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  • Circumvent c++ null-terminated string frustration

    - by ypnos
    I'm using boost::program_options and it suffers from the same as many other c++ libs, even std itself: It still uses C-style null-terminated strings, because nobody really likes the weak std::string. The method in question is: options_description_easy_init& operator()(const char* name, const value_semantic* s, const char* description); The typical use case is just fine: options.add_options() ("graphical", bool_switch(&isGraphical)->default_value(false), "Show any graphical output during runtime") However, I need the name of the option to be set dynamically. The reason is that in some cases I nead a custom prefix, which is added to the string by my function std::string key(const std::string& k): options.add_options() (key("graphical"), bool_switch(&isGraphical)->default_value(false), "Show any graphical output during runtime") This fails. I could now use c_str() on the std::string but that's evil -- I don't know how long program_options keeps the variable around and if my string is still alive when needed. I could also reserve memory in a buffer etc. and hand in that. The buffer is never freed and it sucks/is evil. Is there anything else I can do to circumvent the C-style string mess in this situation?

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  • MAC : How to check if the file is still being copied in cpp?

    - by Peda Pola
    In my current project, we had a requirement to check if the file is still copying. We have already developed a library which will give us OS notification like file_added , file_removed , file_modified, file_renamed on a particular folder along with the corresponding file path. The problem here is that, lets say if you add 1 GB file, it is giving multiple notification such as file_added , file_modified, file_modified as the file is being copied. Now i decided to surpass these notifications by checking if the file is copying or not. Based on that i will ignore events. I have written below code which tells if the file is being copied or not which takes file path as input parameter. Details:- In Mac, while file is being copied the creation date is set as some date less than 1970. Once it is copied the date is set to current date. Am using this technique. Based on this am deciding that file is being copied. Problem:- when we copy file in the terminal it is failing. Please advice me any approach. bool isBeingCopied(const boost::filesystem::path &filePath) { NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init]; bool isBeingCopied = false; if([[[[NSFileManager defaultManager] attributesOfItemAtPath:[NSString stringWithUTF8String:filePath.string().c_str()] error:nil] fileCreationDate] timeIntervalSince1970] < 0) { isBeingCopied = true; } [pool release]; return isBeingCopied; }

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  • Rationale in selecting Hash Key type

    - by Amrish
    Guys, I have a data structure which has 25 distinct keys (integer) and a value. I have a list of these objects (say 50000) and I intend to use a hash table to store/retrieve them. I am planning to take one of these approaches. Create a integer hash from these 25 integer keys and store it on a hash table. (Yeah! I have some means to handle collisions) Make a string concatenation on the individual keys and use it as a hash key for the hash table. For example, if the key values are 1,2,4,6,7 then the hash key would be "12467". Assuming that I have a total of 50000 records each with 25 distinct keys and a value, then will my second approach be a overkill when it comes to the cost of string comparisons it needs to do to retrieve and insert a record? Some more information! Each bucket in the hash table is a balanced binary tree. I am using the boost library's hash_combine method to create the hash from the 25 keys.

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  • Prototyping Qt/C++ in Python

    - by tstenner
    I want to write a C++ application with Qt, but build a prototype first using Python and then gradually replace the Python code with C++. Is this the right approach, and what tools (bindings, binding generators, IDE) should I use? Ideally, everything should be available in the Ubuntu repositories so I wouldn't have to worry about incompatible or old versions and have everything set up with a simple aptitude install. Is there any comprehensive documentation about this process or do I have to learn every single component, and if yes, which ones? Right now I have multiple choices to make: Qt Creator, because of the nice auto completion and Qt integration. Eclipse, as it offers support for both C++ and Python. Eric (haven't used it yet) Vim PySide as it's working with CMake and Boost.Python, so theoretically it will make replacing python code easier. PyQt as it's more widely used (more support) and is available as a Debian package. Edit: As I will have to deploy the program to various computers, the C++-solution would require 1-5 files (the program and some library files if I'm linking it statically), using Python I'd have to build PyQt/PySide/SIP/whatever on every platform and explain how to install Python and everything else.

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  • Interface Builder vs Cocos 2D - how choice the best for your app.

