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  • How to avoid web server traffic peak resulting from iOS Newsstand app receiving a remote notification?

    - by thomers
    I'm developing an iOS Newsstand app. If it is suspended or not running and connected to a WLAN, Newsstand apps can be triggered by a Push remote notification to download the latest issue (in our case around 100MB) in the background. I'm using Urban Airship for the delivery of the Push broadcast. I'm now worrying about many many iOS devices hitting the web server for one big download more or less at the same time, because I expect the majority of the devices will receive the notification in a very short timeframe. Instead of broadcasts to all devices, should I rather send individual notifications to batches of small groups of devices, spreading them out over a longer period of time? And/or would a CDN like Amazon Cloudfront solve that issue easier/anyway?

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  • Any way to avoid a filesort when order by is different to where clause?

    - by Julian
    I have an incredibly simple query (table type InnoDb) and EXPLAIN says that MySQL must do an extra pass to find out how to retrieve the rows in sorted order. SELECT * FROM `comments` WHERE (commentable_id = 1976) ORDER BY created_at desc LIMIT 0, 5 exact explain output: table select_type type extra possible_keys key key length ref rows comments simple ref using where; using filesort common_lookups common_lookups 5 const 89 commentable_id is indexed. Comments has nothing trick in it, just a content field. The manual suggests that if the order by is different to the where, there is no way filesort can be avoided. http://dev.mysql.com/doc/refman/5.0/en/order-by-optimization.html I also tried order by id as well as it's equivalent but makes no difference, even if I add id as an index (which I understand is not required as id is indexed implicitly in MySQL). thanks in advance for any ideas!

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  • How do I avoid a race condition in my Rails app?

    - by Cathal
    Hi, I have a really simple Rails application that allows users to register their attendance on a set of courses. The ActiveRecord models are as follows: class Course < ActiveRecord::Base has_many :scheduled_runs ... end class ScheduledRun < ActiveRecord::Base belongs_to :course has_many :attendances has_many :attendees, :through => :attendances ... end class Attendance < ActiveRecord::Base belongs_to :user belongs_to :scheduled_run, :counter_cache => true ... end class User < ActiveRecord::Base has_many :attendances has_many :registered_courses, :through => :attendances, :source => :scheduled_run end A ScheduledRun instance has a finite number of places available, and once the limit is reached, no more attendances can be accepted. def full? attendances_count == capacity end attendances_count is a counter cache column holding the number of attendance associations created for a particular ScheduledRun record. My problem is that I don't fully know the correct way to ensure that a race condition doesn't occur when 1 or more people attempt to register for the last available place on a course at the same time. My Attendance controller looks like this: class AttendancesController < ApplicationController before_filter :load_scheduled_run before_filter :load_user, :only => :create def new @user = User.new end def create unless @user.valid? render :action => 'new' end @attendance = @user.attendances.build(:scheduled_run_id => params[:scheduled_run_id]) if @attendance.save flash[:notice] = "Successfully created attendance." redirect_to root_url else render :action => 'new' end end protected def load_scheduled_run @run = ScheduledRun.find(params[:scheduled_run_id]) end def load_user @user = User.create_new_or_load_existing(params[:user]) end end As you can see, it doesn't take into account where the ScheduledRun instance has already reached capacity. Any help on this would be greatly appreciated.

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  • How to avoid escaping by accident in PERL using system()?

    - by Brian
    I want to run some commands using the system() command, I do this way: execute_command_error("trash-put '/home/$filename'"); Where execute_command_error will report if there was an error with whatever system command it ran. I know I could just unlink the file using Perl commands, but I want to delete stuff using trash-put as it's a type of recycling program. My problem is that $filename will sometimes have apostrophes, quotes, and other weird characters in it that mess up the system command or Perl itself.

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  • How do I avoid multiple key up/down/press events when holding a key?

    - by Rammay
    I'm creating a web front end to control a small robot. Ajax calls will be made on a keydown, to start the robot, and keyup to stop it. My problem is that when a key is held down the keyup, keydown, and keypress events seem to cycle continually. Does anybody know of a way to only have keydown fire when the key is first pressed and keyup to fire when it has been released?

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  • How to avoid links to map.root getting shortened?

