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  • Should we use temporary variables for the returned values of functions?

    - by totymedli
    I thought about this: Is there a performance difference in these two practices: Store the return value of a function in a temporary variable than give that variable as a parameter to another function. Put the function into the other function. Specification Assuming all classes and functions are written correctly. Case 1. ClassA a = function1(); ClassB b = function2(a); function3(b); Case 2. function3(function2(function1())); I know there aren't a big difference with only one run, but supposed that we could run this a lot of times in a loop, I created some tests. Test #include <iostream> #include <ctime> #include <math.h> using namespace std; int main() { clock_t start = clock(); clock_t ends = clock(); // Case 1. start = clock(); for (int i=0; i<10000000; i++) { double a = cos(1); double b = pow(a, 2); sqrt(b); } ends = clock(); cout << (double) (ends - start) / CLOCKS_PER_SEC << endl; // Case 2. start = clock(); for (int i=0; i<10000000; i++) sqrt(pow(cos(1),2)); ends = clock(); cout << (double) (ends - start) / CLOCKS_PER_SEC << endl; return 0; } Results Case 1 = 6.375 Case 2 = 0.031 Why is the first one is much slower, and if the second one is faster why dont we always write code that way? Anyway does the second pratice has a name? I also wondered what happens if I create the variables outside the for loop in the first case, but the result was the same. Why?

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  • Custom object based on database table

    - by Archangel
    Suppose that I have a database query which looks like below - select name, gender, birthday from person where person_id = 1; When this query is executed, some records from the database are returned. I want to make a custom object which will contain the exact attributes as the column names, with the corresponding values. As an example, suppose that the object is X. So it will have three attributes which are X.name, X.gender and X.birthday, with the corresponding values from the records. Is it doable in PHP? If so, then how?

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  • Javascript memory leak/ performance issue?

    - by Tom
    I just cannot for the life of me figure out this memory leak in Internet Explorer. insertTags simple takes string str and places each word within start and end tags for HTML (usually anchor tags). transliterate is for arabic numbers, and replaces normal numbers 0-9 with a &#..n; XML identity for their arabic counterparts. fragment = document.createDocumentFragment(); for (i = 0, e = response.verses.length; i < e; i++) { fragment.appendChild((function(){ p = document.createElement('p'); p.setAttribute('lang', (response.unicode) ? 'ar' : 'en'); p.innerHTML = ((response.unicode) ? (response.surah + ':' + (i+1)).transliterate() : response.surah + ':' + (i+1)) + ' ' + insertTags(response.verses[i], '<a href="#" onclick="window.popup(this);return false;" class="match">', '</a>'); try { return p } finally { p = null; } })()); } params[0].appendChild( fragment ); fragment = null; I would love some links other than MSDN and about.com, because neither of them have sufficiently explained to me why my script leaks memory. I am sure this is the problem, because without it everything runs fast (but nothing displays). I've read that doing a lot of DOM manipulations can be dangerous, but the for loops a max of 286 times (# of verses in surah 2, the longest surah in the Qur'an).

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  • Design Solution For Storing-Fetching Images

    - by Chaitanya
    This is a design doubt am facing, I have a collection of 1500 images which are to be displayed on an asp.net page, the images to be displayed differ from one page to another, the count of these images will increase in the time to come, a.) is it a good idea to have the images on the database, but the round trip time to fetch the images from the database might be high. b.) is it good to have all the images on a directory, and have a virtual file system over it, and the application will access the images from the directory Do we have in particular any design strategy in a traditional database for fetching images with the least round trip time, does any solution other than usage of a traditional database exists? ps: I use SQL Server to store these images.

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  • Entity framework with Linq to Entities performance

    - by mare
    If I have a static method like this public static string GetTicClassificationTitle(string classI, string classII, string classIII) { using (TicDatabaseEntities ticdb = new TicDatabaseEntities()) { var result = from classes in ticdb.Classifications where classes.ClassI == classI where classes.ClassII == classII where classes.ClassIII == classIII select classes.Description; return result.FirstOrDefault(); } } and use this method in various places in foreach loops or just plain calling it numerous times, does it create and open new connection every time? If so, how can I tackle this? Should I cache the results somewhere, like in this case, I would cache the entire Classifications table in Memory Cache? And then do queries vs this cached object? Or should I make TicDatabaseEntities variable static and initialize it at class level? Should my class be static if it contains only static methods? Because right now it is not.. Also I've noticed that if I return result.First() instead of FirstOrDefault() and the query does not find a match, it will issue an exception (with FirstOrDefault() there is no exception, it returns null). Thank you for clarification.