    - by baDa
    Hello everyone! I was a flash developer for 3 years, and in the last 5 months, i begin the iphone development, i do 2 applications with interface builder for clients, and now i really want to do a little game, is quite simple, one match 3! I made the engine in interface builder, and seens good to me! But after i read some posts, i really want to try it in the cocos2D! So, in 2 days i rewrite all my first engine for cocos2D, very annoying upsidedown coordinates but ok, i really do! But the performance side by side with interface builder version is really scare! Many Many slow downs at the cocos2d side! And the animation seens bugged to me! I really scare! I really don't know what is the best choice for a simple game. And i want some opinions: Using cocos2d when need some physics? When we have many objects at screen? What is the performance boost i have with cocos2D? I have how to share this 2 applications with you guys?! Without your UID?!

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  • Tree iterator, can you optimize this any further?

    - by Ron
    As a follow up to my original question about a small piece of this code I decided to ask a follow up to see if you can do better then what we came up with so far. The code below iterates over a binary tree (left/right = child/next ). I do believe there is room for one less conditional in here (the down boolean). The fastest answer wins! The cnt statement can be multiple statements so lets make sure this appears only once The child() and next() member functions are about 30x as slow as the hasChild() and hasNext() operations. Keep it iterative <-- dropped this requirement as the recursive solution presented was faster. This is C++ code visit order of the nodes must stay as they are in the example below. ( hit parents first then the children then the 'next' nodes). BaseNodePtr is a boost::shared_ptr as thus assignments are slow, avoid any temporary BaseNodePtr variables. Currently this code takes 5897ms to visit 62200000 nodes in a test tree, calling this function 200,000 times. void processTree (BaseNodePtr current, unsigned int & cnt ) { bool down = true; while ( true ) { if ( down ) { while (true) { cnt++; // this can/will be multiple statesments if (!current->hasChild()) break; current = current->child(); } } if ( current->hasNext() ) { down = true; current = current->next(); } else { down = false; current = current->parent(); if (!current) return; // done. } } }

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  • Is it possible to load an entire SQL Server CE database into RAM?

    - by DanM
    I'm using LinqToSql to query a small SQL Server CE database. I've noticed that any operations involving sub-properties are disappointingly slow. For example, if I have a Customer table that is referenced by an Order table via a foreign key, LinqToSql will automatically create an EntitySet<Order> property. This is a nice convenience, allowing me to do things like Customer.Order.Where(o => o.ProductName = "Stopwatch"), but for some reason, SQL Server CE hangs up pretty bad when I try to do stuff like this. One of my queries, which isn't really that complicated takes 3-4 seconds to complete. I can get the speed up to acceptable, even fast, if I just grab the two tables individually and convert them to List<Customer> and List<Order>, then join then manually with my own query, but this is throwing out a lot of the appeal of LinqToSql. So, I'm wondering if I can somehow get the whole database into RAM and just query that way, then occasionally save it. Is this possible? How? If not, is there anything else I can do to boost the performance? Note: My database in its initial state is about 250K and I don't expect it to grow to more than 1-2Mb. So, loading the data into RAM certainly wouldn't be a problem from a memory point of view.

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  • C++/Qt - Memory allocation question

    - by HardCoder1986
    Hello! I recently started investigating Qt for myself and have the following question: Suppose I have some QTreeWidget* widget. At some moment I want to add some items to it and this is done via the following call: QList<QTreeWidgetItem*> items; // Prepare the items QTreeWidgetItem* item1 = new QTreeWidgetItem(...); QTreeWidgetItem* item2 = new QTreeWidgetItem(...); items.append(item1); items.append(item2); widget->addTopLevelItems(items); So far it looks ok, but I don't actually understand who should control the objects' lifetime. I should explain this with an example: Let's say, another function calls widget->clear();. I don't know what happens beneath this call but I do think that memory allocated for item1 and item2 doesn't get disposed here, because their ownage wasn't actually transfered. And, bang, we have a memory leak. The question is the following - does Qt have something to offer for this kind of situation? I could use boost::shared_ptr or any other smart pointer and write something like shared_ptr<QTreeWidgetItem> ptr(new QTreeWidgetItem(...)); items.append(ptr.get()); but I don't know if the Qt itself would try to make explicit delete calls on my pointers (which would be disastrous since I state them as shared_ptr-managed). How would you solve this problem? Maybe everything is evident and I miss something really simple?

