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• My program is spending most of its time in objc_msgSend. Does that mean that Objective-C has bad per

  - by Paperflyer

  Hello Stackoverflow. I have written an application that has a number of custom views and generally draws a lot of lines and bitmaps. Since performance is somewhat critical for the application, I spent a good amount of time optimizing draw performance. Now, activity monitor tells me that my application is usually using about 12% CPU and Instrument (the profiler) says that a whopping 10% CPU is spent in objc_msgSend (mostly in drawing related system calls). On the one hand, I am glad about this since it means that my drawing is about as fast as it gets and my optimizations where a huge success. On the other hand, it seems to imply that the only thing that is still using my CPU is the Objective-C overhead for messages (objc_msgSend). Hence, that if I had written the application in, say, Carbon, its performance would be drastically better. Now I am tempted to conclude that Objective-C is a language with bad performance, even though Cocoa seems to be awfully efficient since it can apparently draw faster than Objective-C can send messages. So, is Objective-C really a language with bad performance? What do you think about that?

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• Database (MySQL) structuring: pros and cons of multiple tables

  - by Gideon

  I am collecting data and storing it MySQL, for: 75 variables 55 countries Each year I have, at this stage since I am building this tool created a single table, of variables / countries (storing 1 year worth of data). Next year (and for several years after that) a new set of data will be input for each country. There are therefore 3 variables in controlling data returned to a user reviewing all collected data. The general form of any query would be: Show me these specifics variables, for these specific countries, for these specific years. (Show me average age and weight, for USA and Canada, for 2012 and 2009, for example) My question is, it seems that I have two options for arranging this data: -Multiple tables where I create a table of country / variable for each year data is collected - Single table and simply add a column (field) for the year that data relates to. As far as I can tell I could make these database calls with either sructure, but is one more powerful / efficient / quicker, and why? Thanks for your consideration. It's a PDO / PHP interface if that is relevent.

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• How can multiple variables be passed to a function cleanly in C?

  - by aquanar

  I am working on an embedded system that has different output capabilities (digital out, serial, analog, etc). I am trying to figure out a clean way to pass many of the variables that will control those functions. I don't need to pass ALL of them too often, but I was hoping to have a function that would read the input data (in this case from a TCP network), and then parse the data (IE, the 3rd byte contains the states of 8 of the digital outputs (according to which bit in that byte is high or low)), and put that into a variable where I can then use elsewhere in the program. I wanted that function to be separate from the main() function, but to do so would require passing pointers to some 20 or so variables that it would be writing to. I know I could make the variables global, but I am trying to make it easier to debug by making it obvious when a function is allowed to edit that variable, by passing it to the function. My best idea was a struct, and just pass a pointer to it, but wasn't sure if there was a more efficient way, especially since there is only really 1 function that would need to access all of them at once, while most others only require parts of the information that will be stored in this bunch of state variables. So anyway, is there a clean way to send many variables between functions at once that need to be edited?

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• Performance issue finding weekdays over a given period

  - by Oysio

  I have some methods that return the number of weekdays between two given dates. Since calling these methods become very expensive to call when the two dates lie years apart, I'm wondering how these methods could be refactored in a more efficient way. The returned result is correct but I feel that the iphone processor is struggling to keep up and consequently freezes up the application when I would call these methods over a period of say 10years. Any suggestions ? //daysList contains all weekdays that need to be found between the two dates -(NSInteger) numberOfWeekdaysFromDaysList:(NSMutableArray*) daysList startingFromDate:(NSDate*)startDate toDate:(NSDate*)endDate { NSInteger retNumdays = 0; for (Day *dayObject in [daysList objectEnumerator]) { if ([dayObject isChecked]) { retNumdays += [self numberOfWeekday:[dayObject weekdayNr] startingFromDate:startDate toDate:endDate]; } } return retNumdays; } -(NSInteger) numberOfWeekday:(NSInteger)day startingFromDate:(NSDate*)startDate toDate:(NSDate*)endDate { NSInteger numWeekdays = 0; NSDate *nextDate = startDate; NSComparisonResult result = [endDate compare:nextDate]; //Do while nextDate is in the past while (result == NSOrderedDescending || result == NSOrderedSame) { if ([NSDate weekdayFromDate:nextDate] == day) { numWeekdays++; } nextDate = [nextDate dateByAddingDays:1]; result = [endDate compare:nextDate]; } return numWeekdays; }

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• How to get notified about changes of the history via history.pushState?

