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• Using Jquery to check if a URL is valid

  - by user102533

  A long running background process creates a text file to indicate the completion of the process. From the frontend, I'd need to check every few seconds if the text file has been created or not. I am doing this check from However the file is created in http://DomainB.com/Mytext.txt Can someone help me write a jquery script that checks for a file across domain? PS: Currently, I am doing a ajax postback that executes a WebMethod in ASP.NET that creates HttpWebRequest. This works functionally, but I have major performance problems. So, I need a light weight way of finding if a URL is valid or not.

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• Separate one-off code paths

  - by DeadMG

  I'm implementing an application with different code paths that shall be chosen once at startup and then fixed forevermore for that execution- for example, choosing D3D11 or D3D9 rendering path. Obviously I don't want to duplicate all my other code. Is run-time inheritance (no virtual inheritance) a fair solution? I don't want to waste a bunch of performance making virtual lookups when the type was fixed long ago. Not just that, but it makes me nervous that the functions can't be inlined and whether or not it affects RVO and NRVO and such. Am I just being over-concerned about this?

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• MySQL indexes - what are the best practises?

  - by Haroldo

  I've been using indexes on my mysql databases for a while now but never properly learnt about them. Generally I put an index on any fields that i will be searching or selecting using a WHERE clause but sometimes it doesn't seem so black and white. What are the best practises for mysql indexes? example situations/dilemas: If a table has six columns and all of them are searchable, should i index all of them or none of them? . What are the negetive performance impacts of indexing? . If i have a VARCHAR 2500 column which is searchable from parts of my site, should i index it?

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• Using locks inside a loop

  - by Xaqron

  // Member Variable private readonly object _syncLock = new object(); // Now inside a static method foreach (var lazyObject in plugins) { if ((string)lazyObject.Metadata["key"] = "something") { lock (_syncLock) { if (!lazyObject.IsValueCreated) lazyObject.value.DoSomething(); } return lazyObject.value; } } Here I need synchronized access per loop. There are many threads iterating this loop and based on the key they are looking for, a lazy instance is created and returned. lazyObject should not be created more that one time. Although Lazy class is for doing so and despite of the used lock, under high threading I have more than one instance created (I track this with a Interlocked.Increment on a volatile shared int and log it somewhere). The problem is I don't have access to definition of Lazy and MEF defines how the Lazy class create objects. My questions: 1) Why the lock doesn't work ? 2) Should I use an array of locks instead of one lock for performance improvement ?

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• What's a good way to set up a development environment on OS X for ruby, rails, and git?

  - by Ein2015

  I'm going to start development on a web app using ruby, rails, probably either postgres or mysql, and most likely apache. I'll be using a git repository with the master repo on another server. I've searched through stackoverflow and done some Googling... so here's what I have so far... What are your opinions on what's described on this page?: http://robots.thoughtbot.com/post/159805668/2009-rubyists-guide-to-a-mac-os-x-development What about this one?: http://www.buildingwebapps.com/articles/79197-setting-up-rails-on-leopard-mac I don't need helping finding an editor, there's plenty out there (TextMate, TextWrangler, MacVim), but I do need help to make sure I'm setting things up correctly to code, build, and run the web app from my mac. Here's a specific set of scenarios I could use some help on: Testing various versions of rails and/or ruby. Testing performance, vulnerabilities, monitoring queries, etc. Testing different versions of gems. Working on other projects on this same machine.

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• Selecting a value from multiple dictionaries inside an enumeration

  - by johaanfaust

  If I have an enumeration of dictionaries IEnumerable<IDictionary<string, float>> enumeration can I perform a Linq query on it so that I can select by a value from each dictionary in the enumeration using the same key? I can do this in a loop: float f; foreach (var dictionary in enumeration) { if (dictionary.TryGetValue("some key", out f)) { Console.WriteLine(f); } } (The eventual plan is to compare the performance of the query verses the equivalent nested looping statements (the enumeration itself is formed from either another query or an equivalent set of loops).)

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• Designing entire webpages as SVG files

  - by user1311390

  Disclaimer I realize that given the absurdity of the title, this sounds like a troll. However, it's a genuine question. My background involves OpenGL / x86 assembly. I've recently started learning web programming. I really like SVG + CSS, and was wondering -- why do people not design entire webpages in SVG? Context SVG provides beautiful primitive: quadratic + cubic bezier curves; lines + filling -- all as vector graphics SVG provides text SVG provides affine transformations Questions Are there examples of people designing entire websites as a giant SVG file? If not, what the limitations? Are there performance hits when using SVG primitives as opposed to divs/tables?