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  • Member function overloading/template specialization issue

    - by Ferruccio
    I've been trying to call the overloaded table::scan_index(std::string, ...) member function without success. For the sake of clarity, I have stripped out all non-relevant code. I have a class called table which has an overloaded/templated member function named scan_index() in order to handle strings as a special case. class table : boost::noncopyable { public: template <typename T> void scan_index(T val, std::function<bool (uint recno, T val)> callback) { // code } void scan_index(std::string val, std::function<bool (uint recno, std::string val)> callback) { // code } }; Then there is a hitlist class which has a number of templated member functions which call table::scan_index(T, ...) class hitlist { public: template <typename T> void eq(uint fieldno, T value) { table* index_table = db.get_index_table(fieldno); // code index_table->scan_index<T>(value, [&](uint recno, T n)->bool { // code }); } }; And, finally, the code which kicks it all off: hitlist hl; // code hl.eq<std::string>(*fieldno, p1.to_string()); The problem is that instead of calling table::scan_index(std::string, ...), it calls the templated version. I have tried using both overloading (as shown above) and a specialized function template (below), but nothing seems to work. After staring at this code for a few hours, I feel like I'm missing something obvious. Any ideas? template <> void scan_index<std::string>(std::string val, std::function<bool (uint recno, std::string val)> callback) { // code }

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  • Creating serializeable unique compile-time identifiers for arbitrary UDT's.

    - by Endiannes
    I would like a generic way to create unique compile-time identifiers for any C++ user defined types. for example: unique_id<my_type>::value == 0 // true unique_id<other_type>::value == 1 // true I've managed to implement something like this using preprocessor meta programming, the problem is, serialization is not consistent. For instance if the class template unique_id is instantiated with other_type first, then any serialization in previous revisions of my program will be invalidated. I've searched for solutions to this problem, and found several ways to implement this with non-consistent serialization if the unique values are compile-time constants. If RTTI or similar methods, like boost::sp_typeinfo are used, then the unique values are obviously not compile-time constants and extra overhead is present. An ad-hoc solution to this problem would be, instantiating all of the unique_id's in a separate header in the correct order, but this causes additional maintenance and boilerplate code, which is not different than using an enum unique_id{my_type, other_type};. A good solution to this problem would be using user-defined literals, unfortunately, as far as I know, no compiler supports them at this moment. The syntax would be 'my_type'_id; 'other_type'_id; with udl's. I'm hoping somebody knows a trick that allows implementing serialize-able unique identifiers in C++ with the current standard (C++03/C++0x), I would be happy if it works with the latest stable MSVC and GNU-G++ compilers, although I expect if there is a solution, it's not portable.

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  • What wrapper class in C++ should I use for automated resource management?

    - by Vilx-
    I'm a C++ amateur. I'm writing some Win32 API code and there are handles and weirdly compositely allocated objects aplenty. So I was wondering - is there some wrapper class that would make resource management easier? For example, when I want to load some data I open a file with CreateFile() and get a HANDLE. When I'm done with it, I should call CloseHandle() on it. But for any reasonably complex loading function there will be dozens of possible exit points, not to mention exceptions. So it would be great if I could wrap the handle in some kind of wrapper class which would automatically call CloseHandle() once execution left the scope. Even better - it could do some reference counting so I can pass it around in and out of other functions, and it would release the resource only when the last reference left scope. The concept is simple - but is there something like that in the standard library? I'm using Visual Studio 2008, by the way, and I don't want to attach a 3rd party framework like Boost or something.

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  • Build OpenGL model in parallel?

    - by Brendan Long
    I have a program which draws some terrain and simulates water flowing over it (in a cheap and easy way). Updating the water was easy to parallelize using OpenMP, so I can do ~50 updates per second. The problem is that even with a small amounts of water, my draws per second are very very low (starts at 5 and drops to around 2 once there's a significant amount of water). It's not a problem with the video card because the terrain is more complicated and gets drawn so quickly that boost::timer tells me that I get infinity draws per second if I turn the water off. It may be related to memory bandwidth though (since I assume the model stays on the card and doesn't have to be transfered every time). What I'm concerned about is that on every draw, I'm calling glVertex3f() about a million times (max size is 450*600, 4 vertices each), and it's done entirely sequentially because Glut won't let me call anything in parallel. So.. is if there's some way of building the list in parallel and then passing it to OpenGL all at once? Or some other way of making it draw this faster? Am I using the wrong method (besides the obvious "use less vertices")?

