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Search found 26 results on 2 pages for 'dimitris stefanidis'.

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  • Data aggregation mongodb vs mysql

    - by Dimitris Stefanidis
    I am currently researching on a backend to use for a project with demanding data aggregation requirements. The main project requirements are the following. Store millions of records for each user. Users might have more than 1 million entries per year so even with 100 users we are talking about 100 million entries per year. Data aggregation on those entries must be performed on the fly. The users need to be able to filter on the entries by a ton of available filters and then present summaries (totals , averages e.t.c) and graphs on the results. Obviously I cannot precalculate any of the aggregation results because the filter combinations (and thus the result sets) are huge. Users are going to have access on their own data only but it would be nice if anonymous stats could be calculated for all the data. The data is going to be most of the time in batch. e.g the user will upload the data every day and it could like 3000 records. In some later version there could be automated programs that upload every few minutes in smaller batches of 100 items for example. I made a simple test of creating a table with 1 million rows and performing a simple sum of 1 column both in mongodb and in mysql and the performance difference was huge. I do not remember the exact numbers but it was something like mysql = 200ms , mongodb = 20 sec. I have also made the test with couchdb and had much worse results. What seems promising speed wise is cassandra which I was very enthusiastic about when I first discovered it. However the documentation is scarce and I haven't found any solid examples on how to perform sums and other aggregate functions on the data. Is that possible ? As it seems from my test (Maybe I have done something wrong) with the current performance its impossible to use mongodb for such a project although the automated sharding functionality seems like a perfect fit for it. Does anybody have experience with data aggregation in mongodb or have any insights that might be of help for the implementation of the project ? Thanks, Dimitris

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  • Gmail-like labelling system

    - by Dimitris
    Hi I am looking into a number of ways to implement a labelling system similar to the one in Gmail. Basically I have a Resource at the lowest level and I would like to provide a number of organisational groupings for that resource in the form of labels. If anyone has implemented something like that I would like to hear your views. My idea is to have within the Resource instance a List<Label>. I need to have an efficient mechanism in order to do very fast searches based on the labels or based on the resources. Thanks Dimitris

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  • Regarding sprite design and resolution for tablets and phones

    - by Dimitris P.
    I am about to start working on a game for android devices, in my spare time, to get familiar with android development. I'm more interested in using the best practices possible than getting a quick result, and that is why I need some guidance regarding graphics. I think the game is going to be fully sprite based. Everything is going to be in .bmp form, or something similar, and my question is: Should I design the sprites in a small resolution (ie for phone screens) and scale them up to fit into larger screens (tablet screens), should I do it vice-versa or should I consider a completely different approach? Would designing a different set of sprites for each of the most used resolution settings be worth it or are there simpler solutions to the problem with fewer drawbacks than the ones I mentioned above? (If I follow the first approach, for example, the larger the screen the worse the graphics will get, since every pixel of the original drawing will cover several pixels on the screen). Is there a standard approach for dealing with this kind of problems? If you need me to be more detailed or more clear about something I mentioned (or forgot to) please don't hesitate to ask. Also, excuse me for any inaccurate use of the English language. Thank you in advance for your input.

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  • HTML5 or Native Android/iOS application?

    - by Dimitris
    I would like to hear your opinion on this debate. I want to build a mobile application which will interact with a server and I was wondering what's the best way to do it. Build the entire application using the HTML5 technology and then just create native "browsing" apps for Android/iOS or to build the Android/iOS apps from scratch? Using the HTML5 will save considerable amounts of time but I don't know if the result will be equally good in both platforms. Building native apps will take much more time but the result will be definitely good. What do you think?

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  • root access on my own server

    - by Dimitris Sapikas
    i have an Ubuntu Server (from virtual server proviler) and i am connecting on it ussing SSH. Ussing PuTTY i have to type sudo su and my password first in order to get full access. But when i am connecting using WinSCP , i dont have permission on my own files. Do you know how i could deal with this ? If i would been using nautilus , i could call sudo nautilus but in this case it does not seem like it could work like that Thank you.

