are represented, using procedures and arrays, control flow, a little bit of algorithms, only very basic I/O). The non-negotiable requirements for this project are: a free up-to-date cross-platform IDE (Win & Mac incl. 64-bit) with debug a compiler where it's easy to learn from your mistakes together with the IDE, a gentle installation+learning curve So far, the best options I see are the following. Are there others I should know about? I am giving a short explanation with each one to generally show what I am looking for. In order from most to least promising: Pascal + FreePascal IDE (it seems a little buggy but actively developed?) Python + Eclipse + PyDev (good but features are overwhelming/hard to navigate) Groovy + Eclipse ('') Python + IDLE (looks unnatural to do debugging, to me) Pascal + Lazarus (IDE overwhelming, e.g. not obvious how to "start from scratch") Preferably, as a rule of thumb, the language should be direct enough that you don't need to wrap every program in a class, don't need to reference a System object to println, etc. I tried a little bit to see if there is something in JavaScript or (non-Visual) Basic along the lines of what I want, but found nothing so far. I would say that C/C++/C#, Java, Ruby, Lisp, VB do not fit my criteria for languages for this project. To reiterate my questions: are any of those 5 options really awesome or un-awesome? Are there other options which are even MORE awesome? Anything for Basic or JavaScript which meets all of the criteria? Thanks!

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