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• Is it really wrong to version documents using CouchDB's behaviour?

  - by Tomas Sedovic

  This is one of those "I know I shouldn't do this but it's oh so convenient." questions. Sorry about that. I plan to use CouchDB for storing a bunch of documents and keeping their entire revision history. CouchDB does the versioning automatically, but it is strongly discouraged for programmer's use: "You cannot rely on document revisions for any other purpose than concurrency control." From what I've found on the CouchDB wiki, the versions can get deleted either during compaction or during replication. As far as I can tell, Compaction must always be triggered manually and Replication occurs only when there's more than one database server. The question is: if I won't run compaction and will use only single database instance for my documents, can I just use CouchDB's document versioning and expect it to work? What other problems I might run into? E.g. does not running compaction hurt the performance or consume significantly more disk space (than if I did handle the versioning manually)?

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• Figuring out what makes a C++ class abstract in VS2008

  - by suszterpatt

  I'm using VS2008 to build a plain old C++ program (not C++/CLI). I have an abstract base class and a non-abstract derived class, and building this: Base* obj; obj = new Derived(); fails with the error "'Derived': cannot instantiate abstract class". (It may be worth noting, however, that if I hover over Base with the cursor, VS will pop up a tooltip saying "class Base abstract", but hovering over Derived will only say "class Derived" (no "abstract")). The definitions of these classes are fairly large and I'd like to avoid manually checking if each method has been overridden. Can VS do this for me somehow? Any general tips on pinpointing the exact parts of the class' definition that make it abstract?

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• Is there a good collection library for C-language?

  - by matti

  We have to maintain and even develop C-code of our legacy system. Is there good collection library that would support Java/C# (new versions) style collections. Hashtable, HashSet, etc. Of course without objects, but with structs. The HashTable key limitations to "strings" and ints is not a problem. It wouldn't be bad if it's free even for commercial use. I'm back to C from C# and I must say i'm depressed using our own libraries and the language in general. We're using VS2005 and MS C-compiler if that has nothing to do with anything. Thanks & BR -Matti

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• Mac OS X: Best way to do runtime check for retina display?

  - by Todd Ditchendorf

  Given a Cocoa application which runs on Mac OS X 10.7 and later: What is the best way to check, at runtime, if your app is currently running on a Mac with at least one retina display attached? If checking for this sort of thing is just really wrong-headed, I fully welcome a well-reasoned explanation of why. But I'd still like to know :). It seems likely you could just do a check specifically for the new Mac Book Pro "Retina" hardware (the only Mac at this time which currently has a retina display), but ideally, I'd really prefer a more general/generic/future-proof way to check than this. Ideally, I'd like to know how to detect the retina display, not the specific Mac model which currently happens to ship with a retina display.

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• What happens when a computer program runs?

  - by gaijinco

  I know the general theory but I can't fit in the details. I know that a program resides in the secondary memory of a computer. Once the program begins execution it is entirely copied to the RAM. Then the processor retrive a few instructions (it depends on the size of the bus) at a time, puts them in registers and executes them. I also know that a computer program uses two kinds of memory: stack and heap, which are also part of the primary memory of the computer. The stack is used for non-dynamic memory, and the heap for dynamic memory (for example, everything related to the new operator in C++) What I can't understand is how those two things connect. At what point is the stack used for the execution of the instructions? Instructions go from the RAM, to the stack, to the registers?

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• Nhibernate Bind

  - by user329983

  I have two oracle user defined types: Audit_Type – A normal object with two fields a string and a number Audit_Table_Type – A table of audit_types, (an array) I have a stored procedure that takes as a parameter an Audit_Table_Type. List<Audit_Type> table = new List<Audit_Type>(); var query = session.CreateSQLQuery("call Audit_Rows(Audit_Table_Type(:table))") .SetParameterList("table", table, NHibernateUtil.Custom(typeof(AuditTypeUDT))) This is what I did intuativly created the ICompositeType and just set in a list of them in but this gives me nothing close to what I wanted. I couldn’t figure out how to bind to a table at all. I have built the inline sql that would do this for me but it would destroy my shared pool (not using binds). So a General question how do I bind to complex/composite types using Nhibernate?

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• How do I calculate a good hash code for a list of strings?