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  • Cannot connect Office 365 email with Outlook 2010

    - by Dimitris
    I have an email address of the form [email protected] that I am accessing through this site. I had connected my email to Outlook 2010 and it was working fine. Recently, it started requesting credentials every time I logged in, without connecting to the email server even after entering the correct password. I had already decided to reinstall Windows 7, so I thought that would also fix this problem. Unfortunately it did not. I tried the troubleshoot function embedded in the Office 365 capabilities, but it did not find anything wrong. I suspect that one possible source of this problem could be the fact that in the control panel it states Mail (32-bit) while Windows is 64-bit (office is 32 as well). In addition when trying to remove an email account from the list it remains there unaffected. Does anybody know what should I do in order to fix this problem?

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  • iPhone Curl Left and Curl Right transitions

    - by Dimitris
    I am looking for a way to do a UIViewAnimationTransitionCurlUp or UIViewAnimationTransitionCurlDown transition on the iPhone but instead of top to bottom, do it from the left to right (or top/bottom in landscape mode). I've seen this asked aroud the internet a few times but none sems to get an answer. However I feel this is doable. I have tried changing the View's transform and the view.layer's transform but that didn't affect the transition. Since the transition changes when the device changes orientation I presume there is a way to fool the device to use the landscape transition in portrait mode and vice versa?

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  • Security failure - This is not a secure document but has security embed parameters

    - by dimitris mistriotis
    I try to create a private version and therefore I used something like this in php: var scribd_doc = scribd.Document.getDoc( 28394353, 'xxx'); scribd_doc.addParam("use_ssl", true); scribd_doc.addParam('public', false); scribd_doc.grantAccess("cbccf6e7-1ff7-9034-8a7c-a0c2a5b225ed", <?php echo "'" . trim($_COOKIE['PHPSESSID']) . "'" ?>, <?php echo "'" . scribd_calculate_signature($documentID = '28394353', $sessionID = trim($_COOKIE['PHPSESSID']), $userID = "cbccf6e7-1ff7-9034-8a7c-a0c2a5b225ed") . "'" ?>); ... ... scribd_doc.write( 'embedded_flash' ); Which is the api of scribd for javascript with the addition of the signature. My result is the "Security failure - This is not a secure document but has security embed parameters" Error, which is not well documented. The document is set to private. Any ideas?

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  • .xcodeproj does not get committed with XCode's SCM Tool

    - by Dimitris
    I am using the SCM Tools embedded in XCode to manage my app's versioning. I have created an iPhone app and I have added/committed it to the Subversion server but the .xcodeproj file won't upload (all the class files, resources etc are there)! I don't even get the option to "Add to Repository". Sometimes it gets an "A" (add) next to it under the "SCM" column but still, the next time I commit changes or commit entire project it still doesn't upload and show up on the server. As a result my team can't get and run the project. Is there a way to so something (other than just use the terminal or Versions)? Thank you.

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  • iPhone UILabel text soft shadow

    - by Dimitris
    I know soft shadows are not supported by the UILabel our of the box, on the iPhone. So what would be the best way to implement my own one? EDIT: Obviously I will subclass the UILabel and draw in the -drawRect: My question is, how do I get the contents of the label as graphics and draw around them, blur them etc...

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  • what is stack overflow

    - by Dimitris Baltas
    Back in the days as freshmen in University, when programming in C on Unix machines, a "stack overflow" error on run-time would occur causing a lot of thought on what went wrong. What exactly is "stack overflow" in programming? What are the possible reasons for its appearance? Can it occur in all programming languages? Does it have other names?

