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• Finding intersection of two spheres

  - by Onkar Deshpande

  Hi, Consider the following problem - I am given 2 links of length L0 and L1. P0 is the point that the first link starts at and P1 is the point that I want the end of second link to be at in 3-D space. I am supposed to write a function that should take in these 3-D points (P0 and P1) as inputs and should find all configurations of the links that put the second link's end point at P1. My understanding of how to go about it is - Each link L0 and L1 will create a sphere S0 and S1 around itself. I should find out the intersection of those two spheres (which will be a circle) and print all points that are on the circumference of that circle. I saw gmatt's first reply on the http://stackoverflow.com/questions/1406375/finding-intersection-points-between-3-spheres but could not understand it properly since the images did not show up. I also saw a formula for finding out the intersection at mathworld[dot]wolfram[dot]com/Sphere-SphereIntersection[dot]html . I could find the radius of intersection by the method given on mathworld. Also I can find the center of that circle and then use the parametric equation of circle to find the points. The only doubt that I have is will this method work for the points P0 and P1 mentioned above ? Please comment and let me know your thoughts.

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• Doing large updates against indexed view

  - by user217136

  We have an indexed view that runs across three large tables. Two of these tables (A & B) are constantly getting updated with user transactions and the other table (C) contains data product info that is needs to be updated once a week. This product table contains over 6 million records. We need this view across these three tables for our core business process and unfortunately we cannot change this aspect. We even had a sql server MVP come in to help test under load to make sure we have the most efficient configuration. There is one column in the product table that gets utilized in the view and has to be updated each week. The problem we are now encountering is that as volume is increasing on our transactions against tables A & B, the update to Table C is causing deadlocks. I have tried several different methods to no avail: 1) I was hoping that we could change the view so that table C could be a dirty read "WITH (NOLOCK)" but apparently that functionality is not available with indexes views. 2) I thought about updating a new column in Table C and then just renaming it when the process is done but you cannot do that due to the dependency in the view. 3) I also entertained the idea of writing this value to a temporary product table, and then running an ALTER statement against the view to have it point to my new table. however when i did that the indexes on my view were dropped and it took quite a bit of time to recreate them. 4) we tried to do the weekly update in small chunks (as small as 100 records at a time) but we still run into dead locks. questions: a) we are using sql server 2005. Does sql server 2008 have a new functionality with their indexed views that would help us? Is there now a way to do dirty reads w/ an indexed view? b) a better approach to altering an existing view to point to a new table? thanks!

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• svcutil, XmlSerializer and xsd:list

  - by Dmitry Ornatsky

  I'm using svcutil to generate classes from service metadata. This XML schema <xsd:complexType name="FindRequest"> ... <xsd:attribute name="Significance" type="Significance" use="optional" /> </xsd:complexType> <xsd:simpleType name="Significance"> <xsd:list> <xsd:simpleType> <xsd:restriction base="xsd:int"> <xsd:enumeration value="1" /> <xsd:enumeration value="2" /> <xsd:enumeration value="3" /> </xsd:restriction> </xsd:simpleType> </xsd:list> produces following code: public partial class FindRequest { ... private int significanceField; private bool significanceFieldSpecified; [System.Xml.Serialization.XmlAttributeAttribute()] public int Significance { get { return this.significanceField; } set { this.significanceField = value; } } [System.Xml.Serialization.XmlIgnoreAttribute()] public bool SignificanceSpecified { get { return this.significanceFieldSpecified; } set { this.significanceFieldSpecified = value; } } } My questions are: Is it possible to make XmlSerializer understand this type of list: <FindRequest Significance="1 2 3"/> For example by using some kind of a flags-style enum: public enum EmployeeStatus { [XmlEnum(Name = "1")] One = 1, [XmlEnum(Name = "2")] Two = 2, [XmlEnum(Name = "3")] Three = 4 } If the answer is yes, Is it possible to make svcutil/xsd.exe generate classes that are serialized that way without changing the schema?

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• How do I begin reading source code?

