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  • Array of Arrays - writing to File problem

    - by iFloh
    Hi, and again my array of arrays ... I try to improve my app performance by buffering arrays on file for later reuse. I have an NSMutableArray that contains about 30 NSMutableArrays with NSNumber, NSDate and NSString Objects. I try to write the file using this call: bool result = [myArray writeToFile:[fileMethods getFullPath:[NSString stringWithFormat:@"iEts%@.arr", [aDate shortDateString]]] atomically:NO]; = result = FALSE. The Path method is: + (NSString *) getFullPath:(NSString *)forFileName { NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES); NSString *documentsDirectory = [paths objectAtIndex:0]; return [documentsDirectory stringByAppendingPathComponent:forFileName]; } and the aDate call returns a shortDateString with ddMMyy. The NSLog NSLog(@"%@", [fileMethods getFullPath:[NSString stringWithFormat:@"iEts%@.arr", [aDate shortDateString]]]); on the path generation returns: /Users/me/Library/Application Support/iPhone Simulator/User/Applications/86729620-EC1D-4C10-A799-0C638BB27933/Documents/iEts010510.arr FURTHER: It must have something to do with the Array of Arrays, since I also write 3 further simple arrays (containing NSStrings) that all succeed. The Array of Arrays gets generated using the addObject method Any ideas what could cause the trouble?

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  • WCF with MANY database connections

    - by Jorge Dominguez
    I'm working in the development of an ERP type .Net WinForms application consuming a WCF service. It's to be used by many small companies (in the range of 100-200). Database is SQL Server 2008 and the service will be hosted as a Windows service. Even thought there will be a single DB Server, our customer insists in having separate databases for each company. That is because of stability/support concerns (like DB being damaged or took offline for some reason thus affecting all clients). Concerns coming from previous experiences (not necessarily with same platform). With a single database, connections to the DB would be opened at service start up and pooling used, but, I'm not sure how connections could be managed in a multiple DB scenario: Could a connection to the corresponding DB be opened and closed for each service request? would performance be acceptable? If a connection is opened and maintained for each company accessing the system, what's the practical limit of opened connections (to different databases)? It would be very interesting to hear your opinions and suggestions for this situation. Tanks

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  • How to give new life into a five years old, simple but reliable PHP form?

    - by Sam
    Hi all. I have a script in php 5.2. I want to use a simple form. I found something a programmer made for me about 5 years ago. When I use it, PHP outputs an error now unless I set register_long_arrays = On, then it works fine. On the PHP website, however, it says: Warning This feature has been DEPRECATED as of PHP 5.3.0. Relying on this feature is highly discouraged. It's recommended to turn them off, for performance reasons. Instead, use the superglobal arrays, like $_GET. Should I listen to PHP's warning, or just enable the option and keep using my old form happily? If the former, then how/where do I change this simple form, so it does not rely on the deprecated setting? Your answer is much appreciated. form.htm <html><body> <form method="POST" action="form_sent.php"> ... </form> </body></html> form_sent.php <html><body> <?php $email = $HTTP_POST_VARS[email]; $mailto = "[email protected]"; $mailsubj = "A Form was Sent from Website!"; $mailhead = "From: $email\n"; reset ($HTTP_POST_VARS); $mailbody = "Values submitted from web site form:\n"; while (list($key, $val) = each ($HTTP_POST_VARS)){$mailbody .= "$key : $val\n";} if (!eregi("\n",$HTTP_POST_VARS[email])) { mail($mailto, $mailsubj, $mailbody, $mailhead); } ?> <b>Form Sent. Thank you.</b> </body></html>

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  • R optimization: How can I avoid a for loop in this situation?

