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  • Counting context switches per thread

    - by Sarmun
    Is there a way to see how many context switches each thread generates? (both in and out if possible) Either in X/s, or to let it run and give aggregated data after some time. (either on linux or on windows) I have found only tools that give aggregated context-switching number for whole os or per process. My program makes many context switches (50k/s), probably a lot not necessary, but I am not sure where to start optimizing, where do most of those happen.

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  • Long primitive or AtomicLong for a counter?

    - by Rich
    Hi I have a need for a counter of type long with the following requirements/facts: Incrementing the counter should take as little time as possible. The counter will only be written to by one thread. Reading from the counter will be done in another thread. The counter will be incremented regularly (as much as a few thousand times per second), but will only be read once every five seconds. Precise accuracy isn't essential, only a rough idea of the size of the counter is good enough. The counter is never cleared, decremented. Based upon these requirements, how would you choose to implement your counter? As a simple long, as a volatile long or using an AtomicLong? Why? At the moment I have a volatile long but was wondering whether another approach would be better. I am also incrementing my long by doing ++counter as opposed to counter++. Is this really any more efficient (as I have been led to believe elsewhere) because there is no assignment being done? Thanks in advance Rich

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  • Help me choose between XML or SQL Lite on android

    - by Ngetha
    I have an android app that periodically, say once a week downloads content from a server in XML. The content is used by the app, different Acitivities use different parts of the content. My question is a design one, should I save the data in SQlite or just keep it as an XML file, which one would be faster to read? The app can only use one content piece at a time, which means subsequent XML content downloads replace the old one.

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  • C: using a lot of structs can make a program slow?

    - by nunos
    I am coding a breakout clone. I had one version in which I only had one level deep of structures. This version runs at 70 fps. For more clarity in the code I decided the code should have more abstractions and created more structs. Most of the times I have two two three level deep of structures. This version runs at 30 fps. Since there are some other differences besides the structures, I ask you: Does using a lot of structs in C can slow down the code significantly? Thanks.

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  • finding long repeated substrings in a massive string

    - by Will
    I naively imagined that I could build a suffix trie where I keep a visit-count for each node, and then the deepest nodes with counts greater than one are the result set I'm looking for. I have a really really long string (hundreds of megabytes). I have about 1 GB of RAM. This is why building a suffix trie with counting data is too inefficient space-wise to work for me. To quote Wikipedia's Suffix tree: storing a string's suffix tree typically requires significantly more space than storing the string itself. The large amount of information in each edge and node makes the suffix tree very expensive, consuming about ten to twenty times the memory size of the source text in good implementations. The suffix array reduces this requirement to a factor of four, and researchers have continued to find smaller indexing structures. And that was wikipedia's comments on the tree, not trie. How can I find long repeated sequences in such a large amount of data, and in a reasonable amount of time (e.g. less than an hour on a modern desktop machine)? (Some wikipedia links to avoid people posting them as the 'answer': Algorithms on strings and especially Longest repeated substring problem ;-) )

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  • Way to know if two partitions are in one physical hard disk without WMI?

    - by Alon
    Hey. I have those partitions (in Windows) for example: Hard Disk 1 - Partition C, Partition D Hard Disk 2 - Partition E Is there any way in a program language to know if for example partition C and partition D are in one physical hard disk without WMI? I don't want to use WMI because it's slow - for this example, it took for me 0.5 seconds. I need it to be fast. Thank you.

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  • Slow first page load on asp.net site

    - by Tabloo Quijico
    Hi, Every now and then (always after a long period of idle-time, e.g. overnight) when I access a site built using asp.net - it takes around 15 seconds to load the page (15 seconds before I see any progress whatsoever, then the page comes up fast). Further pages on that site, or refreshes, are quick as usual - they are also fast on other machines, only the first one seems to take the 'hit'. Page tracing never through anything up (whole cycle was a fraction of a second) So my question is where else should I be looking? Perhaps IIS? Or could it still be my asp.net app and I'm just looking in the wrong place (the trace) for clues? As I don't have much control over the IIS server, anything I can check through asp.net would be more helpful, before I go ask that particular admin. cheers :D

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  • Speed up :visible:input selector avoiding filter

    - by macca1
    I have a jQuery selector that is running way too slow on my unfortunately large page: $("#section").find(":visible:input").filter(":first").focus(); Is there a quicker way to select the first visible input without having to find ALL the visible inputs and then filtering THAT selection for the first? I want something like :visible:input:first but that doesn't seem to work.

