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  • Node & Redis: Crucial Design Issues in Production Mode

    - by Ali
    This question is a hybrid one, being both technical and system design related. I'm developing the backend of an application that will handle approx. 4K request per second. We are using Node.js being super fast and in terms of our database struction we are using MongoDB, with Redis being a layer between Node and MongoDB handling volatile operations. I'm quite stressed because we are expecting concurrent requests that we need to handle carefully and we are quite close to launch. However I do not believe I've applied the correct approach on redis. I have a class Student, and they constantly change stages(such as 'active', 'doing homework','in lesson' etc. Thus I created a Redis DB for each state. (1 for being 'active', 2 for being 'doing homework'). Above I have the structure of the 'active' students table; xa5p - JSON stringified object #1 pQrW - JSON stringified object #2 active_student_table - {{studentId:'xa5p'}, {studentId:'pQrW'}} Since there is no 'select all keys method' in Redis, I've been suggested to use a set such that when I run command 'smembers' I receive the keys and later on do 'get' for each id in order to find a specific user (lets say that age older than 15). I've been also suggested that in fact I used never use keys in production mode. My question is, no matter how 'conceptual' it is, what specific things I should avoid doing in Node & Redis in production stage?. Are they any issues related to my design? Students must be objects and I sure can list them in a list but I haven't done yet. Is it that crucial in production stage?

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  • Rails: Accessing /lib Modules from Controller

    - by Dex
    I have a Module called /lib/string_parser.rb. It looks like: module StringParser def wrap_lines(input, chars) ... end #make available to views def self.included(base) base.send :helper_method, :my_method_for_views if base.respond_to? :helper_method end end I'm trying to call wrap_lines from the create method of my controller but no matter what I do, I keep getting NoMethodErrors for an undefined method.

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  • Pass dynamic data to mvc controller with AJAX

    - by Yustme
    How can I pass dynamic data with an AJAX call to an MVC Controller? Controller: public JsonResult ApplyFilters(dynamic filters){ return null; } The AJAX call: $(':checkbox').click(function (event) { var serviceIds = $('input[type="checkbox"]:checked').map(function () { return $(this).val(); }).toArray(); //alert(serviceIds); $.ajax({ type: 'GET', url: '/home/ApplyFilters', data: JSON.stringify({ name: serviceIds }), contentType: 'application/json', success: function (data) { alert("succeeded"); }, error: function (err, data) { alert("Error " + err.responseText); } }); //return false; }); Ideally would be that the filters would contain the serviceIds as a property For example like this: filters.ServiceIds. I got another filter for a date range and that one would be added like so: filters.DateRange. And server side get the filter as a dynamic object in the ApplyFilters()

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  • jquery selecting element by data attribute

    - by zizo
    Is there an easy and straight-forward method to select elements based on their data attribute? For example, select all anchors that has data attribute named customerID which has value of 22. I am kind of hesitant to use rel or other attributes to store such information, but I find it much harder to select an element based on what data is stored in it. Thanks!

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  • NSUserDefaults: Saved Number Always 0, iPhone

    - by Stumf
    Hello all, I have looked at other answers and the docs. Maybe I am missing something, or maybe I have another issue. I am trying to save a number on exiting the app, and then when the app is loaded I want to check if this value exists and take action accordingly. This is what I have tried: To save on exiting: - (void)applicationWillTerminate: (UIApplication *) application { double save = [label.text doubleValue]; [[NSUserDefaults standardUserDefaults] setDouble: save forKey: @"savedNumber"]; [[NSUserDefaults standardUserDefaults] synchronize]; } To check: - (IBAction)buttonclickSkip{ double save = [[NSUserDefaults standardUserDefaults] doubleForKey: @"savedNumber"]; if (save == 0) { [self performSelector:@selector(displayAlert) withObject:nil]; test.enabled = YES; test.alpha = 1.0; skip.enabled = NO; skip.alpha = 0.0; } else { label.text = [NSString stringWithFormat:@"%.1f %%", save]; } } The problem is I always get my alert message displayed, the saved value is not put into the label so somehow == 0 is always true. If it makes any difference I am testing this on the iPhone simulator. Many thanks, Stu

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  • Fast read of certain bytes of multiple files in C/C++