  - by Ian Ringrose

  Background: I have a short list of strings. The number of strings is not always the same, but are nearly always of the order of a “handful” In our database will store these strings in a 2nd normalised table These strings are never changed once they are written to the database. We wish to be able to match on these strings quickly in a query without the performance hit of doing lots of joins. So I am thinking of storing a hash code of all these strings in the main table and including it in our index, so the joins are only processed by the database when the hash code matches. So how do I get a good hashcode? I could: Xor the hash codes of all the string together Xor with multiply the result after each string (say by 31) Cat all the string together then get the hashcode Some other way So what do people think? (If you care we are using .NET and SqlServer)

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• How to use GWT on mobile devices?

  - by Chris

  hi I have a fairly large web application developed with GWT (and EJB). However on mobile devices (like windows mobile, black berry and such) the GWT start page remains simply white. I'm using GWT 1.6 and also tried 1.7 but nothing helps. It seems that the java script isn't executing and also isn't the noscript tag. Do you know how to make it working without rewriting the whole application in e.g. PHP?? I think it may be a general prob with GWT apps and not with my specific app. thx

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• Cheap shared windows hosting

  - by Elangovan

  Hi I have recently purchased a domain from go daddy, now I am looking for a cheap windows hosting. Following are my requirements Shared Windows hosting Should be cheap in price Should have at least one SQL server Db and one mysql db. Should support atleast asp.net 3.5 and php Will be good if it has support for asp.net mvc (no problem even if it is not available also) Should be able to install third party blog sites. Bandwidth, total space and performance are not very important. Silverlight is also an added advantage (no problem even if it is not available also). There should be no advertisement or banner added by the hosting company in the site.

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• I would like to learn C++, what is the first step ?

  - by Cesar

  My actual experience comes from PHP and Delphi(Borland) and recently also from Obj-C (iPhone sdk). In the past I also used Java, Python, VB 6 and some other scripting language. I would like to learn C++ because i need a standard tool for write compiled applications with good performance but i have no idea about witch environment i have to choose (Ex: Borland, Microsoft, Eclipse+MinGW, ...). Based those parameters: Most useful more opensource project or work requests Most standard not a proprietary versions Biggest community documentation, manuals, tutorials, forums... Better IDE add-ons, highlight, debug, cross platform, autocomplete... Easy setup A simple setup, to focus on learning the basics Actually I'm on OSX but I can use a VM if needed. Advices about tutorial or books are welcome. I hope it's not too generic as question.

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• Examples of fast .NET WPF/WinForms apps?

  - by mythz

  I am currently investigating whether to build a windows application using unmanaged C/C++ or in .NET and would like to know of the kind of performance and responsiveness that is capable with a managed C#/.NET GUI app? Not surprisingly it looks like the fastest most responsive applications (e.g. chrome, spotify, etc) are written in unmanaged C/C++. I've had a hard time finding examples of really good .NET applications and so I would like some help. What's the best example of a fast and responsive .NET windows application?

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• ExtJS Grid slow with 3000+ records

  - by Oliver Watkins

  I am using ExtJS Grid and its getting pretty slow with 3000+ records. Sorting takes about 4 seconds. Compared to other more Javascript tables, this is pretty slow. I am thinking maybe to use pagination in my table. However after reading the documentation, I am still a bit unsure about how pagination works in extjs. Does this pull data from the server each time u turn a page? I would prefer that wasn't the case. I would prefer the 3000 records are saved in the browser and then what is rendered is just a portion of those rows. Also I am using Extjs version 4.2.1. If I upgrade to version 5. will I get some performance improvements?

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• Putting a simple if-then statement on one line

  - by Abizern

  I'm just getting into Python and I really like the terseness of the syntax. However; is there an easier way of writing an if-then statement so it fits on one line? For example; say I have the simple test: if count == N: count = 0 else: count = N + 1 is there a simpler way of writing this? I mean, in Objective-C I would write this as: count = count == N ? count = 0 : count = N + 1; Is there something similar for python? Edit I know that in this instance I can use count == count % N. I'm asking about the general syntax.