  - by Felix Kling

  So now that HTML5 introduces history.pushState to change the browsers history, websites start using this in combination with Ajax instead of changing the fragment identifier of the URL. Sadly that means that those calls cannot be detect anymore by onhashchange. My question is: Is there a reliable way (hack? ;)) to detect when a website uses history.pushState? The specification does not state anything about events that are raised (at least I couldn't find anything). I tried to create a facade and replaced window.history with my own JavaScript object, but it didn't have any effect at all. Further explanation: I'm developing a Firefox add-on that needs to detect these changes and act accordingly. I know there was a similar question a few days ago that asked whether listening to some DOM events would be efficient but I would rather not rely on that because these events can be generated for a lot of different reasons. Update: Here is a jsfiddle (use Firefox 4 or Chrome 8) that shows that onpopstate is not triggered when pushState is called (or am I doing something wrong? Feel free to improve it!). Update 2: Another (side) problem is that window.location is not updated when using pushState (but I read about this already here on SO I think).

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• Best solution for __autoload

  - by tpk

  As our PHP5 OO application grew (in both size and traffic), we decided to revisit the __autoload() strategy. We always name the file by the class definition it contains, so class Customer would be contained within Customer.php. We used to list the directories in which a file can potentially exist, until the right .php file was found. This is quite inefficient, because you're potentially going through a number of directories which you don't need to, and doing so on every request (thus, making loads of stat() calls). Solutions that come to my mind... -use a naming convention that dictates the directory name (similar to PEAR). Disadvantages: doesn't scale too great, resulting in horrible class names. -come up with some kind of pre-built array of the locations (propel does this for its __autoload). Disadvantage: requires a rebuild before any deploy of new code. -build the array "on the fly" and cache it. This seems to be the best solution, as it allows for any class names and directory structure you want, and is fully flexible in that new files just get added to the list. The concerns are: where to store it and what about deleted/moved files. For storage we chose APC, as it doesn't have the disk I/O overhead. With regards to file deletes, it doesn't matter, as you probably don't wanna require them anywhere anyway. As to moves... that's unresolved (we ignore it as historically it didn't happen very often for us). Any other solutions?

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• Combine Arbitrary number of polygons together

  - by Jakobud

  I have an arbitrary number of polygons (hexes in this case) that are arranged randomly, but they are all touching another hex. Each individual hex has 6 x,y vertices. The vertex's are known for all the hexes. Can anyone point me in the direction of an algorithm that will combine all the hexes into a single polygon? Essentially I'm just looking for a function that spits out an array of vertex locations that are ordered in a way that when drawing lines from one to the next, it forms the polygon. This is my method so far: Create array of all the vertices for all the hexes. Determine the number of times a vertex occurs in the array If vertex is in the array 3+ times, delete the vertices from the array. If vertex is in the array 2 times, delete one of them. The next step is tricky though. I'm using canvas to draw out these polygons, which essentially involves drawing a line from one vertex to the next. So the order of the vertices in the final array is important. It can't be sorted arbitrarily. Also, I'm not looking for a "convex hull" algorithm, as that would not draw the polygon correctly. Are there any functions out there that do something like this? Am I on the right track or is there a better more efficient way?

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• SELECT set of most recent id, amount FROM table, where id occurs many times

  - by Jon Cram

  I have a table recording the amount of data transferred by a given service on a given date. One record is entered daily for a given service. I'd like to be able to retrieve the most recent amount for a set of services. Example data set: serviceId | amount | date ------------------------------- 1 | 8 | 2010-04-12 2 | 11 | 2010-04-12 2 | 14 | 2010-04-11 3 | 9 | 2010-04-11 1 | 6 | 2010-04-10 2 | 5 | 2010-04-10 3 | 22 | 2010-04-10 4 | 17 | 2010-04-19 Desired response (service ids 1,2,3): serviceId | amount | date ------------------------------- 1 | 8 | 2010-04-12 2 | 11 | 2010-04-12 3 | 9 | 2010-04-11 Desired response (service ids 2, 4): serviceId | amount | date ------------------------------- 2 | 11 | 2010-04-12 4 | 17 | 2010-04-19 This retrieves the equivalent as running the following once per serviceId: SELECT serviceId, amount, date FROM table WHERE serviceId = <given serviceId> ORDER BY date DESC LIMIT 0,1 I understand how I can retrieve the data I want in X queries. I'm interested to see how I can retrieve the same data using either a single query or at the very least less than X queries. I'm very interested to see what might be the most efficient approach. The table currently contains 28809 records. I appreciate that there are other questions that cover selecting the most recent set of records. I have examined three such questions but have been unable to apply the solutions to my problem.