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  • How can I write a function template for all types with a particular type trait?

    - by TC
    Consider the following example: struct Scanner { template <typename T> T get(); }; template <> string Scanner::get() { return string("string"); } template <> int Scanner::get() { return 10; } int main() { Scanner scanner; string s = scanner.get<string>(); int i = scanner.get<int>(); } The Scanner class is used to extract tokens from some source. The above code works fine, but fails when I try to get other integral types like a char or an unsigned int. The code to read these types is exactly the same as the code to read an int. I could just duplicate the code for all other integral types I'd like to read, but I'd rather define one function template for all integral types. I've tried the following: struct Scanner { template <typename T> typename enable_if<boost::is_integral<T>, T>::type get(); }; Which works like a charm, but I am unsure how to get Scanner::get<string>() to function again. So, how can I write code so that I can do scanner.get<string>() and scanner.get<any integral type>() and have a single definition to read all integral types? Update: bonus question: What if I want to accept more than one range of classes based on some traits? For example: how should I approach this problem if I want to have three get functions that accept (i) integral types (ii) floating point types (iii) strings, respectively.

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  • How string accepting interface should look like?

    - by ybungalobill
    Hello, This is a follow up of this question. Suppose I write a C++ interface that accepts or returns a const string. I can use a const char* zero-terminated string: void f(const char* str); // (1) The other way would be to use an std::string: void f(const string& str); // (2) It's also possible to write an overload and accept both: void f(const char* str); // (3) void f(const string& str); Or even a template in conjunction with boost string algorithms: template<class Range> void f(const Range& str); // (4) My thoughts are: (1) is not C++ish and may be less efficient when subsequent operations may need to know the string length. (2) is bad because now f("long very long C string"); invokes a construction of std::string which involves a heap allocation. If f uses that string just to pass it to some low-level interface that expects a C-string (like fopen) then it is just a waste of resources. (3) causes code duplication. Although one f can call the other depending on what is the most efficient implementation. However we can't overload based on return type, like in case of std::exception::what() that returns a const char*. (4) doesn't work with separate compilation and may cause even larger code bloat. Choosing between (1) and (2) based on what's needed by the implementation is, well, leaking an implementation detail to the interface. The question is: what is the preffered way? Is there any single guideline I can follow? What's your experience?

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  • Is it possible to cache all the data in a SQL Server CE database using LinqToSql?

    - by DanM
    I'm using LinqToSql to query a small, simple SQL Server CE database. I've noticed that any operations involving sub-properties are disappointingly slow. For example, if I have a Customer table that is referenced by an Order table, LinqToSql will automatically create an EntitySet<Order> property. This is a nice convenience, allowing me to do things like Customer.Order.Where(o => o.ProductName = "Stopwatch"), but for some reason, SQL Server CE hangs up pretty bad when I try to do stuff like this. One of my queries, which isn't really that complicated takes 3-4 seconds to complete. I can get the speed up to acceptable, even fast, if I just grab the two tables individually and convert them to List<Customer> and List<Order>, then join then manually with my own query, but this is throwing out a lot of what makes LinqToSql so appealing. So, I'm wondering if I can somehow get the whole database into RAM and just query that way, then occasionally save it. Is this possible? How? If not, is there anything else I can do to boost the performance besides resorting to doing all the joins manually? Note: My database in its initial state is about 250K and I don't expect it to grow to more than 1-2Mb. So, loading the data into RAM certainly wouldn't be a problem from a memory point of view. Update Here are the table definitions for the example I used in my question: create table Order ( Id int identity(1, 1) primary key, ProductName ntext null ) create table Customer ( Id int identity(1, 1) primary key, OrderId int null references Order (Id) )

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  • Portable way of counting milliseconds in C++ ?

    - by ereOn
    Hi, Is there any portable (Windows & Linux) way of counting how many milliseconds elapsed between two calls ? Basically, I want to achieve the same functionnality than the StopWatch class of .NET. (for those who already used it) In a perfect world, I would have used boost::date_time but that's not an option here due to some silly rules I'm enforced to respect. For those who better read code, this is what I'd like to achieve. Timer timer; timer.start(); // Some instructions here timer.stop(); // Print out the elapsed time std::cout << "Elapsed time: " << timer.milliseconds() << "ms" << std::endl; So, if there is a portable (set of) function(s) that can help me implement the Timer class, what is it ? If there is no such function, what Windows & Linux API should I use to achieve this functionnality ? (using #ifdef WINDOWS-like macros) Thanks !