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• how to insert page view of a node in another page in drupal

  - by sprugman

  I have a list of node ids and I want to display the 'page' view of each one. For various reasons, I don't want to do this with views, and don't think I should need a module. Just an API call to theme('node'). Something like: $nids = array(3,4,5); foreach ($nids as $nid) { $node = node_load($nid); $result .= theme('node', $node); } but I'm not getting back the full page view of the node. I added this to my node-[type].tpl.php file: if ($page) print "PAGE MODE "; else print "NOT PAGE "; if ($teaser) print "TEASER MODE "; else print "NOT TEASER "; and got: NOT PAGE NOT TEASER I seem to be in some kind of limbo. I suspect there's an argument that I add to the theme function, but the terms are all so general (theme, teaser, page, node), I'm having trouble with my google-fu.

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• a completely decoupled OO system ?

  - by shrini1000

  To make an OO system as decoupled as possible, I'm thinking of the following approach: 1) we run an RMI/directory like service where objects can register and discover each other. They talk to this service through an interface 2) we run a messaging service to which objects can publish messages, and register subscription callbacks. Again, this happens through interfaces 3) when object A wants to invoke a method on object B, it discovers the target object's unique identity through #1 above, and publishes a message on the message service for object B 4) message services invokes B's callback to give it the message 5) B processes the request and sends the response for A on message service 6) A's callback is called and it gets the response. I feel this system is as decoupled as practically possible, but it has the following problems: 1) communication is typically asynchronous 2) hence it's non real time 3) the system as a whole is less efficient. Are there any other practical problems where this design obviously won't be applicable ? What are your thoughts on this design in general ?

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• How do you make your Java application memory efficient?

  - by Boune

  How do you optimize the heap size usage of an application that has a lot (millions) of long-lived objects? (big cache, loading lots of records from a db) Use the right data type Avoid java.lang.String to represent other data types Avoid duplicated objects Use enums if the values are known in advance Use object pools String.intern() (good idea?) Load/keep only the objects you need I am looking for general programming or Java specific answers. No funky compiler switch. Edit: Optimize the memory representation of a POJO that can appear millions of times in the heap. Use cases Load a huge csv file in memory (converted into POJOs) Use hibernate to retrieve million of records from a database Resume of answers: Use flyweight pattern Copy on write Instead of loading 10M objects with 3 properties, is it more efficient to have 3 arrays (or other data structure) of size 10M? (Could be a pain to manipulate data but if you are really short on memory...)

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• rewrite image URLs

  - by Don

  Hi, I'm writing a Maven plugin that merges CSS files together. So all the CSS files that match /foo/bar/*.css might get merged to /foo/merged.css. A concern is that in a file such as /foo/bar/baz.css there might be a property such as: background: url("images/pic.jpg") So when the file is merged into /foo/merged.css this will need to be changed to background: url("bar/images/pic.jpg") The recalculated URL obviously depends on 3 factors: original URL original CSS file location merged CSS file location Assuming that the original and merged CSS files are both on the same filesystem, is there a general formula (or Java library) that can be used to calculate the new url given these 3 inputs? Thanks, Don

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• Java newbie problem: classes of the same package accessing one another?

  - by HH

  Test.java and SetWord.java belong to the package tools. Test.java needs to access SetWord but an odd error 'cannot find' SetWord appear. The package limits the visibility, it works without 'package tools;' lines. How can I acess the SetWords with Test in the same pkg? In general, how can classes access one another in the same pkg? Test.java package tools; import java.io.*; import java.util.*; public class Test{ public static void main(String[] args) { //IT CANNOT FIND SetWords despite the same folder, why? SetWord sw=new SetWord(); System.out.println(st.set("HELLO)"); } } SetWord.java package tools; import java.io.*; import java.util.*; public class SetWord{ public SetWord(){} public String set(String s) { return s.trim().toLowerCase(); } }

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• CakePHP repeats same queries

  - by Rytis

  I have a model structure: Category hasMany Product hasMany Stockitem belongsTo Warehouse, Manufacturer. I fetch data with this code, using containable to be able to filter deeper in the associated models: $this->Category->find('all', array( 'conditions' => array('Category.id' => $category_id), 'contain' => array( 'Product' => array( 'Stockitem' => array( 'conditions' => array('Stockitem.warehouse_id' => $warehouse_id), 'Warehouse', 'Manufacturer', ) ) ), ) ); Data structure is returned just fine, however, I get multiple repeating queries like, sometimes hundreds of such queries in a row, based on dataset. SELECT `Warehouse`.`id`, `Warehouse`.`title` FROM `beta_warehouses` AS `Warehouse` WHERE `Warehouse`.`id` = 2 Basically, when building data structure Cake is fetching data from mysql over and over again, for each row. We have datasets of several thousand rows, and I have a feeling that it's going to impact performance. Is it possible to make it cache results and not repeat same queries?