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• How to make chrome.tabs.update works with content script

  - by user1673772

  I work on a little extension on Google Chrome, I want to create a new tab, go on the url "sample"+i+".com", launch a content script on this url, update the current tab to "sample"+(i+1)+".com", and launch the same script. I looked the Q&A available on stackoverflow and I google it but I didn't found a solution who works. This is my actually code of background.js (it works), it creates two tabs (i=21 and i=22) and load my content script for each url, when I tried to do a chrome.tabs.update Chrome launchs directly a tab with i = 22 (and the script works only one time) : function extraction(tab) { for (var i =21; i<23;i++) { chrome.storage.sync.set({'extraction' : 1}, function() {}); //for my content script chrome.tabs.create({url: "http://example.com/"+i+".html"}, function() {}); } } chrome.browserAction.onClicked.addListener(function(tab) {extraction(tab);}); If anyone can help me, the content script and manifest.json are not the problem. I want to make that 15000 times so I can't do otherwise. Thank you.

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• Permutations distinct under given symmetry (Mathematica 8 group theory)

  - by Yaroslav Bulatov

  Given a list of integers like {2,1,1,0} I'd like to list all permutations of that list that are not equivalent under given group. For instance, using symmetry of the square, the result would be {{2, 1, 1, 0}, {2, 1, 0, 1}}. Approach below (Mathematica 8) generates all permutations, then weeds out the equivalent ones. I can't use it because I can't afford to generate all permutations, is there a more efficient way? Update: actually, the bottleneck is in DeleteCases. The following list {2, 2, 2, 2, 2, 2, 2, 1, 1, 1, 1, 1, 1, 0, 0, 0} has about a million permutations and takes 0.1 seconds to compute. Apparently there are supposed to be 1292 orderings after removing symmetries, but my approach doesn't finish in 10 minutes removeEquivalent[{}] := {}; removeEquivalent[list_] := ( Sow[First[list]]; equivalents = Permute[First[list], #] & /@ GroupElements[group]; DeleteCases[list, Alternatives @@ equivalents] ); nonequivalentPermutations[list_] := ( reaped = Reap@FixedPoint[removeEquivalent, Permutations@list]; reaped[[2, 1]] ); group = DihedralGroup[4]; nonequivalentPermutations[{2, 1, 1, 0}]

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• Rails: creating a model in the new action

  - by Joseph Silvashy

  I have an interesting situation, well it's probably not that unique at all, but I'm not totally sure how to tackle it. I have a model, in this case a recipe and the user navigates to the new path /recipes/new however the situation is that I need to be able to have the user upload images and make associations to that model in the new action, but the model doesn't have an ID yet. So I assume I need to rethink my controller, but I don't want to have redirects and whatnot, how can accomplish this? Here is the basic controller, barebones obviously: ... def new # I should be creating the model first, so it has an ID @recipe = Recipe.new end def create @recipe = Recipe.new(params[:recipe]) if @recipe.save redirect_to @recipe else render 'new' end end ... update Perhaps I can have a column thats like state which could have values like new/incomplete/complete or what-have-you. I'm mostly trying to figure out what would also be most efficient for the DB. It would be nice if I could still have a url that said '/new', instead of it be the edit path with the id, for usability sake, but I'm not sure this can be simply accomplished in the new action of my controller. Thoughts?

