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  • Linq Query Performance , comparing Compiled query vs Non-Compiled.

    - by AG.
    Hello Guys, I was wondering if i extract the common where clause query into a common expression would it make my query much faster, if i have say something like 10 linq queries on a collection with exact same 1st part of the where clause. I have done a small example to explain a bit more . public class Person { public string First { get; set; } public string Last { get; set; } public int Age { get; set; } public String Born { get; set; } public string Living { get; set; } } public sealed class PersonDetails : List<Person> { } PersonDetails d = new PersonDetails(); d.Add(new Person() {Age = 29, Born = "Timbuk Tu", First = "Joe", Last = "Bloggs", Living = "London"}); d.Add(new Person() { Age = 29, Born = "Timbuk Tu", First = "Foo", Last = "Bar", Living = "NewYork" }); Expression<Func<Person, bool>> exp = (a) => a.Age == 29; Func<Person, bool> commonQuery = exp.Compile(); var lx = from y in d where commonQuery.Invoke(y) && y.Living == "London" select y; var bx = from y in d where y.Age == 29 && y.Living == "NewYork" select y; Console.WriteLine("All Details {0}, {1}, {2}, {3}, {4}", lx.Single().Age, lx.Single().First , lx.Single().Last, lx.Single().Living, lx.Single().Born ); Console.WriteLine("All Details {0}, {1}, {2}, {3}, {4}", bx.Single().Age, bx.Single().First, bx.Single().Last, bx.Single().Living, bx.Single().Born); So can some of the guru's here give me some advice if it would be a good practice to write query like var lx = "Linq Expression " or var bx = "Linq Expression" ? Any inputs would be highly appreciated. Thanks, AG

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  • C++ project type: unicode vs multi-byte; pros and cons

    - by Stefan Valianu
    I'm wondering what the Stack Overflow community thinks when it comes to creating a project (thinking primarily c++ here) with a unicode or a multi-byte character set. Are there pros to going Unicode straight from the start, implying all your strings will be in wide format? Are there performance issues / larger memory requirements because of a standard use of a larger character? Is there an advantage to this method? Do some processor architectures handle wide characters better? Are there any reasons to make your project Unicode if you don't plan on supporting additional languages? What reasons would one have for creating a project with a multi-byte character set? How do all of the factors above collide in a high performance environment (such as a modern video game) ?

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  • Enum.values() vs EnumSet.allOf( ). Which one is more preferable?

    - by Alexander Pogrebnyak
    I looked under the hood for EnumSet.allOf and it looks very efficient, especially for enums with less than 64 values. Basically all sets share the single array of all possible enum values and the only other piece of information is a bitmask which in case of allOf is set in one swoop. On the other hand Enum.values() seems to be a bit of black magic. Moreover it returns an array, not a collection, so in many cases it must be decorated with Arrays.asList( ) to be usable in any place that expects collection. So, should EnumSet.allOf be more preferable to Enum.values? More specifically, which form of for iterator should be used: for ( final MyEnum val: MyEnum.values( ) ); or for ( final MyEnum val: EnumSet.allOf( MyEnum.values ) );

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  • Ruby on Rails: Model.all.each vs find_by_sql("SELECT * FROM model").each ?

    - by B_
    I'm fairly new to RoR. In my controller, I'm iterating over every tuple in the database. For every table, for every column I used to call SomeOtherModel.find_by_sql("SELECT column FROM model").each {|x| #etc } which worked fine enough. When I later changed this to Model.all(:select => "column").each {|x| #etc } the loop starts out at roughly the same speed but quickly slows down to something like 100 times slower than the the find_by_sql command. These calls should be identical so I really don't know what's happening. I know these calls are not the most efficient but this is just an intermediate step and I will optimize it more once this works correctly. Thanks!