    - by Alejandro Cámara
    I've been searching in the web about this question and although there are many similar questions about read/write in C/C++, I haven't found about this specific task. I want to be able to read from multiple files (256x256 files) only sizeof(double) bytes located in a certain position of each file. Right now my solution is, for each file: Open the file (read, binary mode): fstream fTest("current_file", ios_base::out | ios_base::binary); Seek the position I want to read: fTest.seekg(position*sizeof(test_value), ios_base::beg); Read the bytes: fTest.read((char *) &(output[i][j]), sizeof(test_value)); And close the file: fTest.close(); This takes about 350 ms to run inside a for{ for {} } structure with 256x256 iterations (one for each file). Q: Do you think there is a better way to implement this operation? How would you do it?

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  • UITableView with Custom Cell only loads one row of data at a time

    - by Anton
    For my table, I've created a custom cell that has two labels. I also have two arrays with data, that I use to respectively assign each label in the cell. My problem, is that when the table is viewed, only the first row has data, and the rest of the data "sorta" loads when I start scrolling down. By "sorta", only the first row will load at a time. The only time I get to see all the data, is when I scroll to the bottom, then scroll up again. I've used the cellForRowAtIndexPath method to load the data into my cell. - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { static NSString *CustomCellIdentifier = @"CustomCellIdentifier"; CustomCell *cell = (CustomCell *)[tableView dequeueReusableCellWithIdentifier:CustomCellIdentifier]; if (cell == nil) { NSArray *nib = [[NSBundle mainBundle] loadNibNamed:@"CustomCell" owner:self options:nil]; for (id oneObject in nib) if ([oneObject isKindOfClass:[CustomCell class]]) cell = (CustomCell *)oneObject; } NSUInteger row = [indexPath row]; //I have two tables to fill up, hence the tag if statement if ([tableView tag] == 0) { cell.arriveTimeLabel.text = [homeBoundTimes objectAtIndex:row]; cell.departTimeLabel.text = [homeBoundTimes objectAtIndex:row]; } else if ([tableView tag] == 1) { cell.arriveTimeLabel.text = [workBoundTimes objectAtIndex:row]; cell.departTimeLabel.text = [workBoundTimes objectAtIndex:row]; } return cell; } Is it possible that its only getting called when the top cell is being called?

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  • Is there a module that implements an efficient array type in Erlang?

    - by dsmith
    I have been looking for an array type with the following characteristics in Erlang. append(vector(), term()) O(1) nth(Idx, vector()) O(1) set(Idx, vector(), term()) O(1) insert(Idx, vector(), term()) O(N) remove(Idx, vector()) O(N) I normally use a tuple for this purpose, but the performance characteristics are not what I would want for large N. My testing shows the following performance characteristics... erlang:append_element/2 O(N). erlang:setelement/3 O(N). I have started on a module based on the clojure.lang.PersistentVector implementation, but if it's already been done I won't reinvent the wheel.

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  • Should the code being tested compile to a DLL or an executable file?

    - by uriDium
    I have a solution with two projects. One for project for the production code and another project for the unit tests. I did this as per the suggestions I got here from SO. I noticed that in the Debug Folder that it includes the production code in executable form. I used NUnit to run the tests after removing the executable and they all fail trying to find the executable. So it definitely is trying to find it. I then did a quick read to find out which is better, a DLL or an executable. It seems that an DLL is much faster as they share memory space where communication between executables is slower. Unforunately our production code needs to be an exectuable. So the unit tests will be slightly slower. I am not too worried about that. But the project does rely on code written in another library which is also in executable format at the moment. Should the projects that expose some sort of SDK rather be compiled to an DLL and then the projects that use the SDK be compiled to executable?

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  • PHP fastest method of reading server response

    - by Peter John
    Hi there, im having some real problems with the lag produced by using fgets to grab the server's response to some batch database calls im making. Im sending through a batch of say, 10,000 calls and ive tracked the lag down to fgets causing the hold up in the speed of my application as the response for each call needs to be grabbed. I have found this thread http://bugs.php.net/bug.php?id=32806 which explains the problem quite well, but hes reading a file, not a server response so fread could be a bit tricky as i could get part of the next line, and extra stuff which i dont want. Any help much appreciated!