    - by chrisamiller
    I'm trying to do a simple genomic track intersection in R, and running into major performance problems, probably related to my use of for loops. In this situation, I have pre-defined windows at intervals of 100bp and I'm trying to calculate how much of each window is covered by the annotations in mylist. Graphically, it looks something like this: 0 100 200 300 400 500 600 windows: |-----|-----|-----|-----|-----|-----| mylist: |-| |-----------| So I wrote some code to do just that, but it's fairly slow and has become a bottleneck in my code: ##window for each 100-bp segment windows <- numeric(6) ##second track mylist = vector("list") mylist[[1]] = c(1,20) mylist[[2]] = c(120,320) ##do the intersection for(i in 1:length(mylist)){ st <- floor(mylist[[i]][1]/100)+1 sp <- floor(mylist[[i]][2]/100)+1 for(j in st:sp){ b <- max((j-1)*100, mylist[[i]][1]) e <- min(j*100, mylist[[i]][2]) windows[j] <- windows[j] + e - b + 1 } } print(windows) [1] 20 81 101 21 0 0 Naturally, this is being used on data sets that are much larger than the example I provide here. Through some profiling, I can see that the bottleneck is in the for loops, but my clumsy attempt to vectorize it using *apply functions resulted in code that runs an order of magnitude more slowly. I suppose I could write something in C, but I'd like to avoid that if possible. Can anyone suggest another approach that will speed this calculation up?

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  • Setting pixel values in Nvidia NPP ImageCPU objects?

    - by solvingPuzzles
    In the Nvidia Performance Primitives (NPP) image processing examples in the CUDA SDK distribution, images are typically stored on the CPU as ImageCPU objects, and images are stored on the GPU as ImageNPP objects. boxFilterNPP.cpp is an example from the CUDA SDK that uses these ImageCPU and ImageNPP objects. When using a filter (convolution) function like nppiFilter, it makes sense to define a filter as an ImageCPU object. However, I see no clear way setting the values of an ImageCPU object. npp::ImageCPU_32f_C1 hostKernel(3,3); //allocate space for 3x3 convolution kernel //want to set hostKernel to [-1 0 1; -1 0 1; -1 0 1] hostKernel[0][0] = -1; //this doesn't compile hostKernel(0,0) = -1; //this doesn't compile hostKernel.at(0,0) = -1; //this doesn't compile How can I manually put values into an ImageCPU object? Notes: I didn't actually use nppiFilter in the code snippet; I'm just mentioning nppiFilter as a motivating example for writing values into an ImageCPU object. The boxFilterNPP.cpp example doesn't involve writing directly to an ImageCPU object, because nppiFilterBox is a special case of nppiFilter that uses a built-in gaussian smoothing filter (probably something like [1 1 1; 1 1 1; 1 1 1]).

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  • How to control the "flow" of an ASP.NET MVC (3.0) web app that relies on Facebook membership, with Facebook C# SDK?

    - by Chad
    I want to totally remove the standard ASP.NET membership system and use Facebook only for my web app's membership. Note, this is not a Facebook canvas app question. Typically, in an ASP.NET app you have some key properties & methods to control the "flow" of an app. Notably: Request.IsAuthenticated, [Authorize] (in MVC apps), Membership.GetUser() and Roles.IsUserInRole(), among others. It looks like [FacebookAuthorize] is equivalent to [Authorize]. Also, there's some standard work I do across all controllers in my site. So I built a BaseController that overrides OnActionExecuting(FilterContext). Typically, I populate ViewData with the user's profile within this action. Would performance suffer if I made a call to fbApp.Get("me") in this action? I use the Facebook Javascript SDK to do registration, which is nice and easy. But that's all client-side, and I'm having a hard time wrapping my mind around when to use client-side facebook calls versus server-side. There will be a point when I need to grab the user's facebook uid and store it in a "profile" table along with a few other bits of data. That would probably be best handled on the return url from the registration plugin... correct? On a side note, what data is returned from fbApp.Get("me")?

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  • Using an embedded DB (SQLite / SQL Compact) for Message Passing within an app?

