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• Should I trust Redis for data integrity?

  - by Jiaji

  In my current project, I have PostgreSQL as my master DB, and Redis as kind of a slave, e.g., when some user adds another as a friend, first the relationship will be stored in PostgreSQL and then a friend list in Redis will be updated. When some user's friend list is requested, it will be pulled out of Redis instead of PostgreSQL. The question is: when I update the friend list in Redis, should I get a fresh copy outof PostgreSQL, and replace the old list in Redis with the new one or should I keep the old list and simply SADD the userid into the list? The latter is of course best for performance, but intuitively the former does a better job in keep the data integrity? And if something like Celery is used, is the second method worth the risk?

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• know any good sites to place bid on domain names?

  - by sa125

  Hi - I would like to get a domain that's taken (but seems unused). Can anyone recommend good (read as "trusted") sites to make an offer to the domain owner? thanks.

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• variable names in function definition, call and declaration

  - by yCalleecharan

  Hi, I see C books that use the same variable names in the function definition, calling function and declaration. Others use the same variable names in the calling function and in the declaration/prototype but a different one in the definition as in: void blabla(int something); //prototype blabla(something) // calling function inside main after something has been initialized to int void blabla(int something_else) //definition I have two questions: What convention is best to use in C?; Does the convention apply regardless whether a value is being passed "by-value" or if it's being passed by a pointer? Thanks a lot...

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• Generating C++ BackTraces in OS/X (10.5.7)

  - by phillipwei

  I've been utilizing backtrace and backtrace_symbols to generate programmatic stack traces for the purposes of logging/diagnosis. It seems to roughly work, however, I'm getting a little bit of mangling and there are no accompanying file/line numbers associated with each function invocation (as I'd expect within a gdb bt call or something). Here's an example: 1 leonardo 0x00006989 _ZN9ExceptionC2E13ExceptionType + 111 2 leonardo 0x00006a20 _ZN9ExceptionC1E13ExceptionType + 24 3 leonardo 0x0000ab64 _ZN5Rules11ApplyActionER16ApplicableActionR9GameState + 1060 4 leonardo 0x0000ed15 _ZN9Simulator8SimulateEv + 2179 5 leonardo 0x0000eec9 _ZN9Simulator8SimulateEi + 37 6 leonardo 0x00009729 main + 45 7 leonardo 0x000025c6 start + 54 Anything I'm missing something, doing something silly, or is this all I can expect out of backtrace on OS/X? Some other tidbits: I don't see a rdynamic link option for the g++ version (4.0.1) I'm using. -g/-g3 doesn't make any difference. abi::__cxa__demangle doesn't seem to do anything

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• How to populate an array with recordset data

  - by Curtis Inderwiesche

  I am attempting to move data from a recordset directly into an array. I know this is possible, but specifically I want to do this in VBA as this is being done in MS Access 2003. Typically I would do something like the following to archive this: Dim vaData As Variant Dim rst As ADODB.Recordset ' Pull data into recordset code here... ' Populate the array with the whole recordset. vaData = rst.GetRows What differences exist between VB and VBA which makes this type of operation not work? What about performance concerns? Is this an "expensive" operations?

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• PHP MVC Framework Structure

