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• Why is doing a top(1) on an indexed column in SQL Server slow?

  - by reinier

  I'm puzzled by the following. I have a DB with around 10 million rows, and (among other indices) on 1 column (campaignid_int) is an index. Now I have 700k rows where the campaignid is indeed 3835 For all these rows, the connectionid is the same. I just want to find out this connectionid. use messaging_db; SELECT TOP (1) connectionid FROM outgoing_messages WITH (NOLOCK) WHERE (campaignid_int = 3835) Now this query takes approx 30 seconds to perform! I (with my small db knowledge) would expect that it would take any of the rows, and return me that connectionid If I test this same query for a campaign which only has 1 entry, it goes really fast. So the index works. How would I tackle this and why does this not work? edit: estimated execution plan: select (0%) - top (0%) - clustered index scan (100%)

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• Performance difference in for loop condition?

  - by CSharperWithJava

  Hello all, I have a simple question that I am posing mostly for my curiousity. What are the differences between these two lines of code? (in C++) for(int i = 0; i < N, N > 0; i++) for(int i = 0; i < N && N > 0; i++) The selection of the conditions is completely arbitrary, I'm just interested in the differences between , and &&. I'm not a beginner to coding by any means, but I've never bothered with the comma operator. Are there performance/behavior differences or is it purely aesthetic? One last note, I know there are bigger performance fish to fry than a conditional operator, but I'm just curious. Indulge me. Edit Thanks for your answers. It turns out the code that prompted this question had misused the comma operator in the way I've described. I wondered what the difference was and why it wasn't a && operator, but it was just written incorrectly. I didn't think anything was wrong with it because it worked just fine. Thanks for straightening me out.

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• Best Dijkstra papers to explain this quote?

  - by jemfinch

  I was enjoying "The Humble Programmer" earlier today and ran across this choice quote: Therefore, for the time being and perhaps forever, the rules of the second kind present themselves as elements of discipline required from the programmer. Some of the rules I have in mind are so clear that they can be taught and that there never needs to be an argument as to whether a given program violates them or not. Examples are the requirements that no loop should be written down without providing a proof for termination nor without stating the relation whose invariance will not be destroyed by the execution of the repeatable statement. I'm looking for which of Dijkstra's 1300+ writings best describe in further detail rules such as he was describing above.

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• Deal with undefined values in code or in the template?

  - by David

  I'm writing a web application (in Python, not that it matters). One of the features is that people can leave comments on things. I have a class for comments, basically like so: class Comment: user = ... # other stuff where user is an instance of another class, class User: name = ... # other stuff And of course in my template, I have <div>${comment.user.name}</div> Problem: Let's say I allow people to post comments anonymously. In that case comment.user is None (undefined), and of course accessing comment.user.name is going to raise an error. What's the best way to deal with that? I see three possibilities: Use a conditional in the template to test for that case and display something different. This is the most versatile solution, since I can change the way anonymous comments are displayed to, say, "Posted anonymously" (instead of "Posted by ..."), but I've often been told that templates should be mindless display machines and not include logic like that. Also, other people might wind up writing alternate templates for the same application, and I feel like I should be making things as easy as possible for the template writer. Implement an accessor method for the user property of a Comment that returns a dummy user object when the real user is undefined. This dummy object would have user.name = 'Anonymous' or something like that and so the template could access it and print its name with no error. Put an actual record in my database corresponding to a user with user.name = Anonymous (or something like that), and just assign that user to any comment posted when nobody's logged in. I know I've seen some real-world systems that operate this way. (phpBB?) Is there a prevailing wisdom among people who write these sorts of systems about which of these (or some other solution) is the best? Any pitfalls I should watch out for if I go one way vs. another? Whoever gives the best explanation gets the checkmark.