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  • Managing highly repetitive code and documentation in Java

    - by polygenelubricants
    Highly repetitive code is generally a bad thing, and there are design patterns that can help minimize this. However, sometimes it's simply inevitable due to the constraints of the language itself. Take the following example from java.util.Arrays: /** * Assigns the specified long value to each element of the specified * range of the specified array of longs. The range to be filled * extends from index <tt>fromIndex</tt>, inclusive, to index * <tt>toIndex</tt>, exclusive. (If <tt>fromIndex==toIndex</tt>, the * range to be filled is empty.) * * @param a the array to be filled * @param fromIndex the index of the first element (inclusive) to be * filled with the specified value * @param toIndex the index of the last element (exclusive) to be * filled with the specified value * @param val the value to be stored in all elements of the array * @throws IllegalArgumentException if <tt>fromIndex &gt; toIndex</tt> * @throws ArrayIndexOutOfBoundsException if <tt>fromIndex &lt; 0</tt> or * <tt>toIndex &gt; a.length</tt> */ public static void fill(long[] a, int fromIndex, int toIndex, long val) { rangeCheck(a.length, fromIndex, toIndex); for (int i=fromIndex; i<toIndex; i++) a[i] = val; } The above snippet appears in the source code 8 times, with very little variation in the documentation/method signature but exactly the same method body, one for each of the root array types int[], short[], char[], byte[], boolean[], double[], float[], and Object[]. I believe that unless one resorts to reflection (which is an entirely different subject in itself), this repetition is inevitable. I understand that as a utility class, such high concentration of repetitive Java code is highly atypical, but even with the best practice, repetition does happen! Refactoring doesn't always work because it's not always possible (the obvious case is when the repetition is in the documentation). Obviously maintaining this source code is a nightmare. A slight typo in the documentation, or a minor bug in the implementation, is multiplied by however many repetitions was made. In fact, the best example happens to involve this exact class: Google Research Blog - Extra, Extra - Read All About It: Nearly All Binary Searches and Mergesorts are Broken (by Joshua Bloch, Software Engineer) The bug is a surprisingly subtle one, occurring in what many thought to be just a simple and straightforward algorithm. // int mid =(low + high) / 2; // the bug int mid = (low + high) >>> 1; // the fix The above line appears 11 times in the source code! So my questions are: How are these kinds of repetitive Java code/documentation handled in practice? How are they developed, maintained, and tested? Do you start with "the original", and make it as mature as possible, and then copy and paste as necessary and hope you didn't make a mistake? And if you did make a mistake in the original, then just fix it everywhere, unless you're comfortable with deleting the copies and repeating the whole replication process? And you apply this same process for the testing code as well? Would Java benefit from some sort of limited-use source code preprocessing for this kind of thing? Perhaps Sun has their own preprocessor to help write, maintain, document and test these kind of repetitive library code? A comment requested another example, so I pulled this one from Google Collections: com.google.common.base.Predicates lines 276-310 (AndPredicate) vs lines 312-346 (OrPredicate). The source for these two classes are identical, except for: AndPredicate vs OrPredicate (each appears 5 times in its class) "And(" vs Or(" (in the respective toString() methods) #and vs #or (in the @see Javadoc comments) true vs false (in apply; ! can be rewritten out of the expression) -1 /* all bits on */ vs 0 /* all bits off */ in hashCode() &= vs |= in hashCode()

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  • Warning: Ignoring library 'com.motorola.android.iextdispservice', missing property value

    - by user1342684
    Hi I am trying to get my eclipse environment setup so I can start playing with programming for android... The Android SDK Manager is installing the following packages (everything else says installed except these two): Android 2.3.3 (API 10) Dual Screen APIs - Not Installed Android 2.2 (API 8) Dual Screen APIs - Not Installed Error Messages: [2012-04-19 13:06:41 - SDK Manager] Warning: Ignoring library 'com.motorola.android.iextdispservice', missing property value [2012-04-19 13:15:27 - SDK Manager] Operation timed out [2012-04-19 13:18:16 - SDK Manager] Operation timed out Any tips? So close to getting the environment ready! I want to start playing around!

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  • LazyList<T> vs System.Lazy<List<T>> in ASP.NET MVC 2?