    - by wk1989
    Hello, Just out of curiosity, for applications that have a fairly complicated module tree, would something like sqlite/sql compact edition work well for message passing? So if I have modules containing data such as: \SubsystemA\SubSubSysB\ModuleB\ModuleDataC, \SubSystemB\SubSubSystemC\ModuleA\ModuleDataX Using traditional message passing/routing, you have to go through intermediate modules in order to pass a message to ModuleB to request say ModuleDataC. Instead of doing that, if we we simply store "\SubsystemA\SubSubSysB\ModuleB\ModuleDataC" in a sqlite database, getting that data is as simple as a sql query and needs no routing and passing stuff around. Has anyone done this before? Even if you haven't, do you foresee any issues & performance impact? The only concern I have right now would be the passing of custom types, e.g. if ModuleDataC is a custom data structure or a pointer, I'll need some way of storing the data structure into the DB or storing the pointer into the DB. Thanks, JW EDIT One usage case I haven't thought about is when you want to send a message from ModuleA to ModuleB to get ModuleB to do something rather than just getting/setting data. Is it possible to do this using an embedded DB? I believe callback from the DB would be needed, how feasible is this?

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  • Tracking a fragment of a file in two places with git

    - by mabraham
    Hi, I have code such as void myfunc() { introduction(); while(condition()) { complex(); loop(); interior(); code(); } cleanup(); } which I wish to duplicate into two versions, viz: void myfuncA() { introduction(); minorchangeA(); while(condition()) { complex(); loop(); interior(); code(); } cleanup(); } void myfuncB() { introduction(); minorchangeB(); while(condition()) { complex(); modifiedB(); loop(); interior(); code(); } cleanup(); extracleanupB(); } git claims to track content rather than files, so do I need to tell it that there are chunks here that are common to both myfuncA and myfuncB so that when merging with upstream changes to myfunc that those changes should propagate to both myfuncA and myfuncB? If so, how? The code could be written so that myfuncAB did the correct thing at each point by testing for condition A or B, but that could seriously hinder readability or performance.

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  • Datastructure choices for highspeed and memory efficient detection of duplicate of strings

    - by Jonathan Holland
    I have a interesting problem that could be solved in a number of ways: I have a function that takes in a string. If this function has never seen this string before, it needs to perform some processing. If the function has seen the string before, it needs to skip processing. After a specified amount of time, the function should accept duplicate strings. This function may be called thousands of time per second, and the string data may be very large. This is a highly abstracted explanation of the real application, just trying to get down to the core concept for the purpose of the question. The function will need to store state in order to detect duplicates. It also will need to store an associated timestamp in order to expire duplicates. It does NOT need to store the strings, a unique hash of the string would be fine, providing there is no false positives due to collisions (Use a perfect hash?), and the hash function was performant enough. The naive implementation would be simply (in C#): Dictionary<String,DateTime> though in the interest of lowering memory footprint and potentially increasing performance I'm evaluating a custom data structures to handle this instead of a basic hashtable. So, given these constraints, what would you use? EDIT, some additional information that might change proposed implementations: 99% of the strings will not be duplicates. Almost all of the duplicates will arrive back to back, or nearly sequentially. In the real world, the function will be called from multiple worker threads, so state management will need to be synchronized.

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  • C++ design question, container of instances and pointers

    - by Tom
    Hi all, Im wondering something. I have class Polygon, which composes a vector of Line (another class here) class Polygon { std::vector<Line> lines; public: const_iterator begin() const; const_iterator end() const; } On the other hand, I have a function, that calculates a vector of pointers to lines, and based on those lines, should return a pointer to a Polygon. Polygon* foo(Polygon& p){ std::vector<Line> lines = bar (p.begin(),p.end()); return new Polygon(lines); } Here's the question: I can always add a Polygon (vector Is there a better way that dereferencing each element of the vector and assigning it to the existing vector container? //for line in vector<Line*> v //vcopy is an instance of vector<Line> vcopy.push_back(*(v.at(i)) I think not, but I dont really like that approach. Hopefully, I will be able to convince the author of the class to change it, but I cant base my coding right now to that fact (and i'm scared of a performance hit). Thanks in advance.

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  • C++ design question, container of instances and pointers

    - by Tom
    Hi all, Im wondering something. I have class Polygon, which composes a vector of Line (another class here) class Polygon { std::vector<Line> lines; public: const_iterator begin() const; const_iterator end() const; } On the other hand, I have a function, that calculates a vector of pointers to lines, and based on those lines, should return a pointer to a Polygon. Polygon* foo(Polygon& p){ std::vector<Line> lines = bar (p.begin(),p.end()); return new Polygon(lines); } Here's the question: I can always add a Polygon (vector Is there a better way that dereferencing each element of the vector and assigning it to the existing vector container? //for line in vector<Line*> v //vcopy is an instance of vector<Line> vcopy.push_back(*(v.at(i)) I think not, but I dont really like that approach. Hopefully, I will be able to convince the author of the class to change it, but I cant base my coding right now to that fact (and i'm scared of a performance hit). Thanks in advance.

