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  • Using FILE_FLAG_NO_BUFFERING will return noticeable speed gain?

    - by 9dan
    Recently noticed detail description of FILE_FLAG_NO_BUFFERING flag in MSDN, and read several Google search results about unbuffered I/O in Windows. http://msdn.microsoft.com/en-us/library/aa363858(v=vs.85).aspx I wondering now, is it really important to consider unbuffered option in file I/O programming? Because many programs use plain old C stream I/O or C++ iostream, I didn't gave any attention to FILE_FLAG_NO_BUFFERING flag before. Let's say we are developing photo explorer program like Picasa. If we implement unbuffered I/O, could thumbnail display speed show noticeable difference in ordinary users?

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  • can a program written in C be faster than one written in OCaml and translated to C?

    - by Ole Jak
    So I have some cool Image Processing algorithm. I have written it in OCaml. It performs well. I now I can compile it as C code with such command ocamlc -output-obj -o foo.c foo.ml (I have a situation where I am not alowed to use OCaml compiler to bild my programm for my arcetecture, I can use only specialy modified gcc. so I will compile that programm with sometyhing like gcc -L/usr/lib/ocaml foo.c -lcamlrun -lm -lncurses and Itll run on my archetecture.) I want to know in general case can a program written in C be faster than one written in OCaml and translated to C?

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  • sql query is too slow, how to improve speed

    - by user1289282
    I have run into a bottleneck when trying to update one of my tables. The player table has, among other things, id, skill, school, weight. What I am trying to do is: SELECT id, skill FROM player WHERE player.school = (current school of 4500) AND player.weight = (current weight of 14) to find the highest skill of all players returned from the query UPDATE player SET starter = 'TRUE' WHERE id = (highest skill) move to next weight and repeat when all weights have been completed move to next school and start over all schools completed, done I have this code implemented and it works, but I have approximately 4500 schools totaling 172000 players and the way I have it now, it would take probably a half hour or more to complete (did not wait it out), which is way too slow. How to speed this up? Short of reducing the scale of the system, I am willing to do anything that gets the intended result. Thanks! *the weights are the standard folk style wrestling weights ie, 103, 113, 120, 126, 132, 138, 145, 152, 160, 170, 182, 195, 220, 285 pounds

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  • Slowing process creation under Java?

    - by oconnor0
    I have a single, large heap (up to 240GB, though in the 20-40GB range for most of this phase of execution) JVM [1] running under Linux [2] on a server with 24 cores. We have tens of thousands of objects that have to be processed by an external executable & then load the data created by those executables back into the JVM. Each executable produces about half a megabyte of data (on disk) that when read right in, after the process finishes, is, of course, larger. Our first implementation was to have each executable handle only a single object. This involved the spawning of twice as many executables as we had objects (since we called a shell script that called the executable). Our CPU utilization would start off high, but not necessarily 100%, and slowly worsen. As we began measuring to see what was happening we noticed that the process creation time [3] continually slows. While starting at sub-second times it would eventually grow to take a minute or more. The actual processing done by the executable usually takes less than 10 seconds. Next we changed the executable to take a list of objects to process in an attempt to reduce the number of processes created. With batch sizes of a few hundred (~1% of our current sample size), the process creation times start out around 2 seconds & grow to around 5-6 seconds. Basically, why is it taking so long to create these processes as execution continues? [1] Oracle JDK 1.6.0_22 [2] Red Hat Enterprise Linux Advanced Platform 5.3, Linux kernel 2.6.18-194.26.1.el5 #1 SMP [3] Creation of the ProcessBuilder object, redirecting the error stream, and starting it.

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  • Update table with index is too slow

    - by pauloya
    Hi, I was watching the Profiler on a live system of our application and I saw that there was an update instruction that we run periodically (every second) that was quite slow. It took around 400ms every time. The query includes this update (which is the slow part) UPDATE BufferTable SET LrbCount = LrbCount + 1, LrbUpdated = getdate() WHERE LrbId = @LrbId This is the table CREATE TABLE BufferTable( LrbId [bigint] IDENTITY(1,1) NOT NULL, ... LrbInserted [datetime] NOT NULL, LrbProcessed [bit] NOT NULL, LrbUpdated [datetime] NOT NULL, LrbCount [tinyint] NOT NULL, ) The table has 2 indexes (non unique and non clustered) with the fields by this order: * Index1 - (LrbProcessed, LrbCount) * Index2 - (LrbInserted, LrbCount, LrbProcessed) When I looked at this I thought that the problem would come from Index1 since LrbCount is changing a lot and it changes the order of the data in the index. But after desactivating index1 I saw the query was taking the same time as initially. Then I rebuilt index1 and desactivated index2, this time the query was very fast. It seems to me that Index2 should be faster to update, the order of the data shouldn't change since the LrbInserted time is not changed. Can someone explain why index2 is much heavier to update then index1? Thank you!

