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• Best way to have unique key over 500M varchar(255) records in mysql/innodb?

  - by taw

  I have url column with unique key over it - but its performance on updates is absolutely atrocious. I suspect that's because the index doesn't all fit in memory. So I was thinking, how about adding a column of md5(url) with 16 bytes of binary data and unique-keying that instead. What would be the best datatype for that? I'd love to be able to just see 32-character hex hash, while mysql would convert it to/from 16 binary bytes and index that, as programs using the database might have some troubles with arbitrary binary data that I'd rather avoid if possible (also I'm a bit afraid that mysql might get some strange ideas about character sets and for example overalocating storage for that by 3:1 because it thinks it might need utf8, how do I avoid that for cure?).

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• Forcing an app to run single core only?

  - by Kevin

  I have this strange issue with some third party DLL's. The third party provider references some open source DLL's that have a memory exception whenever I try to use a certain method. This issue does not appear when the app is run on a single core machine, but obviously we cannot assume a user will have that. Is there a way to force an app, or even better yet a referenced DLL to run on a single core? Any other way to possibly fix this? Getting the third party to rebuild the OS dll's is apparently out of the question (its a bit of a sore spot with me currently :) ) so I have to handle it myself or just forget about providing this functionality.

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• Authenticating model - best practices

  - by zerkms

  I come into ASP.NET from php so the reason why i ask my question is because it's totally different nature of how application works and handles requests. well, i have an exists table with user creditians, such as: id, login, password (sha hashed), email, phone, room i have built custom membership provider so it can handle my own database authentication schema. and now i'm confused, because User.Identity.Name contains only user's login, but not the complete object (i'm using linq2sql to communicate with database and i need in it's User object to work). at php applications i just store user object at some static method at Auth class (or some another), but here at ASP.NET MVC i cannot do this, because static member is shared across all requests and permanent, and not lives within only current request (as it was at php). so my question is: how and where should i retrieve and store linq2sql user object to work with it within current and only current request? (after request processed successfully i expect it will be disposed from memory and on next request will be created again). or i'm following totally wrong way?

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• I want to make my own Malloc

  - by Unknown

  I want to make my own malloc/free so I can make a precise copying allocator. Any gurus have any tips and suggestions? I have a few questions for now: Should I just malloc large chunks of memory, and then distribute from that so I don't have to call the system calls? How are copying collectors usually done? I would imagine that this part is a bit complicated to do efficiently. My naive implementation would just malloc a block the size of the remaining objects which would require 2x the space.

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• Efficient questions

  - by rayman

  Hi, I have to manage xml's and Strings in my app. by efficenty and memory saving, is collection(ArrayList) will be much more 'expensive' then array of Strings? another issue is: i could use the content as regular String, or XML.. is working with XML also makes it more 'expensive' ? when i say i expensive i talk about taking system sources. please tell me by any of your exprience if the diffrences are significant? thanks, ray.

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• C++ MFC how to compare LPCTSTR in a if statement?

  - by user1078510

  I have the following code: LPCTSTR strPermission = Method(); if (strPermission == L"0") { return true; } else { return false; } While debugging I can see that strPermission does equal "0", yet when I compare it like in the if statement it always returns false. The only thing I can think of is that it is comparing the memory address of the variable rather than the variable value. How do I compare strPermission to L"0" so that it would return true if strPermission equals "0". Thank you!

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• What happens if an asynchronous delegate call never returns?

  - by RichardHowells

  I found a decent looking example of how to call a delegate asynchronously with a timeout... http://www.eggheadcafe.com/tutorials/aspnet/847c94bf-4b8d-4a66-9ae5-5b61f049019f/basics-make-any-method-c.aspx. In summary it uses WaitOne with a timeout to determine if the call does not return before the timeout expires. I also know that you should have an EndInvoke to match each BeginInvoke. So what happens if the wait timeout expires? We (presumably) DON'T want to call EndInvoke as that will block. The code can go on to do 'other things', but have we leaked anything? Is there some poor thread someplace blocked waiting for a return that's never going to happen? Have we leaked some memory where the result-that-will-never-return was going to be placed?

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• Trying to use tcl threads on windows 7 results in access violation.

  - by Juan

  I'm trying to get this simple program to work on windows, but it crashes: unsigned (__stdcall testfoo)(ClientData x) { return 0; } int main() { Tcl_ThreadId testid = 0; Tcl_CreateThread(&testid, testfoo, (ClientData) NULL, TCL_THREAD_STACK_DEFAULT, TCL_THREAD_NOFLAGS); } I am using a makefile generated by cmake and linking against a version of Tcl 8.5.7 I compiled myself using Visual C++ 2008 express. It was compiled using msvcrt,static,threads and the name of the resulting library is tcl85tsx.lib. The error is: Unhandled exception at 0x77448c39 in main.exe: 0xC0000005: Access violation writing location 0x00000014. The Tcl library works fine, and I can even run a threading script example by loading the Thread extension into it. My assumption is that there is something horribly wrong with a memory violation, but I have no idea what. Any help appreciated.