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  • Why is autorelease especially dangerous/expensive for iPhone applications?

    - by e.James
    I'm looking for a primary source (or a really good explanation) to back up the claim that the use of autorelease is dangerous or overly expensive when writing software for the iPhone. Several developers make this claim, and I have even heard that Apple does not recommend it, but I have not been able to turn up any concrete sources to back it up. SO references: autorelease-iphone Why does this create a memory leak (iPhone)? Note: I can see, from a conceptual point of view, that autorelease is slightly more expensive than a simple call to release, but I don't think that small penalty is enough to make Apple recommend against it. What's the real story?

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  • I Can Not Use Session In Page _Load And I Got Bellow Error

    - by LostLord
    hi my dear friends .... why i got this error : (Object reference not set to an instance of an object.) when i put this code in my page_load.: protected void Page_Load(object sender, EventArgs e) { BackEndUtils.OverallLoader(); string Teststr = Session["Co_ID"].ToString(); } ========================================================================== this session is made when user logins to my web site and this session works in other areas... thanks for your attention

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  • C++ Windows IOCP - HTTP POST data missing

    - by Mike Trader
    I have written a very simple IOCP HTTP server that works for the GET verb, but not POST. I create a socket and a listen thread in which accept() is waiting for a connection. When a client connects I call ioctlsocket() to unblock the socket then I associate the socket with IOCP and finally call WSARecv() to read the data. Some data is indeed read and when that has happened, IOCP wakes up a worker thread via GetQueuedCompletionStatus() and I recover the request data. I only ever get the request header when I POST from any browser. Any suggestions as to why? I am assuming the IOCP completes when ALL the data has arrived from TCP?

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  • Parsing data with Clojure, interval problem.

    - by Andrea Di Persio
    Hello! I'm writing a little parser in clojure for learning purpose. basically is a TSV file parser that need to be put in a database, but I added a complication. The complication itself is that in the same file there are more intervals. The file look like this: ###andreadipersio 2010-03-19 16:10:00### USER COMM PID PPID %CPU %MEM TIME root launchd 1 0 0.0 0.0 2:46.97 root DirectoryService 11 1 0.0 0.2 0:34.59 root notifyd 12 1 0.0 0.0 0:20.83 root diskarbitrationd 13 1 0.0 0.0 0:02.84` .... ###andreadipersio 2010-03-19 16:20:00### USER COMM PID PPID %CPU %MEM TIME root launchd 1 0 0.0 0.0 2:46.97 root DirectoryService 11 1 0.0 0.2 0:34.59 root notifyd 12 1 0.0 0.0 0:20.83 root diskarbitrationd 13 1 0.0 0.0 0:02.84 I ended up with this code: (defn is-header? "Return true if a line is header" [line] (> (count (re-find #"^\#{3}" line)) 0)) (defn extract-fields "Return regex matches" [line pattern] (rest (re-find pattern line))) (defn process-lines [lines] (map process-line lines)) (defn process-line [line] (if (is-header? line) (extract-fields line header-pattern)) (extract-fields line data-pattern)) My idea is that in 'process-line' interval need to be merged with data so I have something like this: ('andreadipersio', '2010-03-19', '16:10:00', 'root', 'launchd', 1, 0, 0.0, 0.0, '2:46.97') for every row till the next interval, but I can't figure how to make this happen. I tried with something like this: (def process-line [line] (if is-header? line) (def header-data (extract-fields line header-pattern))) (cons header-data (extract-fields line data-pattern))) But this doesn't work as excepted. Any hints? Thanks!

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  • Java: Embedded Data Base

    - by Dmitry
    Hello! I want to create a desctop application with an embedded data base. Data base is JavaDB(Derby). I have connected a jar file derby.jar to my project. The problem is I don't understand how to register a driver to use this data base. It is said that I should use Class.forName("org.apache.derby.jdbc.EmbeddedDriver") But what if that was another data base and its driver was not in a java standart package? As you can see I'm confused with this. I want to know, how to use my connected derby.jar, how to work with its jdbc driver and how to create tables in a specified directory. Please, give as detailed answer, as you can. (I'm a dummy in this =)) )

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  • What is the impact of a CMS on page load time versus a static site?

