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  • Raid-5 Performance per spindle scaling

    - by Bill N.
    So I am stuck in a corner, I have a storage project that is limited to 24 spindles, and requires heavy random Write (the corresponding read side is purely sequential). Needs every bit of space on my Drives, ~13TB total in a n-1 raid-5, and has to go fast, over 2GB/s sort of fast. The obvious answer is to use a Stripe/Concat (Raid-0/1), or better yet a raid-10 in place of the raid-5, but that is disallowed for reasons beyond my control. So I am here asking for help in getting a sub optimal configuration to be as good as it can be. The array built on direct attached SAS-2 10K rpm drives, backed by a ARECA 18xx series controller with 4GB of cache. 64k array stripes and an 4K stripe aligned XFS File system, with 24 Allocation groups (to avoid some of the penalty for being raid 5). The heart of my question is this: In the same setup with 6 spindles/AG's I see a near disk limited performance on the write, ~100MB/s per spindle, at 12 spindles I see that drop to ~80MB/s and at 24 ~60MB/s. I would expect that with a distributed parity and matched AG's, the performance should scale with the # of spindles, or be worse at small spindle counts, but this array is doing the opposite. What am I missing ? Should Raid-5 performance scale with # of spindles ? Many thanks for your answers and any ideas, input, or guidance. --Bill Edit: Improving RAID performance The other relevant thread I was able to find, discusses some of the same issues in the answers, though it still leaves me with out an answer on the performance scaling.

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  • How to limit disk performance?

    - by DrakeES
    I am load-testing a web application and studying the impact of some config tweaks (related to disk i/o) on the overall app performance, i.e. the amount of users that can be handled simultaneously. But the problem is that I hit 100% CPU before I can see any effect of the disk-related config settings. I am therefore wondering if there is a way I could deliberately limit the disk performance so that it becomes the bottleneck and the tweaks I am trying to play with actually start impacting performance. Should I just make the hard disk busy with something else? What would serve the best for this purpose? More details (probably irrelevant, but anyway): PHP/Magento/Apache, studying the impact of apc.stat. Setting it to 0 makes APC not checking PHP scripts for modification which should increase performance where disk is the bottleneck. Using JMeter for benchmarking.

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  • Good C++ books regarding Performance?

    - by Leon
    Besides the books everyone knows about, like Meyer's 3 Effective C++/STL books, are there any other really good C++ books specifically aimed towards performance code? Maybe this is for gaming, telecommunications, finance/high frequency etc? When I say performance I mean things where a normal C++ book wouldnt bother advising because the gain in performance isn't worthwhile for 95% of C++ developers. Maybe suggestions like avoiding virtual pointers, going into great depth about inlining etc? A book going into great depth on C++ memory allocation or multithreading performance would obviously be very useful.

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  • Better to combine & minify javascript or use Google CDN?

    - by jessegavin
    I am building a site which currently uses javascript from several sources: Group 1: Google Maps API v3 (hosted by Google) Group 2: jQuery & swfobject (hosted on Google CDN) Group 3: Several jQuery plugins and non-jquery javascript files (hosted on my server) I am using Justin Etheredge's tool SquishIt to combine and minify all the javascript files that are hosted on my server (group 3). I am wondering if the site would 'feel' faster to users if I were to host the files in (group 2) locally so that they can be combined with all the other files in (group 3) and requiring only one HTTP request for groups 2 & 3. This would mean that I don't get the benefits of the Google CDN however. Does anyone have any advice on this matter?

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  • How many of you *really* surf around without JavaScript enabled? [closed]

    - by Stephen
    I've decided to rephrase the question. After some deliberation on Meta, I've realized that my question needs to be a bit more focused. The question: Should we (web developers) continue to spend effort progressively enhancing our web applications with JavaScript, ensuring that features gracefully degrade, thereby ensuring accessibility? Or should we spend that time focused on new features or other areas of development? The subtext of that question would be: How many of our customers/clients/users utilize our websites or applications with JavaScript disabled? Do you have any projects with requirements that specifically demand JavaScript functionality (almost all of mine do), and do those requirements also demand graceful degradation? For the sake of asking this question, I pulled up programmers.stackexchange.com without JavaScript enabled, and I was greeted with this message: "Programmers - Stack Exchange works best with JavaScript enabled". It was difficult to log in, albeit the site seemed to generally work okay. (I wasn't able to vote up any questions.) I think this is a satisfactory approach to development. Imagine the effort involved in making all of the site's features work with plain old HTML and server-side logic. OTOH, I wonder how many users have been alienated by this approach. We've all been trained (at least the good developers among us) to use progressive enhancement and to ensure our web applications' dynamic features degrade gracefully. Is this progressive enhancement just pissing into the wind, or do some of our customers actually utilize certain web services without JavaScript enabled? I mean, like really, not figuratively or presumptuously.