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• Get href tags in html data in c#

  - by Nani

  I am using web client class to HTML data from a web page. Now I want to get the complete href tags and there titles from the HTML data. Initially I used loops, Felling inefficient I switched to regExp, but dint got efficient solution. He is the initial code: for (int i = 0; i < htmldata.Length - 5; i++) { if (htmldata.Substring(i, 5) == "href=") { n1 = htmldata.Substring(i + 6, htmldata.Length - (i + 6)).IndexOf("\""); Sublink = htmldata.Substring(i + 6, n1); var absoluteUri = new Uri(baseUri, temp); n2 = htmldata.Substring(i + n1 + 1, htmldata.Length - (i + n1 + 1)).IndexOf("<"); subtitle = htmldata.Substring(i + 6 + n1 + 2, n2 - 7); } } This code is getting some of the links like this. /l.href.replace(new RegExp( /advanced_search?hl=en&q=&hl=en& and titles like this onclick=gbar.qs(this) class=gb2Photos ")+"q="+encodeURIComponent(b)})}i.qs=n;function o(a,b,d,c,f,e){var g=document.getElementById(a);if(g){var Which are absolutely invalid. Please suggest me the correct code for getting valid relative href links and titles. ThankYou.

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• How to render all records from a nested set into a real html tree

  - by Christoph Schiessl

  I'm using the awesome_nested_set plugin in my Rails project. I have two models that look like this (simplified): class Customer < ActiveRecord::Base has_many :categories end class Category < ActiveRecord::Base belongs_to :customer # Columns in the categories table: lft, rgt and parent_id acts_as_nested_set :scope => :customer_id validates_presence_of :name # Further validations... end The tree in the database is constructed as expected. All the values of parent_id, lft and rgt are correct. The tree has multiple root nodes (which is of course allowed in awesome_nested_set). Now, I want to render all categories of a given customer in a correctly sorted tree like structure: for example nested <ul> tags. This wouldn't be too difficult but I need it to be efficient (the less sql queries the better). Update: Figured out that it is possible to calculate the number of children for any given Node in the tree without further SQL queries: number_of_children = (node.rgt - node.lft - 1)/2. This doesn't solve the problem but it may prove to be helpful.

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• LINQ to SQL - Lightweight O/RM?

  - by CoffeeAddict

  I've heard from some that LINQ to SQL is good for lightweight apps. But then I see LINQ to SQL being used for Stackoverflow, and a bunch of other .coms I know (from interviewing with them). Ok, so is this true? for an e-commerce site that's bringing in millions and you're typically only doing basic CRUDs most the time with the exception of an occasional stored proc for something more complex, is LINQ to SQL complete enough and performance-wise good enough or able to be tweaked enough to run happily on an e-commerce site? I've heard that you just need to tweak performance on the DB side when using LINQ to SQL for a better approach. So there are really 2 questions here: 1) Meaning/scope/definition of a "Lightweight" O/RM solution: What the heck does "lightweight" mean when people say LINQ to SQL is a "lightweight O/RM" and is that true??? If this is so lightweight then why do I see a bunch of huge .coms using it? Is it good enough to run major .coms (obviously it looks like it is) and what determines what the context of "lightweight" is...it's such a generic statement. 2) Performance: I'm working on my own .com and researching different O/RMs. I'm not really looking at the Entity Framework (yet), just want to figure out the LINQ to SQL basics here and determine if it will be efficient enough for me. The problem I think is you can't tweak or control the SQL it generates...

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• How to effectively execute this cron job?

  - by Lost_in_code

  I have a table with 200 rows. I'm running a cron job every 10 minutes to perform some kind of insert/update operation on the table. The operation needs to be performed only on 5 rows at a time every time the cron job runs. So in first 10 mins records 1-5 are updated, records 5-10 in the 20th minute and so on. When the cron job runs for the 20th time, all the records in the table would have been updated exactly once. This is what is to be achieved at least. And the next cron job should repeat the process again. The problem: is that, every time a cron job runs, the insert/update operation should be performed on N rows (not just 5 rows). So, if N is 100, all records would've been updated by just 2 cron jobs. And the next cron job would repeat the process again. Here's an example: This is the table I currently have (200 records). Every time a cron job executes, it needs to pick N records (which I set as a variable in PHP) and update the time_md5 field with the current time's MD5 value. +---------+-------------------------------------+ | id | time_md5 | +---------+-------------------------------------+ | 10 | 971324428e62dd6832a2778582559977 | | 72 | 1bd58291594543a8cc239d99843a846c | | 3 | 9300278bc5f114a290f6ed917ee93736 | | 40 | 915bf1c5a1f13404add6612ec452e644 | | 599 | 799671e31d5350ff405c8016a38c74eb | | 56 | 56302bb119f1d03db3c9093caf98c735 | | 798 | 47889aa559636b5512436776afd6ba56 | | 8 | 85fdc72d3b51f0b8b356eceac710df14 | | .. | ....... | | .. | ....... | | .. | ....... | | .. | ....... | | 340 | 9217eab5adcc47b365b2e00bbdcc011a | <-- 200th record +---------+-------------------------------------+ So, the first record(id 10) should not be updated more than once, till all 200 records are updated once - the process should start over once all the records are updated once. I have some idea on how this could be achieved, but I'm sure there are more efficient ways of doing it. Any suggestions?