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• In which controller do you put the CRUD for the child part of a relationship?

  - by uriDium

  I am using ASP.Net MVC but this probably applies to all MVC patterns in general. My problem, for example I have companies and in each company I have a list of contacts. When I have selected a company I can see its details and a list of the contacts for that company. When I want to add a new contact for that company, should the implementation of that action go into the company controller as an "AddContact" action or should it go into the contact controller into a "New" action and we pass the Company ID in the URL? What is the usual way of dealing with this sort of thing in ASP.Net MVC? Is there a better stategy?

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• Virus - How much it can affect?

  - by Sarang

  In our daily life, we come across various Viruses. In this internet world, we do have lots of type of viruses come to visit us ! While for the beginners, Virus is a complicated matter to fight with. Please explain the way how the virus come flow across the PC using Internet. What are the ways to search for them in the Personal Computer ? Also, we do have various solutions available in the market of Anti-Viruses, but also have different comments available for different software. Which is actually, really a useful Anti-Virus in the market that can give reliable performance ? Every Personal Computer connected to internet has to face against the viruses. Isn't there any general solution using Internet itself through which all networked computers get protected against Viruses ? Please give any solution.

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• Giving Users an Option Between UDP & TCP?

  - by cam

  After studying TCP/UDP difference all week, I just can't decide which to use. I have to send a large amount of constant sensor data, while at the same time sending important data that can't be lost. This made a perfect split for me to use both, then I read a paper (http://www.isoc.org/INET97/proceedings/F3/F3_1.HTM) that says using both causes packet/performance loss in the other. Is there any issue presented if I allow the user to choose which protocol to use (if I program both server side) instead of choosing myself? Are there any disadvantages to this? The only other solution I came up with is to use UDP, and if there seems to be too great of loss of packets, switch to TCP (client-side).

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• Secure password transmission over unencrypted tcp/ip

  - by academicRobot

  I'm in the designing stages of a custom tcp/ip protocol for mobile client-server communication. When not required (data is not sensitive), I'd like to avoid using SSL for overhead reasons (both in handshake latency and conserving cycles). My question is, what is the best practices way of transmitting authentication information over an unencrypted connection? Currently, I'm liking SRP or J-PAKE (they generate secure session tokens, are hash/salt friendly, and allow kicking into TLS when necessary), which I believe are both implemented in OpenSSL. However, I am a bit wary since I don't see many people using these algorithms for this purpose. Would also appreciate pointers to any materials discussing this topic in general, since I had trouble finding any.

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• Validating call to web service against schema before sending request

  - by Cen

  I am calling a web service (written in Java) in my web app. I use the WSDL to generate proxy classes using the wsdl.exe command line tool. Everything is working fine. However, I have found out that the web service is not doing any data validation at all when they receive a request from my app. Hence, if I happen to send one minute piece of data that isn't exactly what they want, I receive a general fault error in return, with no specifics at all of what the incorrect (if any) piece of data is. So, before I make the request, I'd like to validate my request against the schema they have provided. Is this possible, and if so, how do I go about this? Thanks in advance

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• What FIX implementation do you recommend for use with .NET

  - by Ajaxx

  I am reviewing implementation choices for FIX when using .NET. A few obvious choices come to mind, but I want to know if there are other options, better choices or if we've made the same decision as a lot of you. QuickFIX - Stable, C++ implementation - so you've got unmanaged code to interop with. FIX4NET - C# implementation - seems to have some gaps in its implementation. DIY - Chime in here if you've made your own FIX engine Let me throw in some caveats here. I'm not looking for sub 100 microsecond processing. Performance is a requirement, but not so much that it's driving my decisions. A solid product that is stable, performs well and is flexible enough to deal with vendor specific dialects is the sweet spot. The more we can do in .NET the better.

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