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  • Java curious Loop Performance

    - by user1680583
    I have a big problem while evaluate my java code. To simplify the problem I wrote the following code which produce the same curious behavior. Important is the method run() and given double value rate. For my runtime test (in the main method) I set the rate to 0.5 one times and 1.0 the other time. With the value 1.0 the if-statement will be executed in each loop iteration and with the value 0.5 the if-statement will be executed half as much. For this reason I expected longer runtime by the first case but opposite is true. Can anybody explain me this phenomenon?? The result of main: Test mit rate = 0.5 Length: 50000000, IF executions: 25000856 Execution time was 4329 ms. Length: 50000000, IF executions: 24999141 Execution time was 4307 ms. Length: 50000000, IF executions: 25001582 Execution time was 4223 ms. Length: 50000000, IF executions: 25000694 Execution time was 4328 ms. Length: 50000000, IF executions: 25004766 Execution time was 4346 ms. ================================= Test mit rate = 1.0 Length: 50000000, IF executions: 50000000 Execution time was 3482 ms. Length: 50000000, IF executions: 50000000 Execution time was 3572 ms. Length: 50000000, IF executions: 50000000 Execution time was 3529 ms. Length: 50000000, IF executions: 50000000 Execution time was 3479 ms. Length: 50000000, IF executions: 50000000 Execution time was 3473 ms. The Code public ArrayList<Byte> list = new ArrayList<Byte>(); public final int LENGTH = 50000000; public PerformanceTest(){ byte[]arr = new byte[LENGTH]; Random random = new Random(); random.nextBytes(arr); for(byte b : arr) list.add(b); } public void run(double rate){ byte b = 0; int count = 0; for (int i = 0; i < LENGTH; i++) { if(getRate(rate)){ list.set(i, b); count++; } } System.out.println("Length: " + LENGTH + ", IF executions: " + count); } public boolean getRate(double rate){ return Math.random() < rate; } public static void main(String[] args) throws InterruptedException { PerformanceTest test = new PerformanceTest(); long start, end; System.out.println("Test mit rate = 0.5"); for (int i = 0; i < 5; i++) { start=System.currentTimeMillis(); test.run(0.5); end = System.currentTimeMillis(); System.out.println("Execution time was "+(end-start)+" ms."); Thread.sleep(500); } System.out.println("================================="); System.out.println("Test mit rate = 1.0"); for (int i = 0; i < 5; i++) { start=System.currentTimeMillis(); test.run(1.0); end = System.currentTimeMillis(); System.out.println("Execution time was "+(end-start)+" ms."); Thread.sleep(500); } }

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  • Can't connect to MySQL database hosted in CloudBees

    - by user3692698
    I have a free CloudBees account and created a free ClearDB database using their wizards. My trouble is when I use their connection information (whether I try to connect from my Java app, or an outside tool - SQLyog to be exact) I take the error: Access denied for user 'b51dbc5757d79f'@'%' to database 'mywiki. The username provided by CloudBees does not contain those extra characters that the error message is displaying which seems like it would be a problem, but I'm not sure there is anything I can do about that since everything is configured for me. The username I am given is: b51dbc5757d79f - which I can delete and rebuild after sharing here :)

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  • glibc regexp performance

    - by Jack
    Anyone has experience measuring glibc regexp functions? Are there any generic tests I need to run to make such a measurements (in addition to testing the exact patterns I intend to search)? Thanks.

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  • Is MySQL Replication Appropriate in this case?

    - by MJB
    I have a series of databases, each of which is basically standalone. It initially seemed like I needed a replication solution, but the more I researched it, the more it felt like replication was overkill and not useful anyway. I have not done MySQL replication before, so I have been reading up on the online docs, googling, and searching SO for relevant questions, but I can't find a scenario quite like mine. Here is a brief description of my issue: The various databases almost never have a live connection to each other. They need to be able to "sync" by copying files to a thumb drive and then moving them to the proper destination. It is OK for the data to not match exactly, but they should have the same parent-child relationships. That is, if a generated key differs between databases, no big deal. But the visible data must match. Timing is not critical. Updates can be done a week later, or even a month later, as long as they are done eventually. Updates cannot be guaranteed to be in the proper order, or in any order for that matter. They will be in order from each database; just not between databases. Rather than a set of master-slave relationships, it is more like a central database (R/W) and multiple remote databases (also R/W). I won't know how many remote databases I have until they are created. And the central DB won't know that a database exists until data arrives from it. (To me, this implies I cannot use the method of giving each its own unique identity range to guarantee uniqueness in the central database.) It appears to me that the bottom line is that I don't want "replication" so much as I want "awareness". I want the central database to know what happened in the remote databases, but there is no time requirement. I want the remote databases to be aware of the central database, but they don't need to know about each other. WTH is my question? It is this: Does this scenario sound like any of the typical replication scenarios, or does it sound like I have to roll my own? Perhaps #7 above is the only one that matters, and given that requirement, out-of-the-box replication is impossible. EDIT: I realize that this question might be more suited to ServerFault. I also searched there and found no answers to my questions. And based on the replication questions I did find both on SO and SF, it seemed that the decision was 50-50 over where to put my question. Sorry if I guessed wrong.

