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  • Are indexes good or bad for a large database?

    - by gmemon
    Hello All, I read on MySQL Performance Blog that when tables are large, it is better to scan full tables, instead of using indexes. I have a table with tens of millions of rows. When conducting queries, if I use no indexes, then queries are 24 times slower than with indexes. I know lot of things may cause this (e.g., are rows stored sequentially), but can you please give me some hints what might be happening? Or how I should start examining this issue? I want to understand when use of indexes is preferred and when it's not Thanks

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  • Many users, many cpus, no delays. Good for cloud?

    - by Eric
    I wish to set up a CPU-intensive time-important query service for users on the internet. A usage scenario is described below. Is cloud computing the right way to go for such an implementation? If so, what cloud vendor(s) cater to this type of application? I ask specifically, in terms of: 1) pricing 2) latency resulting from: - slow CPUs, instance creations, JIT compiles, etc.. - internal management and communication of processes inside the cloud (e.g. a queuing process and a calculation process) - communication between cloud and end user 3) ease of deployment A usage scenario I am expecting is: - A typical user sends a query (XML of size around 1K) once every 30 seconds on average. - Each query requires a numerical computation of average time 0.2 sec and max time 1 sec on a 1 GHz Pentium. The computation requires no data other than the query itself and is performed by the same piece of code each time. - The delay a user experiences between sending a query and receiving a response should be on average no more than 2 seconds and in general no more than 5 seconds. - A background save to a DB of the response should occur (not time critical) - There can be up to 30000 simultaneous users - i.e., on average 1000 queries a second, each requiring an average 0.2 sec calculation, so that would necessitate around 200 CPUs. Currently I'm look at GAE Java (for quicker deployment and less IT hassle) and EC2 (Speed and price optimization) as options. Where can I learn more about the right way to set ups such a system? past threads, different blogs, books, etc.. BTW, if my terminology is wrong or confusing, please let me know. I'd greatly appreciate any help.

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  • Does anyone know of a good script to force file downloads and yet protect download links on a PHP se

    - by racl101
    I tried using a free script that I found on the Internet but it is giving me problems with Windows users (even though they are using IE 8, so it's not an option for me to ask them to upgrade their browsers.) Here's the requirements: I have a bunch of Microsoft Word and pdf files that need to be protected so that only authorized users can download them. I have already created the login system and the current script I have works fine for non-IE browsers. However, I keep getting recurring problems with Windows users who keep complaining that their files download corrupt and yet everyone else either using Mac or Linux or any other browser gets on just fine. The script must allow me to store files in a directory but force download of the file upon the function call. Must work well with most major browsers, especially I.E. If you have any practice suggestions or know of any great scripts (even if they are paid, I'm sick of this problem and would probably pay for a paid script) it would be greatly appreciated in advance.

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  • What's a good place to unregister an observer from the notification center?

    - by mystify
    When I add an observer to the default notification center, where would I unregister that? Example: I have a UIView subclass which lives inside a view controller. That subclass is an observer for the FooBarNotification. If this notification is posted, that view will get it. But now, the view controller decides to throw away the view. Is the best place the -dealloc method of the view itself? Are there any rules like memory management rules? For example: Must I unregister an observer where I registered it? i.e. the view registers itself in it's init method, so it should unregister itself in it's -dealloc method? (not talking about push notifications, but NSNotificationCenter)

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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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  • Is there a good (standalone) PHPDoc parser class or function in PHP?

    - by Kris
    Hi folks, I'm looking for some method of converting a PHP Docblock (as used for generating documentation by tools like Doxygen) into a structure I can inspect in PHP. For example, I want to parse the following lines: /** * Multiply two values * @CHECKME * * @author someone * @created eons ago * * @param integer $x * @param integer $x * * @return integer */ function multiply($x, $y) { return $x * $y; } Into something similar to: array( 'author' = 'someone' ,'created' = 'eons ago' ,'param' = array( 'integer $x' ,'integer $y' ) ,'_flags' = array( '@CHECKME' ) ); I explicitly cannot use PEAR or any such library, it has to be relatively standalone. Any given solution that is better than using a bunch of regexes after stripping away comment outline would be awesome.

