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  • Programming logic to group a users activities like facebook. E.g. Chris is now friends with A, B and C

    - by Chris Dowdeswell
    So I am trying to develop an activity feed for my site, Basically If I UNION a bunch of activities into a feed I would end up with something like the following. Chris is now friends with Mark Chris is now friends with Dave What I want though is a neater way of grouping these similar posts so the feed doesn't give information overload... E.g. Chris is now friends with Mark, Dave and 4 Others Any ideas on how I can approach this logically? I am using Classic ASP on SQL server. Here is the UNION statement I have so far... SELECT U.UserID As UserID, L.UN As UN,Left(U.UID,13) As ProfilePic,U.Fname + ' ' + U.Sname As FullName, 'said ' + WP.Post AS Activity, WP.Ctime FROM Users AS U LEFT JOIN Logins L ON L.userID = U.UserID LEFT OUTER JOIN WallPosts AS WP ON WP.userID = U.userID WHERE WP.Ctime IS NOT NULL UNION SELECT U.UserID As UserID, L.UN As UN,Left(U.UID,13) As ProfilePic,U.Fname + ' ' + U.Sname As FullName, 'commented ' + C.Comment AS Activity, C.Ctime FROM Users AS U LEFT JOIN Logins L ON L.userID = U.UserID LEFT OUTER JOIN Comments AS C ON C.UserID = U.userID WHERE C.Ctime IS NOT NULL UNION SELECT U.UserID As UserID, L.UN As UN,Left(U.UID,13) As ProfilePic, U.Fname + ' ' + U.Sname As FullName, 'connected with <a href="/profile.asp?un='+(SELECT Logins.un FROM Logins WHERE Logins.userID = Cn.ToUserID)+'">' + (SELECT Users.Fname + ' ' + Users.Sname FROM Users WHERE userID = Cn.ToUserID) + '</a>' AS Activity, Cn.Ctime FROM Users AS U LEFT JOIN Logins L ON L.userID = U.UserID LEFT OUTER JOIN Connections AS Cn ON Cn.UserID = U.userID WHERE CN.Ctime IS NOT NULL

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  • The correct way to Fire-and-Forget an asynchronous delegate

    - by Programming Hero
    Consider me rusty on the subject of asynchronous delegates. If I want to call a method asynchronously, in a fire-and-forget style, is this an appropriate way to do it? Action action = DoSomething; action.BeginInvoke(action.EndInvoke, null); The DoSomething() method catches all exceptions and deals with them internally. Is the call to EndInvoke appropriate? Required? Is there a clearer way to achieve the same behaviour?

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  • Map NHibernate entity to multiple tables based on parent

    - by Programming Hero
    I'm creating a domain model where entities often (but not always) have a member of type ActionLog. ActionLog is a simple class which allows for an audit trail of actions being performed on an instance. Each action is recorded as an ActionLogEntry instance. ActionLog is implemented (approximately) as follows: public class ActionLog { public IEnumerable<ActionLogEntry> Entries { get { return EntriesCollection; } } protected ICollection<ActionLogEntry> EntriesCollection { get; set; } public void AddAction(string action) { // Append to entries collection. } } What I would like is to re-use this class amongst my entities and have the entries map to different tables based on which class they are logged against. For example: public class Customer { public ActionLog Actions { get; protected set; } } public class Order { public ActionLog Actions { get; protected set; } } This design is suitable for me in the application, however I can't see a clear way to map this scenario to a database with NHibernate. I typically use Fluent NHibernate for my configuration, but I'm happy to accept answers in more general HBM xml.

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  • WCF Message Debugging on Custom Binding

    - by Programming Hero
    I've created a custom binding in WCF for a custom MessageEncoder to allow messages to be written as XML using a wider range of encodings than WCF supports out of the box. The encoder appears to be working and I am able to send and receive messages, but I want to verify that the XML message being written is exactly as required by the service I am trying to consume. I've turned on message logging for WCF using the diagnostic trace listeners to output the messages sent and received over the wire to a log file. Unfortunately, for calls using my encoder, the message is displayed as ... stream ... EDIT: I don't think it's anything to do with my custom encoding. I have experimented with my custom binding a little, switching to using the built-in text encoding and http transport. I still don't get a message body logged in the message trace. Is there anything that needs to be specified within a custom binding to enable message logging?