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• Const parameter at constructor causes stackoverflow

  - by Luca

  I've found this strange behavior with VS2005 C++ compiler. Here is the situation: I cannot publish the code, but situation is very simple. Here is initial code: it work perfectly class Foo { public: Foo(Bar &bar) { ... } } The constructor implementation stores a reference, setup some members... indeed nothing special. If I change the code in the following way: class Foo { public: Foo(const Bar &bar) { ... } } I've added a const qualifier to the only constructor routine parameter. It compiles correctly, but the compiler outputs a warning saying that the routine Foo::Foo will cause a stackoverflow (even if the execution path doesn't construct any object Foo); effectively this happens. So, why the code without the const parameter works perfectly, while the one with the const qualifier causes a stackoverflow? What can cause this strange behavior?

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• Unable upload large file size on Google Docs

  - by Preeti

  Hi, I am uploading document on Google Docs as: DocumentsService myService = new DocumentsService(""); myService.setUserCredentials("[email protected]", password ); DocumentEntry newEntry = myService.UploadDocument(@"C:\Sample.txt", "Sample.txt"); But when i try to upload a file of 3 MB it result into exception: An unhandled exception of type 'Google.GData.Client.GDataRequestException' occurred in Google.GData.Client.dll Additional information: Execution of request failed: http://docs.google.com/feeds/documents/private/full How can i upload large size file on Google Docs? I am using Google API ver 2. Thanx

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• How can I prevent MEF from throwing an exception when an Export is not found?

  - by Kilhoffer

  I have a class with an IList<T> property decorated with the [ImportMany(allowRecomposition = true)] attribute. There are some conditions in which the application might not find any available Exports of the requested type. Right now, it's throwing a CompositionException if no Exports of the requested type are found. I dislike application flow being determined by thrown exceptions, so I would rather not catch and react in this case. Rather, I just want program execution to continue. Is there a flag or something I can set to make this Import optional? I know for single import properties, you can do this: [Import(AllowDefault = true)] but 'AllowDefault' is not an option on the ImportMany attribute.

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• Can I make valgrind ignore glibc libraries?

  - by Jack

  Is it possible to tell valgrind to ignore some set of libraries? Specifically glibc libraries.. Actual Problem: I have some code that runs fine in normal execution. No leaks etc. When I try to run it through valgrind, I get core dumps and program restarts/stops. Core usually points to glibc functions (usually fseek, mutex etc). I understand that there might be some issue with incompatible glibc / valgrind version. I tried various valgrind releases and glibc versions but no luck. Any suggestions?

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• Processing an n-ary ANTLR AST one child at a time

  - by Chris Lieb

  I currently have a compiler that uses an AST where all children of a code block are on the same level (ie, block.children == {stm1, stm2, stm3, etc...}). I am trying to do liveness analysis on this tree, which means that I need to take the value returned from the processing of stm1 and then pass it to stm2, then take the value returned by stm2 and pass it to stm3, and so on. I do not see a way of executing the child rules in this fashion when the AST is structured this way. Is there a way to allow me to chain the execution of the child grammar items with my given AST, or am I going to have to go through the painful process of refactoring the parser to generate a nested structure and updating the rest of the compiler to work with the new AST? Example ANTLR grammar fragment: block : ^(BLOCK statement*) ; statement : // stuff ; What I hope I don't have to go to: block : ^(BLOCK statementList) ; statementList : ^(StmLst statement statement+) | ^(StmLst statement) ; statement : // stuff ;

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• How does one implement a truly asynchronous java thread

  - by Ritesh M Nayak

  I have a function that needs to perfom two operations, one which finishes fast and one which takes a long time to run. I want to be able to delegate the long running operation to a thread and I dont care when the thread finishes, but the threads needs to complete. I implemented this as shown below , but, my secondoperation never gets done as the function exits after the start() call. How I can ensure that the function returns but the second operation thread finishes its execution as well and is not dependent on the parent thread ? public void someFunction(String data) { smallOperation() Blah a = new Blah(); Thread th = new Thread(a); th.Start(); } class SecondOperation implements Runnable { public void run(){ // doSomething long running } }

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• MS Access: Order of Events in event ApplyFilter (ADP Project)