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  • How do you share pre-calculated data between calls to a Rails web service?

    - by Nigel Thorne
    I have a Rails app that allows users to build up a network structure and then ask questions about how to navigate around it. When adding nodes and connections these are just saved to the database. At the point you make a query of the network I calculate the shortest path from any node to any other node. Constructing this in memory takes a while (something I need to fix), but once it is there, you can instantly get the answer to any of these path questions. The question is... How do I share this network between calls to the website, so each request doesn't regenerate the paths network each time? Note: I am hosting this on apache server using passenger (mod ruby) Thoughts?

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  • UITableView performance degrading after adding subviews on cell iphone sdk

    - by neha
    Hi all, In my application, I'm adding a label and two buttons on cell of UItableView [I have not created a separate cell class]. I'm adding these to cell and not cell.contentview. After I run my application on IPhone, the tableview cell rendering after I move the cells up-down, is very jerky. Is it because I'm not adding the views on cell.contentView or because I've not created a custom class for cell? Can anybody please help? Thanks in advance.

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  • sqlite3.OperationalError: database is locked - non-threaded application

    - by James C
    Hi, I have a Python application which throws the standard sqlite3.OperationalError: database is locked error. I have looked around the internet and could not find any solution which worked (please note that there is no multiprocesses/threading going on, and as you can see I have tried raising the timeout parameter). The sqlite file is stored on the local hard drive. The following function is one of many which accesses the sqlite database, and runs fine the first time it is called, but throws the above error the second time it is called (it is called as part of a for loop in another function): def update_index(filepath): path = get_setting('Local', 'web') stat = os.stat(filepath) modified = stat.st_mtime index_file = get_setting('Local', 'index') connection = sqlite3.connect(index_file, 30) cursor = connection.cursor() head, tail = os.path.split(filepath) cursor.execute('UPDATE hwlive SET date=? WHERE path=? AND name=?;', (modified, head, tail)) connection.commit() connection.close() Many thanks.

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  • Realtime MS SQL Database transfer

    - by user34402
    Hello, I have MS SQL 2005 Standard that is used actively (new data is added every minute). I need to transfer it to another server (new hosting provider), without losing the data and without downtime. Is there any way to do it?

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  • What is "helpx_last_check" from wordpress database

    - by bvandrunen
    I am a developer who works full time with wordpress and I came across something in my database which I have never seen before. I tried the normal search engine approach and have found nothing. Wondering if the wonderful people of stackoverflow have seen this before. I am pretty sure it isn't harmful. This is the entry in the mysql database. Table is "_options" option_id: 1165 blog_id: 0 option_name: helpx_last_check option_value: 1276628545 autoload: yes I am specifically wondering what "helpx_last_check" is. Thanks

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  • When to use @Singleton in a Jersey resource

    - by dexter
    I have a Jersey resource that access the database. Basically it opens a database connection in the initialization of the resource. Performs queries on the resource's methods. I have observed that when I do not use @Singleton, the database is being open at each request. And we know opening a connection is really expensive right? So my question is, should I specify that the resource be singleton or is it really better to keep it at per request especially when the resource is connecting to the database? My resource code looks like this: //Use @Singleton here or not? @Path(/myservice/) public class MyResource { private ResponseGenerator responser; private Log logger = LogFactory.getLog(MyResource.class); public MyResource() { responser = new ResponseGenerator(); } @GET @Path("/clients") public String getClients() { logger.info("GETTING LIST OF CLIENTS"); return responser.returnClients(); } ... // some more methods ... } And I connect to the database using a code similar to this: public class ResponseGenerator { private Connection conn; private PreparedStatement prepStmt; private ResultSet rs; public ResponseGenerator(){ Class.forName("org.h2.Driver"); conn = DriverManager.getConnection("jdbc:h2:testdb"); } public String returnClients(){ String result; try{ prepStmt = conn.prepareStatement("SELECT * FROM hosts"); rs = prepStmt.executeQuery(); ... //do some processing here ... } catch (SQLException se){ logger.warn("Some message"); } finally { rs.close(); prepStmt.close(); // should I also close the connection here (in every method) if I stick to per request // and add getting of connection at the start of every method // conn.close(); } return result } ... // some more methods ... } Some comments on best practices for the code will also be helpful.