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  • C Population Count of unsigned 64-bit integer with a maximum value of 15

    - by BitTwiddler1011
    I use a population count (hamming weight) function intensively in a windows c application and have to optimize it as much as possible in order to boost performance. More than half the cases where I use the function I only need to know the value to a maximum of 15. The software will run on a wide range of processors, both old and new. I already make use of the POPCNT instruction when Intel's SSE4.2 or AMD's SSE4a is present, but would like to optimize the software implementation (used as a fall back if no SSE4 is present) as much as possible. Currently I have the following software implementation of the function: inline int population_count64(unsigned __int64 w) { w -= (w 1) & 0x5555555555555555ULL; w = (w & 0x3333333333333333ULL) + ((w 2) & 0x3333333333333333ULL); w = (w + (w 4)) & 0x0f0f0f0f0f0f0f0fULL; return int(w * 0x0101010101010101ULL) 56; } So to summarize: (1) I would like to know if it is possible to optimize this for the case when I only want to know the value to a maximum of 15. (2) Is there a faster software implementation (for both Intel and AMD CPU's) than the function above?

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  • What to throw in a C++ class wrapping a C library ?

    - by ereOn
    I have to create a set of wrapping C++ classes around an existing C library. For many objects of the C library, the construction is done by calling something like britney_spears* create_britney_spears() and the opposite function void free_britney_spears(britney_spears* brit). If the allocation of a britney_spears fails, create_britney_spears() returns NULL. This is, as far as I know, a very common pattern. Now I want to wrap this inside a C++ class. //britney_spears.hpp class BritneySpears { public: BritneySpears(); private: boost::shared_ptr<britney_spears> m_britney_spears; }; And here is the implementation: // britney_spears.cpp BritneySpears::BritneySpears() : m_britney_spears(create_britney_spears(), free_britney_spears) { if (!m_britney_spears) { // Here I should throw something to abort the construction, but what ??! } } So the question is in the code sample: What should I throw to abort the constructor ? I know I can throw almost anything, but I want to know what is usually done. I have no other information about why the allocation failed. Should I create my own exception class ? Is there a std exception for such cases ? Many thanks.

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  • php / phpDoc - @return instance of $this class ?

    - by searbe
    How do I mark a method as "returns an instance of the current class" in my phpDoc? In the following example my IDE (Netbeans) will see that setSomething always returns a foo object. But that's not true if I extent the object - it'll return $this, which in the second example is a bar object not a foo object. class foo { protected $_value = null; /** * Set something * * @param string $value the value * @return foo */ public function setSomething($value) { $this->_value = $value; return $this; } } $foo = new foo(); $out = $foo->setSomething(); So fine - setSomething returns a foo - but in the following example, it returns a bar..: class bar extends foo { public function someOtherMethod(){} } $bar = new bar(); $out = $bar->setSomething(); $out->someOtherMethod(); // <-- Here, Netbeans will think $out // is a foo, so doesn't see this other // method in $out's code-completion ... it'd be great to solve this as for me, code completion is a massive speed-boost. Anyone got a clever trick, or even better, a proper way to document this with phpDoc?

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  • how to pass vector of string to foo(char const *const *const)?

    - by user347208
    Hi, This is my first post so please be nice. I searched in this forum and googled but I still can not find the answer. This problem has bothered me for more than a day, so please give me some help. Thank you. I need to pass a vector of string to a library function foo(char const *const *const). I can not pass the &Vec[0] since it's a pointer to a string. Therefore, I have an array and pass the c_str() to that array. The following is my code (aNames is the vector of string): const char* aR[aNames.size()]; std::transform(aNames.begin(), aNames.end(), aR, boost::bind(&std::string::c_str, _1)); foo(aR); However, it seems it causes some undefined behavior: If I run the above code, then the function foo throw some warnings about illegal characters ('èI' blablabla) in aR. If I print aR before function foo like this: std::copy(aR, aR+rowNames.size(), std::ostream_iterator<const char*>(std::cout, "\n")); foo(aR); Then, everything is fine. My questions are: Does the conversion causes undefined behavior? If so, why? What is the correct way to pass vector of string to foo(char const *const *const)? Thank you very much for your help!