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  • sharing build artifacts between jobs in hudson

    - by programming panda
    Hi I'm trying to set up our build process in hudson. Job 1 will be a super fast (hopefully) continuous integration build job that will be built frequently. Job 2, will be responsible for running a comprehensive test suite, at a regular interval or triggered manually. Job 3 will be responsible for running analysis tools across the codebase (much like Job 2). I tried using the "Advanced Projects Options use custom workspace" feature so that code compiled in Job 1 can be used in Job 2 and 3. However, it seems that all build artifacts remain inside that Job 1 workspace. I'm I doing this right? Is there a better way of doing this? I guess I'm looking for something similar to a build pipeline setup...so that things can be shared and the appropriate jobs can be executed in stages. (I also considered using 'batch tasks'...but it seems like those can't be scheduled? only triggered manually?) Any suggestions are welcomed. Thanks!

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  • WCF Message Debugging on WebHttpBehavior

    - by Programming Hero
    I've created a custom binding in WCF for a custom MessageEncoder to allow messages to be written as XML using a wider range of encodings than WCF supports out of the box. The encoder appears to be working and I am able to send and receive messages, but I want to verify that the XML message being written is exactly as required by the service I am trying to consume. I've turned on message logging for WCF using the diagnostic trace listeners to output the messages sent and received over the wire to a log file. Unfortunately, for calls using my encoder, the message is displayed as ... stream ... EDIT: I don't think it's anything to do with my custom encoding. I have experimented with my custom binding a little, switching to using the built-in text encoding and http transport. I still don't get a message body logged in the message trace. EDIT2: Having done further investigation, the issue looks to be related not to the custom binding, but the custom behaviour. I'm apply the <webHttp/> behaviour. Once this is specified (along with manual addressing), the tracing behaviour shows up. Is this a known issue with WebHttpBehavior? Am I still barking up the wrong tree?

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  • High level vs. low level programming. Do I really have to choose?

    - by EpsilonVector
    Every once in a while I'm asked in interviews which I like the best- low level or high level. It seems to me that the implicit message is that they are both a specialty and they want to know which direction I'm heading. The trouble is, I seem to like both. Low level is extremely challenging and often requires a great deal of esoteric knowledge. High level is where all the sexy things happen: applications that people use directly, results that can be easily demonstrated (showed off) in a way that is accessible to everybody, and you get to work with really advanced tools and interact with new technologies. I would really love to do both, even if it means alternating between them (I doubt there are jobs that will let me do both simultaneously), but I'm guessing that the industry rewards specialists more than generalists. Will it really be problematic career wise if I never choose one over the other? Is it practical to alternate between the two in the sense that if I were to leave a job doing one of them, I should experience no "friction" trying to get a job doing the other (assuming I'm reasonably in the loop)? Are there career opportunities where you get to do both? Do I really have to choose one over the other?

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  • Tomcat 403 error after LDAP authentication.

    - by user352636
    I'm currently trying to use an LDAP server to authenticate users who are trying to access our Tomcat setup. I believe I have managed to get the LDAP authentication working in the form of a JNDI realm call from Tomcat, but immediately after the user enters their password Tomcat starts throwing 403 (permission denied) errors for everything except from the root page (ttp://localhost:1337/). I have no idea why this is happening. I am following the example at http://blog.mc-thias.org/?title=tomcat_ldap_authentication&more=1&c=1&tb=1&pb=1 . server.xml (the interesting/changed bits) <Realm className="org.apache.catalina.realm.JNDIRealm" debug="99" connectionURL="ldap://localhost:389" userPattern="uid={0},ou=People,o=test,dc=company,dc=uk" userSubTree="true" roleBase="ou=Roles,o=test,dc=company,dc=uk" roleName="cn" roleSearch="memberUid={1}" /> <Valve className="org.apache.catalina.authenticator.SingleSignOn" /> web.xml (the interesting/changed bits) <security-constraint> <display-name>Security Constraint</display-name> <web-resource-collection> <web-resource-name>Protected Area</web-resource-name> <!-- Define the context-relative URL(s) to be protected --> <url-pattern>/*</url-pattern> <!-- If you list http methods, only those methods are protected --> </web-resource-collection> <auth-constraint> <!-- Anyone with one of the listed roles may access this area --> <role-name>admin</role-name> <role-name>regular</role-name> </auth-constraint> </security-constraint> <!-- Default login configuration uses form-based authentication --> <login-config> <auth-method>BASIC</auth-method> </login-config> <!-- Security roles referenced by this web application --> <security-role> <role-name>admin</role-name> <role-name>regular</role-name> </security-role> I cannot access my LDAP setup at the moment, but I believe it is alright as the login is accepted by the BASIC auth method, it's just tomcat that is rejecting it. The roles should be as defined in web.xml - admin and regular. If there is any other information you require me to provide, please just ask! My thanks in advance to anyone who can help, and my apologies for any major mistakes I have made - yesterday was pretty much the first time I'd ever heard of LDAP =D. EDIT: Fixed the second xml segment. Apologies for the formating-fail.

