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• Safe to KILL a mysql process REPLACEing records in a large myisam table?

  - by threecheeseopera

  I have a REPLACE query running for a few days now on a few MyISAM tables, the largest having 20+million records. I need it to stop. It is, basically: REPLACE INTO really_large_table (a,b,c,d) SELECT e,f,g,h FROM big_table INNER JOIN huge_table ON big_table.x LIKE CONCAT('%', huge_table.y, '%'); I need to KILL it, and I am worried that I may corrupt really_large_table. Because the sub-query itself takes a significant amount of time, the REPLACEing probably occurs (relatively) infrequently; if this is true, does this make it less likely for the data to become corrupted? For the curious, here is the SO question asked about the query I am trying to kill.

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• Why is silverlight so slow? (Especially when compared to Flash)

  - by Sahat

  I hope I don't have to explain what is Silverlight to SO community. Anyway TemplateMonster.com has recently released new Silverlight themes that have been ported from Flash. Silverlight Templates | Template Monster I've noticed a significant lag on my Macbook Pro 13" in loading the template page in Silverlight. And not just Template Monster templates but other silverlight applications on the web as well. Now why is that? I've been hearing how great Silverlight is and how it's a great business platform blah blah blah. And now Microsoft plans to build Windows Phone 7 on top of Silverlight framework. As much as I want to praise Silverlight, so far it's been nothing but a disappointment to me. Could someone enlighten me, what is so great about Silverlight, and why should I put up with that starting up lag? Silverlight was really next up on my "stuff to learn" list this summer, but now I am not so sure...

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• Floating point equality and tolerances

  - by doron

  Comparing two floating point number by something like a_float == b_float is looking for trouble since a_float / 3.0 * 3.0 might not be equal to a_float due to round off error. What one normally does is something like fabs(a_float - b_float) < tol. How does one calculate tol? Ideally tolerance should be just larger than the value of one or two of the least significant figures. So if the single precision floating point number is use tol = 10E-6 should be about right. However this does not work well for the general case where a_float might be very small or might be very large. How does one calculate tol correctly for all general cases? I am interested in C or C++ cases specifically.

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• Reporting on release changes when using JIRA, Ivy and SVN

  - by HaveAGuess

  Hey guys, We have an Ivy release procedure where resolve our dependancies using Ivy pre-tagging which means that we can pull in changes for releases by other members of the team that we are not expecting We want to generate reports and track changes to dependancies between releases but there doesn't seem to be an easy way of doing this without a significant effort. We also want to generate a JIRA list of all changes not only in the main project but in dependancies that we own. This is an extension of the problem above. Otherwise we simply don't know what we are releasing - any ideas?!

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• What is the cost in bytes for the overhead of a sql_variant column in SQL Server?

  - by Elan

  I have a table, which contains many columns of float data type with 15 digit precision. Each column consumes 8 bytes of storage. Most of the time the data does not require this amount of precision and could be stored as a real data type. In many cases the value can be 0, in which case I could get away with storing a single byte. My goal here is to optimize space storage requirements, which is an issue I am facing working with a SQL Express 4GB database size limit. If byte, real and float data types are stored in a sql_variant column there is obviously some overhead involved in storing these values. What is the cost of this overhead? I would then need to evaluate whether I would actually end up in significant space savings (or not) switching to using sql_variant column data types. Thanks, Elan

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• Lexing newlines in scala StdLexical?

  - by Nick Fortescue

  I'm trying to lex (then parse) a C like language. In C there are preprocessor directives where line breaks are significant, then the actual code where they are just whitespace. One way of doing this would be do a two pass process like early C compilers - have a separate preprocessor for the # directives, then lex the output of that. However, I wondered if it was possible to do it in a single lexer. I'm pretty happy with writing the scala parser-combinator code, but I'm not so sure of how StdLexical handles whitespace. Could someone write some simple sample code which say could lex a #include line (using the newline) and some trivial code (ignoring the newline)? Or is this not possible, and it is better to go with the 2-pass appproach?

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• Google Web Optimizer -- How long until winning combination?

  - by Django Reinhardt

  I've had an A/B Test running in Google Web Optimizer for six weeks now, and there's still no end in sight. Google is still saying: "We have not gathered enough data yet to show any significant results. When we collect more data we should be able to show you a winning combination." Is there any way of telling how close Google is to making up its mind? (Does anyone know what algorithm does it use to decide if there's been any "high confidence winners"?) According to the Google help documentation: Sometimes we simply need more data to be able to reach a level of high confidence. A tested combination typically needs around 200 conversions for us to judge its performance with certainty. But all of our conversions have over 200 conversations at the moment: 230 / 4061 (Original) 223 / 3937 (Variation 1) 205 / 3984 (Variation 2) 205 / 4007 (Variation 3) How much longer is it going to have to run?? Thanks for any help.