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• Why don't hardware failures show up at the programming language level?

  - by Julian Cienfuegos

  I am wondering if anyone can give my a good answer, or at least point me in the direction of a good reference to the following question: How come I have never heard of a computer breaking in a very fundamental way? How come when I declare x to be a double it stays as a double? How come there is never a short circuit that robs it of some bytes and makes it an integer? Why do we have faith that when we initialize x to 10, there will never be a power surge that will cause it to become 11, or something similar? I think I need a better understanding of memory. Thanks, and please don't bash me over the head for such a simple/abstract question.

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• Good way to send a large file over a network in C#?

  - by BFreeman

  I am trying to build an application that can request files from a service running on another machine in the network. These files can be fairly large (500mb + at times). I was looking into sending it via TCP but I'm worried that it may require that the entire file be stored in memory. There will probably only be one client. Copying to a shared directory isn't acceptable either. The only communication required is for the client to say "gimme xyz" and the server to send it (and whatever it takes to ensure this happens correctly). Any suggestions?

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• Does the Internet make us less good programmers? [closed]

  - by stagas

  With all the information and code available nowadays on the Internet has that diminished our capability of remembering or learning stuff just because we know they're available somewhere out there, just a Google away or a StackOverflow question away? For example I find myself visiting php.net quite often to check the syntax of the same functions over and over again, not because my memory sucks, but I don't feel like keeping the information in me, since I know I'll find it again on the net. And about StackOverflow, isn't the process of figuring things out on your own supposed to improve your programming skills? If the answers are all just clicks away, do we actually learn something or just keep a pointer in our heads where to search for it again when we need it? Your thoughts are welcome. Hope it doesn't shut down as subjective or anything, the answers would be really interesting ;)

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• Reading a bmp file and inverting it in C

  - by user1763396

  I have an assignment that deals with reading a bmp file into memory, inverts the pixels, and then saves the inverted image to a new file. From this description it seems fairly easy, however I don't think my professor did a great job in explaining the necessary steps to go about doing so. He taught us about fread and fwrite but there is so much more. Can anyone explain the process in going about this problem (I'm no looking for a direct answer just an explanation). Here is the link to the problem's description: https://engineering.purdue.edu/OOSD/F2012/Exercises/ex5.html Thanks in advance for any sort of help. NOTE: I actually have looked into this problem but since I don't have a good standing on this info it's not quite "clicking".

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• Performance of Serialized Objects in C++

  - by jm1234567890

  Hi Everyone, I'm wondering if there is a fast way to dump an STL set to disk and then read it back later. The internal structure of a set is a binary tree, so if I serialize it naively, when I read it back the program will have to go though the process of inserting each element again. I think this is slow even if it is read back in correct order, correct me if I am wrong. Is there a way to "dump" the memory containing the set into disk and then read it back later? That is, keep everything in binary format, thus avoiding the re-insertion. Do the boost serialization tools do this? Thanks! EDIT: oh I should probably read, http://www.parashift.com/c++-faq-lite/serialization.html I will read it now... no it doesn't really help

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• how to get stl map to construct/destruct inserted object only once.

  - by Alberto Toglia

  I have found a very prejudicial fact about stl maps. For some reason I cant get objects being inserted in the map to get constructed/destructed only once. Example: struct MyObject{ MyObject(){ cout << "constructor" << endl; } ~MyObject(){ cout << "destructor" << endl; } }; int main() { std::map<int, MyObject> myObjectsMap; myObjectsMap[0] = MyObject(); return 0; } returns: constructor destructor destructor constructor destructor If I do: typedef std::pair<int, MyObject> MyObjectPair; myObjectsMap.insert( MyObjectPair(0,MyObject())); returns: constructor destructor destructor destructor I'm inserting Objects responsible for their own memory allocation, so when destructed they'll clean themselves up, being destructed several times is causing me some trouble.

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• Object for storing strings in Python

  - by evg

  class MyWriter: def __init__(self, stdout): self.stdout = stdout self.dumps = [] def write(self, text): self.stdout.write(smart_unicode(text).encode('cp1251')) self.dumps.append(text) def close(self): self.stdout.close() writer = MyWriter(sys.stdout) save = sys.stdout sys.stdout = writer I use self.dumps list to store data obtained from prints. Is there a more convenient object for storing string lines in memory? Ideally I want dump it to one big string. I can get it like this "\n".join(self.dumps) from code above. May be it's better to just concatenate strings - self.dumps += text?

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• Android - Opening phone deletes app state

  - by Tom G

  Hey everyone, I'm writing an android application that maintains a lot of "state" data...some of it I can save in the form of onSaveInstanceState but some of it is just to complex to save in memory. My problem is that sliding the phone open destroys/recreates the app, and I lose all my application state in the process. The same thing happens with the "back" button, but I overloaded that function on my way. Is there any way to overload the phone opening to prevent it from happening? Thanks in advance.

