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  • C# DLL Deployed in COM+. Error while accessing the methods.

    - by Dakshinamurthy
    I have the C# Dll (ABService) deployed in COM + and my os Is windows 2008. I have given the strong name for this dll and its dependent dll’s When I access the method of this dll through localhost or if I add the reference to the client project the method are executed successfully. Simply if I access the dll from the same machine with the reference it is working. So I think there is no problem with the way I deployed in the COM +. I have the doubt whether I have the problem in OS and Visual Studio 2008 combination. I have built all the dll with the Visual Studio 2008 with Target cpu as x86 and targert framework as 2.0. I have given in below the codes I have tried with and the errors. I need to create the object for the dll in server machine(64 bit) and access its method from the client(32 bit) Code : Type svr = Type.GetTypeFromProgID("ABService.Service", strserver1url[2],false); ABService.Service service1= (ABService.Service)Activator.CreateInstance(svr); strresult = service1.ExecuteService(orequest.xml); Error :{"Retrieving the COM class factory for remote component with CLSID {77BF00E0-41AC-3967-9E72-A4927CC0B880} from machine 10.105.138.64 failed due to the following error: 80040154."} Code Type svr = Type.GetTypeFromProgID("ABService.Service", strserver1url[2],true); object Service1 = null; Service1 = (ABService.Service)Activator.CreateInstance(svr, true); strresult = Convert.ToString(ReflectionHelper.Invoke(Service1, "ExecuteService", new object[] { orequest.xml })); Service1 = null; Error: Retrieving the COM class factory for remote component with CLSID {77BF00E0-41AC-3967-9E72-A4927CC0B880} from machine ftpsite failed due to the following error: 80040154. With the below code instead of C#.Net dll if i have the vb dll in Com + the method is executed successfully. Code ords = new RDS.DataSpace(); ords.InternetTimeout = 600000; object M_Service = null; ABService.Service oabservice = null; M_Service = ords.CreateObject("ABService.Service",url); strresult = Convert.ToString(ReflectionHelper.Invoke(M_Service, "ExecuteService", new object[] { orequest.xml })); Error : {"Object doesn't support this property or method 'ExecuteService'"} Code object obj=Interaction.CreateObject("ABService.Service", "10.105.138.64"); strresult = Convert.ToString(ReflectionHelper.Invoke(obj, "ExecuteService", new object[] { orequest.xml })); Error: {"Cannot create ActiveX component."} Code object obj = Activator.GetObject(typeof(ABService.Service), @"http://10.105.138.64:80/ABANET"); strresult = Convert.ToString(ReflectionHelper.Invoke(obj, "ExecuteService", new object[] { orequest.xml })); Error: InnerException {"The remote server returned an error: (405) Method Not Allowed."} System.Exception {System.Net.WebException} Message "Exception has been thrown by the target of an invocation.”

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  • How to do the processing and keep GUI refreshed using databinding?

    - by macias
    History of the problem This is continuation of my previous question How to start a thread to keep GUI refreshed? but since Jon shed new light on the problem, I would have to completely rewrite original question, which would make that topic unreadable. So, new, very specific question. The problem Two pieces: CPU hungry heavy-weight processing as a library (back-end) WPF GUI with databinding which serves as monitor for the processing (front-end) Current situation -- library sends so many notifications about data changes that despite it works within its own thread it completely jams WPF data binding mechanism, and in result not only monitoring the data does not work (it is not refreshed) but entire GUI is frozen while processing the data. The aim -- well-designed, polished way to keep GUI up to date -- I am not saying it should display the data immediately (it can skip some changes even), but it cannot freeze while doing computation. Example This is simplified example, but it shows the problem. XAML part: <StackPanel Orientation="Vertical"> <Button Click="Button_Click">Start</Button> <TextBlock Text="{Binding Path=Counter}"/> </StackPanel> C# part (please NOTE this is one piece code, but there are two sections of it): public partial class MainWindow : Window,INotifyPropertyChanged { // GUI part public MainWindow() { InitializeComponent(); DataContext = this; } private void Button_Click(object sender, RoutedEventArgs e) { var thread = new Thread(doProcessing); thread.IsBackground = true; thread.Start(); } // this is non-GUI part -- do not mess with GUI here public event PropertyChangedEventHandler PropertyChanged; public void OnPropertyChanged(string property_name) { if (PropertyChanged != null) PropertyChanged(this, new PropertyChangedEventArgs(property_name)); } long counter; public long Counter { get { return counter; } set { if (counter != value) { counter = value; OnPropertyChanged("Counter"); } } } void doProcessing() { var tmp = 10000.0; for (Counter = 0; Counter < 10000000; ++Counter) { if (Counter % 2 == 0) tmp = Math.Sqrt(tmp); else tmp = Math.Pow(tmp, 2.0); } } } Known workarounds (Please do not repost them as answers) Those two first are based on Jon ideas: pass GUI dispatcher to library and use it for sending notifications -- why it is ugly? because it could be no GUI at all give up with data binding COMPLETELY (one widget with databinding is enough for jamming), and instead check from time to time data and update the GUI manually -- well, I didn't learn WPF just to give up with it now ;-) and this is mine, it is ugly, but simplicity of it kills -- before sending notification freeze a thread -- Thread.Sleep(1) -- to let the potential receiver "breathe" -- it works, it is minimalistic, it is ugly though, and it ALWAYS slows down computation even if no GUI is there So... I am all ears for real solutions, not some tricks.

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  • JSON or YAML encoding in GWT/Java on both client and server

    - by KennethJ
    I'm looking for a super simple JSON or YAML library (not particularly bothered which one) written in Java, and can be used in both GWT on the client, and in its original Java form on the server. What I'm trying to do is this: I have my models, which are shared between the client and the server, and these are the primary source of data interchange. I want to design the web service in between to be as simple as possible, and decided to take the RESTful approach. My problem is that I know our application will grow substantially in the future, and writing all the getters, setters, serialization, factories, etc. by hand fills me with absolute dread. So in order to avoid it, I decided to implement annotations to keep track of attributes on the models. The reason I can't just serialize everything directly, using GWT's own one, or one which works through reflection, is because we need a certain amount of logic going on in the serialization process. I.e. whether references to other models get serialized during the serialization of the original model, or whether an ID is just passed, and general simple things like that. I've then written an annotation processor to preprocess my shared models and generate an implementing class with all the getters, setters, serialization, lazy-loading, etc. To make a long story short, I need some type of simple YAML or JSON library, which allows me to encode and decode manually, so I can generate this code through my annotation processor. I have had a look around the interwebs, but every single one I ran into supported some reflection which, while all fine and dandy, make it pretty much useless for GWT. And in the case of GWT's own JSON library, it uses JSNI for speed purposes, making it useless server side. One solution I did think about involved writing writing two sets of serialization methods on the models, one for the client and one for the server, but I'd rather not do that. Also, I'm pretty new to GWT, and even though I have done a lot of Java, it was back in the 1.2 days, so it's a bit rusty. So if you think I'm going about this problem completely the wrong way, I'm open to suggestions.