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  • VS2008 is very slow on a specific large C++ solution

    - by VioletRose
    I have a solution with 21 C++ projects and 1 VB.NET project. The IDE responds very slowly when I simply move the carret in a file or try to open the menu. The process seems to take 50% of CPU for each movement. It only happens with this solution and only on my machine. The solution has total of 2380 source and header files, of which 1280 are header files. I tried to remove all connection to the source control (Perforce) but it didn't help. Also, I have Visual Assist installed but even after removing it (uninstall), the same behavior continued. Any idea?

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  • C++ Function pointers vs Switch

    - by Perfix
    What is faster: Function pointers or switch? The switch statement would have around 30 cases, consisting of enumarated unsigned ints from 0 to 30. I could do the following: class myType { FunctionEnum func; string argv[123]; int someOtherValue; }; // In another file: myType current; // Iterate through a vector containing lots of myTypes // ... for ( i=0; i < myVecSize; i ++ ) switch ( current.func ) { case 1: //... break; // ........ case 30: // blah break; } And go trough the switch with func every time. The good thing about switch would also be that my code is more organized than with 30 functions. Or I could do that (not so sure with that): class myType { myReturnType (*func); string argv[123]; int someOtherValue; }; I'd have 30 different functions then, at the beginning a pointer to one of them is assigned to myType. What is probably faster: Switch statement or function pointer? Calls per second: Around 10 million. I can't just test it out - that would require me to rewrite the whole thing. Currently using switch. I'm building an interpreter which I want to be faster than Python & Ruby - every clock cycle matters!

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  • What can I do to make my eService website customers feel it is a luxurious service? [closed]

    - by Farshid
    I'm developing an e-service website that its monetization model is via paid membership. Beside quality service and content, because I'm serving them for a high fee, I want to make them feel like it is a personal, unparalleled kind of service and I want to spend money for creating things that I give them after their registration such as a beautiful physical membership card so that I can use the effect of mouth-words better and beside that let them be proud about the service. I've tried my best to develop the site experience classy and I'm looking for things in real world to send them after their registration (such as membership card and a small paper tutorial). What are your suggestions? Have you seen things like this before that a website sends you some physical things for making you more loyal and/or something like that? Please kindly share your experiences/suggestions.

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  • What is microbenchmarking?

    - by polygenelubricants
    I've heard this term used, but I'm not entirely sure what it means, so: What DOES it mean and what DOESN'T it mean? What are some examples of what IS and ISN'T microbenchmarking? What are the dangers of microbenchmarking and how do you avoid it? (or is it a good thing?)

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  • Django: IE doesn't load locahost or loads very SLOWLY

    - by reedvoid
    I'm just starting to learn Django, building a project on my computer, running Windows 7 64-bit, Python 2.7, Django 1.3. Basically whatever I write, it loads in Chrome and Firefox instantly. But for IE (version 9), it just stalls there, and does nothing. I can load up "http://127.0.0.1:8000" on IE and leave the computer on for hours and it doesn't load. Sometimes, when I refresh a couple of times or restart IE it'll work. If I change something in the code, again, Chrome and Firefox reflects changes instantly, whereas IE doesn't - if it loads the page at all. What is going on? I'm losing my mind here....

