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  • optimize query: get al votes from user's item

    - by Toni Michel Caubet
    hi there! i did it my way because i'm very bad getting results from two tables... Basically, first i get all the id items that correspond to the user, and then i calculate the ratings of each item. But, there is two different types of object item, so i do this 2 times: show you: function votos_usuario($id){ $previa = "SELECT id FROM preguntas WHERE id_usuario = '$id'"; $r_previo = mysql_query($previa); $ids_p = '0, '; while($items_previos = mysql_fetch_array($r_previo)){ $ids_p .= $items_previos['id'].", "; //echo "ids pregunta usuario: ".$items_previos['id']."<br>"; } $ids = substr($ids_p,0,-2); //echo $ids; $consulta = "SELECT valor FROM votos_pregunta WHERE id_pregunta IN ( $ids )"; //echo $consulta; $resultado = mysql_query($consulta); $votos_preguntas = 0; while($voto = mysql_fetch_array($resultado)){ $votos_preguntas = $votos_preguntas + $voto['valor']; } $previa_r = "SELECT id FROM recetas WHERE id_usuario = '$id'"; $r_previo_r = mysql_query($previa_r); $ids_r = '0, '; while($items_previos_r = mysql_fetch_array($r_previo_r)){ $ids_r .= $items_previos_r['id'].", "; //echo "ids pregunta usuario: ".$items_previos['id']."<br>"; } $ids = substr($ids_r,0,-2); $consulta_b = "SELECT valor FROM votos_receta WHERE id_receta IN ( $ids )"; //echo $consulta; $resultado_b = mysql_query($consulta_b); $votos_recetas = 0; while($voto_r = mysql_fetch_array($resultado_b)){ $votos_recetas = $votos_recetas + $voto_r['valor']; } $total = $votos_preguntas + $votos_recetas; return $total; } As you can si this is two much.. O(n^2) Feel like thinking? thanks!

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  • ActionScript 3 and camelcase package name

    - by Paul Dinh
    I'm using Flash Builder 4 to build my AIR application. For a certain reason, I need to declare my package name in camelcase, and class names in lowercase: //test.as package Core { public class test { } } The folder structure is like this (the dir 'Core' matches the package name): src/ Core/ test.as However, Flash Builder shows error and it doesn't compile at all, only when I put the package name as 'core' then it compiles. Does AS3 syntax allow uppercase letters in package name? Or just because Flash Builder implicitly disallows this?

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  • Retrieve 2 last posts for each category.

    - by Savageman
    Hello, Lets say I have 2 tables: blog_posts and categories. Each blog post belongs to only ONE category, so there is basically a foreign key between the 2 tables here. I would like to retrieve the 2 lasts posts from each category, is it possible to achieve this in a single request? GROUP BY would group everything and leave me with only one row in each category. But I want 2 of them. It would be easy to perform 1 + N query (N = number of category). First retrieve the categories. And then retrieve 2 posts from each category. I believe it would also be quite easy to perform M queries (M = number of posts I want from each category). First query selects the first post for each category (with a group by). Second query retrieves the second post for each category. etc. I'm just wondering if someone has a better solution for this. I don't really mind doing 1+N queries for that, but for curiosity and general SQL knowledge, it would be appreciated! Thanks in advance to whom can help me with this.

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  • Stack / base pointers in assembly

    - by flyingcrab
    I know this topic has been covered ad-naseum here, and other places on the internet - but hopefully the question is a simple one as I try to get my head around assembly... So if i understand correctly the ebp (base pointer) will point to the top of the stack, and the esp (stack pointer) will point to the bottom -- since the stack grows downward. esp therefore points to the 'current location'. So on a function call, once you've saved the ebp on the stack you insert a new stack frame - for the function. So in the case of the image below, if you started from N-3 you would go to N-2 with a function call. But when you are at N-2 - is your ebp == 25 and the esp == 24 (at least initially, before any data is placed on the stack)? Is this correct or am I of on a tangent here? Thanks!