  - by bigstylee

  I am sorry about the amount of code here. I have tried to show enough for understanding while avoiding confusion (I hope). I have included a second copy of the code at Pastebin. (The code does execute without error/notice/warning.) I am currently creating a Content Management System while trying to implement the idea of Model View Controller. I have only recently come across the concept of MVC (within the last week) and trying to implement this into my current project. One of the features of the CMS is dynamic/customisable menu areas and each feature will be represented by a controller. Therefore there will be multiple versions of the Controller Class, each with specific extended functionality. I have looked at a number of tutorials and read some open source solutions to the MVC Framework. I am now trying to create a lightweight solution for my specific requirements. I am not interested in backwards compatibility, I am using PHP 5.3. An advantage of the Base class is not having to use global and can directly access any loaded class using $this->Obj['ClassName']->property/function();. Hoping to get some feedback using the basic structure outlined (with performance in mind). Specifically; a) Have I understood/implemented the concept of MVC correctly? b) Have I understood/implemented Object Orientated techniques with PHP 5 correctly? c) Should the class propertise of Base be static? d) Improvements? Thank you very much in advance! <?php /* A "Super Class" that creates/stores all object instances */ class Base { public static $Obj = array(); // Not sure this is the correct use of the "static" keyword? public static $var; static public function load_class($directory, $class) { echo count(self::$Obj)."\n"; // This does show the array is getting updated and not creating a new array :) if (!isset(self::$Obj[$class]) && !is_object(self::$Obj[$class])) //dont want to load it twice { /* Locate and include the class file based upon name ($class) */ return self::$Obj[$class] = new $class(); } return TRUE; } } /* Loads general configuration objects into the "Super Class" */ class Libraries extends Base { public function __construct(){ $this->load_class('library', 'Database'); $this->load_class('library', 'Session'); self::$var = 'Hello World!'; //testing visibility /* Other general funciton classes */ } } class Database extends Base { /* Connects to the the database and executes all queries */ public function query(){} } class Session extends Base { /* Implements Sessions in database (read/write) */ } /* General functionality of controllers */ abstract class Controller extends Base { protected function load_model($class, $method) { /* Locate and include the model file */ $this->load_class('model', $class); call_user_func(array(self::$Obj[$class], $method)); } protected function load_view($name) { /* Locate and include the view file */ #include('views/'.$name.'.php'); } } abstract class View extends Base { /* ... */ } abstract class Model extends Base { /* ... */ } class News extends Controller { public function index() { /* Displays the 5 most recent News articles and displays with Content Area */ $this->load_model('NewsModel', 'index'); $this->load_view('news', 'index'); echo $this->var; } public function menu() { /* Displays the News Title of the 5 most recent News articles and displays within the Menu Area */ $this->load_model('news/index'); $this->load_view('news/index'); } } class ChatBox extends Controller { /* ... */ } /* Lots of different features extending the controller/view/model class depending upon request and layout */ class NewsModel extends Model { public function index() { echo $this->var; self::$Obj['Database']->query(/*SELECT 5 most recent news articles*/); } public function menu() { /* ... */ } } $Libraries = new Libraries; $controller = 'News'; // Would be determined from Query String $method = 'index'; // Would be determined from Query String $Content = $Libraries->load_class('controller', $controller); //create the controller for the specific page if (in_array($method, get_class_methods($Content))) { call_user_func(array($Content, $method)); } else { die('Bad Request'. $method); } $Content::$var = 'Goodbye World'; echo $Libraries::$var . ' - ' . $Content::$var; ?> /* Ouput */ 0 1 2 3 Goodbye World! - Goodbye World

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• Windows Azure Table Storage LINQ Operators

  - by Ryan Elkins

  Currently Table Storage supports From, Where, Take, and First. Are there plans to support any of the other 29 operators? If we have to code for these ourselves, how much of a performance difference are we looking at to something similar via SQL and SQL Server? Do you see it being somewhat comparable or will it be far far slower if I need to do a Count or Sum or Group By over a gigantic dataset? I like the Azure platform and the idea of cloud based storage. I like Windows Azure for the amount of data it can store and the schema-less nature of table storage. SQL Azure just won't work due to the high cost to storage space.

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• Must .aspx files have a page directive?

  - by Keith Bloom

  Around 90% of the pages for our websites have no .Net code embedded in them yet are published as .aspx files. I want these to render as fast as possible so I'm removing as much as I can. Does the .Net page directive have an impact on performance? I am thinking about two factors; the page speed for each GET and what happens when the file changes. The CMS system re-creates each page daily and I'm wondering if this triggers the ASP.Net compilation process.

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• MySQL: Storage of multiple text fields for a record

  - by Tom

  An inexperienced question: I need to store about 10 unknown-length text fields per record into a MySQL table. I expect no more than 50K rows in total for this table but speed is important. The database actions will be solely SELECTs for all practical purposes. I'm using InnoDB. In other words: id | text1 | text2 | text3 | .... | text10 As I understand that MySQL will store the text elsewhere and use its own indicators on the table itself, I'm wondering whether there's any fundamental performance implications that I should be worrying about given the way the data is stored? (i.e. several "sub-fetches" from the table). Thank you.

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• Strange profiling results: definitely non-bottleneck method pops up

  - by jkff

  I'm profiling a program using sampling profiling in YourKit and JProfiler, and also "manually" (I launch it and press Ctrl-Break several times to get thread dumps). All three methods give me extremely strange results: some tens of percents of time spent in a 3-line method that does not even do any allocation or synchronization and doesn't have loops etc. Moreover, after I made this method into a NOP and even removed its invocation completely, the observable program performance didn't change at all (although it got a negligible memory leak, since it was a method for freeing a cheap resource). I'm thinking that this might be because of the constraints that JVM puts on the moments at which a thread's stacktrace may be taken, and it somehow turns out that in my program it is exactly the moments where this method is invoked, although there is absolutely nothing special about it or the context in which it is invoked. What can be the explanation for this phenomenon? What are the aforementioned constraints? What further measurements can I take to clarify the situation?