  - by Jose Valdes

  I'm having problems with the execution of ServerFilterByForm in Access 2003 When I apply the entered filter it returns the requested data but after it appear on screen (Form) it disappears. Don't know why this is happening Does anyone had the same problem? How can it be solved? Heris is part of the code Private Sub Form_ApplyFilter(Cancel As Integer, ApplyType As Integer) Dim stSql As String If Len(ServerFilter) > 0 Then stSql = "SELECT * FROM v_InitialReviewQuery " & _ " WHERE " + ServerFilter & _ " ORDER BY acctnumber" Else stSql = "SELECT top 1 * FROM v_InitialReviewQuery ORDER BY acctnumber" End If Me.RecordSource = stSql End Sub

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• Php efficiency question --> Database call vs. File Write vs. Calling C++ executable

  - by JP19

  Hi, What I wish to achieve is - log all information about each and every visit to every page ofmy website (like ip address, browser, referring page, etc). Now this is easy to do. What I am interested is doing this in a way so as to cause minimum overhead (runtime) in the php scripts. What is the best approach for this efficiency-wise: 1) Log all information to a database table 2) Write to a file (from php directly) 3) Call a C++ executable, that will write this info to a file in parallel [so the script can continue execution without waiting for the file write to occur ...... is this even possible] I may be trying to optimize unnecessarily/prematurely, but still - any thoughts / ideas on this would be appreciated. (I think efficiency of file write/logging can really be a concern if I have say 100 visits per minute...) Thanks & Regards, JP

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• c# - Object reference not set to an instance of an object.

  - by tom

  Line 30: sUsername.Trim(); Line 31: sPassword.Trim(); Line 32: string ConnectionString = WebConfigurationManager.ConnectionStrings["dbnameConnectionString"].ConnectionString; Line 33: SqlConnection myConnection = new SqlConnection(ConnectionString); Line 34: try Object reference not set to an instance of an object. Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. Exception Details: System.NullReferenceException: Object reference not set to an instance of an object. Any ideas? I don't understand the error.

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• Avoid the use of loops (for) with R

  - by albergali

  Hi, I'm working with R and I have a code like this: i<-1 j<-1 for (i in 1:10) for (j in 1:100) if (data[i] == paths[j,1]) cluster[i,4] <- paths[j,2] where : data is a vector with 100 rows and 1 column paths is a matrix with 100 rows and 5 columns cluster is a matrix with 100 rows and 5 columns My question is: how could I avoid the use of "for" loops to iterate through the matrix? I don't know whether apply functions (lapply, tapply...) are useful in this case. This is a problem when j=10000 for example, because execution time is very long. Thank you

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• Java: Help constructing a fillTextFields() method

  - by Holly

  I have a Java project where I am to connect to a database and create buttons (next, new, save, delete, previous) to navigate through the database content where there are appropriate text fields and labels for the specific information. I'll use the code below as an example (each button is set up very similar)... I have it as follows: JButton jbtnNext = new JButton("Next ->"); jbtnNext.addActionListener(this); if (e.getSource() == jbtnNext) jbtnNext_Click(); private void jbtnNext_Click() { JOptionPane.showMessageDialog(null, "Next" ,"Button Pressed", JOptionPane.INFORMATION_MESSAGE); try { if (rset.next()) { fillTextFields(true); }else{ //Display result in a dialog box JOptionPane.showMessageDialog(null, "Not found"); } } catch (SQLException ex) { ex.printStackTrace(); } } The professor gave the following outline of logic to construct the fillTextFields() method: Construct the method to provide reusable code that would fill the JTextFields on the GUI with appropriate values from current record from the database (when "Previous or "Next" buttons are pressed) or blank values (when the new Button is pressed). To determine when the current record was to provide values (next and previous) or the value would be blank (new button) pass a boolean argument into the method. If data from the current record was to be used as fill values, pass true for both previous and next button code after moving the record pointer. If the new button was pressed and want to fill with blank values, pass false to the method. Inside the method, use a conditional expression to evaluate the boolean variable. If true, The appropriate get----() resultset method is used to fill the JTextFields. If false, fill them with "". The .setText() method of the JTextField is used to fill each JTextField. Make sure the fillTextFields method throws the appropriate exception. I understand and have the previous and next button methods passing true, while the new button method is passing false, but I don't quite understand how to set up the fillTextFields() method correctly or how to "throw the appropriate exception"... Any help would really be appreciated, thank you!