  - by anonnoir

  I understand the value of reading source code, and I am trying my best to read as much as I can. However, every time I try getting into a 'large' (i.e. complete) project of sorts, I am overwhelmed. For example, I use Anki a lot when revising languages. Also, I'm interested in getting to know how an audio player works (because I have some project ideas), hence quodlibet on Google Code. But whenever I open the source code folders for the above programs, there are just so many files that I don't know where or what to begin with. I think that I should start with files marked init.py but I can't see the logical structure of the programs, or what reasoning was applied when the original writer divided his modules the way he did. Hence, my questions: How/where should I begin reading source? Any general tips or ideas? How does a programmer keep in mind the overall structure and logic of the program, especially for large projects, and is it common not to document that structure? As an open source reader, must I look through all of the code and get a bird's eye view of the code and libraries, before even being able to proceed? Would an IDE like Eclipse SDK (with PyDev) help with code-reading? Thanks for the help; I really appreciate your helping me.

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• subtotals in columns usind reshape2 in R

  - by user1043144

  I have spent some time now learning RESHAPE2 and plyr but I still do not get it. This time I have a problem with (a) subtotals and (b) passing different aggregate functions . Here an example using data from the excellent tutorial on the blog of mrdwab http://news.mrdwab.com/ # libraries library(plyr) library(reshape2) # get data and add few more variables book.sales = read.csv("http://news.mrdwab.com/data-booksales") book.sales$Stock = book.sales$Quantity + 10 book.sales$SubjCat[(book.sales$Subject == 'Economics') | (book.sales$Subject == 'Management') ] <- '1_EconSciences' book.sales$SubjCat[book.sales$Subject %in% c('Anthropology', 'Politics', 'Sociology') ] <- '2_SocSciences' book.sales$SubjCat[book.sales$Subject %in% c('Communication', 'Fiction', 'History', 'Research', 'Statistics') ] <- '3_other' # to get to my starting dataframe (close to the project I am working on) book.sales1 <- ddply(book.sales, c('Region', 'Representative', 'SubjCat', 'Subject', 'Publisher'), summarize, Stock = sum(Stock), Sold = sum(Quantity), Ratio = round((100 * sum(Quantity)/ sum(Stock)), digits = 1)) #melt it m.book.sales = melt(data = book.sales1, id.vars = c('Region', 'Representative', 'SubjCat', 'Subject', 'Publisher'), measured.vars = c('Stock', 'Sold', 'Ratio')) # cast it Tab1 <- dcast(data = m.book.sales, formula = Region + Representative ~ Publisher + variable, fun.aggregate = sum, margins = c('Region', 'Representative')) Now my questions : I have been able to add the subtotals in rows. But is it possible also to add margins in the columns. Say for example, Totals of Stock for one Publisher ? Sorry I meant to say example total sold for all publishers There is a problem with the columns with “ratio”. How can I get “mean” instead of “sum” for this variable ? P.S: I have seen some examples using reshape. Will you recommend to use it instead of reshape2 (which seems not to include the functionalities of two functions).

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• Installing and using acts-as-taggable-on

  - by seaneshbaugh

  This is going to be a really dumb question, I just know it, but I'm going to ask anyways because it's driving me crazy. How do I get acts-as-taggable-on to work? I installed it as a gem with gem install acts-as-taggable-on because I can't ever seem to get installing plugins to work, but that's a whole other batch of questions that are all probably really dumb. Anyways, no problems there, it installed correctly. I did ruby script/generate acts_as_taggable_on_migration and rake db:migrate, again no problems. I added acts_as_taggable to the model I want to use tags with, started up the server and then loaded the index for the model just to see if what I've got so far is working and got the following error: undefined local variable or method `acts_as_taggable' for #. I figure that just means I need to do something like require 'acts-as-taggable-on' to my model's file because that's typically what's necessary for gems. So I did that hit refresh and got uninitialized constant ActiveRecord::VERSION. I'm not even going to pretend to begin to know what that means went wrong. Did I go wrong somewhere or there something else I need to do. The installation instructions seem to me like they just assume you generally know what you're doing and don't even begin to explain what to do when things go wrong.

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• yet another question about migrating to Java

  - by aloneguid

  Hi, There are plenty similar questions, but maybe responses to this one will save a developer's life :) I want to migrate to Java. The reasons are very clear: all the .NET vacancies are client and windows oriented (Silverlight developer, ASP.NET developer, WPF developer etc.) and none of them are any interest to me. I worked with .NET since it's beginning as our company decided to invest in .NET having C++ stack and all the natual problems, so I was just blindly following and actually enjoyed it as the products were mostly server oriented with mixed C++/C# code. Today I have beforementioned problem - can't find an inspiring job. I'd rather kill myself than start working on a Silverlight or WPF project. Searching Java vacancies shows promising results, however they all require a huge java-related technology stack and experience. The question is is there any chance to find a job quickly and without dramatic salary drop (I know that Java guys are usually better paid, so there must be a kind of a credit) and if not, how must time and effort does it take to migrate (my .NET knowledge mostly includes server-oriented technologies like NHibernate, WCF, threading, sockets, ASP.NET web services, Enterprise Library, NInject etc etc etc, and (still) some C++ leftovers). Thanks!