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  • JavaScript: Is there a better way to retain your array but efficiently concat or replace items?

    - by Michael Mikowski
    I am looking for the best way to replace or add to elements of an array without deleting the original reference. Here is the set up: var a = [], b = [], c, i, obj; for ( i = 0; i < 100000; i++ ) { a[ i ] = i; b[ i ] = 10000 - i; } obj.data_list = a; Now we want to concatenate b INTO a without changing the reference to a, since it is used in obj.data_list. Here is one method: for ( i = 0; i < b.length; i++ ) { a.push( b[ i ] ); } This seems to be a somewhat terser and 8x (on V8) faster method: a.splice.apply( a, [ a.length, 0 ].concat( b ) ); I have found this useful when iterating over an "in-place" array and don't want to touch the elements as I go (a good practice). I start a new array (let's call it keep_list) with the initial arguments and then add the elements I wish to retain. Finally I use this apply method to quickly replace the truncated array: var keep_list = [ 0, 0 ]; for ( i = 0; i < a.length; i++ ){ if ( some_condition ){ keep_list.push( a[ i ] ); } // truncate array a.length = 0; // And replace contents a.splice.apply( a, keep_list ); There are a few problems with this solution: there is a max call stack size limit of around 50k on V8 I have not tested on other JS engines yet. This solution is a bit cryptic Has anyone found a better way?

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  • effective counter for unique number of visits in PHP & MySQL

    - by Adnan
    Hello, I am creating a counter for unique number of visits on a post, so what I have until now is a table for storing data like this; cvp_post_id | cvp_ip | cvp_user_id In cases a registered user visits a post, for the first time a record is inserted with cpv_post_id and cvp_user_id, so for his next visit I query the table and if the record is available I do not count him as a new visitor. In cases of an anonymous user the same happens but now the cvp_ip and cpv_post_id are used. My concerns is that I do a query every time anyone visits a post for checking if there has been a visit, what would be a more effective way for doing this?

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  • Fastest way for inserting very large number of records into a Table in SQL

    - by Irchi
    The problem is, we have a huge number of records (more than a million) to be inserted into a single table from a Java application. The records are created by the Java code, it's not a move from another table, so INSERT/SELECT won't help. Currently, my bottleneck is the INSERT statements. I'm using PreparedStatement to speed-up the process, but I can't get more than 50 recods per second on a normal server. The table is not complicated at all, and there are no indexes defined on it. The process takes too long, and the time it takes will make problems. What can I do to get the maximum speed (INSERT per second) possible? Database: MS SQL 2008. Application: Java-based, using Microsoft JDBC driver.

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  • Cache bandwidth per tick for modern CPUs

    - by osgx
    Hello What is a speed of cache accessing for modern CPUs? How many bytes can be read or written from memory every processor clock tick by Intel P4, Core2, Corei7, AMD? Please, answer with both theoretical (width of ld/sd unit with its throughput in uOPs/tick) and practical numbers (even memcpy speed tests, or STREAM benchmark), if any. PS it is question, related to maximal rate of load/store instructions in assembler. There can be theoretical rate of loading (all Instructions Per Tick are widest loads), but processor can give only part of such, a practical limit of loading.

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  • Are conditional subqueries optimized out, if the condition is false?

    - by Tobias Schulte
    I have a table foo and a table bar, where each foo might have a bar (and a bar might belong to multiple foos). Now I need to select all foos with a bar. My sql looks like this SELECT * FROM foo f WHERE [...] AND ($param IS NULL OR (SELECT ((COUNT(*))>0) FROM bar b WHERE f.bar = b.id)) with $param being replaced at runtime. The question is: Will the subquery be executed even if param is null, or will the dbms optimize the subquery out? We are using mysql, mssql and oracle. Is there a difference between these regarding the above?