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  • HTML: Place an image on top of another one

    - by Dimitris Baltas
    Inside a div, there is a picture that should have 10px margin in all directions from the DIV's border. On the left bottom corner of the picture there is an about-image. The picture is only displayed when its loaded in the DOM through jquery. The problem is that the existence of the about-image dislocates the picture downwards as many pixels as the height of the about-image. I am looking for the cleanest possible alternative to keep the picture inside the DIV and still display the about-image on top of it. Setting the picture as background will not work since i need the picture to load at once. Any improvement on the #about css would be greatly appreciated. Below is a full html page that reproduces the issue <html> <head> <title>Troubleshooting :: align the main picture inside the DIV</title> <style type="text/css"> html, body { background-color: #000000; } #about { z-index:2; position:relative; top:82%; left:3%; } #pic { width:100%; height:96%; } #main-content-image { height:100%; margin-right:10px; margin-left:10px; margin-top:10px; margin-bottom:10px; } #main-content { height:490px; border-width: 1px; border-style: solid; border-color: #777777; } #main-content-image.loading { background: url(http://farros.gr/images/ajax-loader2.gif) no-repeat center center; } a { text-decoration: none; text-decoration: none; color: #868686; outline:none; } .hide { display:none; } </style> <script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.3.2/jquery.min.js"></script> <script type="text/javascript"> <!-- $(document).ready(function(){ $(function () { var img = new Image(); $(img).load(function () { $(this).hide(); $(this).width('100%'); $(this).height('96%'); $('#main-content-image').removeClass('loading').append(this); $(this).fadeIn(); }).error(function () { // notify the user that the image could not be loaded }).attr('src', 'http://farros.gr/images/bg.jpg'); }); }); </script> </head> <body> <div id="main-content"> <div id="main-content-image" class="loading"> <a href="#"><img id="about" src='http://farros.gr/images/about.png' alt='Haris Farros'/></a> </div> </div> </body> </html>

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  • Install multiple iPhone apps at once from Xcode to device

    - by Dimitris
    Supposing we have an Xcode iPhone project with 2 targets, is it possible to build and install both of them on the device with one click? Of course, I understand we will not be able to "build and run" both, but can we at least install them? And to extend this concept a bit a bit: are there any scripts to achieve the same thing but with multiple iPhone projects instead of multiple targets in one project? This would be useful when you want to load all your apps on a new development device and don't want to go through all your projects one by one and install.

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  • Does GC guarantee that cleared References are enqueued to ReferenceQueue in topological order?

    - by Dimitris Andreou
    Say there are two objects, A and B, and there is a pointer A.x --> B, and we create, say, WeakReferences to both A and B, with an associated ReferenceQueue. Assume that both A and B become unreachable. Intuitively B cannot be considered unreachable before A is. In such a case, do we somehow get a guarantee that the respective references will be enqueued in the intuitive (topological when there are no cycles) order in the ReferenceQueue? I.e. ref(A) before ref(B). I don't know - what if the GC marked a bunch of objects as unreachable, and then enqueued them in no particular order? I was reviewing Finalizer.java of guava, seeing this snippet: private void cleanUp(Reference<?> reference) throws ShutDown { ... if (reference == frqReference) { /* * The client no longer has a reference to the * FinalizableReferenceQueue. We can stop. */ throw new ShutDown(); } frqReference is a PhantomReference to the used ReferenceQueue, so if this is GC'ed, no Finalizable{Weak, Soft, Phantom}References can be alive, since they reference the queue. So they have to be GC'ed before the queue itself can be GC'ed - but still, do we get the guarantee that these references will be enqueued to the ReferenceQueue at the order they get "garbage collected" (as if they get GC'ed one by one)? The code implies that there is some kind of guarantee, otherwise unprocessed references could theoretically remain in the queue. Thanks

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  • display wait gif until image is fully loaded

    - by Dimitris Baltas
    Most popular browsers, while rendering an image, they display it line-by-line top-to-bottom as it loads. I have a requirement that a wait gif should be displayed while the image is loading. When the image is fully loaded then it should be displayed instead of the wait gif. If it helps, the site is http://farros.gr, main image: /images/bg.jpg and the div containing the image is named #main-content-image.