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• Can I spread out a long running stored proc accross multiple CPU's?

  - by Russ

  [Also on SuperUser - http://superuser.com/questions/116600/can-i-spead-out-a-long-running-stored-proc-accross-multiple-cpus] I have a stored procedure in SQL server the gets, and decrypts a block of data. ( Credit cards in this case. ) Most of the time, the performance is tolerable, but there are a couple customers where the process is painfully slow, taking literally 1 minute to complete. ( Well, 59377ms to return from SQL Server to be exact, but it can vary by a few hundred ms based on load ) When I watch the process, I see that SQL is only using a single proc to perform the whole process, and typically only proc 0. Is there a way I can change my stored proc so that SQL can multi-thread the process? Is it even feasible to cheat and to break the calls in half, ( top 50%, bottom 50% ), and spread the load, as a gross hack? ( just spit-balling here ) My stored proc: USE [Commerce] GO /****** Object: StoredProcedure [dbo].[GetAllCreditCardsByCustomerId] Script Date: 03/05/2010 11:50:14 ******/ SET ANSI_NULLS ON GO SET QUOTED_IDENTIFIER ON GO ALTER PROCEDURE [dbo].[GetAllCreditCardsByCustomerId] @companyId UNIQUEIDENTIFIER, @DecryptionKey NVARCHAR (MAX) AS SET NoCount ON DECLARE @cardId uniqueidentifier DECLARE @tmpdecryptedCardData VarChar(MAX); DECLARE @decryptedCardData VarChar(MAX); DECLARE @tmpTable as Table ( CardId uniqueidentifier, DecryptedCard NVarChar(Max) ) DECLARE creditCards CURSOR FAST_FORWARD READ_ONLY FOR Select cardId from CreditCards where companyId = @companyId and Active=1 order by addedBy desc --2 OPEN creditCards --3 FETCH creditCards INTO @cardId -- prime the cursor WHILE @@Fetch_Status = 0 BEGIN --OPEN creditCards DECLARE creditCardData CURSOR FAST_FORWARD READ_ONLY FOR select convert(nvarchar(max), DecryptByCert(Cert_Id('Oh-Nay-Nay'), EncryptedCard, @DecryptionKey)) FROM CreditCardData where cardid = @cardId order by valueOrder OPEN creditCardData FETCH creditCardData INTO @tmpdecryptedCardData -- prime the cursor WHILE @@Fetch_Status = 0 BEGIN print 'CreditCardData' print @tmpdecryptedCardData set @decryptedCardData = ISNULL(@decryptedCardData, '') + @tmpdecryptedCardData print '@decryptedCardData' print @decryptedCardData; FETCH NEXT FROM creditCardData INTO @tmpdecryptedCardData -- fetch next END CLOSE creditCardData DEALLOCATE creditCardData insert into @tmpTable (CardId, DecryptedCard) values ( @cardId, @decryptedCardData ) set @decryptedCardData = '' FETCH NEXT FROM creditCards INTO @cardId -- fetch next END select CardId, DecryptedCard FROM @tmpTable CLOSE creditCards DEALLOCATE creditCards

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• Can I spread out a long running stored proc accross multiple CPU's?