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  • C++ design question, container of instances and pointers

    - by Tom
    Hi all, Im wondering something. I have class Polygon, which composes a vector of Line (another class here) class Polygon { std::vector<Line> lines; public: const_iterator begin() const; const_iterator end() const; } On the other hand, I have a function, that calculates a vector of pointers to lines, and based on those lines, should return a pointer to a Polygon. Polygon* foo(Polygon& p){ std::vector<Line> lines = bar (p.begin(),p.end()); return new Polygon(lines); } Here's the question: I can always add a Polygon (vector Is there a better way that dereferencing each element of the vector and assigning it to the existing vector container? //for line in vector<Line*> v //vcopy is an instance of vector<Line> vcopy.push_back(*(v.at(i)) I think not, but I dont really like that approach. Hopefully, I will be able to convince the author of the class to change it, but I cant base my coding right now to that fact (and i'm scared of a performance hit). Thanks in advance.

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  • Using an unencoded key vs a real Key, benefits?

    - by user246114
    Hi, I am reading the docs for Key generation in app engine. I'm not sure what effect using a simple String key has over a real Key. For example, when my users sign up, they must supply a unique username: class User { /** Key type = unencoded string. */ @PrimaryKey private String name; } now if I understand the docs correctly, I should still be able to generate named keys and entity groups using this, right?: // Find an instance of this entity: User user = pm.findObjectById(User.class, "myusername"); // Create a new obj and put it in same entity group: Key key = new KeyFactory.Builder( User.class.getSimpleName(), "myusername") .addChild(Goat.class.getSimpleName(), "baa").getKey(); Goat goat = new Goat(); goat.setKey(key); pm.makePersistent(goat); the Goat instance should now be in the same entity group as that User, right? I mean there's no problem with leaving the User's primary key as just the raw String? Is there a performance benefit to using a Key though? Should I update to: class User { /** Key type = unencoded string. */ @PrimaryKey private Key key; } // Generate like: Key key = KeyFactory.createKey( User.class.getSimpleName(), "myusername"); user.setKey(key); it's almost the same thing, I'd still just be generating the Key using the unique username anyway, Thanks

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  • C++ Array vs vector

    - by blue_river
    when using C++ vector, time spent is 718 milliseconds, while when I use Array, time is almost 0 milliseconds. Why so much performance difference? int _tmain(int argc, _TCHAR* argv[]) { const int size = 10000; clock_t start, end; start = clock(); vector<int> v(size*size); for(int i = 0; i < size; i++) { for(int j = 0; j < size; j++) { v[i*size+j] = 1; } } end = clock(); cout<< (end - start) <<" milliseconds."<<endl; // 718 milliseconds int f = 0; start = clock(); int arr[size*size]; for(int i = 0; i < size; i++) { for(int j = 0; j < size; j++) { arr[i*size+j] = 1; } } end = clock(); cout<< ( end - start) <<" milliseconds."<<endl; // 0 milliseconds return 0; }

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  • Custom ADO.NET provider to intercept and modify sql queries.

    - by Faisal
    Our client has an application that stores blobs in database which has now grown enough to impact the performance of SQL Server. To overcome this issue, we are planning to offload all blobs to file system and leave the path of file in a new column in user table. Like if user has a table docs with columns id, name and content (blob); we would ask him to add a new column 'filepath' in this table. Our client is willing to make this change in this database. But when it comes to changing the sql queries to read and write into this table, they are not ready to accep this. Actually, they don't want any change that results in recompilation and deployment. Now we are planning to write a custom ADO.NET provider that will intercept the select queries add a column 'filepath' at the end of the select statement retieve the result set and modify the 'content' column value based on 'filepath' value Is there any use case that you think will certainly fail with this approach? I know this sounds dirty but do we have a better way?