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• How to read time from recorded surveillance camera video?

  - by stressed_geek

  I have a problem where I have to read the time of recording from the video recorded by a surveillance camera. The time shows up on the top-left area of the video. Below is a link to screen grab of the area which shows the time. Also, the digit color(white/black) keeps changing during the duration of the video. http://i55.tinypic.com/2j5gca8.png Please guide me in the direction to approach this problem. I am a Java programmer so would prefer an approach through Java. EDIT: Thanks unhillbilly for the comment. I had looked at the Ron Cemer OCR library and its performance is much below our requirement. Since the ocr performance is less than desired, I was planning to build a character set using the screen grabs for all the digits, and using some image/pixel comparison library to compare the frame time with the character-set which will show a probabilistic result after comparison. So I was looking for a good image comparison library(I would be OK with a non-java library which I can run using the command-line). Also any advice on the above approach would be really helpful.

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• Why shouldn't I use Flash?

  - by acidzombie24

  I heard many times i should avoid flash for my website. Yet no one has told me a good reason. I searched for reasons and i see many that are not true (such as text in flash are not indexable by search engines) or may not necessarily be true or significant enough (eating more bandwidth. Would a JS equivalent be bigger or smaller?). My site uses flash to playback sound (m4a). I dont have to worry about indexing, the back button not working, etc. But i have feeling there may be other reasons. What are reasons i shouldnt use flash on my website. I'll note one, the fact iphone/itouch and mobile devices does not support it. Not a big deal for most sites and is obvious. What are reason to avoid flash on my site?

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• Powershell 2.0 - Running scripts for the command line call vs. from the ISE

  - by Gromix

  Hi, After writing deployment scripts from within the ISE, we need our CI server to be able to run them automatically, i.e. from the command line or via a batch file. I have notice some significant differences between the following calls: powershell.exe -File Script.ps1 powershell.exe -Command "& '.\Script.ps1'" powershell.exe .\Script.ps1 Some simple examples: When using -File, errors are handled in the exact same way as the ISE. The other two calls seem to ignore the $ErrorActionPreference variable, and do not catch Write-Error in try/catch blocks. When using pSake: The last 2 calls work perfectly Using the ISE or the -File parameter will fail with the following error: The variable '$script:context' cannot be retrieved because it has not been set Could someone help me understand the implications of each syntax, and why they are behaving differently? I would ideally like to find a syntax that works all the time and behaves like the ISE. Thanks, Romain

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• Are mathamatical Algorithms protected by copyright

  - by analogy

  I wish to implement an algorithm which i read in a journal paper in my software (commercial). I want to know if this is allowed or not. The algorithm in question is described in http://arxiv.org/abs/0709.2938 It is a very simple algorithm and a number of implementations exist in python (http://igraph.sourceforge.net/) and java. One of them is in gpl another which i got from a different researcher and had no license attached. There are significant differences in two implementations, e.g. second one uses threads and multiple cores. It is possible to rewrite/ (not translate) the algorithm. So can I use it in my software or on a server for commercial purpose. Thanks

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• How to reliably measure available memory in Linux?

  - by Alex B

  Linux /proc/meminfo shows a number of memory usage statistics. MemTotal: 4040732 kB MemFree: 23160 kB Buffers: 163340 kB Cached: 3707080 kB SwapCached: 0 kB Active: 1129324 kB Inactive: 2762912 kB There is quite a bit of overlap between them. For example, as far as I understand, there can be active page cache (belongs to "cached" and "active") and inactive page cache ("inactive" + "cached"). What I want to do is to measure "free" memory, but in a way that it includes used pages that are likely to be dropped without a significant impact on overall system's performance. At first, I was inclined to use "free" + "inactive", but Linux's "free" utility uses "free" + "cached" in its "buffer-adjusted" display, so I am curious what a better approach is. When the kernel runs out of memory, what is the priority of pages to drop and what is the more appropriate metric to measure available memory?

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• What's the performance penalty of weak_ptr?

  - by Kornel Kisielewicz

  I'm currently designing a object structure for a game, and the most natural organization in my case became a tree. Being a great fan of smart pointers I use shared_ptr's exclusively. However, in this case, the children in the tree will need access to it's parent (example -- beings on map need to be able to access map data -- ergo the data of their parents. The direction of owning is of course that a map owns it's beings, so holds shared pointers to them. To access the map data from within a being we however need a pointer to the parent -- the smart pointer way is to use a reference, ergo a weak_ptr. However, I once read that locking a weak_ptr is a expensive operation -- maybe that's not true anymore -- but considering that the weak_ptr will be locked very often, I'm concerned that this design is doomed with poor performance. Hence the question: What is the performance penalty of locking a weak_ptr? How significant is it?