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  • remove a:hover using javascript (not using jquery... don't ask)

    - by Cyprus106
    I thought this would be pretty simple.... Basically, it's a 5-star rating system. When a user clicks, for example, three stars... I want to freeze those three stars right where they're at. I've been trying to simply remove the hover for the a href so it stays what it was at... maybe that's not the right method. I've exhausted absolutely everything I can think of... By the way this is straight javascript, not jquery or anything. It's crazy, I know but all of the JS was written straight.... I've got this class: .star-rating li a{ display:block; width:25px; height: 25px; text-decoration: none; text-indent: -9000px; z-index: 20; position: absolute; padding: 0px; } .star-rating li a:hover{ background: url(images/alt_star.png) left bottom; z-index: 2; left: 0px; } .star-rating a:focus, .star-rating a:active{ border:0; -moz-outline-style: none; outline: none; } .star-rating a.one-star{ left: 0px; } .star-rating a.one-star:hover{ width:25px; } and this code: <ul class='star-rating'> <li><a href="#" onclick="javascript: vote(<?=$id;?>, 1); disableStars(); return false;" title='1 star out of 5' id="1s" class='one-star'>1</a></li>

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  • how to update div tag in javascript with data from model for onsubmit form asp.net mvc

    - by michael
    In my page i have a form tag which submits to server ,gets data and redirects to same page. problem is the the div tag which has the data from server is not getting updated. how to do that in javascript <% using (Html.BeginForm("Addfile", "uploadfile", FormMethod.Post, new { id = "uploadform", enctype = "multipart/form-data" })) { %> <input type="file" id="addedFile" name="addedFile" /><br /> <input type="submit" id="addfile" value="Addfile" /> <div id="MyGrid"> //data from the model(server side) filelist is not updating</div> what will be the form onsubmit javascript function to update the div tag with the data from the model. and my uploadfile controller get post methods are as [AcceptVerbs(HttpVerbs.Get)] public ActionResult Upload() { return View(); } [AcceptVerbs(HttpVerbs.Post)] public ActionResult AddFile(HttpPostedFileBase addedFile) { static List<string> fileList = new List<string>(); string filename = Path.GetFileName(addedFile.FileName); file.SaveAs(@"D:\Upload\" + filename); fileList.Add(filename); return("Upload",fileList); } thanks, michaela

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  • How is a functional programming-based javascript app laid out?

    - by user321521
    I've been working with node.js for awhile on a chat app (I know, very original, but I figured it'd be a good learning project). Underscore.js provides a lot of functional programming concepts which look interesting, so I'd like to understand how a functional program in javascript would be setup. From my understanding of functional programming (which may be wrong), the whole idea is to avoid side effects, which are basically having a function which updates another variable outside of the function so something like var external; function foo() { external = 'bar'; } foo(); would be creating a side effect, correct? So as a general rule, you want to avoid disturbing variables in the global scope. Ok, so how does that work when you're dealing with objects and what not? For example, a lot of times, I'll have a constructor and an init method that initializes the object, like so: var Foo = function(initVars) { this.init(initVars); } Foo.prototype.init = function(initVars) { this.bar1 = initVars['bar1']; this.bar2 = initVars['bar2']; //.... } var myFoo = new Foo({'bar1': '1', 'bar2': '2'}); So my init method is intentionally causing side effects, but what would be a functional way to handle the same sort of situation? Also, if anyone could point me to either a python or javascript source code of a program that tries to be as functional as possible, that would also be much appreciated. I feel like I'm close to "getting it", but I'm just not quite there. Mainly I'm interested in how functional programming works with traditional OOP classes concept (or does away with it for something different if that's the case).