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  • The speed of Ruby and Java.

    - by Simon
    In every benchmark that I found on the web it seems that Ruby is slow, much slower than Java. The Ruby folks just state that it doesn't matter. Could you give me any example that the speed of Ruby on Rails (and the Ruby itself) really doesn't matter?

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  • Where is the virtual function call overhead?

    - by Semen Semenych
    Hello everybody, I'm trying to benchmark the difference between a function pointer call and a virtual function call. To do this, I have written two pieces of code, that do the same mathematical computation over an array. One variant uses an array of pointers to functions and calls those in a loop. The other variant uses an array of pointers to a base class and calls its virtual function, which is overloaded in the derived classes to do absolutely the same thing as the functions in the first variant. Then I print the time elapsed and use a simple shell script to run the benchmark many times and compute the average run time. Here is the code: #include <iostream> #include <cstdlib> #include <ctime> #include <cmath> using namespace std; long long timespecDiff(struct timespec *timeA_p, struct timespec *timeB_p) { return ((timeA_p->tv_sec * 1000000000) + timeA_p->tv_nsec) - ((timeB_p->tv_sec * 1000000000) + timeB_p->tv_nsec); } void function_not( double *d ) { *d = sin(*d); } void function_and( double *d ) { *d = cos(*d); } void function_or( double *d ) { *d = tan(*d); } void function_xor( double *d ) { *d = sqrt(*d); } void ( * const function_table[4] )( double* ) = { &function_not, &function_and, &function_or, &function_xor }; int main(void) { srand(time(0)); void ( * index_array[100000] )( double * ); double array[100000]; for ( long int i = 0; i < 100000; ++i ) { index_array[i] = function_table[ rand() % 4 ]; array[i] = ( double )( rand() / 1000 ); } struct timespec start, end; clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &start); for ( long int i = 0; i < 100000; ++i ) { index_array[i]( &array[i] ); } clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &end); unsigned long long time_elapsed = timespecDiff(&end, &start); cout << time_elapsed / 1000000000.0 << endl; } and here is the virtual function variant: #include <iostream> #include <cstdlib> #include <ctime> #include <cmath> using namespace std; long long timespecDiff(struct timespec *timeA_p, struct timespec *timeB_p) { return ((timeA_p->tv_sec * 1000000000) + timeA_p->tv_nsec) - ((timeB_p->tv_sec * 1000000000) + timeB_p->tv_nsec); } class A { public: virtual void calculate( double *i ) = 0; }; class A1 : public A { public: void calculate( double *i ) { *i = sin(*i); } }; class A2 : public A { public: void calculate( double *i ) { *i = cos(*i); } }; class A3 : public A { public: void calculate( double *i ) { *i = tan(*i); } }; class A4 : public A { public: void calculate( double *i ) { *i = sqrt(*i); } }; int main(void) { srand(time(0)); A *base[100000]; double array[100000]; for ( long int i = 0; i < 100000; ++i ) { array[i] = ( double )( rand() / 1000 ); switch ( rand() % 4 ) { case 0: base[i] = new A1(); break; case 1: base[i] = new A2(); break; case 2: base[i] = new A3(); break; case 3: base[i] = new A4(); break; } } struct timespec start, end; clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &start); for ( int i = 0; i < 100000; ++i ) { base[i]->calculate( &array[i] ); } clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &end); unsigned long long time_elapsed = timespecDiff(&end, &start); cout << time_elapsed / 1000000000.0 << endl; } My system is LInux, Fedora 13, gcc 4.4.2. The code is compiled it with g++ -O3. The first one is test1, the second is test2. Now I see this in console: [Ignat@localhost circuit_testing]$ ./test2 && ./test2 0.0153142 0.0153166 Well, more or less, I think. And then, this: [Ignat@localhost circuit_testing]$ ./test2 && ./test2 0.01531 0.0152476 Where are the 25% which should be visible? How can the first executable be even slower than the second one? I'm asking this because I'm doing a project which involves calling a lot of small functions in a row like this in order to compute the values of an array, and the code I've inherited does a very complex manipulation to avoid the virtual function call overhead. Now where is this famous call overhead?