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  • What's a good way to add a large number of small floats together?

    - by splicer
    Say you have 100000000 32-bit floating point values in an array, and each of these floats has a value between 0.0 and 1.0. If you tried to sum them all up like this result = 0.0; for (i = 0; i < 100000000; i++) { result += array[i]; } you'd run into problems as result gets much larger than 1.0. So what are some of the ways to more accurately perform the summation?

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  • Is it good to keep &nbsp; inside blank <td>?

    - by jitendra
    if this is the structure <table cellspacing="0" cellpadding="0"> <tr> <td>I don't need noting here then should i keep &nbsp; here always </td> <td>item </td> </tr> <tr> <td>model</td> <td>one</td> </tr> <tr> <td>model</td> <td>two</td> </tr> <tr> <td>model</td> <td>three</td> </tr> </table> How screen reader will read blank TD, Is it semantically correct?

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  • Can anyone provide a good "idiot's guide" to creating an installer in VS2008 (C#) Pro?

    - by paxdiablo
    I have Visual C# 2008 Professional and have developed the first half of a C# application (console mode) with the second half in progress now (GUI). I'm looking for an easy path to creating an installer for it. What are the steps that need to be taken to produce a professional installer? There's a similar question here regarding the Express edition but I have Pro, and I would like as much as possible to stick with just the standard VS stuff (if you think you can convince me that a third party installer creator is much better than a VS-only solution, give it a shot, by all means). Keep in mind that I have no interest in upgrading to VS2010 yet, even if it's a hundred times easier to create an installer. That can come later, when the revenue starts rolling in :-) Also be aware that the GUI component of this application is a totally separate executable from the console part. The console part is a simple "open file 1, do some work on it, write file 2" type and the GUI is a fairly standard "open file, do some stuff" beast so there's no tricky or wildly undocumented behaviour happening. Basically, I'm looking for (at least) the following: professional looking installer. ability to specify where the application files go. changes to the registry to allow double-clicks on my file extension to open the GUI app with the file as an argument. needs to install everything required (my stuff, .Net if required, and so on).

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  • Is there a good extension for SVN in Emacs?

    - by allyourcode
    I've tried psvn.el, but the command to diff the file you're currently looking at is just hideous: M-x svn-file-show-svn-diff. I tried installing vc-svn.el, but couldn't get that working on my version of Emacs: GNU Emacs 21.3.1 (i386-mingw-nt5.1.2600) of 2004-03-10 on NYAUMO. The emacs wiki page, which mainly focuses on vc-svn.el, seems to be horribly out of date, as many of the links do not work.

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  • Is it a good practice for a .js file to rely on variables declared in the including html

    - by Bozho
    In short: <script type="text/javascript"> var root = '${config.root}'; var userLanguage = '${config.language}'; var userTimezone = '${config.timezone}'; </script> <script type="text/javascript" src="js/scripts.js"></script> And then, in scripts.js, rely on these variables: if (userLanguage == 'en') { .. } The ${..} is simply a placeholder for a value in the script that generates the page. It can be php, jsp, asp, whatever. The point is - it is dynamic, and hence it can't be part of the .js file (which is static). So, is it OK for the static javascript file to rely on these externally defined configuration variables? (they are mainly configuration, of course). Or is it preferred to make the .js file be served dynamically as well (i.e. make it a .php / .jsp, with the proper Content-Type), and have these values defined in there.

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  • Good functions and techniques for dealing with haskell tuples?

    - by toofarsideways
    I've been doing a lot of work with tuples and lists of tuples recently and I've been wondering if I'm being sensible. Things feel awkward and clunky which for me signals that I'm doing something wrong. For example I've written three convenience functions for getting the first, second and third value in a tuple of 3 values. Is there a better way I'm missing? Are there more general functions that allow you to compose and manipulate tuple data? Here are some things I am trying to do that feel should be generalisable. Extracting values: Do I need to create a version of fst,snd,etc... for tuples of size two, three, four and five, etc...? fst3(x,_,_) = x fst4(x,_,_,_) = x Manipulating values: Can you increment the last value in a list of pairs and then use that same function to increment the last value in a list of triples? Zipping and Unzipping values: There is a zip and a zip3. Do I also need a zip4? or is there some way of creating a general zip function? Sorry if this seems subjective, I honestly don't know if this is even possible or if I'm wasting my time writing 3 extra functions every time I need a general solution. Thank you for any help you can give!