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• Small questions on data structure

  - by John Graveston

  Hi, I'm trying to search the parent of a node with Kruskal's algorithm. My program works just fine, but I think I have heard of a method to improve the speed of the algorithm by reconstructing the tree while searching for the parent node and connecting it to the parent node. I'm pretty sure that I've heard of this somewhere, maybe in a lecture. Can anyone refresh my memory? And also, given a number of arrays, when searching for the minimum and the maximum value from a certain section of an array, what is the name of the tree that can calculate the minimum/maximum value from the array by making a binary tree that has the minimum/maximum value of each array in O(log N)?

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• Mootools event leak

  - by user572263

  The example to demonstrate the issue can be found here: link text The test shows a basic Mootools class that contains an element variable with a click event attached. There’s also a “cleanup” function to remove the event and nullify the element variable. My problem is that when I loop a thousand times to create the “LeakClass” instance and clean it up, it causes a major memory leak like there’s no tomorrow. I tested this on IE8 and Chrome. On the other hand what I’ve noticed is that if I comment out the line that adds the “click” event, the code doesn’t leak. Can somebody please help me structure the class/event in a manner that it doesn’t leak. Thanks in advance.

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• Threading and cores

  - by Matt

  If I have X cores on my machine and I start X threads. Let's assume for the sake of argument that each thread is completely separated in terms of the memory, hdd, etc it uses. Is the OS going to know to send each thread to a core or do more time slicing on one core for multiple threads. What the question boils down to, is if I have X cores and my program must do independent calculations, should I start X threads, will they each get piped to a core, or is the presumption that because I have X cores I can start X threads completely wrong? I'm thinking it is. This is with C# --

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• Should I put a try-finally block after every Object.Create?

  - by max

  I have a general question about best practice in OO Delphi. Currently, I put try-finally blocks anywhere I create an object to free that object after usage (to avoid memory leaks). E.g.: aObject := TObject.Create; try aOBject.AProcedure(); ... finally aObject.Free; end; instead of: aObject := TObject.Create; aObject.AProcedure(); .. aObject.Free; Do you think it is good practice, or too much overhead? And what about the performance?

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• How to make an mutable C array for this data type?

  - by mystify

  There's this instance variable in my objective-c class: ALuint source; I need to have an mutable array of OpenAL Sources, so in this case probably I need a mutable C-array. But how would I create one? There are many questions regarding that: 1) How to create an mutable C-array? 2) How to add something to that mutable C-array? 3) How to remove something from that mutable C-array? 4) What memory management pitfalls must I be aware of? Must i free() it in my -dealloc method? And yes, I think this is something for the nice community wiki...

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• INSERT INTO ... SELECT ... vs dumping/loading a file in MySQL

  - by Daniel Huckstep

  What are the implications of using a INSERT INTO foo ... SELECT FROM bar JOIN baz ... style insert statement versus using the same SELECT statement to dump (bar, baz) to a file, and then insert into foo by loading the file? In my messing around, I haven't seen a huge difference. I would assume the former would use more memory, but the machine that this runs on has 8GB of RAM, and I never even see it go past half used. Are there any huge (or long term) performance implications that I'm not seeing? Advantages/disadvantages of either?

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• Heap Error in C++

  - by BobAlmond

  Dear all, I'm a beginner programmer in C++. Recently, I'm working on image processing thing using C++. but I have some problem that I want to ask. Suppose I have some code as follow: for (int i=0;i<100000;i++) { int * a = new int[10000]; //do something delete [] a; } When I executed that code, I receive runtime error, Heap Error... Is there anything wrong with that code, I mean, can I allocate memory and release it in the same loop? Thanks in advance...

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• Change url property of .sitemap

  - by user555209

  Hello I have multiple .sitemap xml defined with different providers. For one xml file, I want to change the url (append Customerid in the url) by taking the existing url in xml file. I want this to be changed when the page is loaded the first time. For eg one of my node is And I want to make it as I have read many articles online talking about changing node in memory but cant make it work. Any help would be appreciated. Not working with breadcrumbs or sitemapPath control.

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• is there a flag "M_FAST" in FreeBSD kernel for Malloc Call ?

  - by KaluSingh Gabbar

  if you know there is one, can you let me know what its for ? if not please say so : ) thanks. Signature : void * malloc(unsigned long size, struct malloc_type type, int flags); for example. other flags are... M_ZERO Causes the allocated memory to be set to all zeros. M_WAITOK Indicates that it is OK to wait for resources. If the request cannot be immediately fulfilled, the current process is put to sleep to wait for resources to be released by other processes. The malloc(), realloc(), and reallocf() functions cannot return NULL if M_WAITOK is specified.** This is the root of my confusion EDIT: The clarification for M_FAST is made in my answer below.

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