    - by FreshCode
    In Rob Conery's Storefront series, Rob makes extensive use of the LazyList<..> construct to pull data from IQueryables. How does this differ from the System.Lazy<...> construct now available in .NET 4.0 (and perhaps earlier)? More depth based on DoctaJones' great answer: Would you recommend one over the other if I wanted to operate on IQueryable as a List<T>? I'm assuming that since Lazy<T> is in the framework now, it is a safer bet for future support and maintainability? If I want to use a strong type instead of an anonymous (var) type would the following statements be functionally equivalent? Lazy<List<Products>> Products = new Lazy<List<Product>>(); LazyList<Product> = new LazyList<Product>();

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  • Relational vs. Dimensional Databases, what's the difference?

    - by grautur
    I'm trying to learn about OLAP and data warehousing, and I'm confused about the difference between relational and dimensional modeling. Is dimensional modeling basically relational modeling, but allowing for redundant/un-normalized data? For example, let's say I have historical sales data on (product, city, # sales). I understand that the following would be a relational point-of-view: Product | City | # Sales Apples, San Francisco, 400 Apples, Boston, 700 Apples, Seattle, 600 Oranges, San Francisco, 550 Oranges, Boston, 500 Oranges, Seattle, 600 While the following is a more dimensional point-of-view: Product | San Francisco | Boston | Seattle Apples, 400, 700, 600 Oranges, 550, 500, 600 But it seems like both points of view would nonetheless be implemented in an identical star schema: Fact table: Product ID, Region ID, # Sales Product dimension: Product ID, Product Name City dimension: City ID, City Name And it's not until you start adding some additional details to each dimension that the differences start popping up. For instance, if you wanted to track regions as well, a relational database would tend to have a separate region table, in order to keep everything normalized: City dimension: City ID, City Name, Region ID Region dimension: Region ID, Region Name, Region Manager, # Regional Stores While a dimensional database would allow for denormalization to keep the region data inside the city dimension, in order to make it easier to slice the data: City dimension: City ID, City Name, Region Name, Region Manager, # Regional Stores Is this correct?

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  • Running Magento for multiple clients - single Installaton vs. multiple installations

    - by Chris Hopkins
    Hi There I am looking to set-up a Magento (Community Edition) installation for multiple clients and have researched the matter for a few days now. I can see that the Enterprise Edition has what I need in it, but surprisingly I am not willing to shell out the $12,000 odd yearly subscription. It seems there are a few options available to be but I am worried about the performance I will get out of the various options. Option 1) Single install using AITOC advanced permissions module So this is really what I am after; one installation so that I can update my core files all at the same time and also manage all my store users from one place. The problems here are that I don't know anything about the reliability of this extra product and that I have to pay a bit extra. I am also worried that if I have 10 stores running off this one installation it might all slow down so much and keel over as I have heard allot about Magento's slowness. Module Link: http://www.aitoc.com/en/magentomods_advanced_permissions.html Option 2) Multiple installations of Magento on one server for each shop So here I have 10 Magento installations on one server all running happily away not using any extra money, but I now have 10 separate stores to update and maintain which could be annoying. Also I haven't been able to find a whole lot of other people using this method and when I have they are usually asking how to stop their servers from dying. So this route seems like it could be even worse on my server as I will have more going on on my server but if my server could take it each Magento installation would be simpler and less likely to slow down due to each one having to run 10 shops on its own? Option 3) Use lots of servers and lots of Magento installations I just so do not want to do this. Option 4) Buy Magento Enterprise I do not have the money to do this. So which route is less likely to blow up my server? And does anyone have experience with this holy grail of a module? Thanks for reading and thanks in advance for any help - Chris Hopkins

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  • C++ .NET DLL vs C# Managed Code ? (File Encrypting AES-128+XTS)