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  • C++0x Smart Pointer Comparisons: Inconsistent, what's the rationale?

    - by GManNickG
    In C++0x (n3126), smart pointers can be compared, both relationally and for equality. However, the way this is done seems inconsistent to me. For example, shared_ptr defines operator< be equivalent to: template <typename T, typename U> bool operator<(const shared_ptr<T>& a, const shared_ptr<T>& b) { return std::less<void*>()(a.get(), b.get()); } Using std::less provides total ordering with respect to pointer values, unlike a vanilla relational pointer comparison, which is unspecified. However, unique_ptr defines the same operator as: template <typename T1, typename D1, typename T2, typename D2> bool operator<(const unique_ptr<T1, D1>& a, const unique_ptr<T2, D2>& b) { return a.get() < b.get(); } It also defined the other relational operators in similar fashion. Why the change in method and "completeness"? That is, why does shared_ptr use std::less while unique_ptr uses the built-in operator<? And why doesn't shared_ptr also provide the other relational operators, like unique_ptr? I can understand the rationale behind either choice: with respect to method: it represents a pointer so just use the built-in pointer operators, versus it needs to be usable within an associative container so provide total ordering (like a vanilla pointer would get with the default std::less predicate template argument) with respect to completeness: it represents a pointer so provide all the same comparisons as a pointer, versus it is a class type and only needs to be less-than comparable to be used in an associative container, so only provide that requirement But I don't see why the choice changes depending on the smart pointer type. What am I missing? Bonus/related: std::shared_ptr seems to have followed from boost::shared_ptr, and the latter omits the other relational operators "by design" (and so std::shared_ptr does too). Why is this?

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  • [c++/STL] Selective iterator

    - by rubenvb
    FYI: no boost, yes it has this, I want to reinvent the wheel ;) Is there some form of a selective iterator (possible) in C++? What I want is to seperate strings like this: some:word{or other to a form like this: some : word { or other I can do that with two loops and find_first_of(":") and ("{") but this seems (very) inefficient to me. I thought that maybe there would be a way to create/define/write an iterator that would iterate over all these values with for_each. I fear this will have me writing a full-fledged custom way-too-complex iterator class for a std::string. So I thought maybe this would do: std::vector<size_t> list; size_t index = mystring.find(":"); while( index != std::string::npos ) { list.push_back(index); index = mystring.find(":", list.back()); } std::for_each(list.begin(), list.end(), addSpaces(mystring)); This looks messy to me, and I'm quite sure a more elegant way of doing this exists. But I can't think of it. Anyone have a bright idea? Thanks PS: I did not test the code posted, just a quick write-up of what I would try

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  • Can someone explain RAID-0 in plain English?

    - by Edward Tanguay
    I've heard about and read about RAID throughout the years and understand it theoretically as a way to help e.g. server PCs reduce the chance of data loss, but now I am buying a new PC which I want to be as fast as possible and have learned that having two drives can considerably increase the perceived performance of your machine. In the question Recommendations for hard drive performance boost, the author says he is going to RAID-0 two 7200 RPM drives together. What does this mean in practical terms for me with Windows 7 installed, e.g. can I buy two drives, go into the device manager and "raid-0 them together"? I am not a network administrator or a hardware guy, I'm just a developer who is going to have a computer store build me a super fast machine next week. I can read the wikipedia page on RAID but it is just way too many trees and not enough forest to help me build a faster PC: RAID-0: "Striped set without parity" or "Striping". Provides improved performance and additional storage but no redundancy or fault tolerance. Because there is no redundancy, this level is not actually a Redundant Array of Inexpensive Disks, i.e. not true RAID. However, because of the similarities to RAID (especially the need for a controller to distribute data across multiple disks), simple strip sets are normally referred to as RAID 0. Any disk failure destroys the array, which has greater consequences with more disks in the array (at a minimum, catastrophic data loss is twice as severe compared to single drives without RAID). A single disk failure destroys the entire array because when data is written to a RAID 0 drive, the data is broken into fragments. The number of fragments is dictated by the number of disks in the array. The fragments are written to their respective disks simultaneously on the same sector. This allows smaller sections of the entire chunk of data to be read off the drive in parallel, increasing bandwidth. RAID 0 does not implement error checking so any error is unrecoverable. More disks in the array means higher bandwidth, but greater risk of data loss. So in plain English, how can "RAID-0" help me build a faster Windows-7 PC that I am going to order next week?