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  • jquery xml slideshow using ajax

    - by Codemaster Snake
    Hi all, I am trying to create a JQuery based slider using ajax to load images url from a xml file and then creating a html li list dynamically. Till now I am able to append and create DOM structure using Jquery. But I am not able to access the dynamically created list. I have also tried custom events using bind but not able to successfully implement it. Following is my jquery plugin code: (function($){ $.fn.genie = function(options) { var genie_dom = "<div class='genie_wrapper'><ul class='genie'></ul></div>"; var o, base; var genie_styles = "<style>.genie_wrapper{overflow:hidden}.genie{position: relative;margin:0;padding:0}.genie li {position: absolute;margin:0;padding:0}</style>"; var defaults = { width : '960px', height : '300px', background_color : '#000000', xml : 'genie.xml', speed : 1000, pause: 1000 }; base = $(this); o = $.extend(defaults, options); return this.each(function() { create_elements(); }); function create_elements() { $(base).html(genie_dom); $('head').append(genie_styles); $('.genie_wrapper').css({'background-color' : o.background_color, width : o.width, height: '300px', overflow: ''}); $.ajax({ type: "GET", url: o.xml, dataType: "xml", success: function(xml) { var slides = $(xml).find('slide'); var count = 0; $(slides).each(function(){ $('.genie').append('<li class="slide" id="slide'+count+'"><img src="' + $(this).text() + '" /></li>'); $('.genie li:last').css({'z-index' : count}); count++; }); } }); } } })(jQuery); In my html file: There is only one empty div to which I am calling my plugin like $(document).ready(function() { $('.slideshow').genie(); }); I have also tried using following everywhere in JS: $(".slide").bind("start_animation", function(e){ $(this).fadeOut(1000); alert($(this).html()); }); $(".slide").trigger("start_animation"); I want to animate li list using animate function, Can anyone please tell me how to implement it... It would be of great help... Regards, Neeraj Kumar EDIT: Can Anyone help me out please????

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  • How to remove music/videos DRM protection and convert to Mobile Devices such as iPod, iPhone, PSP, Z

    - by tonywesley
    The music/video files you purchased from online music stores like iTunes, Yahoo Music or Wal-Mart are under DRM protection. So you can't convert them to the formats supported by your own mobile devices such as Nokia phone, Creative Zen palyer, iPod, PSP, Walkman, Zune… You also can't share your purchased music/videos with your friends. The following step by step tutorial is dedicated to instructing music lovers to how to convert your DRM protected music/videos to mobile devices. Method 1: If you only want to remove DRM protection from your protected music, this method will not spend your money. Step 1: Burn your protected music files to CD-R/RW disc to make an audio CD Step 2: Find a free CD Ripper software to convert the audio CD track back to MP3, WAV, WMA, M4A, AAC, RA… Method 2: This guide will show you how to crack drm from protected wmv, wma, m4p, m4v, m4a, aac files and convert to unprotected WMV, MP4, MP3, WMA or any video and audio formats you like, such as AVI, MP4, Flv, MPEG, MOV, 3GP, m4a, aac, wmv, ogg, wav... I have been using Media Converter software, it is the quickest and easiest solution to remove drm from WMV, M4V, M4P, WMA, M4A, AAC, M4B, AA files by quick recording. It gets audio and video stream at the bottom of operating system, so the output quality is lossless and the conversion speed is fast . The process is as follows. Step 1: Download and install the software Step 2: Run the software and click "Add…" button to load WMA or M4A, M4B, AAC, WMV, M4P, M4V, ASF files Step 3: Choose output formats. If you want to convert protected audio files, please select "Convert audio to" list; If you want to convert protected video files, please select "Convert video to" list. Step 4: You can click "Settings" button to custom preference for output files. Click "Settings" button bellow "Convert audio to" list for protected audio files Click "Settings" button bellow "Convert video to" list for protected video files Step 5: Start remove DRM and convert your DRM protected music and videos by click on "Start" button. What is DRM? DRM, which is most commonly found in movies and music files, doesn't mean just basic copy-protection of video, audio and ebooks, but it basically means full protection for digital content, ranging from delivery to end user's ways to use the content. We can remove the Drm from video and audio files legally by quick recording.

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  • Memory corruption in System.Move due to changed 8087CW mode (png + stretchblt)

    - by André Mussche
    I have strange a memory corruption problem. After many hours debugging and trying I think I found something. For example: I do a simple string assignment: sTest := 'SET LOCK_TIMEOUT '; However, the result sometimes becomes: sTest = 'SET LOCK'#0'TIMEOUT ' So, the _ gets replaced by an 0 byte. I have seen this happening once (reproducing is tricky, dependent on timing) in the System.Move function, when it uses the FPU stack (fild, fistp) for fast memory copy (in case of 9 till 32 bytes to move): ... @@SmallMove: {9..32 Byte Move} fild qword ptr [eax+ecx] {Load Last 8} fild qword ptr [eax] {Load First 8} cmp ecx, 8 jle @@Small16 fild qword ptr [eax+8] {Load Second 8} cmp ecx, 16 jle @@Small24 fild qword ptr [eax+16] {Load Third 8} fistp qword ptr [edx+16] {Save Third 8} ... Using the FPU view and 2 memory debug views (Delphi - View - Debug - CPU - Memory) I saw it going wrong... once... could not reproduce however... This morning I read something about the 8087CW mode, and yes, if this is changed into $27F I get memory corruption! Normally it is $133F: The difference between $133F and $027F is that $027F sets up the FPU for doing less precise calculations (limiting to Double in stead of Extended) and different infiniti handling (which was used for older FPU’s, but is not used any more). Okay, now I found why but not when! I changed the working of my AsmProfiler with a simple check (so all functions are checked at enter and leave): if Get8087CW = $27F then //normally $1372? if MainThreadID = GetCurrentThreadId then //only check mainthread DebugBreak; I "profiled" some units and dll's and bingo (see stack): Windows.StretchBlt(3372289943,0,0,514,345,4211154027,0,0,514,345,13369376) pngimage.TPNGObject.DrawPartialTrans(4211154027,(0, 0, 514, 345, (0, 0), (514, 345))) pngimage.TPNGObject.Draw($7FF62450,(0, 0, 514, 345, (0, 0), (514, 345))) Graphics.TCanvas.StretchDraw((0, 0, 514, 345, (0, 0), (514, 345)),$7FECF3D0) ExtCtrls.TImage.Paint Controls.TGraphicControl.WMPaint((15, 4211154027, 0, 0)) So it is happening in StretchBlt... What to do now? Is it a fault of Windows, or a bug in PNG (included in D2007)? Or is the System.Move function not failsafe?