    - by Ranhiru
    I need to create a Windows Mobile Application (WinMo 6.x - C#) which is used to encrypt/decrypt files. However it is my duty to write the encryption algorithm which is AES-128 along with XTS as the mode of operation. RijndaelManaged just doesn't cut it :( Very much slower than DES and 3DES CryptoServiceProviders :O I know it all depends on how good I am at writing the algorithm in the most efficient way. (And yes I my self have to write it from scratch but i can take a look @ other implementations) Nevertheless, does writing a C++ .NET DLL to create the encryption/decryption algorithm + all the file handling and using it from C# have a significant performance advantage OVER writing the encryption algorithm + file handling in completely managed C# code? If I use C++ .NET to create the encryption algorithm, should I use MFC Smart Device DLL or ATL? What is the difference and is there any impact on which one I choose? And can i just add a reference to the C++ DLL from C# or should I use P/Invoke? I am fairly competent with C# than C++ but performance plays a major role as I have convinced my lecturers that AES is a very efficient cryptographic algorithm for resource constrained devices. Thanx a bunch :)

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  • Which of these is pythonic? and Pythonic vs. Speed

    - by Kashyap Nadig
    Hi! I'm new to python and just wrote this module level function: def _interval(patt): """ Converts a string pattern of the form '1y 42d 14h56m' to a timedelta object. y - years (365 days), M - months (30 days), w - weeks, d - days, h - hours, m - minutes, s - seconds""" m = _re.findall(r'([+-]?\d*(?:\.\d+)?)([yMwdhms])', patt) args = {'weeks': 0.0, 'days': 0.0, 'hours': 0.0, 'minutes': 0.0, 'seconds': 0.0} for (n,q) in m: if q=='y': args['days'] += float(n)*365 elif q=='M': args['days'] += float(n)*30 elif q=='w': args['weeks'] += float(n) elif q=='d': args['days'] += float(n) elif q=='h': args['hours'] += float(n) elif q=='m': args['minutes'] += float(n) elif q=='s': args['seconds'] += float(n) return _dt.timedelta(**args) My issue is with the for loop here i.e the long if elif block, and was wondering if there is a more pythonic way of doing it. So I re-wrote the function as: def _interval2(patt): m = _re.findall(r'([+-]?\d*(?:\.\d+)?)([yMwdhms])', patt) args = {'weeks': 0.0, 'days': 0.0, 'hours': 0.0, 'minutes': 0.0, 'seconds': 0.0} argsmap = {'y': ('days', lambda x: float(x)*365), 'M': ('days', lambda x: float(x)*30), 'w': ('weeks', lambda x: float(x)), 'd': ('days', lambda x: float(x)), 'h': ('hours', lambda x: float(x)), 'm': ('minutes', lambda x: float(x)), 's': ('seconds', lambda x: float(x))} for (n,q) in m: args[argsmap[q][0]] += argsmap[q][1](n) return _dt.timedelta(**args) I tested the execution times of both the codes using timeit module and found that the second one took about 5-6 seconds longer (for the default number of repeats). So my question is: 1. Which code is considered more pythonic? 2. Is there still a more pythonic was of writing this function? 3. What about the trade-offs between pythonicity and other aspects (like speed in this case) of programming? p.s. I kinda have an OCD for elegant code. EDITED _interval2 after seeing this answer: argsmap = {'y': ('days', 365), 'M': ('days', 30), 'w': ('weeks', 1), 'd': ('days', 1), 'h': ('hours', 1), 'm': ('minutes', 1), 's': ('seconds', 1)} for (n,q) in m: args[argsmap[q][0]] += float(n)*argsmap[q][1]

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  • delayed evaluation of code in subroutines - 5.8 vs. 5.10 and 5.12

    - by Brock
    This bit of code behaves differently under perl 5.8 than it does under perl 5.12: my $badcode = sub { 1 / 0 }; print "Made it past the bad code.\n"; [brock@chase tmp]$ /usr/bin/perl -v This is perl, v5.8.8 built for i486-linux-gnu-thread-multi [brock@chase tmp]$ /usr/bin/perl badcode.pl Illegal division by zero at badcode.pl line 1. [brock@chase tmp]$ /usr/local/bin/perl -v This is perl 5, version 12, subversion 0 (v5.12.0) built for i686-linux [brock@chase tmp]$ /usr/local/bin/perl badcode.pl Made it past the bad code. Under perl 5.10.1, it behaves as it does under 5.12: brock@laptop:/var/tmp$ perl -v This is perl, v5.10.1 (*) built for i486-linux-gnu-thread-multi brock@laptop:/var/tmp$ perl badcode.pl Made it past the bad code. I get the same results with a named subroutine, e.g. sub badcode { 1 / 0 } I don't see anything about this in the perl5100delta pod. Is this an undocumented change? A unintended side effect of some other change? (For the record, I think 5.10 and 5.12 are doing the Right Thing.)