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• Best data-structure to use for two ended sorted list

  - by fmark

  I need a collection data-structure that can do the following: Be sorted Allow me to quickly pop values off the front and back of the list Remain sorted after I insert a new value Allow a user-specified comparison function, as I will be storing tuples and want to sort on a particular value Thread-safety is not required Optionally allow efficient haskey() lookups (I'm happy to maintain a separate hash-table for this though) My thoughts at this stage are that I need a priority queue and a hash table, although I don't know if I can quickly pop values off both ends of a priority queue. I'm interested in performance for a moderate number of items (I would estimate less than 200,000). Another possibility is simply maintaining an OrderedDictionary and doing an insertion sort it every-time I add more data to it. Furthermore, are there any particular implementations in Python. I would really like to avoid writing this code myself.

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• What to monitor on MSSQL Server

  - by user361434

  Hi all I have been asked to monitor MSSQL Server (2005 & 2008) and am wondering what are good metrics to look at? I can access WMI counters but am slightly lost as to how much depth is going to be useful. Currently I have on my list: user connections logins per second latch waits per second total latch wait time dead locks per second errors per second Log and data file sizes I am looking to be able to monitor values that will indicate a degradation of performance on the machine or a potential serious issue. To this end I am also wondering at what values some of these things would be considered normal vs problematic? As I reckon it would probably be a really good question to have answered for the general community I thought i'd court some of you DBA experts out there (I am certainly not one of them!) Apologies if a rather open ended question. Ry

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• Oracle - timed sampling from v$session_longops

  - by FrustratedWithFormsDesigner

  I am trying to track performance on some procedures that run too slow (and seem to keep getting slower). I am using v$session_longops to track how much work has been done, and I have a query (sofar/((v$session_longops.LAST_UPDATE_TIME-v$session_longops.start_time)*24*60*60)) that tells me the rate at which work is being done. What I'd like to be able to do is capture the rate at which work is being done and how it changes over time. Right now, I just re-execute the query manually, and then copy/paste to Excel. Not very optimal, especially when the phone rings or something else happens to interrupt my sampling frequency. Is there a way to have script in SQL*Plus run a query evern n seconds, spool the results to a file, and then continue doing this until the job ends? (Oracle 10g)

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• How do I list the symbols in a .so file

  - by Moe

  How do list the symbols being exported from a .so file. If possible, I'd also like to know their source (e.g. if they are pulled in from a static library). I'm using gcc 4.0.2, if that makes a difference

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• Using install_name_tool what's going wrong?

  - by 0x80

  I'm trying to change the install path of a dylib after it has been build. I use "otool -L" to check what the current path is. And then I do: $ install_name_tool -change /my/current/path/libmine.dylib /my/new/path/libmine.dylib libmine.dylib I don't get an error, but nothing changes. If I check the path again the old one is still there. Also the new path is a lot shorter then the old one, so no problem there, and I think the lib is even compiled with extra flag for more filepath space. Any ideas?

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• Avoiding string copying in Lua

  - by Matt Sheppard

  Say I have a C program which wants to call a very simple Lua function with two strings (let's say two comma separated lists, returning true if the lists intersect at all, false if not). The obvious way to do this is to push them onto the stack with lua_pushstring, which works fine, however, from the doc it looks like lua_pushstring but makes a copy of the string for Lua to work with. That means that to cross over to the Lua function is going to require two string copies which I could avoid by rewriting the Lua function in C. Is there any way to arrange things so that the existing C strings could be reused on the Lua side for the sake of performance (or would the strcpy cost pale into insignificance anyway)? From my investigation so far (my first couple of hours looking seriously at Lua), lite userdata seems like the sort of thing I want, but in the form of a string.

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• COMET chat application - IIS7 slows down over time

  - by Yaron

  I have built a chat application which uses this code to push messages to clients (web pages) and to monitor online users and their information. Basically, the code creates and manages a custom thread pool for maintaining the list of connected users & their state. The application was hosted on a shared hosting account (IIS6), and worked fine. After moving the site (ASP.Net App) to a dedicated virtual server it seems I have a problem where IIS7 gets slower and slower as time passes, and my only "solution" is to restart IIS. I am trying to look at the performance counters and have do idea on which one to look.

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• Avoid IF statement after condition has been met

  - by greye

  I have a division operation inside a cycle that repeats many times. It so happens that in the first few passes through the loop (more or less first 10 loops) the divisor is zero. Once it gains value, a div by zero error is not longer possible. I have an if condition to test the divisor value in order to avoid the div by zero, but I am wondering that there is a performance impact that evaluating this if will have for each run in subsequent loops, especially since I know it's of no use anymore. How should this be coded? in Python?