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  • I've been hired on as a entry-level game developer at a company and have little/no experience in API programming, what should I expect?

    - by Mr. Geneth
    So, I've been hired on as an entry level game developer with little/no experience working with any API other than Win32. This will be an overall learning experience for me as a person and I have gone over this multiple times with the boss and he has no problem with my inexperience. He says that if I'm not worth it now, I will be later. This gives me confidence, but I still feel that I should know a lot more before tackling this position. I would be stupid to pass it up. This is one of my favorite places to come for advice and help and have tried to just accept this, but it just keeps bothering that I can't go in knowing how to at least do the basics. I want to give the company its money's worth. Ya know? My questions are: What should I expect from the other programmers in this project (In terms of patience with me and working together, and being taught)? Is this normal? Any other advice on this sort of thing would be wonderful. I just want to feel comfortable with it.

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  • Storing website hierarchy in Sql Server 2008

    - by Mika Kolari
    I want to store website page hierarchy in a table. What I would like to achieve is efficiently 1) resolve (last valid) item by path (e.g. "/blogs/programming/tags/asp.net,sql-server", "/blogs/programming/hello-world" ) 2) get ancestor items for breadcrump 3) edit an item without updating the whole tree of children, grand children etc. Because of the 3rd point I thought the table could be like ITEM id type slug title parentId 1 area blogs Blogs 2 blog programming Programming blog 1 3 tagsearch tags 2 4 post hello-world Hello World! 2 Could I use Sql Server's hierarchyid type somehow (especially point 1, "/blogs/programming/tags" is the last valid item)? Tree depth would usually be around 3-4. What would be the best way to achieve all this?

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  • Configuring a Context specific Tomcat Security Realm

    - by Andy Mc
    I am trying to get a context specific security Realm in Tomcat 6.0, but when I start Tomcat I get the following error: 09-Dec-2010 16:12:40 org.apache.catalina.startup.ContextConfig validateSecurityRoles INFO: WARNING: Security role name myrole used in an <auth-constraint> without being defined in a <security-role> I have created the following context.xml file: <Context debug="0" reloadable="true"> <Resource name="MyUserDatabase" type="org.apache.catalina.UserDatabase" description="User database that can be updated and saved" factory="org.apache.catalina.users.MemoryUserDatabaseFactory" pathname="conf/my-users.xml" /> <Realm className="org.apache.catalina.realm.UserDatabaseRealm" resourceName="MyUserDatabase"/> </Context> Created a file: my-users.xml which I have placed under WEB-INF/conf which contains the following: <tomcat-users> <role rolename="myrole"/> <user username="test" password="changeit" roles="myrole" /> </tomcat-users> Added the following lines to my web.xml file: <web-app ...> ... <security-constraint> <web-resource-collection> <web-resource-name>Entire Application</web-resource-name> <url-pattern>/*</url-pattern> </web-resource-collection> <auth-constraint> <role-name>myrole</role-name> </auth-constraint> </security-constraint> <login-config> <auth-method>BASIC</auth-method> </login-config> ... </web-app> But seem to get the error wherever I put conf/my-users.xml. Do I have to specify an explicit PATH in the pathname or is it relative to somewhere? Ideally I would like to have it packaged up as part of my WAR file. Any ideas?

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  • Routing redirection decision

    - by programming late night
    I have really no idea why I'm asking this as this a really completely irrelevant question for which I should have figured out an answer within milliseconds, yet I'm doing it. So in my project I have a Router class which splits up the request and selects the right page to be loaded. Fine so far. Now I have a page displayed when the user requests a page that doesn't exist, you know, 404. So theoretically, if the user entered mydomain.com/404 (I use mod_rewrite with a requests collector via index.php?req=*) the 404 error would be shown to him, but in fact there was no error - the 404 page would be displayed as a perfectly normal page. So if someone would try out requesting the 404 page via /404, he would be shown the page but he can't tell if the 404 page he requested doesn't exist and he is actually getting a, you guessed it, 404 error or if he actually found some flaw in the system that makes him able to see an error page when there is no error. I don't know how dumb this whole thing here is but I'm sure some of you have in fact ran into this problem already. Short version: If the user enters mydomain.com/404 the 404 page is shown even though there is no 404 error. I know this is a completely irrelevant question, please don't tell me, but I just spontaneously wanted to hear your thoughts on it. Strange eh? Should I redirect direct access to my 404-page to the home page? Should I do nothing? Should I just go to bed and stop asking irrelevant stuff?