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  • What's the best practice for handling system-specific information under version control?

    - by Joe
    I'm new to version control, so I apologize if there is a well-known solution to this. For this problem in particular, I'm using git, but I'm curious about how to deal with this for all version control systems. I'm developing a web application on a development server. I have defined the absolute path name to the web application (not the document root) in two places. On the production server, this path is different. I'm confused about how to deal with this. I could either: Reconfigure the development server to share the same path as the production Edit the two occurrences each time production is updated. I don't like #1 because I'd rather keep the application flexible for any future changes. I don't like #2 because if I start developing on a second development server with a third path, I would have to change this for every commit and update. What is the best way to handle this? I thought of: Using custom keywords and variable expansion (such as setting the property $PATH$ in the version control properties and having it expanded in all the files). Git doesn't support this because it would be a huge performance hit. Using post-update and pre-commit hooks. Possibly the likely solution for git, but every time I looked at the status, it would report the two files as being changed. Not really clean. Pulling the path from a config file outside of version control. Then I would have to have the config file in the same location on all servers. Might as well just have the same path to begin with. Is there an easy way to deal with this? Am I over thinking it?

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  • Do I need a spatial index in my database?

    - by Sanoj
    I am designing an application that needs to save geometric shapes in a database. I haven't choosen the database management system yet. In my application, all database queries will have an bounding box as input, and as output I want all shapes within that database. I know that databases with a spatial index is used for this kind of application. But in my application there will not be any queries of type "give me objects nearby x/y" or other more complex queries that are useful in a GIS application. I am planning of having a database without a spatial index and have queries looking like: SELECT * FROM shapes WHERE x < max_x AND x > min_x AND y < max_y AND y > min_y And have an index on the columns x (double) and y (double). As long I can see, I don't really need a database with an spatial index, howsoever my application is close to that kind of applications. And even if I would like to have nearby queries, then I could create a big enough bounding box around that point. Or will this lead to poor performance? Do I really need a spatial database? And when is a spatial index needed?

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  • Why would one want to use the public constructors on Boolean and similar immutable classes?

    - by Robert J. Walker
    (For the purposes of this question, let us assume that one is intentionally not using auto(un)boxing, either because one is writing pre-Java 1.5 code, or because one feels that autounboxing makes it too easy to create NullPointerExceptions.) Take Boolean, for example. The documentation for the Boolean(boolean) constructor says: Note: It is rarely appropriate to use this constructor. Unless a new instance is required, the static factory valueOf(boolean) is generally a better choice. It is likely to yield significantly better space and time performance. My question is, why would you ever want to get a new instance in the first place? It seems like things would be simpler if constructors like that were private. For example, if they were, you could write this with no danger (even if myBoolean were null): if (myBoolean == Boolean.TRUE) It'd be safe because all true Booleans would be references to Boolean.TRUE and all false Booleans would be references to Boolean.FALSE. But because the constructors are public, someone may have used them, which means that you have to write this instead: if (Boolean.TRUE.equals(myBoolean)) But where it really gets bad is when you want to check two Booleans for equality. Something like this: if (myBooleanA == myBooleanB) ...becomes this: if ( (myBooleanA == null && myBooleanB == null) || (myBooleanA == null && myBooleanA.equals(myBooleanB)) ) I can't think of any reason to have separate instances of these objects which is more compelling than not having to do the nonsense above. What say you?

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  • Cannot disable index during PL/SQL procedure

    - by nw
    I've written a PL/SQL procedure that would benefit if indexes were first disabled, then rebuilt upon completion. An existing thread suggests this approach: alter session set skip_unusable_indexes = true; alter index your_index unusable; [do import] alter index your_index rebuild; However, I get the following error on the first alter index statement: SQL Error: ORA-14048: a partition maintenance operation may not be combined with other operations ORA-06512: [...] 14048. 00000 - "a partition maintenance operation may not be combined with other operations" *Cause: ALTER TABLE or ALTER INDEX statement attempted to combine a partition maintenance operation (e.g. MOVE PARTITION) with some other operation (e.g. ADD PARTITION or PCTFREE which is illegal *Action: Ensure that a partition maintenance operation is the sole operation specified in ALTER TABLE or ALTER INDEX statement; operations other than those dealing with partitions, default attributes of partitioned tables/indices or specifying that a table be renamed (ALTER TABLE RENAME) may be combined at will The problem index is defined so: CREATE INDEX A11_IX1 ON STREETS ("SHAPE") INDEXTYPE IS "SDE"."ST_SPATIAL_INDEX" PARAMETERS ('ST_GRIDS=890,8010,72090 ST_SRID=2'); This is a custom index type from a 3rd-party vendor, and it causes chronic performance degradation during high-volume update/insert/delete operations. Any suggestions on how to work around this error? By the way, this error only occurs within a PL/SQL block.