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  • How to prevent C6284 when using CString::Format?

    - by Sorin Sbarnea
    The following code is generating warning C6284 when compiled with /analyze on MSVC 2008 : object passed as parameter '%s' when string is required in call to function. CString strTmp, str; str = L"aaa.txt" strTmp.Format (L"File: %s", str); I'm looking for a nice solution for this that would not require static_cast

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  • Optimizing Oracle query

    - by Omnipresent
    SELECT MAX(verification_id) FROM VERIFICATION_TABLE WHERE head = 687422 AND mbr = 23102 AND RTRIM(LTRIM(lname)) = '.iq bzw' AND TO_CHAR(dob,'MM/DD/YYYY')= '08/10/2004' AND system_code = 'M'; This query is taking 153 seconds to run. there are millions of rows in VERIFICATION_TABLE. I think query is taking long because of the functions in where clause. However, I need to do ltrim rtrim on the columns and also date has to be matched in MM/DD/YYYY format. How can I optimize this query?

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  • Is there an offline version of Smush.it available?

    - by Jonathon Watney
    Sometimes I use Smush.it via the YSlow Firefox plugin to non-destructively reduce the file size of JPG images. Is there an offline version available that runs on Windows? And if not is there an alternative? The reason I'd like an offline version is that I'd like to optimize images before I deploy them. Currently Smush.it accepts only public facing URLs for images or a web page (via YSlow) and can't access my internal network. That means I have to deploy, optimize, replace images and deploy again. I'd really like to deploy the optimized images on the first deploy. Update: Here's a very similar question.

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  • Strange VS2005 compile errors: unable to copy resource file

    - by Velika
    I AM GETTING THE FOLLOWING ERROR IN A VERY SIMPLE CLASS LIBRARY: Error 1 Unable to copy file "obj\Debug\SMIT.SysAdmin.BusinessLayer.Resources.resources" to "obj\Debug\SMIT.SysAdmin.BusinessLayer.SMIT.SysAdmin.BusinessLayer.Resources.resources". Could not find file 'obj\Debug\SMIT.SysAdmin.BusinessLayer.Resources.resources'. SMIT.SysAdmin.BusinessLayer Going to the Project Properties-Resource tab, I see that I defined do resources. Still, I tried to delete the resource file and recreate by going to the resource tab. When I recompile, I still get the same error. Any suggestions of things to try?

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  • How to outperform this regex replacement?

    - by spender
    After considerable measurement, I have identified a hotspot in one of our windows services that I'd like to optimize. We are processing strings that may have multiple consecutive spaces in it, and we'd like to reduce to only single spaces. We use a static compiled regex for this task: private static readonly Regex regex_select_all_multiple_whitespace_chars = new Regex(@"\s+",RegexOptions.Compiled); and then use it as follows: var cleanString= regex_select_all_multiple_whitespace_chars.Replace(dirtyString.Trim(), " "); This line is being invoked several million times, and is proving to be fairly intensive. I've tried to write something better, but I'm stumped. Given the fairly modest processing requirements of the regex, surely there's something faster. Could unsafe processing with pointers speed things further?

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  • Strange C++ performance difference?