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• Is str.replace(..).replace(..) ad nauseam a standard idiom in Python?

  - by meeselet

  For instance, say I wanted a function to escape a string for use in HTML (as in Django's escape filter): def escape(string): """ Returns the given string with ampersands, quotes and angle brackets encoded. """ return string.replace('&', '&amp;').replace('<', '&lt;').replace('>', '&gt;').replace("'", '&#39;').replace('"', '&quot;') This works, but it gets ugly quickly and appears to have poor algorithmic performance (in this example, the string is repeatedly traversed 5 times). What would be better is something like this: def escape(string): """ Returns the given string with ampersands, quotes and angle brackets encoded. """ # Note that ampersands must be escaped first; the rest can be escaped in # any order. return replace_multi(string.replace('&', '&amp;'), {'<': '&lt;', '>': '&gt;', "'": '&#39;', '"': '&quot;'}) Does such a function exist, or is the standard Python idiom to use what I wrote before?

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• How to calculate a operation's time in micro second precision

  - by Sanjeet Daga

  I want to calculate performance of a function in micro second precision on Windows platform. Now Windows itself has milisecond granuality, so how can I achieve this. I tried following sample, but not getting correct results. LARGE_INTEGER ticksPerSecond = {0}; LARGE_INTEGER tick_1 = {0}; LARGE_INTEGER tick_2 = {0}; double uSec = 1000000; // Get the frequency QueryPerformanceFrequency(&ticksPerSecond); //Calculate per uSec freq double uFreq = ticksPerSecond.QuadPart/uSec; // Get counter b4 start of op QueryPerformanceCounter(&tick_1); // The ope itself Sleep(10); // Get counter after opfinished QueryPerformanceCounter(&tick_2); // And now the op time in uSec double diff = (tick_2.QuadPart/uFreq) - (tick_1.QuadPart/uFreq);

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• Will PHP Die In Web Page Development World?

  - by Morgan Cheng

  I know that PHP is still the most popular web programming language in the world. This question just want to bring some of my concerns about PHP. PHP is naturally bound to C10K problem. Since PHP (generally run in Apache) cannot be event-driven or asynchronous, each HTTP request will occupy at least one thread or process. This makes it resistant to be more scalable. Currently, a lot of web sites (like Facebook) with high performance and scalability still depends on PHP in their front end servers. I suppose it is due to legacy reason. Is it possible that PHP will be replaced by language more suitable for C10K?

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• Reading from a file not line-by-line

  - by MadH

  Assigning a QTextStream to a QFile and reading it line-by-line is easy and works fine, but I wonder if the performance can be inreased by first storing the file in memory and then processing it line-by-line. Using FileMon from sysinternals, I've encountered that the file is read in chunks of 16KB and since the files I've to process are not that big (~2MB, but many!), loading them into memory would be a nice thing to try. Any ideas how can I do so? QFile is inhereted from QIODevice, which allows me to ReadAll() it into QByteArray, but how to proceed then and divide it into lines?

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• Under what circumstances does Groovy use AbstractConcurrentMap?

  - by Electrons_Ahoy

  (Specifically, org.codehaus.groovy.util.AbstractConcurrentMap) While doing some profiling of our application thats mixed Java/Groovy, I'm seeing a lot of references to the AbstractConcurrentMap class, none of which are explicit in the code base. Does groovy use this class when maps are instantiated in the groovy dynamic def myMap = [:] style? Are there rules somewhere about when groovy chooses to use this as opposed to, say, java.util.HashMap? And does anyone have any performance information comparing the two? My rough "eyeball check" says that AbstractConcurrentMap seems to be much slower - anyone know if I'm right?

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• Should I use integer primary IDs?

  - by arthurprs

  For example, I always generate an auto-increment field for the users table, but I also specify a UNIQUE index on their usernames. There are situations that I first need to get the userId for a given username and then execute the desired query, or use a JOIN in the desired query. It's 2 trips to the database or a JOIN vs. a varchar index. Should I use integer primary IDs? Is there a real performance benefit on INT over small VARCHAR indexes?

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• C++ Asymptotic Profiling

  - by Travis

  I have a performance issue where I suspect one standard C library function is taking too long and causing my entire system (suite of processes) to basically "hiccup". Sure enough if I comment out the library function call, the hiccup goes away. This prompted me to investigate what standard methods there are to prove this type of thing? What would be the best practice for testing a function to see if it causes an entire system to hang for a sec (causing other processes to be momentarily starved)? I would at least like to definitively correlate the function being called and the visible freeze. Thanks

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