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• Matching on search attributes selected by customer on front end

  - by CodeNinja1974

  I have a method in a class that allows me to return results based on a certain set of Customer specified criteria. The method matches what the Customer specifies on the front end with each item in a collection that comes from the database. In cases where the customer does not specify any of the attributes, the ID of the attibute is passed into the method being equal to 0 (The database has an identity on all tables that is seeded at 1 and is incremental). In this case that attribute should be ignored, for example if the Customer does not specify the Location then customerSearchCriteria.LocationID = 0 coming into the method. The matching would then match on the other attributes and return all Locations matching the other attibutes, example below: public IEnumerable<Pet> FindPetsMatchingCustomerCriteria(CustomerPetSearchCriteria customerSearchCriteria) { if(customerSearchCriteria.LocationID == 0) { return repository.GetAllPetsLinkedCriteria() .Where(x => x.TypeID == customerSearchCriteria.TypeID && x.FeedingMethodID == customerSearchCriteria.FeedingMethodID && x.FlyAblityID == customerSearchCriteria.FlyAblityID ) .Select(y => y.Pet); } } The code for when all criteria is specified is shown below: private PetsRepository repository = new PetsRepository(); public IEnumerable<Pet> FindPetsMatchingCustomerCriteria(CustomerPetSearchCriteria customerSearchCriteria) { return repository.GetAllPetsLinkedCriteria() .Where(x => x.TypeID == customerSearchCriteria.TypeID && x.FeedingMethodID == customerSearchCriteria.FeedingMethodID && x.FlyAblityID == customerSearchCriteria.FlyAblityID && x.LocationID == customerSearchCriteria.LocationID ) .Select(y => y.Pet); } I want to avoid having a whole set of if and else statements to cater for each time the Customer does not explicitly select an attribute of the results they are looking for. What is the most succint and efficient way in which I could achieve this?

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• "date_part('epoch', now() at time zone 'UTC')" not the same time as "now() at time zone 'UTC'" in po

  - by sirlark

  I'm writing a web based front end to a database (PHP/Postgresql) in which I need to store various dates/times. The times are meant to be always be entered on the client side in the local time, and displayed in the local time too. For storage purposes, I store all dates/times as integers (UNIX timestamps) and normalised to UTC. One particular field has a restriction that the timestamp filled in is not allowed to be in the future, so I tried this with a database constraint... CONSTRAINT not_future CHECK (timestamp-300 <= date_part('epoch', now() at time zone 'UTC')) The -300 is to give 5 minutes leeway in case of slightly desynchronised times between browser and server. The problem is, this constraint always fails when submitting the current time. I've done testing, and found the following. In PostgreSQL client: SELECT now() -- returns correct local time SELECT date_part('epoch', now()) -- returns a unix timestamp at UTC (tested by feeding the value into the date function in PHP correcting for its compensation to my time zone) SELECT date_part('epoch', now() at time zone 'UTC') -- returns a unix timestamp at two time zone offsets west, e.g. I am at GMT+2, I get a GMT-2 timestamp. I've figured out obviously that dropping the "at time zone 'UTC'" will solve my problem, but my question is if 'epoch' is meant to return a unix timestamp which AFAIK is always meant to be in UTC, why would the 'epoch' of a time already in UTC be corrected? Is this a bug, or I am I missing something about the defined/normal behaviour here.

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• Quickest way to compare a buch of array or list of values.