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  • In China. Want to set up my own private proxy. Already have website/webhosting. Help please! n00b with respect to coding/programming, go easy on me [closed]

    - by user1725461
    I am in China and have used freegate in the past -- http://en.wikipedia.org/wiki/Freegate Recently I've been having too many problems with that and some other web-based proxies I usually use. I have a website that is hosted in the US which I can access from China. Is there an easy way for me to setup my own secure private proxy? I'm sick of all my internet problems and looking for a new workable solution. Thank you! PS: and I really hope this is the right place for such a question...

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  • Iphone memory leak with malloc

    - by Icky
    Hello. I have memory leak, found by instruments and it is supposed to be in this line of code: indices = malloc( sizeof(indices[0]) * totalQuads * 6); This is actually a code snippet from a tutorial, something which i think is leak-free so to say. Now I reckon, the error is somewhere else, but I do not know, where. These are the last trackbacks: 5 ColorRun -[EAGLView initWithCoder:] /Users/thomaskopinski/programming/colorrun_3.26/Classes/EAGLView.m:98 4 ColorRun -[EAGLView initGame] /Users/thomaskopinski/programming/colorrun_3.26/Classes/EAGLView.m:201 3 ColorRun -[SpriteSheet initWithImageNamed:spriteWidth:spriteHeight:spacing:imageScale:] /Users/thomaskopinski/programming/colorrun_3.26/SpriteSheet.m:68 2 ColorRun -[Image initWithImage:scale:] /Users/thomaskopinski/programming/colorrun_3.26/Image.m:122 1 ColorRun -[Image initImpl] /Users/thomaskopinski/programming/colorrun_3.26/Image.m:158 0 libSystem.B.dylib malloc Does anyone know how to approach this?

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  • What is the benefits and drawbacks of using header files?

    - by vodkhang
    I had some experience on programming languages like Java, C#, Scala as well as some lower level programming language like C, C++, Objective - C. My observation is that low level languages separate out header files and implementation files while other higher level programming language never separate it out. They use some identifiers like public, private, protected to do the jobs of header files. I saw one benefit of using header file (in some book like Code Complete), they talk about that using header files, people can never look at our implementation file and it helps with encapsulation. A drawback is that it creates too many files for me. Sometimes, it looks like verbose. It is just my thought and I don't know if there are any other benefits and drawbacks that people ever see and work with header file This question may not relate directly to programming but I think that if I can understand better about programming to interface, design software.

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  • LINQ to SQL - database relationships won't update after submit

    - by Quantic Programming
    I have a Database with the tables Users and Uploads. The important columns are: Users -> UserID Uploads -> UploadID, UserID The primary key in the relationship is Users -> UserID and the foreign key is Uploads -> UserID. In LINQ to SQL, I do the following operations: Retrieve files var upload = new Upload(); upload.UserID = user.UserID; upload.UploadID = XXX; db.Uploads.InsertOnSubmit(upload) db.SubmitChanges(); If I do that and rerun the application (and the db object is re-built, of course) - if do something like this: foreach(var upload in user.Uploads) I get all the uploads with that user's ID. (like added in the previous example) The problem is, that my application, after adding an upload an submitting changes, doesn't update the user.Uploads collection. i.e - I don't get the newly added uploads. The user object is stored in the Session object. At first, I though that the LINQ to SQL Framework doesn't update the reference of the object, therefore I should simply "reset" the user object from a new SQL request. I mean this: Session["user"] = db.Users.Where(u => u.UserID == user.UserID).SingleOrDefault(); (Where user is the previous user) But it didn't help. Please note: After rerunning the application, user.Uploads does have the new upload! Did anyone experience this type of problem, or is it normal behavior? I am a newbie to this framework. I would gladly take any advice. Thank you!