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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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• Phonegap and JqueryMobile freeze UI events and functions

  - by techytee

  I am developing a Phonegap app with JQuery mobile with their latest stable versinos (Phonegap 3 and JQM 1.3.2) for Android platform. My app downloads feeds from Google Feeds API and saves in a SQLite database. But whenever it starts fetching and saving data from the web (the no of feeds that download at a time can be many), the other functionality such as button events halt and freeze. To be precise the a button that opens and closes a panel does not either open or close the panel until the data fetching stops. How am I supposed to solve this issue? The performance has dropped drastically due to this issue in my app.

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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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• How can I change column fore color in DataGridview as per condition?

  - by Ashish

  hi, i have one table like employee and one of its row is 'status' if status value is 'approve' then i want to show that row in green color and else i want to show it in red color. i have tried following but not working if (e.Row.RowType == DataControlRowType.Header) { string status = DataBinder.Eval(e.Row.DataItem, "IsApprove").ToString(); if (status == "pending") { e.Row.ForeColor = System.Drawing.Color.Red; // Change the row's Text color } } ALSO THIS ONE private void gvleavedetail_cellformatting(object sender, datagridviewcellformattingeventargs e) { // if the column is the artist column, check the // value. if (this.gvleavedetail.columns[e.columnindex].name == "artist") { if (e.value != null) { // check for the string "pink" in the cell. string stringvalue = (string)e.value; stringvalue = stringvalue.tolower(); if (stringvalue == "high") { e.cellstyle.backcolor = color.pink; } } } But in this case i'm getting error for datagridviewcellformattingeventargs I'm using VS2010

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• matrix = *((fxMatrix*)&d3dMatrix); //Evil?

  - by Xilliah

  I've been using matrix = *((fxMatrix*)&d3dMatrix); for quite a while. It worked fine until my screen turned black and received a bucket of frustration on my desk. fxMatrix contains 4 fxVectors. fxVector used to be 16 bytes, but now it was suddenly 20. This was because it inherited fxStreamable, which added the vTable. So one solution is of course just to not inherit fxStreamable, and leave a comment saying that it must always be 16 bytes and never more. Another solution would be to make conversion functions, and copy the matrix completely. This makes it more secure, but has an impact on the performance. I suppose this is the best idea. Another solution is to not convert at all, and stick to D3DXMATRIX, but this makes the engine inconsistent and I personally really dislike this idea. What is your opinion?

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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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• misleading plot issue in mathematica

  - by Qiang Li

  I want to study some "strange" functions by plotting them out in mathematica. One example is the following: mod2[x_] := Which[Mod[x, 2] >= 1, -2 + Mod[x, 2], True, Mod[x, 2]]; f[x_] := Which[-1 <= x <= 1, Abs[x], True, Abs[mod2[x]]]; fn[x_, n_] := Sum[(3/4)^i*f[4^n*x], {i, 0, n}] Plot[{fn[x, 0], fn[x, 1], fn[x, 2], fn[x, 5]}, {x, -2, 2}] However, the plot I got from mma is misleading, in the sense that the maxima and minima of fn[x, 5] should be on the same two levels. But due to high oscillation of the function, and the fact that clearly mma only takes limited number of points to draw the function, you see the plot exhibit strange behavior. Is there any option in plot to remedy for this? Many thanks.

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• How do I change the class of an object to a subclass of its current class in C++?

  - by Jared P

  I have an array of pointers to a base class, so that I can make those pointers point to (different) subclasses of the base class, but still interact with them. (really only a couple of methods which I made virtual and overloaded) I'm wondering if I can avoid using the pointers, and instead just make an array of the base class, but have some way to set the class to the subclass of my choosing. I know there must be something there specifying the class, as it needs to use that to look up the function pointer for virtual methods. By the way, the subclasses all have the same ivars and layout. Note: the design is actually based on using a template argument instead of a variable, due to performance increases, so really the abstract base class is just the interface for the subclasses, which are all the same except for their compiled code. Thanks

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• Which is more efficent PHP: array_intersect() OR array_intersect_key()

  - by Jordan Rutty

  Is it more efficient to use the key intersect or the value intersect if both key and value have the same contents for example: Array ( [743] => 743 [744] => 744 [745] => 745 [746] => 746 [747] => 747 [748] => 748 ) Is there any difference in performance in using one or the other with the same values. Similar to the difference of using double or single quotes?

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• Is referencing a selector faster in jquery than actually calling the selector? if so, how much does it make a difference?