  - by Russ

  [Also on SuperUser - http://superuser.com/questions/116600/can-i-spead-out-a-long-running-stored-proc-accross-multiple-cpus] I have a stored procedure in SQL server the gets, and decrypts a block of data. ( Credit cards in this case. ) Most of the time, the performance is tolerable, but there are a couple customers where the process is painfully slow, taking literally 1 minute to complete. ( Well, 59377ms to return from SQL Server to be exact, but it can vary by a few hundred ms based on load ) When I watch the process, I see that SQL is only using a single proc to perform the whole process, and typically only proc 0. Is there a way I can change my stored proc so that SQL can multi-thread the process? Is it even feasible to cheat and to break the calls in half, ( top 50%, bottom 50% ), and spread the load, as a gross hack? ( just spit-balling here ) My stored proc: USE [Commerce] GO /****** Object: StoredProcedure [dbo].[GetAllCreditCardsByCustomerId] Script Date: 03/05/2010 11:50:14 ******/ SET ANSI_NULLS ON GO SET QUOTED_IDENTIFIER ON GO ALTER PROCEDURE [dbo].[GetAllCreditCardsByCustomerId] @companyId UNIQUEIDENTIFIER, @DecryptionKey NVARCHAR (MAX) AS SET NoCount ON DECLARE @cardId uniqueidentifier DECLARE @tmpdecryptedCardData VarChar(MAX); DECLARE @decryptedCardData VarChar(MAX); DECLARE @tmpTable as Table ( CardId uniqueidentifier, DecryptedCard NVarChar(Max) ) DECLARE creditCards CURSOR FAST_FORWARD READ_ONLY FOR Select cardId from CreditCards where companyId = @companyId and Active=1 order by addedBy desc --2 OPEN creditCards --3 FETCH creditCards INTO @cardId -- prime the cursor WHILE @@Fetch_Status = 0 BEGIN --OPEN creditCards DECLARE creditCardData CURSOR FAST_FORWARD READ_ONLY FOR select convert(nvarchar(max), DecryptByCert(Cert_Id('Oh-Nay-Nay'), EncryptedCard, @DecryptionKey)) FROM CreditCardData where cardid = @cardId order by valueOrder OPEN creditCardData FETCH creditCardData INTO @tmpdecryptedCardData -- prime the cursor WHILE @@Fetch_Status = 0 BEGIN print 'CreditCardData' print @tmpdecryptedCardData set @decryptedCardData = ISNULL(@decryptedCardData, '') + @tmpdecryptedCardData print '@decryptedCardData' print @decryptedCardData; FETCH NEXT FROM creditCardData INTO @tmpdecryptedCardData -- fetch next END CLOSE creditCardData DEALLOCATE creditCardData insert into @tmpTable (CardId, DecryptedCard) values ( @cardId, @decryptedCardData ) set @decryptedCardData = '' FETCH NEXT FROM creditCards INTO @cardId -- fetch next END select CardId, DecryptedCard FROM @tmpTable CLOSE creditCards DEALLOCATE creditCards

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• How to connect remote EJB module from application client

  - by Zeck

  Hi guys, I have a EJB module in remote Glassfish server and application client in my computer. I want to connect from the application client to the remote EJB. Here is the my EJB interface: @Remote public interface BookEJBRemote { public String getTitle(); } Here is the my ejb: @Stateless public class BookEJB implements BookEJBRemote { @Override public String getTitle() { return "Twenty Thousand Leagues Under the Sea"; } } I have several questions : Can I use Dependency Injection in the remote application client to connect to the ejb? If so what can i do to achieve this. Do i need to configure in the sun-ejb-jar.xml and sun-application-client.xml? In other words, if i use DI like @EJB MyEJBRemote ejb; How application client container know what ejb to be injected? Where should i specify the information? How can i run the application client? I tried to run package-appclient in the glassfish server to get appclient.jar and copy it to my computer. Then i type appclient.jar -client myAppClient.jar . It didn't work. How do i point the target server? if i cannot use DI in the client then i guess i have to use JNDI lookup. Do i need to configure jndi name in sun-ejb-jar.xml or in the sun-application-client.xml? No matter how i try i never manage to run application client ? Can you guys put some working example? And thank you for every advises and examples?

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• Using Excel as front end to Access database (with VBA)

  - by Alex

  I am building a small application for a friend and they'd like to be able to use Excel as the front end. (the UI will basically be userforms in Excel). They have a bunch of data in Excel that they would like to be able to query but I do not want to use excel as a database as I don't think it is fit for that purpose and am considering using Access. [BTW, I know Access has its shortcomings but there is zero budget available and Access already on friend's PC] To summarise, I am considering dumping a bunch of data into Access and then using Excel as a front end to query the database and display results in a userform style environment. Questions: How easy is it to link to Access from Excel using ADO / DAO? Is it quite limited in terms of functionality or can I get creative? Do I pay a performance penalty (vs.using forms in Access as the UI)? Assuming that the database will always be updated using ADO / DAO commands from within Excel VBA, does that mean I can have multiple Excel users using that one single Access database and not run into any concurrency issues etc.? Any other things I should be aware of? I have strong Excel VBA skills and think I can overcome Access VBA quite quickly but never really done Excel / Access link before. I could shoehorn the data into Excel and use as a quasi-database but that just seems more pain than it is worth (and not a robust long term solution) Any advice appreciated. Alex