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• how sort recursively by maximum fileze and counts files type?

  - by user599395

  Hello! I'm beginner in bash programming. I want to display head -n $1 results of sorting files by size in /etc/*. The problem is that at final search, I must know how many directories and files has processed. I compose following code: #!/bash/bin let countF=0; let countD=0; for file in $(du -sk /etc/* |sort +0n | head $1); do if [ -f "file" ] then echo $file; let countF=countF+1; else if [ -d "file" ] then let countD=countD+1; fi done echo $countF echo $countD I have errors at execution. How use find with du, because I must search recursively?

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• Sql CLR calling webservice throws exception

  - by TonyP

  I have clr stored procedure that calls a Webservice method. Webmethod in turn call a com object .. and do some processing on a remote Unix server. When I invoke webmethod by it self it works fine. But when called from the CLR I get the following exception.. What am I doing wrong ? Msg 6522, Level 16, State 1, Procedure PrintOa, Line 0 A .NET Framework error occurred during execution of user-defined routine or aggregate "PrintOa": System.Security.HostProtectionException: Attempted to perform an operation that was forbidden by the CLR host. The protected resources (only available with full trust) were: All The demanded resources were: Synchronization System.Security.HostProtectionException: at System.Reflection.MethodBase.PerformSecurityCheck(Object obj, RuntimeMethodHandle method, IntPtr parent, UInt32 invocationFlags) at System.Reflection.RuntimeConstructorInfo.Invoke(BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture) at System.Diagnostics.TraceUtils.GetRuntimeObject(String className, Type baseType, String initializeData) at System.Diagnostics.TypedElement.BaseGetRuntimeObject() at System.Diagnostics.ListenerElement.GetRuntimeObject() at System.Diagnostics.ListenerElementsCollection.GetRuntimeObject() at System.Diagnostics.TraceInternal.get_Listeners() at System.Diagnostics.TraceInternal.WriteLine(Object value) at System.Diagnostics.Debug.WriteLine(Object value) at BaaNOA.PrintOA(String trid)

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• How to printf a time_t variable as a floating point number?

  - by soneangel

  Hi guys, I'm using a time_t variable in C (openMP enviroment) to keep cpu execution time...I define a float value sum_tot_time to sum time for all cpu's...I mean sum_tot_time is the sum of cpu's time_t values. The problem is that printing the value sum_tot_time it appear as an integer or long, by the way without its decimal part! I tried in these ways: to printf sum_tot_time as a double being a double value to printf sum_tot_time as float being a float value to printf sum_tot_time as double being a time_t value to printf sum_tot_time as float being a time_t value Please help me!!

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• Using "CASE" in Where clause to choose various column harm the performance

  - by zivgabo

  I have query which needs to be dynamic on some of the columns, meaning I get a parameter and according its value I decide which column to fetch in my Where clause. I've implemented this request using "CASE" expression: (CASE @isArrivalTime WHEN 1 THEN ArrivalTime ELSE PickedupTime END) >= DATEADD(mi, -@TZOffsetInMins, @sTime) AND (CASE @isArrivalTime WHEN 1 THEN ArrivalTime ELSE PickedupTime END) < DATEADD(mi, -@TZOffsetInMins, @fTime) If @isArrivalTime = 1 then chose ArrivalTime column else chose PickedupTime column. I have a clustered index on ArrivalTime and nonclustered index on PickedupTime. I've noticed that when I'm using this query (with @isArrivalTime = 1), my performance is a lot worse comparing to only using ArrivalTime. Maybe the query optimizer can't use\choose the index properly in this way? I compared the execution plans an noticed that when I'm using the CASE 32% of the time is being wasted on the index scan, but when I didn't use the CASE(just usedArrivalTime`) only 3% were wasted on this index scan. Anyone know the reason for this?

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• Error occured during the debugging the page?