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  • fast load big object graph from DB

    - by Famos
    Hi I have my own data structure written in C# like: public class ElectricScheme { public List<Element> Elements { get; set; } public List<Net> Nets { get; set; } } public class Element { public string IdName { get; set; } public string Func { get; set; } public string Name { get; set; } public BaseElementType Type { get; set; } public List<Pin> Pins { get; set; } } public class Pin { public string IdName { get; set; } public string Name { get; set; } public BasePinType PinType { get; set; } public BasePinDirection PinDirection { get; set; } } public class Net { public string IdName { get; set; } public string Name { get; set; } public List<Tuple<Element,Pin>> ConnectionPoints { get; set; } } Where Elements count ~19000, each element contain =3 Pin, Nets count ~20000, each net contain =3 pair (Element, Pin) Parse txt (file size ~17mb) file takes 5 minutes. Serilization / Deserialization by default serializer ~3 minutes. Load from DB 20 minutes and not loaded... I use Entity Framework like public ElectricScheme LoadScheme(int schemeId) { var eScheme = (from s in container.ElectricSchemesSet where s.IdElectricScheme.Equals(schemeId) select s).FirstOrDefault(); if (eScheme == null) return null; container.LoadProperty(eScheme, "Elements"); container.LoadProperty(eScheme, "Nets"); container.LoadProperty(eScheme, "Elements.Pins"); return eScheme; } The problem is dependencies between Element and Pin... (for ~19000 elements ~95000 pins) Any ideas?

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  • SQL Server - Missing Indexes - What would use the index?

    - by BankZ
    I am using SQL Server 2008 and we are using the DMV's to find missing indexes. However, before I create the new index I am trying to figure out what proc/query is wanting that index. I want the most information I can get so I can make informed decision on my indexes. Sometimes the indexes SQL Server wants does not make sense to me. Does anyone know how I can figure out what wants it?

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  • Nested loop traversing arrays

    - by alecco
    There are 2 very big series of elements, the second 100 times bigger than the first. For each element of the first series, there are 0 or more elements on the second series. This can be traversed and processed with 2 nested loops. But the unpredictability of the amount of matching elements for each member of the first array makes things very, very slow. The actual processing of the 2nd series of elements involves logical and (&) and a population count. I couldn't find good optimizations using C but I am considering doing inline asm, doing rep* mov* or similar for each element of the first series and then doing the batch processing of the matching bytes of the second series, perhaps in buffers of 1MB or something. But the code would be get quite messy. Does anybody know of a better way? C preferred but x86 ASM OK too. Many thanks! Sample/demo code with simplified problem, first series are "people" and second series are "events", for clarity's sake. (the original problem is actually 100m and 10,000m entries!) #include <stdio.h> #include <stdint.h> #define PEOPLE 1000000 // 1m struct Person { uint8_t age; // Filtering condition uint8_t cnt; // Number of events for this person in E } P[PEOPLE]; // Each has 0 or more bytes with bit flags #define EVENTS 100000000 // 100m uint8_t P1[EVENTS]; // Property 1 flags uint8_t P2[EVENTS]; // Property 2 flags void init_arrays() { for (int i = 0; i < PEOPLE; i++) { // just some stuff P[i].age = i & 0x07; P[i].cnt = i % 220; // assert( sum < EVENTS ); } for (int i = 0; i < EVENTS; i++) { P1[i] = i % 7; // just some stuff P2[i] = i % 9; // just some other stuff } } int main(int argc, char *argv[]) { uint64_t sum = 0, fcur = 0; int age_filter = 7; // just some init_arrays(); // Init P, P1, P2 for (int64_t p = 0; p < PEOPLE ; p++) if (P[p].age < age_filter) for (int64_t e = 0; e < P[p].cnt ; e++, fcur++) sum += __builtin_popcount( P1[fcur] & P2[fcur] ); else fcur += P[p].cnt; // skip this person's events printf("(dummy %ld %ld)\n", sum, fcur ); return 0; } gcc -O5 -march=native -std=c99 test.c -o test

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  • Best way to get distinct values from large table

    - by derivation
    I have a db table with about 10 or so columns, two of which are month and year. The table has about 250k rows now, and we expect it to grow by about 100-150k records a month. A lot of queries involve the month and year column (ex, all records from march 2010), and so we frequently need to get the available month and year combinations (ie do we have records for april 2010?). A coworker thinks that we should have a separate table from our main one that only contains the months and years we have data for. We only add records to our main table once a month, so it would just be a small update on the end of our scripts to add the new entry to this second table. This second table would be queried whenever we need to find the available month/year entries on the first table. This solution feels kludgy to me and a violation of DRY. What do you think is the correct way of solving this problem? Is there a better way than having two tables?