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  • Entity Framework in n-layered application - Lazy loading vs. Eager loading patterns

    - by Marconline
    Hi all. This questions doesn't let me sleep as it's since one year I'm trying to find a solution but... still nothing happened in my mind. Probably you can help me, because I think this is a very common issue. I've a n-layered application: presentation layer, business logic layer, model layer. Suppose for simplicity that my application contains, in the presentation layer, a form that allows a user to search for a customer. Now the user fills the filters through the UI and clicks a button. Something happens and the request arrives to presentation layer to a method like CustomerSearch(CustomerFilter myFilter). This business logic layer now keeps it simple: creates a query on the model and gets back results. Now the question: how do you face the problem of loading data? I mean business logic layer doesn't know that that particular method will be invoked just by that form. So I think that it doesn't know if the requesting form needs just the Customer objects back or the Customer objects with the linked Order entities. I try to explain better: our form just wants to list Customers searching by surname. It has nothing to do with orders. So the business logic query will be something like: (from c in ctx.CustomerSet where c.Name.Contains(strQry) select c).ToList(); now this is working correctly. Two days later your boss asks you to add a form that let you search for customers like the other and you need to show the total count of orders created by each customer. Now I'd like to reuse that query and add the piece of logic that attach (includes) orders and gets back that. How would you front this request? Here is the best (I think) idea I had since now. I'd like to hear from you: my CustomerSearch method in BLL doesn't create the query directly but passes through private extension methods that compose the ObjectQuery like: private ObjectQuery<Customer> SearchCustomers(this ObjectQuery<Customer> qry, CustomerFilter myFilter) and private ObjectQuery<Customer> IncludeOrders(this ObjectQuery<Customer> qry) but this doesn't convince me as it seems too complex. Thanks, Marco

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  • Idiomatic Scala way to deal with base vs derived class field names?

    - by Gregor Scheidt
    Consider the following base and derived classes in Scala: abstract class Base( val x : String ) final class Derived( x : String ) extends Base( "Base's " + x ) { override def toString = x } Here, the identifier 'x' of the Derived class parameter overrides the field of the Base class, so invoking toString like this: println( new Derived( "string" ).toString ) returns the Derived value and gives the result "string". So a reference to the 'x' parameter prompts the compiler to automatically generate a field on Derived, which is served up in the call to toString. This is very convenient usually, but leads to a replication of the field (I'm now storing the field on both Base and Derived), which may be undesirable. To avoid this replication, I can rename the Derived class parameter from 'x' to something else, like '_x': abstract class Base( val x : String ) final class Derived( _x : String ) extends Base( "Base's " + _x ) { override def toString = x } Now a call to toString returns "Base's string", which is what I want. Unfortunately, the code now looks somewhat ugly, and using named parameters to initialize the class also becomes less elegant: new Derived( _x = "string" ) There is also a risk of forgetting to give the derived classes' initialization parameters different names and inadvertently referring to the wrong field (undesirable since the Base class might actually hold a different value). Is there a better way? Edit: To clarify, I really only want the Base values; the Derived ones just seem necessary for initializing the Base ones. The example only references them to illustrate the ensuing issues. It might be nice to have a way to suppress automatic field generation if the derived class would otherwise end up hiding a base class field.

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  • How to order <script> tags vs. <style> tags in HTML markup for best results.