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  • A better way to delete a list of elements from multiple tables

    - by manyxcxi
    I know this looks like a 'please write the code' request, but some basic pointer/principles for doing this the right way should be enough to get me going. I have the following stored procedure: CREATE PROCEDURE `TAA`.`runClean` (IN idlist varchar(1000)) BEGIN DECLARE EXIT HANDLER FOR NOT FOUND ROLLBACK; DECLARE EXIT HANDLER FOR SQLEXCEPTION ROLLBACK; DECLARE EXIT HANDLER FOR SQLWARNING ROLLBACK; START TRANSACTION; DELETE FROM RunningReports WHERE run_id IN (idlist); DELETE FROM TMD_INDATA_INVOICE WHERE run_id IN (idlist); DELETE FROM TMD_INDATA_LINE WHERE run_id IN (idlist); DELETE FROM TMD_OUTDATA_INVOICE WHERE run_id IN (idlist); DELETE FROM TMD_OUTDATA_LINE WHERE run_id IN (idlist); DELETE FROM TMD_TEST WHERE run_id IN (idlist); DELETE FROM RunHistory WHERE id IN (idlist); COMMIT; END $$ It is called by a PHP script to clean out old run history. It is not particularly efficient as you can see and I would like to speed it up. The PHP script gathers the ids to remove from the tables with the following query: $query = "SELECT id, stop_time FROM RunHistory WHERE config_id = $configId AND save = 0 AND NOT(stop_time IS NULL) ORDER BY stop_time"; It keeps the last five run entries and deletes all the rest. So using this query to bring back all the IDs, it determines which ones to delete and keeps the 'newest' five. After gathering the IDs it sends them to the stored procedure to remove them from the associated tables. I'm not very good with SQL, but I ASSUME that using an IN statement and not joining these tables together is probably the least efficient way I can do this, but I don't know enough to ask anything but "how do I do this better?" If possible, I would like to do this all in my stored procedure using a query to gather all the IDs except for the five 'newest', then delete them. Another twist, run entries can be marked save (save = 1) and should not be deleted. The RunHistory table looks like this: CREATE TABLE `TAA`.`RunHistory` ( `id` int(11) NOT NULL auto_increment, `start_time` datetime default NULL, `stop_time` datetime default NULL, `config_id` int(11) NOT NULL, [...] `save` tinyint(1) NOT NULL default '0', PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=0 DEFAULT CHARSET=utf8;

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  • Moving a unit precisely along a path in x,y coordinates

    - by Adam Eberbach
    I am playing around with a strategy game where squads move around a map. Each turn a certain amount of movement is allocated to a squad and if the squad has a destination the points are applied each turn until the destination is reached. Actual distance is used so if a squad moves one position in the x or y direction it uses one point, but moving diagonally takes ~1.4 points. The squad maintains actual position as float which is then rounded to allow drawing the position on the map. The path is described by touching the squad and dragging to the end position then lifting the pen or finger. (I'm doing this on an iPhone now but Android/Qt/Windows Mobile would work the same) As the pointer moves x, y points are recorded so that the squad gains a list of intermediate destinations on the way to the final destination. I'm finding that the destinations are not evenly spaced but can be further apart depending on the speed of the pointer movement. Following the path is important because obstacles or terrain matter in this game. I'm not trying to remake Flight Control but that's a similar mechanic. Here's what I've been doing, but it just seems too complicated (pseudocode): getDestination() { - self.nextDestination = remove_from_array(destinations) - self.gradient = delta y to destination / delta x to destination - self.angle = atan(self.gradient) - self.cosAngle = cos(self.angle) - self.sinAngle = sin(self.angle) } move() { - get movement allocation for this turn - if self.nextDestination not valid - - getNextDestination() - while(nextDestination valid) && (movement allocation remains) { - - find xStep and yStep using movement allocation and sinAngle/cosAngle calculated for current self.nextDestination - - if current position + xStep crosses the destination - - - find x movement remaining after self.nextDestination reached - - - calculate remaining direct path movement allocation (xStep remaining / cosAngle) - - - make self.position equal to self.nextDestination - - else - - - apply xStep and yStep to current position - } - round squad's float coordinates to integer screen coordinates - draw squad image on map } That's simplified of course, stuff like sign needs to be tweaked to ensure movement is in the right direction. If trig is the best way to do it then lookup tables can be used or maybe it doesn't matter on modern devices like it used to. Suggestions for a better way to do it? an update - iPhone has zero issues with trig and tracking tens of positions and tracks implemented as described above and it draws in floats anyway. The Bresenham method is more efficient, trig is more precise. If I was to use integer Bresenham I would want to multiply by ten or so to maintain a little more positional accuracy to benefit collisions/terrain detection.

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  • Improving performance on data pasting 2000 rows with validations