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  • GPGPU

    WhatGPU obviously stands for Graphics Processing Unit (the silicon powering the display you are using to read this blog post). The extra GP in front of that stands for General Purpose computing.So, altogether GPGPU refers to computing we can perform on GPU for purposes beyond just drawing on the screen. In effect, we can use a GPGPU a bit like we already use a CPU: to perform some calculation (that doesn’t have to have any visual element to it). The attraction is that a GPGPU can be orders of magnitude faster than a CPU.WhyWhen I was at the SuperComputing conference in Portland last November, GPGPUs were all the rage. A quick online search reveals many articles introducing the GPGPU topic. I'll just share 3 here: pcper (ignoring all pages except the first, it is a good consumer perspective), gizmodo (nice take using mostly layman terms) and vizworld (answering the question on "what's the big deal").The GPGPU programming paradigm (from a high level) is simple: in your CPU program you define functions (aka kernels) that take some input, can perform the costly operation and return the output. The kernels are the things that execute on the GPGPU leveraging its power (and hence execute faster than what they could on the CPU) while the host CPU program waits for the results or asynchronously performs other tasks.However, GPGPUs have different characteristics to CPUs which means they are suitable only for certain classes of problem (i.e. data parallel algorithms) and not for others (e.g. algorithms with branching or recursion or other complex flow control). You also pay a high cost for transferring the input data from the CPU to the GPU (and vice versa the results back to the CPU), so the computation itself has to be long enough to justify the overhead transfer costs. If your problem space fits the criteria then you probably want to check out this technology.HowSo where can you get a graphics card to start playing with all this? At the time of writing, the two main vendors ATI (owned by AMD) and NVIDIA are the obvious players in this industry. You can read about GPGPU on this AMD page and also on this NVIDIA page. NVIDIA's website also has a free chapter on the topic from the "GPU Gems" book: A Toolkit for Computation on GPUs.If you followed the links above, then you've already come across some of the choices of programming models that are available today. Essentially, AMD is offering their ATI Stream technology accessible via a language they call Brook+; NVIDIA offers their CUDA platform which is accessible from CUDA C. Choosing either of those locks you into the GPU vendor and hence your code cannot run on systems with cards from the other vendor (e.g. imagine if your CPU code would run on Intel chips but not AMD chips). Having said that, both vendors plan to support a new emerging standard called OpenCL, which theoretically means your kernels can execute on any GPU that supports it. To learn more about all of these there is a website: gpgpu.org. The caveat about that site is that (currently) it completely ignores the Microsoft approach, which I touch on next.On Windows, there is already a cross-GPU-vendor way of programming GPUs and that is the DirectX API. Specifically, on Windows Vista and Windows 7, the DirectX 11 API offers a dedicated subset of the API for GPGPU programming: DirectCompute. You use this API on the CPU side, to set up and execute the kernels that run on the GPU. The kernels are written in a language called HLSL (High Level Shader Language). You can use DirectCompute with HLSL to write a "compute shader", which is the term DirectX uses for what I've been referring to in this post as a "kernel". For a comprehensive collection of links about this (including tutorials, videos and samples) please see my blog post: DirectCompute.Note that there are many efforts to build even higher level languages on top of DirectX that aim to expose GPGPU programming to a wider audience by making it as easy as today's mainstream programming models. I'll mention here just two of those efforts: Accelerator from MSR and Brahma by Ananth. Comments about this post welcome at the original blog.

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  • Stale statistics on a newly created temporary table in a stored procedure can lead to poor performance