    - by STingRaySC
    I just stumbled upon a change that seems to have counterintuitive performance ramifications. Can anyone provide a possible explanation for this behavior? Original code: for (int i = 0; i < ct; ++i) { // do some stuff... int iFreq = getFreq(i); double dFreq = iFreq; if (iFreq != 0) { // do some stuff with iFreq... // do some calculations with dFreq... } } While cleaning up this code during a "performance pass," I decided to move the definition of dFreq inside the if block, as it was only used inside the if. There are several calculations involving dFreq so I didn't eliminate it entirely as it does save the cost of multiple run-time conversions from int to double. I expected no performance difference, or if any at all, a negligible improvement. However, the perfomance decreased by nearly 10%. I have measured this many times, and this is indeed the only change I've made. The code snippet shown above executes inside a couple other loops. I get very consistent timings across runs and can definitely confirm that the change I'm describing decreases performance by ~10%. I would expect performance to increase because the int to double conversion would only occur when iFreq != 0. Chnaged code: for (int i = 0; i < ct; ++i) { // do some stuff... int iFreq = getFreq(i); if (iFreq != 0) { // do some stuff with iFreq... double dFreq = iFreq; // do some stuff with dFreq... } } Can anyone explain this? I am using VC++ 9.0 with /O2. I just want to understand what I'm not accounting for here.

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  • Benchmarking a particular method in Objective-C

    - by Jasconius
    I have a critical method in an Objective-C application that I need to optimize as much as possible. I first need to take some easy benchmarks on this one single method so I can compare my progress as I optimize. What is the easiest way to track the execution time of a given method in, say, milliseconds, and print that to console.

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  • Creating thousands of records in Rails

    - by willCosgrove
    Let me set the stage: My application deals with gift cards. When we create cards they have to have a unique string that the user can use to redeem it with. So when someone orders our gift cards, like a retailer, we need to make a lot of new card objects and store them in the DB. With that in mind, I'm trying to see how quickly I can have my application generate 100,000 Cards. Database expert, I am not, so I need someone to explain this little phenomena: When I create 1000 Cards, it takes 5 seconds. When I create 100,000 cards it should take 500 seconds right? Now I know what you're wanting to see, the card creation method I'm using, because the first assumption would be that it's getting slower because it's checking the uniqueness of a bunch of cards, more as it goes along. But I can show you my rake task desc "Creates cards for a retailer" task :order_cards, [:number_of_cards, :value, :retailer_name] => :environment do |t, args| t = Time.now puts "Searching for retailer" @retailer = Retailer.find_by_name(args[:retailer_name]) puts "Retailer found" puts "Generating codes" value = args[:value].to_i number_of_cards = args[:number_of_cards].to_i codes = [] top_off_codes(codes, number_of_cards) while codes != codes.uniq codes.uniq! top_off_codes(codes, number_of_cards) end stored_codes = Card.all.collect do |c| c.code end while codes != (codes - stored_codes) codes -= stored_codes top_off_codes(codes, number_of_cards) end puts "Codes are unique and generated" puts "Creating bundle" @bundle = @retailer.bundles.create!(:value => value) puts "Bundle created" puts "Creating cards" @bundle.transaction do codes.each do |code| @bundle.cards.create!(:code => code) end end puts "Cards generated in #{Time.now - t}s" end def top_off_codes(codes, intended_number) (intended_number - codes.size).times do codes << ReadableRandom.get(CODE_LENGTH) end end I'm using a gem called readable_random for the unique code. So if you read through all of that code, you'll see that it does all of it's uniqueness testing before it ever starts creating cards. It also writes status updates to the screen while it's running, and it always sits for a while at creating. Meanwhile it flies through the uniqueness tests. So my question to the stackoverflow community is: Why is my database slowing down as I add more cards? Why is this not a linear function in regards to time per card? I'm sure the answer is simple and I'm just a moron who knows nothing about data storage. And if anyone has any suggestions, how would you optimize this method, and how fast do you think you could get it to create 100,000 cards? (When I plotted out my times on a graph and did a quick curve fit to get my line formula, I calculated how long it would take to create 100,000 cards with my current code and it says 5.5 hours. That maybe completely wrong, I'm not sure. But if it stays on the line I curve fitted, it would be right around there.)

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  • Start Codeblocks project from external code

    - by Dnaiel
    I have C++ code that depends on boost and other libraries, and therefore this code has a makefile that invokes boost. I am now trying to start developing this code in codeblocks in linux, so in order to do that I have two basic questions: (1) How can I import the code into codeblocks as a codeblocks new project? (2) How do I invoke the makefile with codeblocks instead of codeblocks trying to compile the code (which it would fail since codeblocks does not know that it needs to invoke boost). Sorry if it's too basic but I am quite new to C++ and codeblocks. Thanks!