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• virtualenv macosX --no-site-package ignored

  - by Tristram Gräbener

  Hello, I'm having problems with macOSX and virtualenv. It seems to ignore --no-site-package. Using exactly the same commands with linux (archlinux) it works. It it macOSX 10.5 with python 2.5 curl -o virtualenv.py 'http://bitbucket.org/ianb/virtualenv/raw/tip/virtualenv.py Create a new environment python virtualenv.py --no-site-packages foo New python executable in foo/bin/python Installing setuptools...........................done. Activate it source foo/bin/activate Try to install something in it. Despite virtualenv it looks for the system-wide install easy_install cherrypy Searching for cherrypy Best match: CherryPy 3.1.2 Adding CherryPy 3.1.2 to easy-install.pth file Using /Library/Python/2.5/site-packages Processing dependencies for cherrypy Finished processing dependencies for cherrypy Yet it doesn't find the module (foo)guidage-multimodal:~ tristram$ python Python 2.5.1 (r251:54863, Feb 6 2009, 19:02:12) [GCC 4.0.1 (Apple Inc. build 5465)] on darwin Type "help", "copyright", "credits" or "license" for more information. >>> import cherrypy Traceback (most recent call last): File "<stdin>", line 1, in <module> ImportError: No module named cherrypy I tried PIP after looking at http://stackoverflow.com/questions/1382925/virtualenv-no-site-packages-and-pip-still-finding-global-packages However it fails installing psycopg2 (some problems with gcc). Also I would like to be able to have a setup.py (from distribute) that does the whole woork

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• In SQL, if we rename INNER JOIN as INTERSECT JOIN, LEFT OUTER JOIN as LEFT UNION JOIN, and FULL OUTE

  - by Jian Lin

  In SQL, the name Join gives an idea of "merging" or a sense of "union", making something bigger. But in fact, as in the other post http://stackoverflow.com/questions/2706051/in-sql-a-join-is-actually-an-intersection-and-it-is-also-a-linkage-or-a-sidew it turns out that a Join (Inner Join) is actually an Intersection. So if we think of Join = Inner Join = Intersect Join Left Outer Join = Left Union Join Full Outer Join = Full Union Join = Union Join then we always get a feel of what's happening, and maybe never forget what they are easily. In a way, we can think of Intersect as "making it less", therefore it is excluding something. That's why the name "Join" won't go with the idea of "Intersect". But in fact, both Intersect and Union can be thought of as: Union: bringing something together and merge them unconditionally. Intersect: bringing something together and merge them based on some condition. so the "bringing something together" is probably what "Join" is all about. It is like, Intersection is a "half glass of water" -- we can thinking of it as "excluding something" or as "bringing something together and accepting the common ones". So if the word "Intersect Join" is used, maybe a clear picture is there, and "Union Join" can be a clear picture too. Maybe the word "Inner Join" and "Outer Join" is very clear when we use SQL a lot. Somehow, the word "Outer" tends to give a feeling that it is "outside" and excluding something rather than a "Union".

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• Getting hardware floating point with android NDK

  - by Goz

  Hi All, I've begun playing with the android NDK. One of the things I've just learnt is about creating an application.mk file to specify the armv7 abi. I'm building the san-angeles example with the following parameters. APP_MODULES := sanangeles APP_PROJECT_PATH := $(call my-dir)/../ APP_OPTIM := release APP_ABI := armeabi-v7a However this seems to run at exactly the same speed as it did before (ie badly). Am I just GL limited and not CPU limited or is something wrong here? I have noticed when I compile that I get the following command line options emitted: -march=armv7-a -mfloat-abi=softfp -mfpu=vfp -mthumb The thing that worries me there is the "softfp". There IS mention of the v7 abi, the VFP fpu stuff and I'm guessing the "thumb" refers to the "thumb-2" instructions (Though I don't know what exactly these are). However that "softfp" does concern me. Shouldn't it be "hardfp"? Anyone got any ideas on these questions? I think I'm probably about ready to start implementing some GL ES 2.0 code for my HTC Desire but I'd like to make sure I'm getting the best possible speed out of it :) Cheers in advance!