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  • Capture text typed by user on website and allow user to email a link to someone else so that they can view the message [on hold]

    - by Dano007
    Using the following html, css,jquery, js, what would be the best approach to achieving this. A visitor hits the website. The website page is displaying html and a css3 animation. The visitor is given the option to enter text freely into a text box, they enter an email address and hit send. The person receiving the message gets an email with a link, when they click the link it takes them to the webpage with the animation and the custom message their friend entered. Is this easy to achieve, what would be the best approach? anyone know of existing code I could use? Thanks

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  • PHP : flatten array - fastest way?

    - by Industrial
    Is there any fast way to flatten an array and select subkeys ('key'&'value' in this case) without running a foreach loop, or is the foreach always the fastest way? Array ( [0] => Array ( [key] => string [value] => a simple string [cas] => 0 ) [1] => Array ( [key] => int [value] => 99 [cas] => 0 ) [2] => Array ( [key] => array [value] => Array ( [0] => 11 [1] => 12 ) [cas] => 0 ) ) To: Array ( [int] => 99 [string] => a simple string [array] => Array ( [0] => 11 [1] => 12 ) )

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  • SQL Server - how to determine if indexes aren't being used?

    - by rwmnau
    I have a high-demand transactional database that I think is over-indexed. Originally, it didn't have any indexes at all, so adding some for common processes made a huge difference. However, over time, we've created indexes to speed up individual queries, and some of the most popular tables have 10-15 different indexes on them, and in some cases, the indexes are only slightly different from each other, or are the same columns in a different order. Is there a straightforward way to watch database activity and tell if any indexes are not hit anymore, or what their usage percentage is? I'm concerned that indexes were created to speed up either a single daily/weekly query, or even a query that's not being run anymore, but the index still has to be kept up to date every time the data changes. In the case of the high-traffic tables, that's a dozen times/second, and I want to eliminate indexes that are weighing down data updates while providing only marginal improvement.

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  • Start all tab's activities for pre-cache

    - by Pentium10
    I have a TabActivity with three tabs defined. The first tab is light-weight and renders in acceptable time. But the 2nd and 3rd tab, does need a couple of seconds to get visually rendered, after I click them. I would like to launch them, after I've loaded my first tab, in background for pre-cache. Once they are loaded, I can switch quickly between them. So I am wondering how can I launch the 2nd and 3rd tab. They are intents loaded in the view area.

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  • Does beginTransaction in Hibernate allocate a new DB connection?

    - by illscience
    Hi folks - Just wondering if beginning a new transaction in Hibernate actually allocates a connection to the DB? I'm concerned b/c our server begins a new transaction for each request received, even if that request doesn't interact with the DB. We're seeing DB connections as a major bottleneck, so I'm wondering if I should take the time narrow the scope of my transactions. Searched everywhere and haven't been able to find a good answer. The very simple code is here: SessionFactory sessionFactory = (SessionFactory) Context.getContext().getBean("sessionFactory"); sessionFactory.getCurrentSession().beginTransaction(); sessionFactory.getCurrentSession().setFlushMode(FlushMode.AUTO); thanks very much! a

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  • What is the time complexity of LinkedList.getLast() in Java?

    - by i.
    I have a private LinkedList in a Java class & will frequently need to retrieve the last element in the list. The lists need to scale, so I'm trying to decide whether I need to keep a reference to the last element when I make changes (to achieve O(1)) or if the LinkedList class does that already with the getLast() call. What is the big-O cost of LinkedList.getLast() and is it documented? (i.e. can I rely on this answer or should I make no assumptions & cache it even if it's O(1)?)

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  • Fastest way to read/store lots of multidimensional data? (Java)

    - by RemiX
    I have three questions about three nested loops: for (int x=0; x<400; x++) { for (int y=0; y<300; y++) { for (int z=0; z<400; z++) { // compute and store value } } } And I need to store all computed values. My standard approach would be to use a 3D-array: values[x][y][z] = 1; // test value but this turns out to be slow: it takes 192 ms to complete this loop, where a single int-assignment int value = 1; // test value takes only 66 ms. 1) Why is an array so relatively slow? 2) And why does it get even slower when I put this in the inner loop: values[z][y][x] = 1; // (notice x and z switched) This takes more than 4 seconds! 3) Most importantly: Can I use a data structure that is as quick as the assignment of a single integer, but can store as much data as the 3D-array?

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  • Why is Python so slow?

    - by Riemannliness
    Why is Python such a slow language, on average, compared to C/C++? I learned Python as my first programming language, but I've only just started with C and already I can feel and see the difference.

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