    - by Guy C
    I have a Reports controller and various reports: http://localhost/reports/main/this_month http://localhost/reports/main/last_month http://localhost/reports/main/this_year I wanted http://localhost to default to http://localhost/reports/main/this_month. That is easy enough using map.root in my routes.rb. However when I do this any links to http://localhost/reports/main/this_month are now shortened to just http://localhost. I want the links to stay full

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  • Should we avoid to use Object as the input parameter/ output value of a method?

    - by developer.cyrus
    Take Java syntax as an example, though the question itself is language independent. If the following snippet takes an object MyAbstractEmailTemplate as input argument in the method setTemplate, the class MyGateway will then become tightly-coupled with the object MyAbstractEmailTemplate, which lessens the re-usability of the class MyGateway. A compromise is to use dependency-injection to ease the instantiation of MyAbstractEmailTemplate. This might solve the coupling problem to some extent, but the interface is still rigid, hardly providing enough ?exibility to other developers/ applications. So if we only use primitive data type (or even plain XML in web service) as the input/ output of a method, it seems the coupling problem no longer exists. So what do you think? public class MyGateway { protected MyAbstractEmailTemplate template; publoc void setTemplate(MyAbstractEmailTemplate template) { this.template = template; } }

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  • JQUERY common function library create script errors. How to avoid?

    - by Cesar Lopez
    Hi all, I am building a common function library but the functions inside need to reference different jquery files, which they may need to be referenced in some pages but not in others. When I called this common function library in one web page which is only going to use one function, and I don't reference the files need it for the other function, then it will create a script error. My question is if it would be possible to stop this script errors like... //This if statement is what I was thinking to stop going through if ($(".objectdate") != null){ //This is the function that is calling other jquery files and creates error. $(document).ready(function() { $(".objectdate").datepicker({ //Code inside. }); }); } Thanks.

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  • I am having trouble using jquery to submit a form. It was working before

    - by noah
    When a user clicks a link it uses jquery ajax to submit a form to go to paypal. Not working for some reason. Really appreciate any help... LINK TO CLICK I put this in an href for onClick: javascript:go_paypal(); CODE TO EXECUTE ON CLICK function go_paypal() { data = 'req_paypal=1'; $.blockUI({ message: '<h1> Going to Paypal...</h1>',css:{background:'#000'} }); $.ajax({ type: "POST", url: "index.php", data: data, success: function(data) { $("#paypal_form").html(data); $("#payPalForm").submit(); } , error: function() {$.unblockUI(); alert('Unable to communicate to server.'); } }); return false; } CODE TO GO ON SUBMIT if(isset($_POST['req_paypal']) && $_POST['req_paypal'] == 1 ) { $sql = 'INSERT INTO `transactions` (id,type,ip,time,ammount,status) VALUES (NULL,1,\''.$_SERVER['REMOTE_ADDR'].'\',\''.time().'\',\''.$global['paypal_prod_amount'].'\',0) '; echo $sql; mysql_query($sql); $id = mysql_insert_id(); $html = ' <form action="https://www.sandbox.paypal.com/cgi-bin/webscr" method="post" id="payPalForm"> <input type="hidden" name="item_number" value="One Year of Imgur Pro"> <input type="hidden" name="cmd" value="_xclick"> <input type="hidden" name="no_note" value="1"> <input type="hidden" name="business" value="'.$global['paypal_email'].'"> <input type="hidden" name="custom" value="'.base64_encode($id).'"> <input type="hidden" name="currency_code" value="USD"> <input type="hidden" name="return" value="'.$global['paypal_return'].'"> <input name="item_name" type="hidden" id="item_name" value="One Year of Imgur Pro" > <input name="amount" type="hidden" id="amount" value="'.$global['paypal_prod_amount'].'" > </form> '; echo $html;exit; }

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  • Php/MySQL to ASP.NET/MSSQL, Suggest if its worth the trouble.

    - by user302656
    Hello Guys, We have been using PHP/MySQL for our web application which has been growing a lot, the database is around 4-5GB and one of the table is 2GB sometimes, hence slowing down whenever any queries to that table is called. Should we just try to optimize, or are we using MySQL above its limit? Will switching our web app to .NET/MSSQL resolve the issues? Thanks

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  • C++ Virtual keyword as away to avoid including code units.