  - by zapping

  Can you please let me know on the quickest and efficient way to compare a large set of values. Its like there are a list of parent codes(string) and each code has a series of child values(string). The child lists have to be compared with each other and find out duplicates and count how many times they repeat. code1(code1_value1, code1_value2, code3_value3, ..., code1_valueN); code2(code2_value1, code1_value2, code2_value3, ..., code2_valueN); code3(code2_value1, code3_value2, code3_value3, ..., code3_valueN); . . . codeN(codeN_value1, codeN_value2, codeN_value3, ..., codeN_valueN); The lists are huge say like there are 100 parent codes and each has about 250 values in them. There will not be duplicates within a code list. Doing it in java and the solution i could figure out is. Store the values of first set of code in as codeMap.put(codeValue, duplicateCount). The count initialized to 0. Then compare the rest of the values with this. If its in the map then increment the count otherwise append it to the map. The downfall of this is to get the duplicates. Another iteration needs to be performed on a very large list. An alternative is to maintain another hashmap for duplicates like duplicateCodeMap.put(codeValue, duplicateCount) and change the initial hashmap to codeMap.put(codeValue, codeValue). Speed is what is requirement. Hope one of you can help me with it.

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• When to use a foreign key in MySQL

  - by Mel

  Is there official guidance or a threshold to indicate when it is best practice to use a foreign key in a MySQL database? Suppose you created a table for movies. One way to do it is to integrate the producer and director data into the same table. (movieID, movieName, directorName, producerName). However, suppose most directors and producers have worked on many movies. Would it be best to create two other tables for producers and directors, and use a foreign key in the movie table? When does it become best practice to do this? When many of the directors and producers are appearing several times in the column? Or is it best practice to employ a foreign key approach at the start? While it seems more efficient to use a foreign key, it also raises the complexity of the database. So when does the trade off between complexity and normalization become worth it? I'm not sure if there is a threshold or a certain number of cell repetitions that makes it more sensible to use a foreign key. I'm thinking about a database that will be used by hundreds of users, many concurrently. Many thanks!

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• Project Euler #119 Make Faster

  - by gangqinlaohu

  Trying to solve Project Euler problem 119: The number 512 is interesting because it is equal to the sum of its digits raised to some power: 5 + 1 + 2 = 8, and 8^3 = 512. Another example of a number with this property is 614656 = 28^4. We shall define an to be the nth term of this sequence and insist that a number must contain at least two digits to have a sum. You are given that a2 = 512 and a10 = 614656. Find a30. Question: Is there a more efficient way to find the answer than just checking every number until a30 is found? My Code int currentNum = 0; long value = 0; for (long a = 11; currentNum != 30; a++){ //maybe a++ is inefficient int test = Util.sumDigits(a); if (isPower(a, test)) { currentNum++; value = a; System.out.println(value + ":" + currentNum); } } System.out.println(value); isPower checks if a is a power of test. Util.sumDigits: public static int sumDigits(long n){ int sum = 0; String s = "" + n; while (!s.equals("")){ sum += Integer.parseInt("" + s.charAt(0)); s = s.substring(1); } return sum; } program has been running for about 30 minutes (might be overflow on the long). Output (so far): 81:1 512:2 2401:3 4913:4 5832:5 17576:6 19683:7 234256:8 390625:9 614656:10 1679616:11 17210368:12 34012224:13 52521875:14 60466176:15 205962976:16 612220032:17

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• Stable/repeatable random sort (MySQL, Rails)

  - by Matt Rogish

  I'd like to paginate through a randomly sorted list of ActiveRecord models (rows from MySQL database). However, this randomization needs to persist on a per-session basis, so that other people that visit the website also receive a random, paginate-able list of records. Let's say there are enough entities (tens of thousands) that storing the randomly sorted ID values in either the session or a cookie is too large, so I must temporarily persist it in some other way (MySQL, file, etc.). Initially I thought I could create a function based on the session ID and the page ID (returning the object IDs for that page) however since the object ID values in MySQL are not sequential (there are gaps), that seemed to fall apart as I was poking at it. The nice thing is that it would require no/minimal storage but the downsides are that it is likely pretty complex to implement and probably CPU intensive. My feeling is I should create an intersection table, something like: random_sorts( sort_id, created_at, user_id NULL if guest) random_sort_items( sort_id, item_id, position ) And then simply store the 'sort_id' in the session. Then, I can paginate the random_sorts WHERE sort_id = n ORDER BY position LIMIT... as usual. Of course, I'd have to put some sort of a reaper in there to remove them after some period of inactivity (based on random_sorts.created_at). Unfortunately, I'd have to invalidate the sort as new objects were created (and/or old objects being removed, although deletion is very rare). And, as load increases the size/performance of this table (even properly indexed) drops. It seems like this ought to be a solved problem but I can't find any rails plugins that do this... Any ideas? Thanks!!