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  • Using a single texture image unit with multiple sampler uniforms

    - by bcrist
    I am writing a batching system which tracks currently bound textures in order to avoid unnecessary glBindTexture() calls. I'm not sure if I need to keep track of which textures have already been used by a particular batch so that if a texture is used twice, it will be bound to a different TIU for the second sampler which requires it. Is it acceptable for an OpenGL application to use the same texture image unit for multiple samplers within the same shader stage? What about samplers in different shader stages? For example: Fragment shader: ... uniform sampler2D samp1; uniform sampler2D samp2; void main() { ... } Main program: ... glActiveTexture(GL_TEXTURE0); glBindTexture(GL_TEXTURE_2D, tex_id); glUniform1i(samp1_location, 0); glUniform1i(samp2_location, 0); ... I don't see any reason why this shouldn't work, but what about if the shader program also included a vertex shader like this: Vertex shader: ... uniform sampler2D samp1; void main() { ... } In this case, OpenGL is supposed to treat both instances of samp1 as the same variable, and exposes a single location for them. Therefore, the same texture unit is being used in the vertex and fragment shaders. I have read that using the same texture in two different shader stages counts doubly against GL_MAX_COMBINED_TEXTURE_IMAGE_UNITS but this would seem to contradict that. In a quick test on my hardware (HD 6870), all of the following scenarios worked as expected: 1 TIU used for 2 sampler uniforms in same shader stage 1 TIU used for 1 sampler uniform which is used in 2 shader stages 1 TIU used for 2 sampler uniforms, each occurring in a different stage. However, I don't know if this is behavior that I should expect on all hardware/drivers, or if there are performance implications.

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  • Getting the Item Count of a large sharepoint list in fastest way

    - by sooraj
    I am trying to get the count of the items in a sharepoint document library programatically. The scale I am working with is 30-70000 items. We have usercontrol in a smartpart to display the count . Ours is a TEAM site. This is the code to get the total count SPList VoulnterrList = web.Lists[ListTitle]; SPQuery query = new SPQuery(); query.ViewAttributes = "Scope=\"Recursive\""; string queries = "<Where><Eq><FieldRef Name='ApprovalStatus' /><Value Type='Choice'>Pending</Value></Eq></Where>"; query.Query = queries; SPListItemCollection lstitemcollAssoID = VoulnterrList.GetItems(query); lblCount.Text = "Total Proofs: " + VoulnterrList.Items.Count.ToString() + " Pending Proofs: " + lstitemcollAssoID.Count.ToString(); The problem is this has serious performance issue it takes 75 to 80 sec to load the page. if we comment this page load will decrees to 4 sec. Any better approch for this problem Ours is sharepoint 2007

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  • Inline form editing on client side

    - by bykasif
    I see some web sites use dynamic forms(I am not sure about how to call them!) to edit a group of data. For example: there is a group of data such as name, last name, city, country.etc. when user clicks on EDIT button, instead of doing postback, a form, consisisting of 2 textboxes + 2 comboboxes, dynamically opens to edit,And then when you click on Save button, edit form disappears, and all data updates.. Now, I know what happens over here is using Ajax for server calls and some javascript for dom manipulation.. I even found some jquery plugins for textbox editing.. However, I could not found anything for full implementation of form fields. Therefore I have implemented it on asp.net by jquery ajax calls and dom manipulation manually. here is my process: 1) when Edit button clicked: Make a ajax call to server to retrieve necessary formedit.aspx 2) it returns editable form fields with values assigned. 3) when Save button clicked: make ajax call to server to retrieve formupdateprocess.aspx page. it basically do the database updates and then return necessary DOM snipplet (...) to insert current page.. well it works but MY PROBLEM, is performance.. Result seems slower than samples I see in other sites.:(( IS there anything that I dont know? a better way to implement this??