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  • Cost of exception handlers in Python

    - by Thilo
    In another question, the accepted answer suggested replacing a (very cheap) if statement in Python code with a try/except block to improve performance. Coding style issues aside, and assuming that the exception is never triggered, how much difference does it make (performance-wise) to have an exception handler, versus not having one, versus having a compare-to-zero if-statement?

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  • Software to Tune/Calibrate Properties for Heuristic Algorithms

    - by Karussell
    Today I read that there is a software called WinCalibra (scroll a bit down) which can take a text file with properties as input. This program can then optimize the input properties based on the output values of your algorithm. See this paper or the user documentation for more information (see link above; sadly doc is a zipped exe). Do you know other software which can do the same which runs under Linux? (preferable Open Source) EDIT: Since I need this for a java application I will now invest my research in java libraries like jgap. Other ideas and links would be appreciated!

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  • Software to Tune/Calibrate Properties for Heuristic Algorithms

    - by Karussell
    Today I read that there is a software called WinCalibra (scroll a bit down) which can take a text file with properties as input. This program can then optimize the input properties based on the output values of your algorithm. See this paper or the user documentation for more information (see link above; sadly doc is a zipped exe). Do you know other software which can do the same which runs under Linux? (preferable Open Source)

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  • What's the difference between !col and col=false in MySQL?

    - by Mask
    The two statements have totally different performance: mysql> explain select * from jobs where createIndexed=false; +----+-------------+-------+------+----------------------+----------------------+---------+-------+------+-------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+------+----------------------+----------------------+---------+-------+------+-------+ | 1 | SIMPLE | jobs | ref | i_jobs_createIndexed | i_jobs_createIndexed | 1 | const | 1 | | +----+-------------+-------+------+----------------------+----------------------+---------+-------+------+-------+ 1 row in set (0.01 sec) mysql> explain select * from jobs where !createIndexed; +----+-------------+-------+------+---------------+------+---------+------+-------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+------+---------------+------+---------+------+-------+-------------+ | 1 | SIMPLE | jobs | ALL | NULL | NULL | NULL | NULL | 17996 | Using where | +----+-------------+-------+------+---------------+------+---------+------+-------+-------------+ Column definition and related index for aiding analysis: createIndexed tinyint(1) NOT NULL DEFAULT 0, create index i_jobs_createIndexed on jobs(createIndexed);

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  • What is the difference between LR, SLR, and LALR parsers?

    - by equilibrium
    What is the actual difference between LR, SLR, and LALR parsers? I know that SLR and LALR are types of LR parsers, but what is the actual difference as far as their parsing tables are concerned? And how to show whether a grammar is LR, SLR, or LALR? For an LL grammar we just have to show that any cell of the parsing table should not contain multiple production rules. Any similar rules for LALR, SLR, and LR? For example, how can we show that the grammar S --> Aa | bAc | dc | bda A --> d is LALR(1) but not SLR(1)?

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  • Does visibility affect DOM manipulation performance?

    - by Chetan Sastry
    IE7/Windows XP I have a third party component in my page that does a lot of DOM manipulation to adjust itself each time the browser window is resized. Unfortunately I have little control of what it does internally and I have optimized everything else (such as callbacks and event handlers) as much as I can. I can't take the component off the flow by setting display:none because it fails measuring itself if I do so. In general, does setting visibility of the container to invisible during the resize help improve DOM rendering performance?

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  • What are good memory management techniques in Flash/as3

    - by Parris
    Hello! So I am pretty familiar with memory management in Java, C and C++; however, in flash what constructs are there for memory management? I assume flash has a sort of virtual machine like java, and I have been assuming that things get garbage collected when they are set to null. I am not sure if this is actually the case though. Also is there a way to force garbage collection in Flash? Any other tips? Thanks

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