    - by sqlworkshops
    When you create a temporary table you expect a new table with no past history (statistics based on past existence), this is not true if you have less than 6 updates to the temporary table. This might lead to poor performance of queries which are sensitive to the content of temporary tables.I was optimizing SQL Server Performance at one of my customers who provides search functionality on their website. They use stored procedure with temporary table for the search. The performance of the search depended on who searched what in the past, option (recompile) by itself had no effect. Sometimes a simple search led to timeout because of non-optimal plan usage due to this behavior. This is not a plan caching issue rather temporary table statistics caching issue, which was part of the temporary object caching feature that was introduced in SQL Server 2005 and is also present in SQL Server 2008 and SQL Server 2012. In this customer case we implemented a workaround to avoid this issue (see below for example for workarounds).When temporary tables are cached, the statistics are not newly created rather cached from the past and updated based on automatic update statistics threshold. Caching temporary tables/objects is good for performance, but caching stale statistics from the past is not optimal.We can work around this issue by disabling temporary table caching by explicitly executing a DDL statement on the temporary table. One possibility is to execute an alter table statement, but this can lead to duplicate constraint name error on concurrent stored procedure execution. The other way to work around this is to create an index.I think there might be many customers in such a situation without knowing that stale statistics are being cached along with temporary table leading to poor performance.Ideal solution is to have more aggressive statistics update when the temporary table has less number of rows when temporary table caching is used. I will open a connect item to report this issue.Meanwhile you can mitigate the issue by creating an index on the temporary table. You can monitor active temporary tables using Windows Server Performance Monitor counter: SQL Server: General Statistics->Active Temp Tables. The script to understand the issue and the workaround is listed below:set nocount onset statistics time offset statistics io offdrop table tab7gocreate table tab7 (c1 int primary key clustered, c2 int, c3 char(200))gocreate index test on tab7(c2, c1, c3)gobegin trandeclare @i intset @i = 1while @i <= 50000begininsert into tab7 values (@i, 1, ‘a’)set @i = @i + 1endcommit trangoinsert into tab7 values (50001, 1, ‘a’)gocheckpointgodrop proc test_slowgocreate proc test_slow @i intasbegindeclare @j intcreate table #temp1 (c1 int primary key)insert into #temp1 (c1) select @iselect @j = t7.c1 from tab7 t7 inner join #temp1 t on (t7.c2 = t.c1)endgodbcc dropcleanbuffersset statistics time onset statistics io ongo–high reads as expected for parameter ’1'exec test_slow 1godbcc dropcleanbuffersgo–high reads that are not expected for parameter ’2'exec test_slow 2godrop proc test_with_recompilegocreate proc test_with_recompile @i intasbegindeclare @j intcreate table #temp1 (c1 int primary key)insert into #temp1 (c1) select @iselect @j = t7.c1 from tab7 t7 inner join #temp1 t on (t7.c2 = t.c1)option (recompile)endgodbcc dropcleanbuffersset statistics time onset statistics io ongo–high reads as expected for parameter ’1'exec test_with_recompile 1godbcc dropcleanbuffersgo–high reads that are not expected for parameter ’2'–low reads on 3rd execution as expected for parameter ’2'exec test_with_recompile 2godrop proc test_with_alter_table_recompilegocreate proc test_with_alter_table_recompile @i intasbegindeclare @j intcreate table #temp1 (c1 int primary key)–to avoid caching of temporary tables one can create a constraint–but this might lead to duplicate constraint name error on concurrent usagealter table #temp1 add constraint test123 unique(c1)insert into #temp1 (c1) select @iselect @j = t7.c1 from tab7 t7 inner join #temp1 t on (t7.c2 = t.c1)option (recompile)endgodbcc dropcleanbuffersset statistics time onset statistics io ongo–high reads as expected for parameter ’1'exec test_with_alter_table_recompile 1godbcc dropcleanbuffersgo–low reads as expected for parameter ’2'exec test_with_alter_table_recompile 2godrop proc test_with_index_recompilegocreate proc test_with_index_recompile @i intasbegindeclare @j intcreate table #temp1 (c1 int primary key)–to avoid caching of temporary tables one can create an indexcreate index test on #temp1(c1)insert into #temp1 (c1) select @iselect @j = t7.c1 from tab7 t7 inner join #temp1 t on (t7.c2 = t.c1)option (recompile)endgoset statistics time onset statistics io ondbcc dropcleanbuffersgo–high reads as expected for parameter ’1'exec test_with_index_recompile 1godbcc dropcleanbuffersgo–low reads as expected for parameter ’2'exec test_with_index_recompile 2go

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  • The long road to bug-free software