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  • How to load a database of countries in a web application

    - by lance_klusener
    Hello All, I am new to web application development, so sorry in advance if this question is too basic. The following are the details of the question: A] Platform being used -- google app engine with python, django. B] Tutorial link being used -- http://code.google.com/appengine/articles/djangoforms.html C] Question: In the application i am building, there is a drop down box which allows the user to select their country. Since the list of countries is above 200, i want to construct a database of the countries before the application loads. Once this application is deployed, i dont want the database to get re-loaded again, since the entries are constant for all the users. How does one achieve this ? thanks, Lance.

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  • "Did you mean" feature on a dictionary database

    - by Hazar
    I have a ~300.000 row table; which includes technical terms; queried using PHP and MySQL + FULLTEXT indexes. But when I searching a wrong typed term; for example "hyperpext"; naturally giving no results. I need to "compansate" little writing errors and getting nearest record from database. How I can accomplish such feaure? I know (actually, learned today) about Levenshtein distance, Soundex and Metaphone algorithms but currently not having a solid idea to implement this to querying against database. Best regards. (Sorry about my poor English, I'm trying to do my best)

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  • JQuery Ajax Updating MySQL Database, But Not Running Success Function

    - by myrmidon16
    I am currently using the JQuery ajax function to call an exterior PHP file, in which I select and add data in a database. Once this is done, I run a success function in JavaScript. What's weird is that the database is updating successfully when ajax is called, however the success function is not running. Here is my code: <!DOCTYPE html> <head> <script type="text/javascript" src="jquery-1.6.4.js"></script> </head> <body> <div onclick="addtask();" style="width:400px; height:200px; background:#000000;"></div> <script> function addtask() { var tid = (Math.floor(Math.random() * 3)) + 1; var tsk = (Math.floor(Math.random() * 10)) + 1; if(tsk !== 1) { $.ajax({ type: "POST", url: "taskcheck.php", dataType: "json", data: {taskid:tid}, success: function(task) {alert(task.name);} }); } } </script> </body> </html> And the PHP file: session_start(); $connect = mysql_connect('x', 'x', 'x') or die('Not Connecting'); mysql_select_db('x') or die ('No Database Selected'); $task = $_REQUEST['taskid']; $uid = $_SESSION['user_id']; $q = "SELECT task_id, taskname FROM tasks WHERE task_id=" .$task. " LIMIT 1"; $gettask = mysql_fetch_assoc(mysql_query($q)); $q = "INSERT INTO user_tasks (ut_id, user_id, task_id, taskstatus, taskactive) VALUES (null, " .$uid. ", '{$gettask['task_id']}', 0, 1)"; $puttask = mysql_fetch_assoc(mysql_query($q)); $json = array( "name" => $gettask['taskname'] ); $output = json_encode($json); echo $output; Let me know if you have any questions or comments, thanks.

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  • Performance of jquery visible

    - by Mark Steudel
    I have a bunch of checkboxes on a page, and I only show a subset of those checkboxes at a time. I then perform some action which loops through all of the checkboxes and sees if they are checked or not: e.g. $(".delete_items").click( function() { $('.checkboxes' ).each(function(){ //do stuff } } Then I was thinking, well since the user can never interact with the hidden checkboxes, that adding :visible to checkboxes would speed up the loop e.g. $(".delete_items").click( function() { $('.checkboxes :visible' ).each(function(){ //do stuff } } But I don't know if adding :visible adds more overhead. Any thoughts?

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  • Accessing global variables within functions in PHP

    - by st3
    There are multiple times in one page where I need to connect and subsequently query a MySQL database, yet my code won't let me. I think it might be something to do with how my files are nested but it makes no sense. I am opening the SQL connection in the header file. The top of the offending page looks like the following: <?php $page_title = 'Dashboard'; include('templates/header.inc'); // includes a 'require_once('mysqli_connect.php') and a small query to the database; require_once('includes/functions.php'); require_once('includes/dashboard_sql.php'); // Contains functions which connect to database (which are failing.) ?> I get the PHP error Notice: Undefined variable: dbc in /Library/WebServer/Documents/pediatory_site/includes/dashboard_sql.php Where $dbc is the database connection defined in mysqli_connect.php. If anyone could help me out that would be great.

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  • Data Usage Checker Tools

    - by Lucifer
    Hey All, I am about to begin a project for a new client, and am worried about a few things concerning data usage on their internet plan. We're in an area where most of the major networks don't cover the area, and the ones that do, have very expensive plans, with very low data allowance per month. I need to develop an app, but part of the problem lies with checking database values every 30 seconds. It's pretty important that this check is happening every 30 seconds, as the database is actually updated all day everyday, approx. every 5seconds (apparently). Each row in the database consists of about a page full of text if you were to paste it into MS Word. So, are there any logical ways of minimizing data usage in my case, and also how am I able to see exactly how much data is used just to establish a connection to the database? Are there any tools for this kind of info? Thanks :)

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