  - by anthonypliu

  Hi, I have this code: $(preview-button).click(...) $(preview-button).slide(...) $(preview-button).whatever(...) Is it a better practice to do this: var preview-button = $(preview-button); preview-button.click(...); preview-button.click(...); preview-button).slide(...); preview-button.whatever(...); It probably would be better practice to do this for the sake of keeping code clean and modular, BUT does it make a difference performance wise? Does one take longer to process than the other? Thanks guys.

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• Microphone input

  - by George

  I'm trying to build a gadget that detects pistol shots using Android. It's a part of a training aid for pistol shooters that tells how the shots are distributed in time and I use a HTC Tattoo for testing. I use the MediaRecorder and its getMaxAmplitude method to get the highest amplitude during the last 1/100 s but it does not work as expected; speech gives me values from getMaxAmplitude in the range from 0 to about 25000 while the pistol shots (or shouting!) only reaches about 15000. With a sampling frequency of 8kHz there should be some samples with considerably high level. Anyone who knows how these things work? Are there filters that are applied before registering the max amplitude. If so, is it hardware or software? Thanks, /George

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• Filtering with joined tables

  - by viraptor

  I'm trying to get some query performance improved, but the generated query does not look the way I expect it to. The results are retrieved using: query = session.query(SomeModel). options(joinedload_all('foo.bar')). options(joinedload_all('foo.baz')). options(joinedload('quux.other')) What I want to do is filter on the table joined via 'first', but this way doesn't work: query = query.filter(FooModel.address == '1.2.3.4') It results in a clause like this attached to the query: WHERE foos.address = '1.2.3.4' Which doesn't do the filtering in a proper way, since the generated joins attach tables foos_1 and foos_2. If I try that query manually but change the filtering clause to: WHERE foos_1.address = '1.2.3.4' AND foos_2.address = '1.2.3.4' It works fine. The question is of course - how can I achieve this with sqlalchemy itself?

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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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• 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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• Java Web Server with Jetty - TCP Connections Taking Long

  - by daysleeper

  I have an application with fairly high traffic (20K req/min) running on the JVM with a Jetty servlet container on Ubuntu. Below is my Jetty configuration: 10 20 2000 2 When I analyze the network traffic, I realize that sometimes it is taking long to establish TCP connections on the port that Jetty is running. The long connections are varying between 3.0s and 9.0s. The port is configured to accept MAX number of TCP connections. Do you know what might be causing the delay in accepting connections? Thanks

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• Why is 'using namespace std;' considered a bad practice in C++?

  - by Mana

  Okay, sorry for the simplistic question, but this has been bugging me ever since I finished high school C++ last year. I've been told by others on numerous occasions that my teacher was wrong in saying that we should have "using namespace std;" in our programs, and that std::cout and std::cin are more proper. However, they would always be vague as to why this is a bad practice. So, I'm asking now: Why is "using namespace std;" considered bad? Is it really that inefficient, or risk declaring ambiguous vars(variables that share the same name as a function in std namespace) that much? Or does this impact program performance noticeably as you get into writing larger applications? I'm sorry if this is something I should have googled to solve; I figured it would be nice to have this question on here regardless in case anyone else was wondering.

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• DB management for Heroku apps

  - by zetarun

  Hi all, I'm fairly new to both Rails and Heroku but I'm seriously thinking of using it as a platform to deploy my Ruby/Rails applications. I want to use all the power of Heroku, so I prefer the "embedded" PostgreSQL managed by Heroku instead of the addon for Amazon RDS for MySQL, but I'm not so confident without the possibility to access my data in a SQL client... I know that in a well made app you have no need to access DB, but there are some situations (add rows to a config table, see data not mapped in a view, update some columns for debugging issues, performance monitoring, running queries for reporting, etc.) when this can be good... How do you solve this problem? What's you experience in a real life app powered by Heroku? Thanks!

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• Hard drive randomly sppeeding up

  - by Glenn Taylor

  Having a weird issue with my hard drive. Running Windows 7 with an I5 processor. At random times the hard drive will start running at top speed and gradually return to normal over the next two minutes or so. Going to Resource Monitor it shows a variety of things with high read or write numbers. Log files NTFS volume log, Windows prefetch, System/user/appdata, and Program data Norton are the usual top ones listed. This just started about three months ago although the computer is about 3 years old. Have run in safe mode with internet over the weekend going to all of my usual sites with no such speed up. Question 1 - what can be causing this? Question 2 - how can I find out where data is being sent(especially if over the net)? Thank you.

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