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• What should every developer know about databases?

  - by Aaronaught

  Whether we like it or not, many if not most of us developers either regularly work with databases or may have to work with one someday. And considering the amount of misuse and abuse in the wild, and the volume of database-related questions that come up every day, it's fair to say that there are certain concepts that developers should know - even if they don't design or work with databases today. So: What are the important concepts that developers and other software professionals ought to know about databases? Guidelines for Responses: Keep your list short. One concept per answer is best. Be specific. "Data modelling" may be an important skill, but what does that mean precisely? Explain your rationale. Why is your concept important? Don't just say "use indexes." Don't fall into "best practices." Convince your audience to go learn more. Upvote answers you agree with. Read other people's answers first. One high-ranked answer is a more effective statement than two low-ranked ones. If you have more to add, either add a comment or reference the original. Don't downvote something just because it doesn't apply to you personally. We all work in different domains. The objective here is to provide direction for database novices to gain a well-founded, well-rounded understanding of database design and database-driven development, not to compete for the title of most-important.

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• Is this a good way to expose generic base class methods through an interface?

  - by Nate Heinrich

  I am trying to provide an interface to an abstract generic base class. I want to have a method exposed on the interface that consumes the generic type, but whose implementation is ultimately handled by the classes that inherit from my abstract generic base. However I don't want the subclasses to have to downcast to work with the generic type (as they already know what the type should be). Here is a simple version of the only way I can see to get it to work at the moment. public interface IFoo { void Process(Bar_base bar); } public abstract class FooBase<T> : IFoo where T : Bar_base { abstract void Process(T bar); // Explicit IFoo Implementation void IFoo.Process(Bar_base bar) { if (bar == null) throw new ArgumentNullException(); // Downcast here in base class (less for subclasses to worry about) T downcasted_bar = bar as T; if (downcasted_bar == null) { throw new InvalidOperationException( string.Format("Expected type '{0}', not type '{1}'", T.ToString(), bar.GetType().ToString()); } //Process downcasted object. Process(downcasted_bar); } } Then subclasses of FooBase would look like this... public class Foo_impl1 : FooBase<Bar_impl1> { void override Process(Bar_impl1 bar) { //No need to downcast here! } } Obviously this won't provide me compile time Type Checking, but I think it will get the job done... Questions: 1. Will this function as I think it will? 2. Is this the best way to do this? 3. What are the issues with doing it this way? 4. Can you suggest a different approach? Thanks!

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• High-concurrency counters without sharding

  - by dound

  This question concerns two implementations of counters which are intended to scale without sharding (with a tradeoff that they might under-count in some situations): http://appengine-cookbook.appspot.com/recipe/high-concurrency-counters-without-sharding/ (the code in the comments) http://blog.notdot.net/2010/04/High-concurrency-counters-without-sharding My questions: With respect to #1: Running memcache.decr() in a deferred, transactional task seems like overkill. If memcache.decr() is done outside the transaction, I think the worst-case is the transaction fails and we miss counting whatever we decremented. Am I overlooking some other problem that could occur by doing this? What are the significiant tradeoffs between the two implementations? Here are the tradeoffs I see: #2 does not require datastore transactions. To get the counter's value, #2 requires a datastore fetch while with #1 typically only needs to do a memcache.get() and memcache.add(). When incrementing a counter, both call memcache.incr(). Periodically, #2 adds a task to the task queue while #1 transactionally performs a datastore get and put. #1 also always performs memcache.add() (to test whether it is time to persist the counter to the datastore). Conclusions (without actually running any performance tests): #1 should typically be faster at retrieving a counter (#1 memcache vs #2 datastore). Though #1 has to perform an extra memcache.add() too. However, #2 should be faster when updating counters (#1 datastore get+put vs #2 enqueue a task). On the other hand, with #1 you have to be a bit more careful with the update interval since the task queue quota is almost 100x smaller than either the datastore or memcahce APIs.