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  • Sysadmin 101: How can I figure out why my server crashes and monitor performance?

    - by bflora
    I have a Drupal-powered site that seems to have neverending performance problems. It was butt-slow about 5 months ago. I brought in some guys who installed nginx for anonymous visitors, ajaxified a few queries so they wouldn't fire during page load, and helped me find a few bottlenecks in the code. For about a month, the site was significantly faster, though not "fast" by any stretch of the word. Meanwhile, I'm now shelling out $400/month to Slicehost to host a site that gets less than 5,000/uniques a day. Yes, you read that right. Go Drupal. Recently the site started crashing again and is slow again. I can't afford to hire people to come in, study my code from top to bottom, and make changes that may or may not help anymore. And I can't afford to throw more hardware at the problem. So I need to figure out what the problem is myself. Questions: When apache crashes, is it possible to find out what caused it to crash? There has to be a way, right? If so, how can I do this? Is there software I can use that will tell me which process caused my server to die? (e.g. "Apache crashed because someone visited page X." or "Apache crashed because you were importing too many RSS items from feed X.") There's got to be a way to learn this, right? What's a good, noob-friendly way to monitor my current apache performance? My developer friends tell me to "just use Top, dude," but Top shows me a bunch of numbers without any context. I have no clue what qualifies as a bad number or a good number in Top, or which processes are relevant and which aren't. Are there any noob-friendly server monitoring tools out there? Ideally, I could have a page that would give me a color-coded indicator about how apache is performing and then show me a list of processes or pages that are sucking right now. This way, I could know when performance is bad and then what's causing it to be so bad. Why does PHP memory matter? My apparently has a 30MB memory foot print. Will it run faster if I bring that number down? Thanks for any advice. I spent a year or so trying to boost my advertising income so I could hire a contractor to solve my performance woes. I didn't want to have to learn all this sysadmin voodoo. I'm now resigned to the fact that might not have a choice.

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  • How can I verify that my SSD is performing as it should?

    - by Jon Skeet
    EDIT: Okay, so I've no idea what caused the change, but after trying loads of different things to work out what was wrong, I've rerun the WEI (about the 4th time in total) and the score has jumped to a far more respectable 7.3. I'm going to leave well alone now :) I've got a brand new 256GB SSD (Crucial CT256M225) which should have stellar performance. However, on my (also brand new) Dell Studio 1557 with Windows 7 Professional 64 bit, it's only giving a performance index of 5.9. I realise the performance index should be taken with a bit of a pinch of salt, but I wonder whether something's wrong. Given this paragraph from this MSDN article on Windows 7, I'd expect to see a high 6.X or possible a 7.X figure: In Windows 7, there are new random read, random write and flush assessments. Better SSDs can score above 6.5 all the way to 7.9. To be included in that range, an SSD has to have outstanding random read rates and be resilient to flush and random write workloads. In the Beta timeframe of Windows 7, there was a capping of scores at 1.9, 2.9 or the like if a disk (SSD or HDD) didn’t perform adequately when confronted with our random write and flush assessments. Feedback on this was pretty consistent, with most feeling the level of capping to be excessive. As a result, we now simply restrict SSDs with performance issues from joining the newly added 6.0+ and 7.0+ ranges. SSDs that are not solid performers across all assessments effectively get scored in a manner similar to what they would have been in Windows Vista, gaining no Win7 boost for great random read performance. How can I diagnose any performance issues with either the disk or how Windows 7 is handling it? Are there any particularly good tools you'd recommend? One note of curiosity: I couldn't install the firmware update (to 1916) until I changed my BIOS handling of the drive to ATA mode; after installing the firmware I tried to boot the Windows installation DVD - but that only worked after turning it back to AHCI mode (which I've left it in). Installing Windows 7 took longer than I expected - it sat at the "Windows is loading files" prompt for a very long time. Likewise it was on "Expanding files (0%)" for a long time. Since installation it's been fine though - but I don't know whether it's really providing quite as beefy performance as it should. EDIT: My netbook with the 64GB equivalent drive has a performance index of 6.6...

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