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  • Speed/expensive of SQLite query vs. List.contains() for "in-set" icon on list rows

    - by kpdvx
    An application I'm developing requires that the app main a local list of things, let's say books, in a local "library." Users can access their local library of books and search for books using a remote web service. The app will be aware of other users of the app through this web service, and users can browse other users' lists of books in their library. Each book is identified by a unique bookId (represented as an int). When viewing books returned through a search result or when viewing another user's book library, the individual list row cells need to visually represent if the book is in the user's local library or not. A user can have at most 5,000 books in the library, stored in SQLite on the device (and synchronized with the remote web service). My question is, to determine if the book shown in the list row is in the user's library, would it be better to directly ask SQLite (via SELECT COUNT(*)...) or to maintain, in-memory, a List or int[] array of some sort containing the unique bookIds. So, on each row display do I query SQLite or check if the List or int[] array contains the unique bookId? Because the user can have at most 5,000 books, each bookId occupies 4 bytes so at most this would use ~ 20kB. In thinking about this, and in typing this out, it seems obvious to me that it would be far better for performance if I maintained a list or int[] array of in-library bookIds vs. querying SQLite (the only caveat to maintaining an int[] array is that if books are added or removed I'll need to grow or shrink the array by hand, so with this option I'll most likely use an ArrayList or Vector, though I'm not sure of the additional memory overhead of using Integer objects as opposed to primitives). Opinions, thoughts, suggestions?

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  • Merging two arrays in PHP

    - by Industrial
    Hi everyone, I am trying to create a new array from two current arrays. Tried array_merge, but it will not give me what I want. $array1 is a list of keys that I pass to a function. $array2 holds the results from that function, but doesn't contain any non-available resuls for keys. So, I want to make sure that all requested keys comes out with 'null':ed values, as according to the shown $result array. It goes a little something like this: $array1 = array('item1', 'item2', 'item3', 'item4'); $array2 = array( 'item1' => 'value1', 'item2' => 'value2', 'item3' => 'value3' ); Here's the result I want: $result = array( 'item1' => 'value1', 'item2' => 'value2', 'item3' => 'value3', 'item4' => '' ); It can be done this way, but I don't think that it's a good solution - I really don't like to take the easy way out and suppress PHP errors by adding @:s in the code. This sample would obviously throw errors since 'item4' is not in $array2, based on the example. foreach ($keys as $k => $v){ @$array[$v] = $items[$v]; } So, what's the fastest (performance-wise) way to accomplish the same result?

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  • Grouping by date, with 0 when count() yields no lines

    - by SCO
    I'm using Postgresql 9 and I'm fighting with counting and grouping when no lines are counted. Let's assume the following schema : create table views { date_event timestamp with time zone ; event_id integer; } Let's imagine the following content : 2012-01-01 00:00:05 2 2012-01-01 01:00:05 5 2012-01-01 03:00:05 8 2012-01-01 03:00:15 20 I want to group by hour, and count the number of lines. I wish I could retrieve the following : 2012-01-01 00:00:00 1 2012-01-01 01:00:00 1 2012-01-01 02:00:00 0 2012-01-01 03:00:00 2 2012-01-01 04:00:00 0 2012-01-01 05:00:00 0 . . 2012-01-07 23:00:00 0 I mean that for each time range slot, I count the number of lines in my table whose date correspond, otherwise, I return a line with a count at zero. The following will definitely not work (will yeld only lines with counted lines 0). SELECT extract ( hour from date_event ),count(*) FROM views where date_event > '2012-01-01' and date_event <'2012-01-07' GROUP BY extract ( hour from date_event ); Please note I might also need to group by minute, or by hour, or by day, or by month, or by year (multiple queries is possible of course). I can only use plain old sql, and since my views table can be very big (100M records), I try to keep performance in mind. How can this be achieved ? Thank you !

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