    - by PleaseStand
    I am creating a 20-page site that will go on shared hosting. Each page will be about 20 KB (including HTML, CSS, and images common to all pages). To avoid manually adding navigation elements to each page, I am considering using a CMS. However, I am concerned that on a busy server, using a CMS would make the site load more slowly. In a shared hosting environment where PHP is run as a CGI binary, how much does a CMS (WordPress, Drupal, etc.) generally affect page load time, compared to both "plain HTML" static sites and those using PHP as merely a templating language?

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  • Unicorn: Which number of worker processes to use?

    - by blackbird07
    I am running a Ruby on Rails app on a virtual Linux server that is capped at 1GB RAM. Currently, I am constantly hitting the limit and would like to optimize memory utilization. One option I am looking at is reducing the number of unicorn workers. So what is the best way to determine the number of unicorn workers to use? The current setting is 10 workers, but the maximum number of requests per second I have seen on Google Analytics Real-Time is 3 (only scored once at a peak time; in 99% of the time not going above 1 request per second). So is it a save assumption that I can - for now - go with 4 workers, leaving room for unexpected amounts of requests? What are the metrics I should have a look at for determining the number of workers and what are the tools I can use for that on my Ubuntu machine?

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  • How to shift pixels of a pixmap efficient in Qt4

    - by stanleyxu2005
    Hello, I have implemented a marquee text widget using Qt4. I painted the text content onto a pixmap first. And then paint a portion of this pixmap onto a paint device by calling painter.drawTiledPixmap(offsetX, offsetY, myPixmap) My Imagination is that, Qt will fill the whole marquee text rectangle with the content from myPixmap. Is there a ever faster way, to shift all existing content to left by 1px and than fill the newly exposed 1px wide and N-px high area with the content from myPixmap?

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  • Change Powerpoint chart data with .NET

    - by mc6688
    I have a Powerpoint template that contains 1 slide and on that slide is a chart. I'd like to be able to manipulate that charts data using .NET. So far I have code that... unzips the Powerpoint file. unzips the embedded excel file (ppt\embeddings\Microsoft_Office_Excel_Worksheet1.xlsx) It successfully manipulates the data in the excel sheet and zips it back up. Opens and manipulates ppt\charts\chart1.xml Powerpoint is then zipped up and delivered to the user The result of this is a Powerpoint file that shows a blank chart. But when I click on the chart and go to edit data it updates the data and shows the correct chart. I believe my problem is with the chart1.xml that I am generating. I have compared my generated version with a version created by Powerpoint and they are almost identical. The only differences are in the values for <c:crossAx> and <c:axId>. There are also some rounding difference in the data. But I do not feel like that would result in an blank chart. Is there another file that I need to edit? Does anyone have any ideas as to what else I should try to get this working?

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  • WCF high instance count: anyone knows negative sideffects?

    - by Alex
    Hi there! Did anyone experience or know of negative side effects from having a high service instance count like 60k? Aside from the memory consumption of course. I am planning to increase the threshold for the maximum allowed instance count in our production environments. I am basically sick of severe production incidents just because "something" forgot to close a proxy properly. I plan to go to something like 60k instances which will allow the service to survive using default session timeouts at a call rate average for our clients. Thanks, Alex

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  • mysql subquery strangely slow

    - by aviv
    I have a query to select from another sub-query select. While the two queries look almost the same the second query (in this sample) runs much slower: SELECT user.id ,user.first_name -- user.* FROM user WHERE user.id IN (SELECT ref_id FROM education WHERE ref_type='user' AND education.institute_id='58' AND education.institute_type='1' ); This query takes 1.2s Explain on this query results: id select_type table type possible_keys key key_len ref rows Extra 1 PRIMARY user index first_name 152 141192 Using where; Using index 2 DEPENDENT SUBQUERY education index_subquery ref_type,ref_id,institute_id,institute_type,ref_type_2 ref_id 4 func 1 Using where The second query: SELECT -- user.id -- user.first_name user.* FROM user WHERE user.id IN (SELECT ref_id FROM education WHERE ref_type='user' AND education.institute_id='58' AND education.institute_type='1' ); Takes 45sec to run, with explain: id select_type table type possible_keys key key_len ref rows Extra 1 PRIMARY user ALL 141192 Using where 2 DEPENDENT SUBQUERY education index_subquery ref_type,ref_id,institute_id,institute_type,ref_type_2 ref_id 4 func 1 Using where Why is it slower if i query only by index fields? Why both queries scans the full length of the user table? Any ideas how to improve? Thanks.