    - by Lohit
    I have N rows (which could be nothing less than 1000) on an excel spreadsheet. And in this sheet our project has 150 columns like this: Now, our application needs data to be copied (using normal Ctrl+C) and pasted (using Ctrl+V) from the excel file sheet on our GUI sheet. Copy pasting 1000 records takes around 5-6 seconds which is okay for our requirement, but the problem is when we need to make sure the data entered is valid. So we have to validate data in each row generate appropriate error messages and format the data as per requirement. So we need to at runtime parse and evaluate data in each row. Now all the formatting of data and validations come from the back-end database and we have it in a data-table (dtValidateAndFormatConditions). The conditions would be around 50. So you can see how slow this whole process becomes since N X 150 X 50 operations are required to complete this whole process. Initially it took approximately 2-3 minutes but now i have reduced it to 20 - 30 seconds. However i have increased the speed by making an expression parser of my own - and not by any algorithm, is there any other way i can improve performance, by using Divide and Conquer or some other mechanism. Currently i am not really sure how to go about this. Here is what part of my code looks like: public virtual void ValidateAndFormatOnCopyPaste(DataTable DtCopied, int CurRow) { foreach (DataRow dRow in dtValidateAndFormatConditions.Rows) { string Condition = dRow["Condition"]; string FormatValue = Value = dRow["Value"]; GetValidatedFormattedData(DtCopied,ref Condition, ref FormatValue ,iRowIndex); Condition = Parse(Condition); dRow["Condition"] = Condition; FormatValue = Parse(FormatValue ); dRow["Value"] = FormatValue; } } The above code gets called row-wise like this: public override void ValidateAndFormat(DataTable dtChangedRecords, CellRange cr) { int iRowStart = cr.Row, iRowEnd = cr.Row + cr.RowCount; for (int iRow = iRowStart; iRow < iRowEnd; iRow++) { ValidateAndFormatOnCopyPaste(dtChangedRecords,iRow); } } Please know my question needs a more algorithmic solution than code optimization, however any answers containing code related optimizations will be appreciated as well. (Tagged Linq because although not seen i have been using linq in some parts of my code).

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  • SQL/Schema comparison and upgrade

    - by Workshop Alex
    I have a simple situation. A large organisation is using several different versions of some (desktop) application and each version has it's own database structure. There are about 200 offices and each office will have it's own version, which can be one of 7 different ones. The company wants to upgrade all applications to the latest versions, which will be version 8. The problem is that they don't have a separate database for each version. Nor do they have a separate database for each office. They have one single database which is handled by a dedicated server, thus keeping things like management and backups easier. Every office has it's own database schema and within the schema there's the whole database structure for their specific application version. As a result, I'm dealing with 200 different schema's which need to be upgraded, each with 7 possible versions. Fortunately, every schema knows the proper version so checking the version isn't difficult. But my problem is that I need to create upgrade scripts which can upgrade from version 1 to version 2 to version 3 to etc... Basically, all schema's need to be bumped up one version until they're all version 8. Writing the code that will do this is no problem. the challenge is how to create the upgrade script from one version to the other? Preferably with some automated tool. I've examined RedGate's SQL Compare and Altova's DatabaseSpy but they're not practical. Altova is way too slow. RedGate requires too much processing afterwards, since the generated SQL Script still has a few errors and it refers to the schema name. Furthermore, the code needs to become part of a stored procedure and the code generated by RedGate doesn't really fit inside a single procedure. (Plus, it's doing too much transaction-handling, while I need everything within a single transaction. I have been considering using another SQL Comparison tool but it seems to me that my case is just too different from what standard tools can deliver. So I'm going to write my own comparison tool. To do this, I'll be using ADOX with Delphi to read the catalogues for every schema version in the database, then use this to write the SQL Statements that will need to upgrade these schema's to their next version. (Comparing 1 with 2, 2 with 3, 3 with 4, etc.) I'm not unfamiliar with generating SQL-Script-Generators so I don't expect too many problems. And I'll only be upgrading the table structures, not any of the other database objects. So, does anyone have some good tips and tricks to apply when doing this kind of comparisons? Things to be aware of? Practical tips to increase speed?

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  • Migrating from hand-written persistence layer to ORM

    - by Sergey Mikhanov
    Hi community, We are currently evaluating options for migrating from hand-written persistence layer to ORM. We have a bunch of legacy persistent objects (~200), that implement simple interface like this: interface JDBC { public long getId(); public void setId(long id); public void retrieve(); public void setDataSource(DataSource ds); } When retrieve() is called, object populates itself by issuing handwritten SQL queries to the connection provided using the ID it received in the setter (this usually is the only parameter to the query). It manages its statements, result sets, etc itself. Some of the objects have special flavors of retrive() method, like retrieveByName(), in this case a different SQL is issued. Queries could be quite complex, we often join several tables to populate the sets representing relations to other objects, sometimes join queries are issued on-demand in the specific getter (lazy loading). So basically, we have implemented most of the ORM's functionality manually. The reason for that was performance. We have very strong requirements for speed, and back in 2005 (when this code was written) performance tests has shown that none of mainstream ORMs were that fast as hand-written SQL. The problems we are facing now that make us think of ORM are: Most of the paths in this code are well-tested and are stable. However, some rarely-used code is prone to result set and connection leaks that are very hard to detect We are currently squeezing some additional performance by adding caching to our persistence layer and it's a huge pain to maintain the cached objects manually in this setup Support of this code when DB schema changes is a big problem. I am looking for an advice on what could be the best alternative for us. As far as I know, ORMs has advanced in last 5 years, so it might be that now there's one that offers an acceptable performance. As I see this issue, we need to address those points: Find some way to reuse at least some of the written SQL to express mappings Have the possibility to issue native SQL queries without the necessity to manually decompose their results (i.e. avoid manual rs.getInt(42) as they are very sensitive to schema changes) Add a non-intrusive caching layer Keep the performance figures. Is there any ORM framework you could recommend with regards to that?

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  • What is fastest way to convert bool to byte?

    - by Amir Rezaei
    What is fastest way to convert bool to byte? I want this mapping: False=0, True=1 Note: I don't want to use any if statement. Update: I don't want to use conditional statement. I don't want the CPU to halt or guess next statement. I want to optimize this code: private static string ByteArrayToHex(byte[] barray) { char[] c = new char[barray.Length * 2]; byte k; for (int i = 0; i < barray.Length; ++i) { k = ((byte)(barray[i] >> 4)); c[i * 2] = (char)(k > 9 ? k + 0x37 : k + 0x30); k = ((byte)(barray[i] & 0xF)); c[i * 2 + 1] = (char)(k > 9 ? k + 0x37 : k + 0x30); } return new string(c); } Update: The length of the array is very large, it's in terabyte order! Therefore I need to do optimization if possible. I shouldn't need to explain my self. The question is still valid. Update: I'm working on a project and looking at others code. That's why I didn't provide with the function at first place. I didn't want to spend time on explaining for people when they have opinion about the code. I shouldn’y need to provide in my question the background of my work, and a function that is not written by me. I have started to optimize it part by part. If I needed help with the whole function I would asked that in another question. That is why I asked this very simple at the beginning. Unfortunately people couldn’t keep themselves to the question. So please if you want to help answer the question. Update: For dose who want to see the point of this question. This example shows how two if statement are reduced from the code. byte A = k > 9 ; //If it was possible (k>9) == 0 || 1 c[i * 2] = A * (k + 0x30) - (A - 1) * (k + 0x30);