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• Open txt files from a directory, compare the values, and output the top 15 in PHP

  - by Anon

  Hello, I recently designed a referral game website for the fun of it. There's a simple MySQL user system with a email verification. It's using the UserCake user management system. On top of this i added a php page that the user could give to "victims" that when they visit it they get "infected" and can infect other users or "victims". This page uses GET to get the username from the url. I have a folder that when a user registers it creates a file with 4 digits and then the username. (ex; 0000Username.txt) All the numbers are the same, it's just so that if a user discovers the folder they won't be able to find the files. There is also a txt file in the same format with IPS in the name. (ex; 0000IPSUsername.txt) The file when visited gets the username from the url, then checks if the text file for that username exists. If the username is present in the url, and a valid user it opens the IPS file and adds the IP of the visitor, then opens the user text file, takes the value and adds one to it, and saves. At the end it makes the difference between saying "You are infected, Username has infected (amount) people." or just you have been infected. Now to what i need! I need to add a hi-scores to the website so people can compete to be the one with the most "infections". I thought i could use readdir to get a list of the files and open them with the value in an array, but i need it to also strip the username from the file name. It would be best if it just saves to a text file like "Username | value" because then i can add echo's of the html tags and have it include the file in the page i want it to be one. Many thanks in advance.

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• ^+Left Arrow and ^+Right Arrow suddenly stopped working on OS X

  - by user293261

  Hello. I'm not really sure what to make of this. The key combination of ^← and ^→ have stopped working for one of the two users on my OS X installation. I use these keys all the time (switching tabs in terminal, IntelliJ primarily), and it's driving me crazy. On one user account, it works fine. On the other, it doesn't. This happened today and nothing significant comes to mind that would have caused some weird keybinding issue. If anyone has heard of or experienced anything like this, I would very much appreciate your advice! Thanks.

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• VB.NET: Can the .EXE built by VS2005 be deployed as a standalone EXE?

  - by Craig Johnston

  VB.NET: Can the .EXE built by VS2005 be deployed as a standalone EXE? When I change the mode in VS2005 to "Release" and build the solution, the bin\Release directory then contains the solution .EXE file, but also a .pdb, vshost.exe and .xml file. What are these extra files and are they necessary? I copied the .exe file to another machine and it executed properly, but there was a significant delay when it first executed - thereafter it was like any other program. What is the reason for this, and can it be helped? Is it because the other 3 files in the Release folder are not there with it?

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• Uploadify and Image Compression

  - by Ilya Biryukov

  Hi, I am using Uploadify on one of my client's web sites to allow them to upload a large amount of pictures at once to their photo gallery. I am seeing issues lately. They seem to upload large photographs (3 MB and above). I am wondering, is it possible to compress (reduce their size) on the client side, instead of doing it on the server (just like facebook does it). I know I could easily do it on the server, but I am working on another project right now, where I am expecting a large flow of photo uploads. It would require significant amount of CPU time to process them all. So I thought, I'd ask about the client side processing. Thanks.

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• If we make a number every millisecond, how much data would we have in a day?

  - by Roger Travis

  I'm a bit confused here... I'm being offered to get into a project, where would be an array of certain sensors, that would give off reading every millisecond ( yes, 1000 reading in a second ). Reading would be a 3 or 4 digit number, for example like 818 or 1529. This reading need to be stored in a database on a server and accessed remotely. I never worked with such big amounts of data, what do you think, how much in terms of MBs reading from one sensor for a day would be?... 4(digits)x1000x60x60x24 ... = 345600000 bits ... right ? about 42 MB per day... doesn't seem too bad, right? therefor a DB of, say, 1 GB, would hold 23 days of info from 1 sensor, correct? I understand that MySQL & PHP probably would not be able to handle it... what would you suggest, maybe some aps? azure? oracle? ... Thansk!

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• How do I deliver mail for wildcard addresses to a particular user/alias/program?

  - by David M

  I need to configure sendmail so that mail delivered for wildcard addresses is accepted for delivery and then delivered to a user, alias, or directly to a script. I can rewrite the envelope/headers any number of ways, but I don't know how to accept the wildcard address when it's provided in RCPT TO: Everything I've tried so far winds up with a 550 user unknown error. So here's a specific example: I want to be able to handle any address that consists of a series of digits followed by a dot followed by a word, then pipe that to a script. If the headers get rewritten, that's OK, but I need the envelope to contain the actual Delivered-To address. Here's the sort of SMTP session I need: 220 blah.foo.com ESMTP server ready; Thu, 22 Apr 2010 20:41:08 -0700 (PDT) HELO blort.foo.com 250 blah.foo.com Hello blort.foo.com [10.1.2.3], pleased to meet you MAIL FROM: <[email protected]> 250 2.1.0 <[email protected]>... Sender ok RCPT TO: <[email protected]> 250 2.1.5 <[email protected]>... Recipient ok I tried some stuff with regex maps, but I never got past 550 user unknown.