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• Speed vs security vs compatibility over methods to do string concatenation in Python

  - by Cawas

  Similar questions have been brought (good speed comparison there) on this same subject. Hopefully this question is different and updated to Python 2.6 and 3.0. So far I believe the faster and most compatible method (among different Python versions) is the plain simple + sign: text = "whatever" + " you " + SAY But I keep hearing and reading it's not secure and / or advisable. I'm not even sure how many methods are there to manipulate strings! I could count only about 4: There's interpolation and all its sub-options such as % and format and then there's the simple ones, join and +. Finally, the new approach to string formatting, which is with format, is certainly not good for backwards compatibility at same time making % not good for forward compatibility. But should it be used for every string manipulation, including every concatenation, whenever we restrict ourselves to 3.x only? Well, maybe this is more of a wiki than a question, but I do wish to have an answer on which is the proper usage of each string manipulation method. And which one could be generally used with each focus in mind (best all around for compatibility, for speed and for security). Thanks.

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• When virtual inheritance IS a good design?

  - by 7vies

  EDIT3: Please be sure to clearly understand what I am asking before answering (there are EDIT2 and lots of comments around). There are (or were) many answers which clearly show misunderstanding of the question (I know that's also my fault, sorry for that) Hi, I've looked over the questions on virtual inheritance (class B: public virtual A {...}) in C++, but did not find an answer to my question. I know that there are some issues with virtual inheritance, but what I'd like to know is in which cases virtual inheritance would be considered a good design. I saw people mentioning interfaces like IUnknown or ISerializable, and also that iostream design is based on virtual inheritance. Would those be good examples of a good use of virtual inheritance, is that just because there is no better alternative, or because virtual inheritance is the proper design in this case? Thanks. EDIT: To clarify, I'm asking about real-life examples, please don't give abstract ones. I know what virtual inheritance is and which inheritance pattern requires it, what I want to know is when it is the good way to do things and not just a consequence of complex inheritance. EDIT2: In other words, I want to know when the diamond hierarchy (which is the reason for virtual inheritance) is a good design

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• Self-referencing tables in Linq2Sql

  - by J-Man

  Hi, I've seen a lot of questions on self-referencing tables in Linq2Sql and how to eagerly load all child records for a particular root object. I've implemented a temporary solution by accessing all underlying properties, but you can see that this doesn't do the performance any good. The thing is though, that all records are correlated with each-other using a correlation GUID. Example below: RootElement - Id: 1 - ParentId: null - CorrelationId: 4D68E512-4B55-44f4-BA5A-174B630A03DD ChildElement1 - Id: 2 - ParentId: 1 - CorrelationId: 4D68E512-4B55-44f4-BA5A-174B630A03DD ChildElement2 - Id: 3 - ParentId: 2 - CorrelationId: 4D68E512-4B55-44f4-BA5A-174B630A03DD ChildElement1 - Id: 4 - ParentId: 2 - CorrelationId: 4D68E512-4B55-44f4-BA5A-174B630A03DD In my case, I do have access to the correlationId, so I can retrieve all of my records by performing the following query: from element in db.Elements where element.CorrelationId == '4D68E512-4B55-44f4-BA5A-174B630A03DD' select element; But, of course, I want these elements associated with each other by executing this query: from element in db.Elements where element.CorrelationId == '4D68E512-4B55-44f4-BA5A-174B630A03DD' && element.ParentId == null select element; My question is: is it possible to combine the results the first query as some sort of 'caching mechanism' for the query where I get the root element? Thanks for the input. J.

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• MVC Paging and Sorting Patterns: How to Page or Sort Re-Using Form Criteria

  - by CRice

  What is the best ASP.NET MVC pattern for paging data when the data is filtered by form criteria? This question is similar to: http://stackoverflow.com/questions/1425000/preserve-data-in-net-mvc but surely there is a better answer? Currently, when I click the search button this action is called: [AcceptVerbs(HttpVerbs.Post)] public ActionResult Search(MemberSearchForm formSp, int? pageIndex, string sortExpression) {} That is perfect for the initial display of the results in the table. But I want to have page number links or sort expression links re-post the current form data (the user entered it the first time - persisted because it is returned as viewdata), along with extra route params 'pageIndex' or 'sortExpression', Can an ActionLink or RouteLink (which I would use for page numbers) post the form to the url they specify? <%= Html.RouteLink("page 2", "MemberSearch", new { pageIndex = 1 })%> At the moment they just do a basic redirect and do not post the form values so the search page loads fresh. In regular old web forms I used to persist the search params (MemberSearchForm) in the ViewState and have a GridView paging or sorting event reuse it.