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  • Implementing coroutines in Java

    - by JUST MY correct OPINION
    This question is related to my question on existing coroutine implementations in Java. If, as I suspect, it turns out that there is no full implementation of coroutines currently available in Java, what would be required to implement them? As I said in that question, I know about the following: You can implement "coroutines" as threads/thread pools behind the scenes. You can do tricksy things with JVM bytecode behind the scenes to make coroutines possible. The so-called "Da Vinci Machine" JVM implementation has primitives that make coroutines doable without bytecode manipulation. There are various JNI-based approaches to coroutines also possible. I'll address each one's deficiencies in turn. Thread-based coroutines This "solution" is pathological. The whole point of coroutines is to avoid the overhead of threading, locking, kernel scheduling, etc. Coroutines are supposed to be light and fast and to execute only in user space. Implementing them in terms of full-tilt threads with tight restrictions gets rid of all the advantages. JVM bytecode manipulation This solution is more practical, albeit a bit difficult to pull off. This is roughly the same as jumping down into assembly language for coroutine libraries in C (which is how many of them work) with the advantage that you have only one architecture to worry about and get right. It also ties you down to only running your code on fully-compliant JVM stacks (which means, for example, no Android) unless you can find a way to do the same thing on the non-compliant stack. If you do find a way to do this, however, you have now doubled your system complexity and testing needs. The Da Vinci Machine The Da Vinci Machine is cool for experimentation, but since it is not a standard JVM its features aren't going to be available everywhere. Indeed I suspect most production environments would specifically forbid the use of the Da Vinci Machine. Thus I could use this to make cool experiments but not for any code I expect to release to the real world. This also has the added problem similar to the JVM bytecode manipulation solution above: won't work on alternative stacks (like Android's). JNI implementation This solution renders the point of doing this in Java at all moot. Each combination of CPU and operating system requires independent testing and each is a point of potentially frustrating subtle failure. Alternatively, of course, I could tie myself down to one platform entirely but this, too, makes the point of doing things in Java entirely moot. So... Is there any way to implement coroutines in Java without using one of these four techniques? Or will I be forced to use the one of those four that smells the least (JVM manipulation) instead?

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  • XML pass values to timer, AS3

    - by VideoDnd
    My timer has three variables that I can trace to the output window, but don't know how to pass them to the timer. How to I pass the XML values to my timer? Purpose I want to test with an XML document, before I try connecting it to an XML socket. myXML <?xml version="1.0" encoding="utf-8"?> <SESSION> <TIMER TITLE="speed">100</TIMER> <COUNT TITLE="starting position">-77777</COUNT> <FCOUNT TITLE="ramp">1000</FCOUNT> </SESSION> myFlash //myTimer 'instance of mytext on stage' /* fields I want to change with XML */ //CHANGE TO 100 var timer:Timer = new Timer(10); //CHANGE TO -77777 var count:int = 0; //CHANGE TO 1000 var fcount:int = 0; timer.addEventListener(TimerEvent.TIMER, incrementCounter); timer.start(); function incrementCounter(event:TimerEvent) { count++; fcount=int(count*count/1000);//starts out slow... then speeds up mytext.text = formatCount(fcount); } function formatCount(i:int):String { var fraction:int = i % 100; var whole:int = i / 100; return ("0000000" + whole).substr(-7, 7) + "." + (fraction < 10 ? "0" + fraction : fraction); } //LOAD XML var myXML:XML; var myLoader:URLLoader = new URLLoader(); myLoader.load(new URLRequest("time.xml")); myLoader.addEventListener(Event.COMPLETE, processXML); //PARSE XML function processXML(e:Event):void { myXML = new XML(e.target.data); trace(myXML.ROGUE.*); trace(myXML); //TEXT var text:TextField = new TextField(); text.text = myXML.TIMER.*; text.textColor = 0xFF0000; addChild(text); } RESOURCES OReilly's ActionScript 3.0 Cookbook, Chapter 12 Strings, Chapter 20 XML

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  • java web application best practices

    - by Bruce
    Hi all I'm trying to figure out the optimum way to develop and release a fairly simple web application, and I'm running into several problems. I'll outline the decisions I've made, because somewhere I've clearly gone off the rails.. Hugely grateful for any help! I have what I think is a fairly simple web application. It contains a couple of jsps that reference a couple of java beans, and the usual static html, js, css and images. Decision 1) I wanted to have a clear and clean release procedure, such that I could develop on my local machine and then release reliably to a production machine. I therefore made the decision to package the application into a war file (including all the static resources), to minimize the separate bits and pieces I would need to release. So far so good? Decision 2) I wanted things on my local machine to be as similar as possible to the production environment. So in my html, for example, I may have a reference to a static file such as http://static.foo.com/file . To keep this code working seamlessly on dev and prod, I decided to put static.foo.com in my /etc/hosts when developing locally, so that all the urls work correctly without changing anything. Decision 3) I decided to use eclipse and maven to give me a best practice environment for administering and building my project. So I have a nice tight set up now, except that: Every time I want to change anything in development, like one line in an html file, I have to rebuild the entire project and then wait for tomcat to load the war before I can see if it's what I wanted. So my questions are: 1) Is there a way to connect up eclipse and tomcat so that I don't have to rebuild the war each time? ie tomcat is looking straight at my actual workspace to serve up the static files? 2)I think I'm maybe making things harder by using /etc/hosts to reflect production urls - is there a better way that doesn't involve manually changing over urls (relative urls are fine of course, but where you have many subdomains, say one for static files and one for dynamic, you have to write out the full path, surely?) 3) Is this really best practice?? How do people set things up so that they balance the requirement for an automated, all-encompassing build process on the one hand, and the speed and flexibility to be able to develop javascript and html and css quickly, as quickly as if one just pointed apache at the directory and developed live? What do people find works? Many thanks!