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  • Is it good practise to blank out inherited functionality that will not be used?

    - by Timo Kosig
    I'm wondering if I should change the software architecture of one of my projects. I'm developing software for a project where two sides (in fact a host and a device) use shared code. That helps because shared data, e.g. enums can be stored in one central place. I'm working with what we call a "channel" to transfer data between device and host. Each channel has to be implemented on device and host side. We have different kinds of channels, ordinary ones and special channels which transfer measurement data. My current solution has the shared code in an abstract base class. From there on code is split between the two sides. As it has turned out there are a few cases when we would have shared code but we can't share it, we have to implement it on each side. The principle of DRY (don't repeat yourself) says that you shouldn't have code twice. My thought was now to concatenate the functionality of e.g. the abstract measurement channel on the device side and the host side in an abstract class with shared code. That means though that once we create an actual class for either the device or the host side for that channel we have to hide the functionality that is used by the other side. Is this an acceptable thing to do: public abstract class MeasurementChannelAbstract { protected void MethodUsedByDeviceSide() { } protected void MethodUsedByHostSide() { } } public class DeviceMeasurementChannel : MeasurementChannelAbstract { public new void MethodUsedByDeviceSide() { base.MethodUsedByDeviceSide(); } } Now, DeviceMeasurementChannel is only using the functionality for the device side from MeasurementChannelAbstract. By declaring all methods/members of MeasurementChannelAbstract protected you have to use the new keyword to enable that functionality to be accessed from the outside. Is that acceptable or are there any pitfalls, caveats, etc. that could arise later when using the code?

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  • What would be a good starting point for development of a 3D application for representation of struct

    - by Lela Dax
    I was thinking QT on OpenGL. Multiplatform ability and being able to be closed (at no cost) at a later point would be important points. But I'm very interested in finding a way that is not only viable but also has the least amount of reinvention of the wheel. e.g. "Why not Ogre? A ready powerful 3D engine without reinventing that part". But I'm very uncertain in what is the optimal collection of tools for that job.

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  • Is it a good or bad practice to call instance methods from a java constructor?

    - by Steve
    There are several different ways I can initialize complex objects (with injected dependencies and required set-up of injected members), are all seem reasonable, but have various advantages and disadvantages. I'll give a concrete example: final class MyClass { private final Dependency dependency; @Inject public MyClass(Dependency dependency) { this.dependency = dependency; dependency.addHandler(new Handler() { @Override void handle(int foo) { MyClass.this.doSomething(foo); } }); doSomething(0); } private void doSomething(int foo) { dependency.doSomethingElse(foo+1); } } As you can see, the constructor does 3 things, including calling an instance method. I've been told that calling instance methods from a constructor is unsafe because it circumvents the compiler's checks for uninitialized members. I.e. I could have called doSomething(0) before setting this.dependency, which would have compiled but not worked. What is the best way to refactor this? Make doSomething static and pass in the dependency explicitly? In my actual case I have three instance methods and three member fields that all depend on one another, so this seems like a lot of extra boilerplate to make all three of these static. Move the addHandler and doSomething into an @Inject public void init() method. While use with Guice will be transparent, it requires any manual construction to be sure to call init() or else the object won't be fully-functional if someone forgets. Also, this exposes more of the API, both of which seem like bad ideas. Wrap a nested class to keep the dependency to make sure it behaves properly without exposing additional API:class DependencyManager { private final Dependency dependency; public DependecyManager(Dependency dependency) { ... } public doSomething(int foo) { ... } } @Inject public MyClass(Dependency dependency) { DependencyManager manager = new DependencyManager(dependency); manager.doSomething(0); } This pulls instance methods out of all constructors, but generates an extra layer of classes, and when I already had inner and anonymous classes (e.g. that handler) it can become confusing - when I tried this I was told to move the DependencyManager to a separate file, which is also distasteful because it's now multiple files to do a single thing. So what is the preferred way to deal with this sort of situation?

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