    - by user394663
    Currently we have a body of code that allows service plugins which offer forms of communication to the core e.g tcp/ip, udp/ip, usb, etc... These service plugins feedback notifier class instances to the core for further processing. In the current implementation a service project (which is a separate dynamically linked library brought in at runtime by the core via dlopen and friends) will compile against the notifier.cpp file that resides in the core source code (a separate project). This gives access to the notifiers method implementations. This works perfectly no complaints. Two alternative options: 1. put the notifier method implementations in the header file. 2. declare the notifier methods virtual and delay binding until runtime. Avoiding the issues of computational overhead what are the impacts of option 2? Are there any other options available to us? Thanks

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  • Is it good practice to avoid declaring a pointer to BOOL type in objective C?

    - by Krishnan
    I read this question in stackoverflow. The excerpt answer provided by bbum is below: The problem isn't the assignment, it is much more likely that you declared your instance variable to be BOOL *initialBroadcast;. There is no reason to declare the instance variable to be a pointer (at least not unless you really do need a C array of BOOLs).. Remove the * from the declaration. 1.Is there anything wrong in using a pointer variable even when I do not have to maintain an array of BOOLs? 2.I think even if avoiding them a good practice, it is not specific to objective-C and applies to all programming languages which has pointers. Please answer my questions.

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  • SELECT SQL Variable - should i avoid using this syntax and always use SET?

    - by Sholom
    Hi All, This may look like a duplicate to here, but it's not. I am trying to get a best practice, not a technical answer (which i already (think) i know). New to SQL Server and trying to form good habits. I found a great explanation of the functional differences between SET @var = and SELECT @var = here: http://vyaskn.tripod.com/differences_between_set_and_select.htm To summarize what each has that the other hasn't (see source for examples): SET: ANSI and portable, recommended by Microsoft. SET @var = (SELECT column_name FROM table_name) fails when the select returns more then one value, eliminating the possibility of unpredictable results. SET @var = (SELECT column_name FROM table_name) will set @var to NULL if that's what SELECT column_name FROM table_name returned, thus never leaving @var at it's prior value. SELECT: Multiple variables can be set in one statement Can return multiple system variables set by the prior DML statement SELECT @var = column_name FROM table_name would set @var to (according to my testing) the last value returned by the select. This could be a feature or a bug. Behavior can be changed with SELECT @j = (SELECT column_name FROM table_name) syntax. Speed. Setting multiple variables with a single SELECT statement as opposed to multiple SET/SELECT statements is much quicker. He has a sample test to prove his point. If you could design a test to prove the otherwise, bring it on! So, what do i do? (Almost) always use SET @var =, using SELECT @var = is messy coding and not standard. OR Use SELECT @var = freely, it could accomplish more for me, unless the code is likely to be ported to another environment. Thanks

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  • How to avoid StaleObjectStateException when transaction updates thousands of entities?

    - by ThinkFloyd
    We are using Hibernate 3.6.0.Final with JPA 2 and Spring 3.0.5 for a large scale enterprise application running on tomcat 7 and MySQL 5.5. Most of the transactions in application, lives for less than a second and update 5-10 entities but in some use cases we need to update more than 10-20K entities in single transaction, which takes few minutes and hence more than 70% of times such transaction fails with StaleObjectStateException because some of those entities got updated by some other transaction. We generally maintain version column in all tables and in case of StaleObjectStateException we generally retry but since these longs transactions are anyways very long so if we keep on retrying then also I am not very sure that we'll be able to escape StaleObjectStateException. Also lot of activities keep updating these entities in busy hours so we cannot go with pessimistic approach because it can potentially halt many activities in system. Please suggest how to fix such long transaction issue because we cannot spawn thousands of independent and small transactions because we cannot afford messed up data in case of some failed & some successful transactions.

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  • Trouble using 'eval' to define a toplevel function when called from within an object.

    - by mschaef
    I've written (in JavaScript) an interactive read-eval-print-loop that is encapsulated within an object. However, I recently noticed that toplevel function definitions specified to the interpreter do not appear to be 'remembered' by the interpreter. After some diagnostic work, I've reduced the core problem to this: var evaler = { eval: function (str) { return eval(str); }, }; eval("function t1() { return 1; }"); // GOOD evaler.eval("function t2() { return 2; }"); // FAIL After running this script, I have a definition for t1, and no defintion for t2. The act of calling eval from within evaler is sufficiently different from the toplevel call that the global definition does not get recorded. What does happen is that the call to evaler.eval returns a function object, so I'm presuming that t2 is being defined and stored in some other set of bindings that I don't have access to. (It's not defined as a member in evaler.) Is there any easy fix for this? I've tried all sorts of fixes, and haven't stumbled upon one that works. (Most of what I've done has centered around putting the call to eval in an anonymous function, and altering the way that's called, chainging __parent__, etc.) Any thoughts on how to fix this?