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• Autorotation and multiple view controllers

  - by alku83

  I'm creating an iPad application which should only work in portrait and portait upsidedown modes. For performance reasons in my applicationDidFinishLaunching method I'm creating several viewControllers, and adding them to my main window as subviews. I then hide the ones I don't want to see straight away. There is no tab bar or navigation controller. My problem is that only the first viewController seems to be receiving the rotate calls. I have verified this by swapping around the order in which I add the subviews to the main window and NSLog's. Is there some way I can force all the controllers to receive the calls? Some of my views are designed to lay over the top of another view, but this behind view will not always be the same one - so it seems to make sense to have the overlay view in a separate view controller. Am I doing something fundamentally wrong, and that's why it's not behaving as I would expect? EDIT: The accepted answer for this question seems to indicate the exact problem I'm facing: http://stackoverflow.com/questions/548142/uiviewcontroller-rotate-methods

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• Multithreading and Interrupts

  - by Nicholas Flynt

  I'm doing some work on the input buffers for my kernel, and I had some questions. On Dual Core machines, I know that more than one "process" can be running simultaneously. What I don't know is how the OS and the individual programs work to protect collisions in data. There are two things I'd like to know on this topic: (1) Where do interrupts occur? Are they guaranteed to occur on one core and not the other, and could this be used to make sure that real-time operations on one core were not interrupted by, say, file IO which could be handled on the other core? (I'd logically assume that the interrupts would happen on the 1st core, but is that always true, and how would you tell? Or perhaps does each core have its own settings for interrupts? Wouldn't that lead to a scenario where each core could react simultaneously to the same interrupt, possibly in different ways?) (2) How does the dual core processor handle opcode memory collision? If one core is reading an address in memory at exactly the same time that another core is writing to that same address in memory, what happens? Is an exception thrown, or is a value read? (I'd assume the write would work either way.) If a value is read, is it guaranteed to be either the old or new value at the time of the collision? I understand that programs should ideally be written to avoid these kinds of complications, but the OS certainly can't expect that, and will need to be able to handle such events without choking on itself.

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• What are the reasons to store documents into DBMS when using Alfresco DMS

  - by Julia

  Hello guys! I have interview for an internship with company that wants to implement document management system and they are considering on the first place open source solutions, their top choice being Alfresco, but decision is still not final, part of my work there would be to investigate is Alfresco the best solution. What I have seen from project description, is that they would implement Alfresco with MySQL database, and not to use DBMS just for document metadata and indexing, but they actually want to store documents inside. By company profile, type of documents would be mostly PDF and .doc, not images. I have researched a bit, and I have read all the topics here related to storing files into the database, not to duplicate a question. So from what I understand, storing BLOBS is generally not recomendable, and by the profile of the company and their legal obligations with archiving, I see they will have to store larger amount of docs. I would like to be ready as much as I can for the interview and that is why I would like your opinion on these questions: 1) What will be your reasons for deciding to store documents into the DBMS, (especially having in mind that you are installing Alfresco, which stores files in the FS)??? 2) Do you have any experiences with storing documents into the MySQL database specifically??? All the help is very much appreciated, I am really excited about interview and really want this internship, so this is one of things i really want to understand before!! Thank you!!!!

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• Vertically center a fluid image in a fluid container

  - by Ferdy

  I certainly do not want to add to the pile of vertical alignments CSS questions, but I've spent hours trying to find a solution to no avail yet. Here's the situation: I am building a slideshow gallery of images. I want the images to be displayed as large as the user's window allows. So I have this outer placeholder: <section class="photo full"> (Yes, I'm using HTML5 elements). Which has the following CSS: section.photo.full { display:inline-block; width:100%; height:100%; position:absolute; overflow:hidden; text-align:center; } Next, the image is placed inside it. Depending on the orientation of the image, I set either the width or height to 75%, and the other axis to auto: $wide = $bigimage['width'] >= $bigimage['height'] ? true: false; ?> <img src="<?= $bigimage['url'] ?>" width="<?= $wide? "75%" : "auto"?>" height="<?= $wide? "auto" : "75%"?>"/> So, we have a fluid outer container, with inside a fluid image. The horizontal centering of the image works, yet I cannot seem to find a way to vertically center the image within it's container. I have researched centering methods but most assume either the container or image has a known width or height. Then there is the display:table-cell method, which does not seem to work for me either. I'm stuck. I'm looking for a CSS solution, but am open to js solutions too.

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