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  • Read large amount of data from file in Java

    - by Crozin
    Hello I've got text file that contains 1 000 002 numbers in following formation: 123 456 1 2 3 4 5 6 .... 999999 100000 Now I need to read that data and allocate it to int variables (the very first two numbers) and all the rest (1 000 000 numbers) to an array int[]. It's not a hard task, but - it's horrible slow. My first attempt was java.util.Scanner: Scanner stdin = new Scanner(new File("./path")); int n = stdin.nextInt(); int t = stdin.nextInt(); int array[] = new array[n]; for (int i = 0; i < n; i++) { array[i] = stdin.nextInt(); } It works as excepted but it takes about 7500 ms to execute. I need to fetch that data in up to several hundred of milliseconds. Then I tried java.io.BufferedReader: Using BufferedReader.readLine() and String.split() I got the same results in about 1700 ms, but it's still too many. How can I read that amount of data in less that 1 second? The final result should be equal to: int n = 123; int t = 456; int array[] = { 1, 2, 3, 4, ..., 999999, 100000 };

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  • Converting keys of an array/object-tree to lowercase

    - by tstenner
    Im currently optimizing a PHP application and found one function being called around 10-20k times, so I'd thought I'd start optimization there. function keysToLower($obj) { if(!is_object($obj) && !is_array($obj)) return $obj; foreach($obj as $key=>$element) { $element=keysToLower($element); if(is_object($obj)) { $obj->{strtolower($key)}=$element; if(!ctype_lower($key)) unset($obj->{$key}); } else if(is_array($obj) && ctype_upper($key)) { $obj[strtolower($key)]=$element; unset($obj[$key]); } } return $obj; } Most of the time is spent in recursive calls (which are quite slow in PHP), but I don't see any way to convert it to a loop. What would you do?

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  • Intersection() and Except() is too slow with large collections of custom objects

    - by Theo
    I am importing data from another database. My process is importing data from a remote DB into a List<DataModel> named remoteData and also importing data from the local DB into a List<DataModel> named localData. I am then using LINQ to create a list of records that are different so that I can update the local DB to match the data pulled from remote DB. Like this: var outdatedData = this.localData.Intersect(this.remoteData, new OutdatedDataComparer()).ToList(); I am then using LINQ to create a list of records that no longer exist in remoteData, but do exist in localData, so that I delete them from local database. Like this: var oldData = this.localData.Except(this.remoteData, new MatchingDataComparer()).ToList(); I am then using LINQ to do the opposite of the above to add the new data to the local database. Like this: var newData = this.remoteData.Except(this.localData, new MatchingDataComparer()).ToList(); Each collection imports about 70k records, and each of the 3 LINQ operation take between 5 - 10 minutes to complete. How can I make this faster? Here is the object the collections are using: internal class DataModel { public string Key1{ get; set; } public string Key2{ get; set; } public string Value1{ get; set; } public string Value2{ get; set; } public byte? Value3{ get; set; } } The comparer used to check for outdated records: class OutdatedDataComparer : IEqualityComparer<DataModel> { public bool Equals(DataModel x, DataModel y) { var e = string.Equals(x.Key1, y.Key1) && string.Equals(x.Key2, y.Key2) && ( !string.Equals(x.Value1, y.Value1) || !string.Equals(x.Value2, y.Value2) || x.Value3 != y.Value3 ); return e; } public int GetHashCode(DataModel obj) { return 0; } } The comparer used to find old and new records: internal class MatchingDataComparer : IEqualityComparer<DataModel> { public bool Equals(DataModel x, DataModel y) { return string.Equals(x.Key1, y.Key1) && string.Equals(x.Key2, y.Key2); } public int GetHashCode(DataModel obj) { return 0; } }

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  • Java JRE vs GCJ

    - by Martijn Courteaux
    Hi, I have this results from a speed test I wrote in Java: Java real 0m20.626s user 0m20.257s sys 0m0.244s GCJ real 3m10.567s user 3m5.168s sys 0m0.676s So, what is the but of GCJ then? With this results I'm sure I'm not going to compile it with GCJ! I tested this on Linux, are the results in Windows maybe better than that? This was the code from the application: public static void main(String[] args) { String str = ""; System.out.println("Start!!!"); for (long i = 0; i < 5000000L; i++) { Math.sqrt((double) i); Math.pow((double) i, 2.56); long j = i * 745L; String string = new String(String.valueOf(i)); string = string.concat(" kaka pipi"); // "Kaka pipi" is a kind of childly call in Dutch. string = new String(string.toUpperCase()); if (i % 300 == 0) { str = ""; } else { str += Long.toHexString(i); } } System.out.println("Stop!!!"); }

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  • Visual Studio 2010 - Is it slow for anyone else?