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• Is there a standard format string in ASP.NET to convert 1/2/3/... to 1st/2nd/3rd...?

  - by Dr. Monkey

  I have an integer in an Access database, which is being displayed in ASP.NET. The integer represents the position achieved by a competitor in a sporting event (1st, 2nd, 3rd, etc.), and I'd like to display it with a standard suffix like 'st', 'nd', 'rd' as appropriate, rather than just a naked number. An important limitation is that this is for an assignment which specifies that no VB or C# code be written (in fact it instructs code behind files to be deleted entirely). Ideally I'd like to use a standard format string if available, otherwise perhaps a custom string (I haven't worked with format strings much, and this isn't high enough priority to dedicate significant time to*, but I am very curious about whether there's a standard string for this). (* The assignment is due tonight, and I've learned the hard way that I can't afford to spend time on things that don't get the marks, even if they irk me significantly.)

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• Performance characteristics of pthreads vs ucontext

  - by Robert Mason

  I'm trying to port a library that uses ucontext over to a platform which supports pthreads but not ucontext. The code is pretty well written so it should be relatively easy to replace all the calls to the ucontext API with a call to pthread routines. However, does this introduce a significant amount of additional overhead? Or is this a satisfactory replacement. I'm not sure how ucontext maps to operating system threads, and the purpose of this facility is to make coroutine spawning fairly cheap and easy. So, question is: Does replacing ucontext calls with pthread calls significantly change the performance characteristics of a library?

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• Best solution for an StringToInt function in C#

  - by StefanE

  Hi, I were asked to do an StringToInt / Int.parse function on the white board in an job interview last week and did not perform very good but I came up with some sort of solution. Later when back home I made one in Visual Studion and I wonder if there are any better solution than mine below. Have not bothred with any more error handling except checking that the string only contains digits. private int StrToInt(string tmpString) { int tmpResult = 0; System.Text.Encoding ascii = System.Text.Encoding.ASCII; byte[] tmpByte = ascii.GetBytes(tmpString); for (int i = 0; i <= tmpString.Length-1; i++) { // Check whatever the Character is an valid digit if (tmpByte[i] > 47 && tmpByte[i] <= 58) // Here I'm using the lenght-1 of the string to set the power and multiply this to the value tmpResult += (tmpByte[i] - 48) * ((int)Math.Pow(10, (tmpString.Length-i)-1)); else throw new Exception("Non valid character in string"); } return tmpResult; }

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• Can you safely rely upon Yahoo Pipes to offload ETL for your application?

  - by Daniel DiPaolo

  Yahoo Pipes are a very intriguing choice for sort of a poor-man's server-free ETL solution, but would it be a good idea to build an application around one or many Pipes? I've really only used them for toy things here and there, with the only thing I've used longer than a week or two being one amalgamated and filtered RSS feed that I've plugged into Google Reader (which has worked great, but if it goes out for a while I wouldn't notice). So, my question is, would building an application around Yahoo Pipes be reliable (available most of the time)? Ideally it'd be something I could rely on being up 99+% of the time. It looks like the Pipes Terms of Use permit building apps around it, but I am unfamiliar with anyone building anything significant using them.

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• Measuring the performance of classification algorithm

  - by Silver Dragon

  I've got a classification problem in my hand, which I'd like to address with a machine learning algorithm ( Bayes, or Markovian probably, the question is independent on the classifier to be used). Given a number of training instances, I'm looking for a way to measure the performance of an implemented classificator, with taking data overfitting problem into account. That is: given N[1..100] training samples, if I run the training algorithm on every one of the samples, and use this very same samples to measure fitness, it might stuck into a data overfitting problem -the classifier will know the exact answers for the training instances, without having much predictive power, rendering the fitness results useless. An obvious solution would be seperating the hand-tagged samples into training, and test samples; and I'd like to learn about methods selecting the statistically significant samples for training. White papers, book pointers, and PDFs much appreciated!

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• What to do with a big image that's slowing website loading down significantly

  - by Dave

  Hi I'm working on a website that's already been designed by someone else. The designer has used a big image (900x700 100KB) which contains a big logo right across the top, then the background for two columns. This image loads every time a page is loaded as it forms the basis for the website. What should I do with it to improve loading time? I'm considering splitting it up into two or more images, especially the logo on the top. Does splitting up images like that decrease loading time in any significant way? Thanks -edit: Also, all the images are .jpg, would changing this to .gif or .png help anything?

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