  - by Surya sasidhar

  hi, when i run my application it is the error i get... This application has failed to start because the application configuration is incorrect. Reinstalling the application may fix this problem. (Exception from HRESULT: 0x800736B1) Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. Exception Details: System.Runtime.InteropServices.COMException: This application has failed to start because the application configuration is incorrect. Reinstalling the application may fix this problem. (Exception from HRESULT: 0x800736B1)

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• How to implement arrays in an interpreter?

  - by Ray

  I have managed to write several interpreters including Tokenizing Parsing, including more complicated expressions such as ((x+y)*z)/2 Building bytecode from syntax trees Actual bytecode execution What I didn't manage: Implementation of dictionaries/lists/arrays. I always got stuck with getting multiple values into one variable. My value structure (used for all values passed around, including variables) looks like this, for example: class Value { public: ValueType type; int integerValue; string stringValue; } Works fine with integers and strings, but how could I implement arrays? (From now on with array I mean arrays in my experimental language, not in C++) How can I fit the array concept into the Value class above? Is it possible? How should I make arrays able to be passed around just as you could pass around integers and strings in my language, using the class above? Accessing array elements or memory allocation wouldn't be the problem, I just don't know how to store them.

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• what is value of x for load and store

  - by Kevinniceguy

  This is some challenge On a single processor system, in which load and store are assumed to be atomic, what are all the possible values for x after both threads have completed in the following execution, assuming that x is initialised to O? Hint: you need to consider how this code might be compiled into machine language. for (int i = 0; i < 5; i++) : x = x + 1; for (int j = 0; j < 5; j++) : x = x + 1;

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• Lifetime of javacript variables.

  - by The Machine

  What is the lifetime of a variable in javascript, declared with "var". I am sure, it is definitely not according to expectation. <script> function(){ var a; var fun=function(){ // a is accessed and modified } }(); </script> Here how and when does javascript garbage collect the variable a? Since 'a' is a part of the closure of the inner function, it ideally should never get garbage collected, since the inner function 'fun', may be passed as a reference to an external context.So 'fun' should still be able to access 'a', from the external context. If my understanding is correct, how does garbage collection happen then, and how does it ensure to have enough memory space, since keeping all variables in memory until the execution of the program might not be tenable ?

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• How to insert zeros between bits in a bitmap?

  - by anatolyg

  I have some performance-heavy code that performs bit manipulations. It can be reduced to the following well-defined problem: Given a 13-bit bitmap, construct a 26-bit bitmap that contains the original bits spaced at even positions. To illustrate: 0000000000000000000abcdefghijklm (input, 32 bits) 0000000a0b0c0d0e0f0g0h0i0j0k0l0m (output, 32 bits) I currently have it implemented in the following way in C: if (input & (1 << 12)) output |= 1 << 24; if (input & (1 << 11)) output |= 1 << 22; if (input & (1 << 10)) output |= 1 << 20; ... My compiler (MS Visual Studio) turned this into the following: test eax,1000h jne 0064F5EC or edx,1000000h ... (repeated 13 times with minor differences in constants) I wonder whether i can make it any faster. I would like to have my code written in C, but switching to assembly language is possible. Can i use some MMX/SSE instructions to process all bits at once? Maybe i can use multiplication? (multiply by 0x11111111 or some other magical constant) Would it be better to use condition-set instruction (SETcc) instead of conditional-jump instruction? If yes, how can i make the compiler produce such code for me? Any other idea how to make it faster? Any idea how to do the inverse bitmap transformation (i have to implement it too, bit it's less critical)?

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• How can I optimize MVC and IIS pipeline to obtain higher speed?

  - by Andy

  Hi, I am doing performance tweaking of a simple app that uses MVC on IIS 7.5. I have a StopWatch starting up in Application_BeginRequest and I take a snapshot at Controller.OnActionExecuting. So I measure the time spend in the entire IIS pipeline: from request receipt to the moment execution finally gets to my controller. I obtain 700 microseconds on my 3GHz quad-core (project compiled Release x64), and I wonder where the bottleneck is, especially hearing some people say that one can get up to 8000 page loads per second with MVC. How can I optimize MVC and IIS pipeline to obtain higher speed?

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