    - by AngryHacker
    I've read a lot of stuff about VS2010 being much more performant than VS2008. When I've finally installed it, I found that it, in fact, is much slower (save for the Add References dialog). For instance, Silverlight projects take twice as long to load, the startup of the IDE itself is much slower, etc... Am I missing something here or is it like this for everyone?

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  • Running Boggle Solver takes over an hour to run. What is wrong with my code?

    - by user1872912
    So I am running a Boggle Solver in java on the NetBeans IDE. When I run it, i have to quit after 10 minutes or so because it will end up taking about 2 hour to run completely. Is there something wrong with my code or a way that will make is substantially faster? public void findWords(String word, int iLoc, int jLoc, ArrayList<JLabel> labelsUsed){ if(iLoc < 0 || iLoc >= 4 || jLoc < 0 || jLoc >= 4){ return; } if(labelsUsed.contains(jLabels[iLoc][jLoc])){ return; } word += jLabels[iLoc][jLoc].getText(); labelsUsed.add(jLabels[iLoc][jLoc]); if(word.length() >= 3 && wordsPossible.contains(word)){ wordsMade.add(word); } findWords(word, iLoc-1, jLoc, labelsUsed); findWords(word, iLoc+1, jLoc, labelsUsed); findWords(word, iLoc, jLoc-1, labelsUsed); findWords(word, iLoc, jLoc+1, labelsUsed); findWords(word, iLoc-1, jLoc+1, labelsUsed); findWords(word, iLoc-1, jLoc-1, labelsUsed); findWords(word, iLoc+1, jLoc-1, labelsUsed); findWords(word, iLoc+1, jLoc+1, labelsUsed); labelsUsed.remove(jLabels[iLoc][jLoc]); } here is where I call this method from: public void findWords(){ ArrayList <JLabel> labelsUsed = new ArrayList<JLabel>(); for(int i=0; i<jLabels.length; i++){ for(int j=0; j<jLabels[i].length; j++){ findWords(jLabels[i][j].getText(), i, j, labelsUsed); //System.out.println("Done"); } } } edit: BTW I am using a GUI and the letters on the board are displayed by using a JLabel.

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  • JAVA bytecode optimization

    - by Idob
    This is a basic question. I have code which shouldn't run on metadata beans. All metadata beans are located under metadata package. Now, I use reflection API to find out whether a class is located in the the metadata package. if (newEntity.getClass().getPackage().getName().contains("metadata")) I use this If in several places within this code. The question is: Should I do this once with: boolean isMetadata = false if (newEntity.getClass().getPackage().getName().contains("metadata")) { isMetadata = true; } C++ makes optimizations and knows that this code was already called and it won't call it again. Does JAVA makes optimization? I know reflection API is a beat heavy and I prefer not to lose expensive runtime.

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  • Why is Dictionary.First() so slow?

    - by Rotsor
    Not a real question because I already found out the answer, but still interesting thing. I always thought that hash table is the fastest associative container if you hash properly. However, the following code is terribly slow. It executes only about 1 million iterations and takes more than 2 minutes of time on a Core 2 CPU. The code does the following: it maintains the collection todo of items it needs to process. At each iteration it takes an item from this collection (doesn't matter which item), deletes it, processes it if it wasn't processed (possibly adding more items to process), and repeats this until there are no items to process. The culprit seems to be the Dictionary.Keys.First() operation. The question is why is it slow? Stopwatch watch = new Stopwatch(); watch.Start(); HashSet<int> processed = new HashSet<int>(); Dictionary<int, int> todo = new Dictionary<int, int>(); todo.Add(1, 1); int iterations = 0; int limit = 500000; while (todo.Count > 0) { iterations++; var key = todo.Keys.First(); var value = todo[key]; todo.Remove(key); if (!processed.Contains(key)) { processed.Add(key); // process item here if (key < limit) { todo[key + 13] = value + 1; todo[key + 7] = value + 1; } // doesn't matter much how } } Console.WriteLine("Iterations: {0}; Time: {1}.", iterations, watch.Elapsed); This results in: Iterations: 923007; Time: 00:02:09.8414388. Simply changing Dictionary to SortedDictionary yields: Iterations: 499976; Time: 00:00:00.4451514. 300 times faster while having only 2 times less iterations. The same happens in java. Used HashMap instead of Dictionary and keySet().iterator().next() instead of Keys.First().

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