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  • Is "Systems Designer" the job title that best describes what I do? [closed]

    - by ivo-rossi
    After having worked as Java developer for almost 3 years in the same company that I currently work at, I moved to a new position associated with the development of the same application. I’m in this new position for more than 1 year now. My official job title is Systems Designer, but I’m not sure this is a title that expresses well what I do. So my question here is what would be the most appropriate job title for me? I see this question as important for my career development. After all, I should be able to explain in one word what I do. And it’s no longer “Java Developer”. Well, in more than one word, this is what I do: The business analysts gather requirements / business problems to be solved with the clients and then discuss these requirements with me. Given the requirements, I design the high level solutions to be implemented in our system (e.g. a new screen on the client application, modifications to existing reports, extension to the XML export format of some objects, etc). I base my decision on the current capabilities of the system, the overall impact that the solutions would have on the system and the estimated effort to implement them (as I was a developer of this same application for almost 3 years before I moved to this position, I’m confident in my estimates). The solutions are discussed iteratively with the business analysts until we agree that they are good. The outcome of this analysis is what we call the “requirements design” document, which is written by me, shared with clients for approval and then also with the team that is going to implement the solutions and test them. Note that there are a few problems that I need to find a solution for that are non-functional. If the users are unhappy with the performance of a certain tool, I will investigate what can be done to speed it up. I will do some research – often based in the Java code itself - to identify possibilities of optimizations. But in this new position I no longer code, the main outcome of my work is really the “requirements design”. Is “Systems Designer” really the most appropriate job title?

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  • web service filling gridview awfully slow, as is paging/sorting

    - by nat
    Hi I am making a page which calls a web service to fill a gridview this is returning alot of data, and is horribly slow. i ran the svcutil.exe on the wsdl page and it generated me the class and config so i have a load of strongly typed objects coming back from each request to the many service functions. i am then using LINQ to loop around the objects grabbing the necessary information as i go, but for each row in the grid i need to loop around an object, and grab another list of objects (from the same request) and loop around each of them.. 1 to many parent object child one.. all of this then gets dropped into a custom datatable a row at a time.. hope that makes sense.... im not sure there is any way to speed up the initial load. but surely i should be able to page/sort alot faster than it is doing. as at the moment, it appears to be taking as long to page/sort as it is to load initially. i thought if when i first loaded i put the datasource of the grid in the session, that i could whip it out of the session to deal with paging/sorting and the like. basically it is doing the below protected void Page_Load(object sender, EventArgs e) { //init the datatable //grab the filter vars (if there are any) WebServiceObj WS = WSClient.Method(args); //fill the datatable (around and around we go) foreach (ParentObject po in WS.ReturnedObj) { var COs = from ChildObject c in WS.AnotherReturnedObj where c.whatever.equals(...) ...etc foreach(ChildObject c in COs){ myDataTable.Rows.Add(tlo.this, tlo.that, c.thisthing, c.thatthing, etc......); } } grdListing.DataSource = myDataTable; Session["dt"] = myDataTable; grdListing.DataBind(); } protected void Listing_PageIndexChanging(object sender, GridViewPageEventArgs e) { grdListing.PageIndex = e.NewPageIndex; grdListing.DataSource = Session["dt"] as DataTable; grdListing.DataBind(); } protected void Listing_Sorting(object sender, GridViewSortEventArgs e) { DataTable dt = Session["dt"] as DataTable; DataView dv = new DataView(dt); string sortDirection = " ASC"; if (e.SortDirection == SortDirection.Descending) sortDirection = " DESC"; dv.Sort = e.SortExpression + sortDirection; grdListing.DataSource = dv.ToTable(); grdListing.DataBind(); } am i doing this totally wrongly? or is the slowness just coming from the amount of data being bound in/return from the Web Service.. there are maybe 15 columns(ish) and a whole load of rows.. with more being added to the data the webservice is querying from all the time any suggestions / tips happily received thanks

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  • which way is correct to retrive data from oracle??

    - by rima
    before answer me plz thinking about the futures of these kind of program and answer me plz. I wanna get some data from oracle server like: 1-get all the function,package,procedure and etc for showing them or drop them & etc... 2-compile my *.sql files,get the result if they have problem & etc... becuz I was beginner in oracle first of all I for solve the second problem I try to connect to sqlPlus by RUN sqlplus and trace the output(I mean,I change the output stream of shell and trace what happend and handle the assigned message to customer. NOW THIS PART SUCCEED. just a little bit I have problem with get all result because the output is asynchronous.any way... [in this case I log in to oracle Server by send argument to the sqlplus by make a process in c#] after that I try to get all function,package or procedure name,but I have problem in speed!so I try to use oracle.DataAccess.dll to connect the database. now I m so confusing about: which way is correct way to build a program that work like Oracle Developer! I do not have any experience for like these program how work. If Your answer is I must use the second way follow this part plz: I search a little bit the Golden,PLedit (Benthic software),I have little bit problem how I must create the connection string?because I thinking about how I can find the host name or port number that oracle work on them?? am I need read the TNSNames.Ora file? IF your answer is I must use the first way follow this part plz: do u have any Idea for how I parse the output?because for example the result of a table is so confusing...[i can handle & program it but I really need someone experience,because the important things to me learn how such software work so nice and with quick response?] All of the has different style in output... If you are not sure Can u help me which book can help me in this way i become expert? becuz for example all the C# write just about how u can connect to DB and the DB books write how u can use this DB program,I looking for a book that give me some Idea how develop an interface for do transaction between these two.not simple send and receive data,for example how write a compiler for them. the language of book is not different for me i know C#,java,VB,sql,Oracle Thanks.

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  • Writing a managed wrapper for unmanaged (C++) code - custom types/structs

    - by Bobby
    faacEncConfigurationPtr FAACAPI faacEncGetCurrentConfiguration( faacEncHandle hEncoder); I'm trying to come up with a simple wrapper for this C++ library; I've never done more than very simple p/invoke interop before - like one function call with primitive arguments. So, given the above C++ function, for example, what should I do to deal with the return type, and parameter? FAACAPI is defined as: #define FAACAPI __stdcall faacEncConfigurationPtr is defined: typedef struct faacEncConfiguration { int version; char *name; char *copyright; unsigned int mpegVersion; unsigned long bitRate; unsigned int inputFormat; int shortctl; psymodellist_t *psymodellist; int channel_map[64]; } faacEncConfiguration, *faacEncConfigurationPtr; AFAIK this means that the return type of the function is a reference to this struct? And faacEncHandle is: typedef struct { unsigned int numChannels; unsigned long sampleRate; ... SR_INFO *srInfo; double *sampleBuff[MAX_CHANNELS]; ... double *freqBuff[MAX_CHANNELS]; double *overlapBuff[MAX_CHANNELS]; double *msSpectrum[MAX_CHANNELS]; CoderInfo coderInfo[MAX_CHANNELS]; ChannelInfo channelInfo[MAX_CHANNELS]; PsyInfo psyInfo[MAX_CHANNELS]; GlobalPsyInfo gpsyInfo; faacEncConfiguration config; psymodel_t *psymodel; /* quantizer specific config */ AACQuantCfg aacquantCfg; /* FFT Tables */ FFT_Tables fft_tables; int bitDiff; } faacEncStruct, *faacEncHandle; So within that struct we see a lot of other types... hmm. Essentially, I'm trying to figure out how to deal with these types in my managed wrapper? Do I need to create versions of these types/structs, in C#? Something like this: [StructLayout(LayoutKind.Sequential)] struct faacEncConfiguration { uint useTns; ulong bitRate; ... } If so then can the runtime automatically "map" these objects onto eachother? And, would I have to create these "mapped" types for all the types in these return types/parameter type hierarchies, all the way down until I get to all primitives? I know this is a broad topic, any advice on getting up-to-speed quickly on what I need to learn to make this happen would be very much appreciated! Thanks!