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  • How to decide on what hardware to deploy web application

    - by Yuval A
    Suppose you have a web application, no specific stack (Java/.NET/LAMP/Django/Rails, all good). How would you decide on which hardware to deploy it? What rules of thumb exist when determining how many machines you need? How would you formulate parameters such as concurrent users, simultaneous connections and DB read/write ratio to a decision on how much, and which, hardware you need? Any resources on this issue would be very helpful...

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  • What is the most efficient way to store a mapping "key -> event stream"?

    - by jkff
    Suppose there are ~10,000's of keys, where each key corresponds to a stream of events. I'd like to support the following operations: push(key, timestamp, event) - pushes event to the event queue for key, marked with the given timestamp. It is guaranteed that event timestamps for a particular key are pushed in sorted or almost sorted order. tail(key, timestamp) - get all events for key since the given timestamp. Usually the timestamp requests for a given key are almost monotonically increasing, almost synchronously with pushes for the same key. This stuff has to be persistent (although it is not absolutely necessary to persist pushes immediately and to keep tails with pushes strictly in sync), so I'm going to use some kind of database. What is the optimal kind of database structure for this task? Would it be better to use a relational database, a key-value storage, or something else?

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  • Partial Shader Signatures HLSL D3D11 C++

    - by ThePhD
    I had been debugging a problem I was having in a single shader file with 2 functions in it. I'm using DirectX 11, vs_5_0 and ps_5_0. I have stripped it down to its basic components to understand what was going wrong with the shaders, because the different named components of the Pixel and Vertex shaders were swapping the data being input: void QuadVertex ( inout float4 position : SV_Position, inout float4 color : COLOR0, inout float2 tex : TEXCOORD0 ) { // ViewProject is a 4x4 matrix, // just included here to show the simple passthrough of the data position = mul(position, ViewProjection); } And a Pixel Shader: float4 QuadPixel ( float4 color : COLOR0, float2 tex : TEXCOORD0 ) : SV_Target0 { // Color is filled with position data and tex is // filled with color values from the Vertex Shader return color; } The ID3D11InputLayout and associated C++ code correctly compiles the shaders and sets them up with some simple primitive data: data[0].Position.x = 0.0f * 210; data[0].Position.y = 1.0f * 160; data[0].Position.z = 0.0f; data[1].Position.x = 0.0f * 210; data[1].Position.y = 0.0f * 160; data[1].Position.z = 0.0f; data[2].Position.x = 1.0f * 210; data[2].Position.y = 1.0f * 160; data[2].Position.z = 0.0f; data[0].Colour = Colors::Red; data[1].Colour = Colors::Red; data[2].Colour = Colors::Red; data[0].Texture = Vector2::Zero; data[1].Texture = Vector2::Zero; data[2].Texture = Vector2::Zero; When used with the shader, the float4 color always ended up with the position data, and the float2 tex always ended up with the color data. After a moment, I figured out that the shader's input and output signatures needed to be in the correct order and the correct format and be laid out in the exact order of the output from the Vertex Shader, regardless of the semantics: float4 QuadPixel ( float4 pos : SV_Position, float4 color : COLOR0, float2 tex : TEXCOORD0 ) : SV_Target0 { return color; } After finding this out, My question is: Why don't the semantics map the appropriate components when going from Vertex Shader to Pixel Shader? Is there any way that I can make it so certain semantics are always mapped to other semantics, or do I always have to follow the rigid Shader Signature (in this case, Position, Color, and Texture) ? As a side note for why I'm asking: I know that when using XNA, my shader signatures for functions could differ in position and even drop items from Vertex Shader to Pixel Shader function parameters, having only the COLOR0 and TEXCOORD0 components being used (and it would still match up correctly). However, I also know that XNA relied on DX9 (and maybe a little DX10) implementation, and that maybe this kind of flexibility no longer exists in DX11?

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