    - by Tony Davis
    The past decade has seen a burgeoning interest in functional programming languages such as Haskell or, in the Microsoft world, F#. Though still on the periphery of mainstream programming, functional programming concepts are gradually seeping into the imperative C# language (for example, Lambda expressions have their root in functional programming). One of the more interesting concepts from functional programming languages is the use of formal methods, the lofty ideal behind which is bug-free software. The idea is that we write a specification that describes exactly how our function (say) should behave. We then prove that our function conforms to it, and in doing so have proved beyond any doubt that it is free from bugs. All programmers already use one form of specification, specifically their programming language's type system. If a value has a specific type then, in a type-safe language, the compiler guarantees that value cannot be an instance of a different type. Many extensions to existing type systems, such as generics in Java and .NET, extend the range of programs that can be type-checked. Unfortunately, type systems can only prevent some bugs. To take a classic problem of retrieving an index value from an array, since the type system doesn't specify the length of the array, the compiler has no way of knowing that a request for the "value of index 4" from an array of only two elements is "unsafe". We restore safety via exception handling, but the ideal type system will prevent us from doing anything that is unsafe in the first place and this is where we start to borrow ideas from a language such as Haskell, with its concept of "dependent types". If the type of an array includes its length, we can ensure that any index accesses into the array are valid. The problem is that we now need to carry around the length of arrays and the values of indices throughout our code so that it can be type-checked. In general, writing the specification to prove a positive property, even for a problem very amenable to specification, such as a simple sorting algorithm, turns out to be very hard and the specification will be different for every program. Extend this to writing a specification for, say, Microsoft Word and we can see that the specification would end up being no simpler, and therefore no less buggy, than the implementation. Fortunately, it is easier to write a specification that proves that a program doesn't have certain, specific and undesirable properties, such as infinite loops or accesses to the wrong bit of memory. If we can write the specifications to prove that a program is immune to such problems, we could reuse them in many places. The problem is the lack of specification "provers" that can do this without a lot of manual intervention (i.e. hints from the programmer). All this might feel a very long way off, but computing power and our understanding of the theory of "provers" advances quickly, and Microsoft is doing some of it already. Via their Terminator research project they have started to prove that their device drivers will always terminate, and in so doing have suddenly eliminated a vast range of possible bugs. This is a huge step forward from saying, "we've tested it lots and it seems fine". What do you think? What might be good targets for specification and verification? SQL could be one: the cost of a bug in SQL Server is quite high given how many important systems rely on it, so there's a good incentive to eliminate bugs, even at high initial cost. [Many thanks to Mike Williamson for guidance and useful conversations during the writing of this piece] Cheers, Tony.

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  • The long road to bug-free software

    - by Tony Davis
    The past decade has seen a burgeoning interest in functional programming languages such as Haskell or, in the Microsoft world, F#. Though still on the periphery of mainstream programming, functional programming concepts are gradually seeping into the imperative C# language (for example, Lambda expressions have their root in functional programming). One of the more interesting concepts from functional programming languages is the use of formal methods, the lofty ideal behind which is bug-free software. The idea is that we write a specification that describes exactly how our function (say) should behave. We then prove that our function conforms to it, and in doing so have proved beyond any doubt that it is free from bugs. All programmers already use one form of specification, specifically their programming language's type system. If a value has a specific type then, in a type-safe language, the compiler guarantees that value cannot be an instance of a different type. Many extensions to existing type systems, such as generics in Java and .NET, extend the range of programs that can be type-checked. Unfortunately, type systems can only prevent some bugs. To take a classic problem of retrieving an index value from an array, since the type system doesn't specify the length of the array, the compiler has no way of knowing that a request for the "value of index 4" from an array of only two elements is "unsafe". We restore safety via exception handling, but the ideal type system will prevent us from doing anything that is unsafe in the first place and this is where we start to borrow ideas from a language such as Haskell, with its concept of "dependent types". If the type of an array includes its length, we can ensure that any index accesses into the array are valid. The problem is that we now need to carry around the length of arrays and the values of indices throughout our code so that it can be type-checked. In general, writing the specification to prove a positive property, even for a problem very amenable to specification, such as a simple sorting algorithm, turns out to be very hard and the specification will be different for every program. Extend this to writing a specification for, say, Microsoft Word and we can see that the specification would end up being no simpler, and therefore no less buggy, than the implementation. Fortunately, it is easier to write a specification that proves that a program doesn't have certain, specific and undesirable properties, such as infinite loops or accesses to the wrong bit of memory. If we can write the specifications to prove that a program is immune to such problems, we could reuse them in many places. The problem is the lack of specification "provers" that can do this without a lot of manual intervention (i.e. hints from the programmer). All this might feel a very long way off, but computing power and our understanding of the theory of "provers" advances quickly, and Microsoft is doing some of it already. Via their Terminator research project they have started to prove that their device drivers will always terminate, and in so doing have suddenly eliminated a vast range of possible bugs. This is a huge step forward from saying, "we've tested it lots and it seems fine". What do you think? What might be good targets for specification and verification? SQL could be one: the cost of a bug in SQL Server is quite high given how many important systems rely on it, so there's a good incentive to eliminate bugs, even at high initial cost. [Many thanks to Mike Williamson for guidance and useful conversations during the writing of this piece] Cheers, Tony.