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  • Mysql select - improve performances

    - by realshadow
    Hey, I am working on an e-shop which sells products only via loans. I display 10 products per page in any category, each product has 3 different price tags - 3 different loan types. Everything went pretty well during testing time, query execution time was perfect, but today when transfered the changes to the production server, the site "collapsed" in about 2 minutes. The query that is used to select loan types sometimes hangs for ~10 seconds and it happens frequently and thus it cant keep up and its hella slow. The table that is used to store the data has approximately 2 milion records and each select looks like this: SELECT * FROM products_loans WHERE KOD IN("X17/Q30-10", "X17/12", "X17/5-24") AND 369.27 BETWEEN CENA_OD AND CENA_DO; 3 loan types and the price that needs to be in range between CENA_OD and CENA_DO, thus 3 rows are returned. But since I need to display 10 products per page, I need to run it trough a modified select using OR, since I didnt find any other solution to this. I have asked about it here, but got no answer. As mentioned in the referencing post, this has to be done separately since there is no column that could be used in a join (except of course price and code, but that ended very, very badly). Here is the show create table, kod and CENA_OD/CENA_DO very indexed via INDEX. CREATE TABLE `products_loans` ( `KOEF_ID` bigint(20) NOT NULL, `KOD` varchar(30) NOT NULL, `AKONTACIA` int(11) NOT NULL, `POCET_SPLATOK` int(11) NOT NULL, `koeficient` decimal(10,2) NOT NULL default '0.00', `CENA_OD` decimal(10,2) default NULL, `CENA_DO` decimal(10,2) default NULL, `PREDAJNA_CENA` decimal(10,2) default NULL, `AKONTACIA_SUMA` decimal(10,2) default NULL, `TYP_VYHODY` varchar(4) default NULL, `stage` smallint(6) NOT NULL default '1', PRIMARY KEY (`KOEF_ID`), KEY `CENA_OD` (`CENA_OD`), KEY `CENA_DO` (`CENA_DO`), KEY `KOD` (`KOD`), KEY `stage` (`stage`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8 And also selecting all loan types and later filtering them trough php doesnt work good, since each type has over 50k records and the select takes too much time as well... Any ides about improving the speed are appreciated. Edit: Here is the explain +----+-------------+----------------+-------+---------------------+------+---------+------+--------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+----------------+-------+---------------------+------+---------+------+--------+-------------+ | 1 | SIMPLE | products_loans | range | CENA_OD,CENA_DO,KOD | KOD | 92 | NULL | 190158 | Using where | +----+-------------+----------------+-------+---------------------+------+---------+------+--------+-------------+ I have tried the combined index and it improved the performance on the test server from 0.44 sec to 0.06 sec, I cant access the production server from home though, so I will have to try it tomorrow.

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  • Just a small problem regarding javscript BOM question

    - by caramel1991
    The question is this: Create a page with a number of links. Then write code that fires on the window onload event, displaying the href of each of the links on the page. And this is my solution <html> <body language="Javascript" onload="displayLink()"> <a href="http://www.google.com/">First link</a> <a href="http://www.yahoo.com/">Second link</a> <a href="http://www.msn.com/">Third link</a> <script type="text/javascript" language="Javascript"> function displayLink() { for(var i = 0;document.links[i];i++) { alert(document.links[i].href); } } </script> </body> </html> This is the answer provided by the book <html> <head> <script language=”JavaScript” type=”text/javascript”> function displayLinks() { var linksCounter; for (linksCounter = 0; linksCounter < document.links.length; linksCounter++) { alert(document.links[linksCounter].href); } } </script> </head> <body onload=”displayLinks()”> <A href=”link0.htm” >Link 0</A> <A href=”link1.htm”>Link 2</A> <A href=”link2.htm”>Link 2</A> </body> </html> Before I get into the javascript tutorial on how to check user browser version or model,I was using the same method as the example,by acessing the length property of the links array for the loop,but after I read through the tutorial,I find out that I can also use this alternative ways,by using the method that the test condition will evalute to true only if the document.links[i] return a valid value,so does my code is written using the valid method??If it's not,any comment regarding how to write a better code??Correct me if I'm wrong,I heard some of the people say "a good code is not evaluate solely on whether it works or not,but in terms of speed,the ability to comprehend the code,and could posssibly let others to understand the code easily".Is is true??

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  • Primary language - C++/Qt, C#, Java?

    - by Airjoe
    I'm looking for some input, but let me start with a bit of background (for tl;dr skip to end). I'm an IT major with a concentration in networking. While I'm not a CS major nor do I want to program as a vocation, I do consider myself a programmer and do pretty well with the concepts involved. I've been programming since about 6th grade, started out with a proprietary game creation language that made my transition into C++ at college pretty easy. I like to make programs for myself and friends, and have been paid to program for local businesses. A bit about that- I wrote some programs for a couple local businesses in my senior year in high school. I wrote management systems for local shops (inventory, phone/pos orders, timeclock, customer info, and more stuff I can't remember). It definitely turned out to be over my head, as I had never had any formal programming education. It was a great learning experience, but damn was it crappy code. Oh yeah, by the way, it was all vb6. So, I've used vb6 pretty extensively, I've used c++ in my classes (intro to programming up to algorithms), used Java a little bit in another class (had to write a ping client program, pretty easy) and used Java for some simple Project Euler problems to help learn syntax and such when writing the program for the class. I've also used C# a bit for my own simple personal projects (simple programs, one which would just generate an HTTP request on a list of websites and notify if one responded unexpectedly or not at all, and another which just held a list of things to do and periodically reminded me to do them), things I would've written in vb6 a year or two ago. I've just started using Qt C++ for some undergrad research I'm working on. Now I've had some formal education, I [think I] understand organization in programming a lot better (I didn't even use classes in my vb6 programs where I really should have), how it's important to structure code, split into functions where appropriate, document properly, efficiency both in memory and speed, dynamic and modular programming etc. I was looking for some input on which language to pick up as my "primary". As I'm not a "real programmer", it will be mostly hobby projects, but will include some 'real' projects I'm sure. From my perspective: QtC++ and Java are cross platform, which is cool. Java and C# run in a virtual machine, but I'm not sure if that's a big deal (something extra to distribute, possibly a bit slower? I think Qt would require additional distributables too, right?). I don't really know too much more than this, so I appreciate any help, thanks! TL;DR Am an avocational programmer looking for a language, want quick and straight forward development, liked vb6, will be working with database driven GUI apps- should I go with QtC++, Java, C#, or perhaps something else?