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  • Is it posible to Build & Run on TWO iPhones/iPods at once?

    - by Dimitris
    When I connect two iPhones at the same time to my computer and Build and Run a project the app only installs and plays on one of the devices. Now, with the iPhone 3.0, that supports bluetooth peer-to-peer connectivity, to test a multiplayer project you have to install and run it on two devices at the same time. It would be very helpful to be able to do that with one click instead of: install on one phone, disconnect, connect the other, wait a 10 seconds to recognize the phone and install again and run... Is anyone aware of a method to do such a thing? Thanks

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  • Suspend file validation on Zend Framework

    - by dimitris mistriotis
    Hi, Currently on my application I have a form where I ask the user to upload an image file to be used as a logo. I want to allow the user to reset that to nothing by supplying no file (by just pressing the upload button from the browser). In this scenario the only thing left is to suspend file validation when no file is included. Currently I get the *self::NO_FILE* error from the *Zend_Validate_File_Upload* class. Is there any way to suspend the validation so that nothing will be checked if no file has been provided?

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  • How to run R through PHP with exec?

    - by dkar
    I am going to ask something, that I know that it has been asked already some times. But since, all of the past posts are quite old and none of them answer my problem..I try again. I am completely new in R language and relative new in php. What I want to do is to use the exec() function from php in order to execute a R script. Most of the people here will start talking about rapache, rserve and I don't know what else..but since I am not familiar with all these technologies, I prefer just using exec. The code I will show here is working just fine when I run it with Rscript from the terminal. # R script png("temp.png") plot(5,5) dev.off() But when I try to run it either with Rscript or with R CMD BATCH from PHP, like this: echo exec("Rscript my_rscript.R"); //OR //echo exec("R CMD BATCH my_rscript.R"); I get nothing back. I have checked if exec() function is available and if it works. Everything is ok with this. I read also, that I might have to change the permissions of the webserver...but I don't know how to do this in mamp. I hope I am clear with my problem and someone can help. Thanks Dimitris

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  • can i know the Thread runnable class attributes in java?

    - by dori naji
    probability this question have been asked before but i cant find anything in my searching mechanism. I am trying to create a multiple threads, in an array list but i want to retrieve them from an arraylist and filter them by the attribute of w1 i used in my code. any ideas ? w1 = new FirstWorker(ProductsList, OrdersList, s); FirstWorkerThread = new Thread(w1); ThreadArrayList.add(FirstWorkerThread); //I know i cant do the code below but i want to do that how ? for(Thread x : ThreadArrayList){ x.ProductsList } this is FirstWorker class import java.lang.String; import java.util.HashMap; /* * To change this template, choose Tools | Templates and open the template in * the editor. */ /** * * @author Dimitris */ public class FirstWorker extends Thread implements Runnable { private OrderList orderlist; private ProductList productlist; private String Worker; boolean Stop; private int speed = 1000; public FirstWorker(ProductList productlist, OrderList orderlist, String Worker) { this.productlist = productlist; this.orderlist = orderlist; this.Worker = Worker; this.Stop = true; } public void run() { if (Stop == true) { try { Thread.sleep(100); } catch (InterruptedException e) { } while (orderlist.returnLengthofOrder() != 0) { if (Thread.interrupted()) { System.out.println("I am in the thread inturrupt"); // We've been interrupted: no more crunching. return; } if (orderlist.getDone() == true) { } else if (orderlist.getDone() == false) { orderlist.setDoneTrue(); orderlist.Purchased(Worker); orderlist.setDoneFalse(); try { Thread.sleep(this.speed); } catch (InterruptedException e) { return; } } } } } public void setWork() { Stop = false; } public void setSpeed(int speed) { this.speed = speed; } }

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