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• Parallelizing L2S Entity Retrieval

  - by MarkB

  Assuming a typical domain entity approach with SQL Server and a dbml/L2S DAL with a logic layer on top of that: In situations where lazy loading is not an option, I have settled on a convention where getting a list of entities does not also get each item's child entities (no loading), but getting a single entity does (eager loading). Since getting a single entity also gets children, it causes a cascading effect in which each child then gets its children too. This sounds bad, but as long as the model is not too deep, I usually don't see performance problems that outweigh the benefits of the ease of use. So if I want to get a list in which each of the items is fully hydrated with children, I combine the GetList and GetItem methods. So I'll get a list and then loop through it getting each item with the full cascade. Even this is generally acceptable in many of the projects I've worked on - but I have recently encountered situations with larger models and/or more data in which it needs to be more efficient. I've found that partitioning the loop and executing it on multiple threads yields excellent results. In my first experiment with a list of 50 items from one particular project, I did 5 threads of 10 items each and got a 3X improvement in time. Of course, the mileage will vary depending on the project but all else being equal this is clearly a big opportunity. However, before I go further, I was wondering what others have done that have already been through this. What are some good approaches to parallelizing this type of thing?

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• PHP Arrays: Pop an array of single-element arrays into one array.

  - by Rob Drimmie

  Using a proprietary framework, I am frequently finding myself in the situation where I get a resultset from the database in the following format: array(5) { [0] => array(1) { ["id"] => int(241) } [1] => array(1) { ["id"] => int(2) } [2] => array(1) { ["id"] => int(81) } [3] => array(1) { ["id"] => int(560) } [4] => array(1) { ["id"] => int(10) } } I'd much rather have a single array of ids, such as: array(5) { [0] => int(241) [1] => int(2) [2] => int(81) [3] => int(560) [4] => int(10) } To get there, I frequently find myself writing: $justIds = array(); foreach( $allIds as $id ) { $justIds[] = $id["id"]; } Is there a more efficient way to do this?

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• Is programming overrated?

  - by aengine

  [Subjective and intended to be a community wiki] I am sorry for such an offensive question: But here are my arguments Most of the progress in "computing" has came from non-programming sources. i.e. People invented faster microprocessors and better routers and novel memory devices. I dont think on average people are writting more efficient programs than those written 10 years ago. And the newer and popular languages are infact slower than C. though speed is one of the lesser criterias. Most of the progress came from novel paradigms. Web, Internet, Cloud computing and Social networking are novel paradigms and did not involve progress in programming as such. Heck even facebook was written in PHP and not some extreme language. Though it did face scalability issues (same with twitter) but i believe money and better programmers (who came in much later) took care of that. Thus ideating capability trumped programming capability/ Even things like Map-Reduce, Column oriented database and Probablistic algorithms (E.g. bloom filters) came from hardcore Algorithms research, rather than some programming convention. Thus my final point is why programming skill is so overstressed? To point a recent example about how only 10% of programmers can "write code" (binary search) without debugging. Isnt it a bit hypocritical, considering your real successs lies in coming up with better algorithm or a novel feature rather than getting right first time???

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• Accessing HTML DOM elements from javascript using `.childNodes`

  - by Martin

  I'm wondering about the .childNodes property, I have the code below, and for some reason I get 18 children, while 6 are HTMLInputElements as expected, and the rest are undefined. What is this about? Is there an efficient way to iterate over the input elements? <html> <head> <script> window.onload = function(e){ form = document.getElementById('myForm'); alert(form.childNodes.length); for(i=0; i<form.childNodes.length; i++){ alert(form[i]); } } </script> </head> <body> <form id='myForm' action="haha" method="post"> Name: <input type="text" id="fnameAdd" name="name" /><br /> Phone1: <input type="text" id="phone1Add" name="phone1" /><br /> Phone2: <input type="text" id="phone2Add" name="phone2" /><br /> E-Mail: <input type="text" id="emailAdd" name="email" /><br /> Address: <input type="text" id="addressAdd" name="address" /><br /> <input type="submit" value="Save" /> </body> </html>

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