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  • Search row with highest number of cells in a row with colspan

    - by user593029
    What is the efficient way to search highest number of cells in big table with numerous colspan (merge cells ** colspan should be ignored so in below example highest number of cells is 4 in first row). Is it js/jquery with reg expression or just the loop with bubble sorting. I got one link as below explainig use of regex is it ideal way ... can someone suggest pseudo code for this. High cpu consumption due to a jquery regex patch <table width="156" height="84" border="0" > <tbody> <tr style="height:10px"> <td width="10" style="width:10px; height:10px"/> <td width="10" style="width:10px; height:10px"/> <td width="10" style="width:10px; height:10px"/> <td width="10" style="width:10px; height:10px"/> </tr> <tr style="height:10px"> <td width="10" style="width:10px; height:10px" colspan="2"/> <td width="10" style="width:10px; height:10px"/> <td width="10" style="width:10px; height:10px"/> </tr> <tr style="height:10px"> <td width="10" style="width:10px; height:10px"/> <td width="10" style="width:10px; height:10px"/> <td width="10" style="width:10px; height:10px" colspan="2"/> </tr> <tr style="height:10px"> <td width="10" style="width:10px; height:10px" colspan="2"/> <td width="10" style="width:10px; height:10px"/> <td width="10" style="width:10px; height:10px"/> </tr> </tbody> </table>

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  • Stored procedure performance randomly plummets; trivial ALTER fixes it. Why?

    - by gWiz
    I have a couple of stored procedures on SQL Server 2005 that I've noticed will suddenly take a significantly long time to complete when invoked from my ASP.NET MVC app running in an IIS6 web farm of four servers. Normal, expected completion time is less than a second; unexpected anomalous completion time is 25-45 seconds. The problem doesn't seem to ever correct itself. However, if I ALTER the stored procedure (even if I don't change anything in the procedure, except to perhaps add a space to the script created by SSMS Modify command), the completion time reverts to expected completion time. IIS and SQL Server are running on separate boxes, both running Windows Server 2003 R2 Enterprise Edition. SQL Server is Standard Edition. All machines have dual Xeon E5450 3GHz CPUs and 4GB RAM. SQL Server is accessed using its TCP/IP protocol over gigabit ethernet (not sure what physical medium). The problem is present from all web servers in the web farm. When I invoke the procedure from a query window in SSMS on my development machine, the procedure completes in normal time. This is strange because I was under the impression that SSMS used the same SqlClient driver as in .NET. When I point my development instance of the web app to the production database, I again get the anomalous long completion time. If my SqlCommand Timeout is too short, I get System.Data.SqlClient.SqlException: Timeout expired. The timeout period elapsed prior to completion of the operation or the server is not responding. Question: Why would performing ALTER on the stored procedure, without actually changing anything in it, restore the completion time to less than a second, as expected? Edit: To clarify, when the procedure is running slow for the app, it simultaneously runs fine in SSMS with the same parameters. The only difference I can discern is login credentials (next time I notice the behavior, I'll be checking from SSMS with the same creds). The ultimate goal is to get the procs to sustainably run with expected speed without requiring occasional intervention. Resolution: I wanted to to update this question in case others are experiencing this issue. Following the leads of the answers below, I was able to consistently reproduce this behavior. In order to test, I utilize sp_recompile and pass it one of the susceptible sprocs. I then initiate a website request from my browser that will invoke the sproc with atypical parameters. Lastly, I initiate a website request to a page that invokes the sproc with typical parameters, and observe that the request does not complete because of a SQL timeout on the sproc invocation. To resolve this on SQL Server 2005, I've added OPTIMIZE FOR hints to my SELECT. The sprocs that were vulnerable all have the "all-in-one" pattern described in this article. This pattern is certainly not ideal but was a necessary trade-off given the timeframe for the project.

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  • MySQL - Calculating fields on the fly vs storing calculated data

    - by Christian Varga
    Hi Everyone, I apologise if this has been asked before, but I can't seem to find an answer to a question that I have about calculating on the fly vs storing fields in a database. I read a few articles that suggested it was preferable to calculate when you can, but I would just like to know if that still applies to the following 2 examples. Example 1. Say you are storing data relating to a car. You store the fuel tank size in litres, and how many litres it uses per 100km. You also want to know how many KMs it can travel, which can be calculated from the tank size and economy. I see 2 ways of doing this: When a car is added or updated, calculate the amount of KMs and store this as a static field in the database. Every time a car is accessed, calculate the amount of KMs on the fly. Because the cars economy/tank size doesn't change (although it could be edited), the KMs is a pretty static value. I don't see why we would calculate it every single time the car is accessed. Wouldn't this waste cpu time as opposed to simply storing it in a separate field in the database and calculating only when a car is added or updated? My next example, which is almost an entirely different question (but on the same topic), relates to counting children. Let's say we have a app which has categories and items. We have a view where we display all the categories, and a count of all the items inside each category. Again, I'm wondering what's better. To perform a MySQL query to count all the items in each category every single time the page is accessed? Or store the count in a field in the categories table and update when an item is added / deleted? I know it is redundant to store anything that can be calculated, but I worry that calculating fields or counting records might be slow as opposed to storing the data in a field. If it's not then please let me know, I just want to learn about when to use either method. On a small scale I guess it wouldn't matter either way, but apps like Facebook, would they really count the amount of friends you have every time someone views your profile or would they just store it as a field? I'd appreciate any responses to both of these scenarios, and any resource that might explain the benefits of calculating vs storing. Thanks in advance, Christian

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