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  • Rewriting jQuery to plain old javascript - are the performance gains worth it?

    - by Swader
    Since jQuery is an incredibly easy and banal library, I've developed a rather complex project fairly quickly with it. The entire interface is jQuery based, and memory is cleaned regularly to maintain optimum performance. Everything works very well in Firefox, and exceptionally so in Chrome (other browsers are of no concern for me as this is not a commercial or publicly available product). What I'm wondering now is - since pure plain old javascript is really not a complicated language to master, would it be performance enhancing to rewrite the whole thing in plain old JS, and if so, how much of a boost would you expect to get from it? If the answers prove positive enough, I'll go ahead and do it, run a benchmark and report back with the precise findings. Cheers Edit: Thanks guys, valuable insight. The purpose was not to "re-invent the wheel" - it was just for experience and personal improvement. Just because something exists, doesn't mean you shouldn't explore it into greater detail, know how it works or try to recreate it. This is the same reason I seldom use frameworks, I would much rather use my own code and iron it out and gain massive experience doing it, than start off by using someone else's code, regardless of how ironed out it is. Anyway, won't be doing it, thanks for saving me the effort :)

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  • puzzled with java if else performance

    - by user1906966
    I am doing an investigation on a method's performance and finally identified the overhead was caused by the "else" portion of the if else statement. I have written a small program to illustrate the performance difference even when the else portion of the code never gets executed: public class TestIfPerf { public static void main( String[] args ) { boolean condition = true; long time = 0L; int value = 0; // warm up test for( int count=0; count<10000000; count++ ) { if ( condition ) { value = 1 + 2; } else { value = 1 + 3; } } // benchmark if condition only time = System.nanoTime(); for( int count=0; count<10000000; count++ ) { if ( condition ) { value = 1 + 2; } } time = System.nanoTime() - time; System.out.println( "1) performance " + time ); time = System.nanoTime(); // benchmark if else condition for( int count=0; count<10000000; count++ ) { if ( condition ) { value = 1 + 2; } else { value = 1 + 3; } } time = System.nanoTime() - time; System.out.println( "2) performance " + time ); } } and run the test program with java -classpath . -Dmx=800m -Dms=800m TestIfPerf. I performed this on both Mac and Linux Java with 1.6 latest build. Consistently the first benchmark, without the else is much faster than the second benchmark with the else section even though the code is structured such that the else portion is never executed because of the condition. I understand that to some, the difference might not be significant but the relative performance difference is large. I wonder if anyone has any insight to this (or maybe there is something I did incorrectly). Linux benchmark (in nano) performance 1215488 performance 2629531 Mac benchmark (in nano) performance 1667000 performance 4208000

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  • Is there a way to get SSL certificate details using JavaScript?

    - by sHz
    Hi all, I'd like to gather certain details of an SSL certificate on a particular web-site. I know this is straightforward using the openssl tool on Linux/MacOSX. However is the same or similar possible in JavaScript? I understand that the browser handles socket connections and that the SSL handshake occurs prior to any party sending data. However in an XMLHTTPRequest, I'd like to know if its possible to get these details as some sort of response code etc?

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  • Get the coordinates of a drop event in Javascript?

    - by Sebastián Grignoli
    I made a javascript library that lets me drag a marker from a dragzone to one or more dropzones. The problem is... the mouseup event happens over the marker I'm dragging, no te dropzone. How can I detect in wich dropzone was the marker dropped, and in wich coordinates? Here's my script: http://dl.dropbox.com/u/186012/demos/dragger/drag.html

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  • Where is a good javascript reference for object event handlers?

    - by GregH
    I am relatively new to Javascript and constantly need to look up how to handle various events for objects. For example, I have a table containing a few text fields and need to know when somebody starts typing in any of the text boxes. Is there any good concise reference on the web anyplace that documents all of the objects and event handlers associated with all objects? I'd like to be able to look up the object and see all of the events I can handle for that object.