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  • Problem resolving a generic Repository with Entity Framework and Castle Windsor Container

    - by user368776
    Hi, im working in a generic repository implementarion with EF v4, the repository must be resolved by Windsor Container. First the interface public interface IRepository<T> { void Add(T entity); void Delete(T entity); T Find(int key) } Then a concrete class implements the interface public class Repository<T> : IRepository<T> where T: class { private IObjectSet<T> _objectSet; } So i need _objectSet to do stuff like this in the previous class public void Add(T entity) { _objectSet.AddObject(entity); } And now the problem, as you can see im using a EF interface like IObjectSet to do the work, but this type requires a constraint for the T generic type "where T: class". That constrait is causing an exception when Windsor tries to resolve its concrete type. Windsor configuration look like this. <castle> <components> <component id="LVRepository" service="Repository.Infraestructure.IRepository`1, Repository" type="Repository.Infraestructure.Repository`1, Repository" lifestyle="transient"> </component> </components> The container resolve code IRepository<Product> productsRep =_container.Resolve<IRepository<Product>>(); Now the exception im gettin System.ArgumentException: GenericArguments[0], 'T', on 'Repository.Infraestructure.Repository`1[T]' violates the constraint of type 'T'. ---> System.TypeLoadException: GenericArguments[0], 'T', on 'Repository.Infraestructure.Repository`1[T]' violates the constraint of type parameter 'T'. If i remove the constraint in the concrete class and the depedency on IObjectSet (if i dont do it get a compile error) everything works FINE, so i dont think is a container issue, but IObjectSet is a MUST in the implementation. Some help with this, please.

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  • Setup SSL (self signed cert) with tomcat

    - by Danny
    I am mostly following this page: http://tomcat.apache.org/tomcat-6.0-doc/ssl-howto.html I used this command to create the keystore keytool -genkey -alias tomcat -keyalg RSA -keystore /etc/tomcat6/keystore and answered the prompts Then i edited my server.xml file and uncommented/edited this line <Connector port="8443" protocol="HTTP/1.1" SSLEnabled="true" maxThreads="150" scheme="https" secure="true" clientAuth="false" sslProtocol="TLS" keystoreFile="/etc/tomcat6/keystore" keystorePass="tomcat" /> then I go to the web.xml file for my project and add this into the file <security-constraint> <web-resource-collection> <web-resource-name>Security</web-resource-name> <url-pattern>/*</url-pattern> </web-resource-collection> <user-data-constraint> <transport-guarantee>CONFIDENTIAL</transport-guarantee> </user-data-constraint> </security-constraint> When I try to run my webapp I am met with this: Unable to connect Firefox can't establish a connection to the server at localhost:8443. * The site could be temporarily unavailable or too busy. Try again in a few moments. * If you are unable to load any pages, check your computer's network connection. If I comment out the lines I've added to my web.xml file, the webapp works fine. My log file in /var/lib/tomcat6/logs says nothing. I can't figure out if this is a problem with my keystore file, my server.xml file or my web.xml file.... Any assistance is appreciated I am using tomcat 6 on ubuntu.

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  • General many-to-many relationship problem ( Postgresql )

    - by David
    Hi, i have two tables: CREATE TABLE "public"."auctions" ( "id" VARCHAR(255) NOT NULL, "auction_value_key" VARCHAR(255) NOT NULL, "ctime" TIMESTAMP WITHOUT TIME ZONE NOT NULL, "mtime" TIMESTAMP WITHOUT TIME ZONE NOT NULL, CONSTRAINT "pk_XXXX2" PRIMARY KEY("id"), ); and CREATE TABLE "public"."auction_values" ( "id" NUMERIC DEFAULT nextval('default_seq'::regclass) NOT NULL, "fk_auction_value_key" VARCHAR(255) NOT NULL, "key" VARCHAR(255) NOT NULL, "value" TEXT, "ctime" TIMESTAMP WITHOUT TIME ZONE NOT NULL, "mtime" TIMESTAMP WITHOUT TIME ZONE NOT NULL, CONSTRAINT "pk_XXXX1" PRIMARY KEY("id"), ); if i want to create a many-to-many relationship on the auction_value_key like this: ALTER TABLE "public"."auction_values" ADD CONSTRAINT "auction_values_fk" FOREIGN KEY ("fk_auction_value_key") REFERENCES "public"."auctions"("auction_value_key") ON DELETE NO ACTION ON UPDATE NO ACTION NOT DEFERRABLE; i get this SQL error: ERROR: there is no unique constraint matching given keys for referenced table "auctions" Question: As you might see, i want "auction_values" to be be "reused" by different auctions without duplicating them for every auction... So i don't want a key relation on the "id" field in the auctions table... Am i thinking wrong here or what is the deal? ;) Thanks

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