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  • How to avoid Mercurial repo corruption when sharing a repository between Windows/Mac?

    - by Stabledog
    I have several projects which are shared between Windows and Mac. The dev machine is a Mac running Parallels: the files are stored on the Mac side, and the source is shared to the Windows side. This is very convenient, as I can switch back and forth between Windows and Mac tools rapidly without having to sync files. Recently I switched from Subversion to Mercurial, and now I'm having problems with the Mercurial repository becoming corrupt if I use the Windows tools to add/update, etc. I have to be very careful about which operations on the Windows side are safe (mainly the read-only stuff) and of course I forget rather regularly. Does anybody know why the corruption occurs? I thought Mercurial repositories were platform-agnostic. Any ideas how to prevent it without removing the Windows tools entirely?

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  • How can I improve this SQL to avoid several problems with its results?

    - by Josh Curren
    I am having some problems with trying to search. Currently this will only return results that have at least 1 row in the maintenance_parts table. I would like it to return results even if there are 0 parts rows. My second problem is that when you search for a vehicle and it should return multiple results (multiple maintenance rows) it will only return 1 result for that vehicle. Some Background Info: The user has 2 fields to fill out. The fields are vehicle and keywords. The vehicle field is meant to allow searching based on the make, model, VIN, truck number (often is 2 - 3 digits or a letter prefix followed by 2 digits), and a few other fields that belong to the truck table. The keywords are meant to search most fields in the maintenance and maintenance_parts tables (things like the description of the work, parts name, parts number). The maintenance_parts table can contain 0, 1, or more rows for each maintenance row. The truck table contains exactly 1 row for every maintenance row. A truck can have multiple maintenance records. "SELECT M.maintenance_id, M.some_id, M.type_code, M.service_date, M.mileage, M.mg_id, M.mg_type, M.comments, M.work_done, MATCH( M.comments, M.work_done) AGAINST( '$keywords' ) + MATCH( P.part_num, P.part_desc, P.part_ref) AGAINST( '$keywords' ) + MATCH( T.truck_number, T.make, T.model, T.engine, T.vin_number, T.transmission_number, T.comments) AGAINST( '$vehicle' ) AS score FROM maintenance M, maintenance_parts P, truck T WHERE M.maintenance_id = P.maintenance_id AND M.some_id = T.truck_id AND M.type_code = 'truck' AND ( (MATCH( T.truck_number, T.make, T.model, T.engine, T.vin_number, T.transmission_number, T.comments) AGAINST( '$vehicle' ) OR T.truck_number LIKE '%$vehicle%') OR MATCH( P.part_num, P.part_desc, P.part_ref) AGAINST( '$keywords' ) OR MATCH( M.comments, M.work_done) AGAINST( '$keywords' ) ) AND M.status = 'A' GROUP BY maintenance_id ORDER BY score DESC, maintenance_id DESC LIMIT 0, $limit"

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  • Why and How to avoid Event Handler memory leaks ?

    - by gillyb
    Hey There, I just came to realize, by reading some questions and answers on StackOverflow, that adding event handlers using += in C# (or i guess, other .net languages) can cause common memory leaks... I have used event handlers like this in the past many times, and never realized that they can cause, or have caused, memory leaks in my applications. How does this work (meaning, why does this actually cause a memory leak) ? How can I fix this problem ? Is using -= to the same event handler enough ? Are there common design patterns or best practices for handling situations like this ? Example : How am I supposed to handle an application that has many different threads, using many different event handlers to raise several events on the UI ? Are there any good and simple ways to monitor this efficiently in an already built big application ? Thanks in advance!

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  • Does std::vector change its address? How to avoid

    - by kunigami
    Since vector elements are stored contiguously, I guess it may not have the same address after some push_back's , because the initial allocated space could not suffice. I'm working on a code where I need a reference to an element in a vector, like: int main(){ vector<int> v; v.push_back(1); int *ptr = &v[0]; for(int i=2; i<100; i++) v.push_back(i); cout << *ptr << endl; //? return 0; } But it's not necessarily true that ptr contains a reference to v[0], right? How would be a good way to guarantee it? My first idea would be to use a vector of pointers and dynamic allocation. I'm wondering if there's an easier way to do that? PS.: Actually I'm using a vector of a class instead of int, but I think the issues are the same.

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