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  • Performance Testing Versus Unit Testing

    - by Mystagogue
    I'm reading Osherove's "The Art of Unit Testing," and though I've not yet seen him say anything about performance testing, two thoughts still cross my mind: Performance tests generally can't be unit tests, because performance tests generally need to run for long periods of time. Performance tests generally can't be unit tests, because performance issues too often manifest at an integration or system level (or at least the logic of a single unit test needed to re-create the performance of the integration environment would be too involved to be a unit test). Particularly for the first reason stated above, I doubt it makes sense for performance tests to be handled by a unit testing framework (such as NUnit). My question is: do my findings / leanings correspond with the thoughts of the community?

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  • What do you think of a performance engineer should have?

    - by Vance
    I believe performance tuning (or even testing) is one the most challenging for an engineer. Well, in lots of company, this is the lowest priority than others "important" thing. My purpose of opening this post is to know what do you think*good* performance engineer should have. I can list some things like: Solid database,programming knowledge. Do single thread performance testing. Good knowledge of using the load generator tools to simulate the concurrent loads. Use different tools to monitor/measure the app/db server performance status Understand and can debug the codes. Even tune the codes. Any more ideas are always appreciated!

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  • In MATLAB, how can 'preallocating' cell arrays improve performance?

    - by Alex McMurray
    I was reading this article on MathWorks about improving MATLAB performance and you will notice that one of the first suggestions is to preallocate arrays, which makes sense. But it also says that preallocating Cell arrays (that is arrays which may contain different, unknown datatypes) will improve performance. But how will doing so improve performance because the datatypes are unknown so it doesn't know how much contiguous memory it will require even if it knows the shape of the cell array, and therefore it can't preallocate the memory surely? So how does this result in any improvement in performance? I apologise if this question is better suited for StackOverflow than Programmers but it isn't asking about a specific problem so I thought it fit better here, please let me know if I am mistaken though. Any explanation would be greatly appreciated :)

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  • Does software rot refer primarily to performance, or to messy code?

    - by Kazark
    Wikipedia's definition of software rot focuses on the performance of the software. This is a different usage than I am used to; I had thought of it much more in terms of the cleanliness and design of the code—in terms of the code's having all the standard quality characteristics: readability, maintainability, etc. Now, performance is likely to go down when the code becomes unreadable, because no one knows what is going on. But does the term software rot have special reference to performance? or am I right in thinking it refers to the cleanliness of the code? or is this perhaps a case of multiple senses of the term being in common usage—from the user's perspective, it has do with performance; but for the software craftsman, it has to do more specifically with how the code reads?

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  • Simple vs Complex (but performance efficient) solution - which one to choose and when?

    - by ManojGumber
    I have been programming for a couple of years and have often found myself at a dilemma. There are two solutions - one is simple one i.e. simple approach, easier to understand and maintain. It involves some redundancy, some extra work (extra IO, extra processing) and therefore is not the most optimal solution. but other uses a complex approach,difficult to implement, often involving interaction between lot of modules and is a performance efficient solution. Which solution should I strive for when I do not have hard performance SLA to meet and even the simple solution can meet the performance SLA? I have felt disdain among my fellow developers for simple solution. Is it good practice to come up with most optimal complex solution if your performance SLA can be met by a simple solution?

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  • In the days of modern computing, in 'typical business apps' - why does performance matter?

    - by Prog
    This may seem like an odd question to some of you. I'm a hobbyist Java programmer. I have developed several games, an AI program that creates music, another program for painting, and similar stuff. This is to tell you that I have an experience in programming, but not in professional development of business applications. I see a lot of talk on this site about performance. People often debate what would be the most efficient algorithm in C# to perform a task, or why Python is slow and Java is faster, etc. What I'm trying to understand is: why does this matter? There are specific areas of computing where I see why performance matters: games, where tens of thousands of computations are happening every second in a constant-update loop, or low level systems which other programs rely on, such as OSs and VMs, etc. But for the normal, typical high-level business app, why does performance matter? I can understand why it used to matter, decades ago. Computers were much slower and had much less memory, so you had to think carefully about these things. But today, we have so much memory to spare and computers are so fast: does it actually matter if a particular Java algorithm is O(n^2)? Will it actually make a difference for the end users of this typical business app? When you press a GUI button in a typical business app, and behind the scenes it invokes an O(n^2) algorithm, in these days of modern computing - do you actually feel the inefficiency? My question is split in two: In practice, today does performance matter in a typical normal business program? If it does, please give me real-world examples of places in such an application, where performance and optimizations are important.

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