    - by Tchalvak
    I'm building up my site over at http://royronalds.com, and I'm trying to figure out what order of elements in the <head> makes most sense. Just to take from what I current have, I have: <head> <style> external stylesheet <meta> <title> <link> to favicon <script> for jQuery <script> main javascript for site <script> google analytics, asynchronous script. </head> Are there reasons to order these differently so that load times and other issues happen more smoothly, and if so, what would the ideal order be?

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  • log4j vs. System.out.println - logger advantages?

    - by wishi_
    Hi! I'm newly using log4j in a project. A fellow programmer told me that using System.out.println is considered bas style and that log4j is something like standard for logging matters nowadays. We do lots of JUnit testing - System.out stuff turns out to be harder to test. Therefore I began utilizing log4j for a Console controller class, that's just handling commandline parameters. // some logger config org.apache.log4j.BasicConfigurator.configure(); Logger logger = LoggerFactory.getLogger(Console.class); Category cat = Category.getRoot(); Seems to work: logger.debug("String"); Produces: 1 [main] DEBUG project.prototype.controller.Console - String I got two questions regarding this: From my basic understanding using this logger should provide me comfortable options to write a logfile with timestamps - instead of spamming the console - if debug mode is enabled at the logger? Why is System.out.println harder to test? I searched stackoverflow and found a testing recipe. So I wonder what kind of advantage I really get by using log4j.

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  • No compile errors when reference added, but errors seen upon build

    - by cjs
    A solution was just converted from VS 2008 to VS 2010. My VS 2010 build is failing with the popular "The type or namespace X could not be found". When I go to the project and go to Add References and add the appropriate project dll, the class name appears in blue text as if .NET found the correct class. However, when I go to the Build menu and select "Build Solution" I get the "namespace not found error" and the class name is no longer blue. Thanks.

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  • Working with android and ant scripts for building applications

    - by y ramesh rao
    I want to know if we can create builds using ant's build.xml and when i'm trying to do this an error is displayed SDK location not mentioned and besides that I'm unable to find local.properties file to mention the SDK Location My aim is that I want to use my exiting code and make a build for new Android SDK's with changes in the resources and and some constant values is this task Possible with making a build using Ant and if by some other way. I have no idea about Ant and its functioning so it would very appreciable if minute details are also provided.

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  • QtCreator on linux: 32-bits vs. 64-bits.

    - by Claire Huang
    My laptop is 64-bits, so when I start to use Qt, I chose 64-bit QtCreator. Now I'm facing a problem, I wish that the executable files I generated are runnnable on 32-bit linux system. Can I set QtCreator to generate 32-bit executable files? So that I can decide I want to generate 32-bit ones or 64-bit ones. I don't want to install another 32-bit QtCreator <.

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  • Online voice chat: Why client-server model vs. peer-to-peer model?

    - by sstallings
    I am adding online voice chat to a Silverlight app. I've been reviewing current apps, services and SDKs found thru online searches and forums. I'm finding that the majority of these implement a client-server (C/S) model and I'm trying to understand why that model versus a peer-to-peer (PTP) model. To me PTP would be preferable because going direct between peers would be more efficient (fewer IP hops and no processing along the way by a server computer) and no need for a server and its costs and dependencies. I found some products offer the ability to switch from PTP to C/S if the PTP proves insufficient. As I thought more about it, I could see that C/S could be better if there are more than two peers involved in a conversation, then the server (supposedly with more bandwidth) could do a better job of relaying each peers outgoing traffic to the multiple other peers. In C/S many-to-many voice chatting, each peer's upstream broadband (which is where the bottleneck inherently is) would only have to carry each item of voice traffic once, then the server would use its superior bandwidth to relay the message to the multiple other peers. But, in a situation with one-on-one voice chatting it seems that PTP would be best. A server would not reduce each of the two peer's bandwidth requirements and would only add unnecessary overhead, dependency and cost. In one-on-one voice chatting: Am I mistaken on anything above? Would peer-to-peer be best? Would a server provide anything of value that could not be provided by a client-only program? Is there anything else that I should be taking into consideration? And lastly, can you recommend any Silverlight PTP or C/S voice chat products? Thanks in advance for any info.

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