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  • SEO TLC For Your Current Web Site

    Many of our new clients come to us thinking they need a new website, when in fact what they need to start with is a little search engine optimization. Before you spend thousands on a brand new website design, why not spend one hour testing your current site's SEO?

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  • Importance of SEO in Designing a Website

    If you are really interested in marking a successful online presence, you first need to understand that SEO is a long term approach that you have to abide by from the very start of designing of your website. Many people often wonder regarding what initiated first - search engine optimization or web design? The truth is that one needs to plan for both of them since the designing of the very first page of your website.

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  • Business Owners - Does Your Website Have This One Very Common Mistake?

    This article is for business owners who do not like to get involved in the technical side of their website, and pay someone in-house or outsource a third-party to do it for them. I just attended a weekend Internet Marketing seminar and was really shocked to learn that a lot of websites out there make this one very common mistake which I had always assumed that any half-witted website design or hosting company should know about: having relevant, targeted niche keywords in your website code.

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  • Why You Should Learn HTML

    HTML stands for hyper text markup language. This is the coding that is used to create and design webpages. There are other codes, but they are not as essential that you learn them as you can still get by without knowing those codes. But if you are serious about making money online, then it is necessary that you learn HTML.

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  • The Importance of Onsite and Offsite SEO

    The Internet has become one of the major sources of information on almost any topic imaginable. More importantly, it provides people and companies a venue to introduce themselves, their products, and their expertise such as multimedia or web design to a larger demographic unbounded by place or time.

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  • How I Create My Own Website

    When I create my own website, I have a set list of things that I know that I must do before I can truly get started with the design process. This article goes into that and the benefits of creating your own website.

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  • SEO Company Tips

    It is very important to get your website search engine optimized. No matter how hard you work on the website and how well you design it, chances are the website will remain largely unnoticed if you cannot ensure a good SEO for it.

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  • ????showPopupBehavior??region??popup??

    - by Todd Bao
    ???????ADF??????????????:?????????showPopupBehavior???jsp?,???????popup????jsp??region(??Bounded Taskflow)????jsff?????????showPopupBehavior?poupId???????????????<af:region value="#{bindings.inner1.regionModel}" id="r1"/><af:commandButton text="Pop UP" id="cb1">  <af:showPopupBehavior popupId="r1:p1"/></af:commandButton>?????popupId - r1:p1 - ?????id?r1?region????id?p1?popup???jsff?id??????????????,expression builder???????,design time checker????popupId????,?????????????????? Todd

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  • How do you read from a file into an array of struct?

    - by Thomas.Winsnes
    I'm currently working on an assignment and this have had me stuck for hours. Can someone please help me point out why this isn't working for me? struct book { char title[25]; char author[50]; char subject[20]; int callNumber; char publisher[250]; char publishDate[11]; char location[20]; char status[11]; char type[12]; int circulationPeriod; int costOfBook; }; void PrintBookList(struct book **bookList) { int i; for(i = 0; i < sizeof(bookList); i++) { struct book newBook = *bookList[i]; printf("%s;%s;%s;%d;%s;%s;%s;%s;%s;%d;%d\n",newBook.title, newBook.author, newBook.subject, newBook.callNumber,newBook.publisher, newBook.publishDate, newBook.location, newBook.status, newBook.type,newBook.circulationPeriod, newBook.costOfBook); } } void GetBookList(struct book** bookList) { FILE* file = fopen("book.txt", "r"); struct book newBook[1024]; int i = 0; while(fscanf(file, "%s;%s;%s;%d;%s;%s;%s;%s;%s;%d;%d", &newBook[i].title, &newBook[i].author, &newBook[i].subject, &newBook[i].callNumber,&newBook[i].publisher, &newBook[i].publishDate, &newBook[i].location, &newBook[i].status, &newBook[i].type,&newBook[i].circulationPeriod, &newBook[i].costOfBook) != EOF) { bookList[i] = &newBook[i]; i++; } /*while(fscanf(file, "%s;%s;%s;%d;%s;%s;%s;%s;%s;%d;%d", &bookList[i].title, &bookList[i].author, &bookList[i].subject, &bookList[i].callNumber, &bookList[i].publisher, &bookList[i].publishDate, &bookList[i].location, &bookList[i].status, &bookList[i].type, &bookList[i].circulationPeriod, &bookList[i].costOfBook) != EOF) { i++; }*/ PrintBookList(bookList); fclose(file); } int main() { struct book *bookList[1024]; GetBookList(bookList); } I get no errors or warnings on compile it should print the content of the file, just like it is in the file. Like this: OperatingSystems Internals and Design principles;William.S;IT;741012759;Upper Saddle River;2009;QA7676063;Available;circulation;3;11200 Communication skills handbook;Summers.J;Accounting;771239216;Milton;2010;BF637C451;Available;circulation;3;7900 Business marketing management:B2B;Hutt.D;Management;741912319;Mason;2010;HF5415131;Available;circulation;3;1053 Patient education rehabilitation;Dreeben.O;Education;745121511;Sudbury;2010;CF5671A98;Available;reference;0;6895 Tomorrow's technology and you;Beekman.G;Science;764102174;Upper Saddle River;2009;QA76B41;Out;reserved;1;7825 Property & security: selected essay;Cathy.S;Law;750131231;Rozelle;2010;D4A3C56;Available;reference;0;20075 Introducing communication theory;Richard.W;IT;714789013;McGraw-Hill;2010;Q360W47;Available;circulation;3;12150 Maths for computing and information technology;Giannasi.F;Mathematics;729890537;Longman;Scientific;1995;QA769M35G;Available;reference;0;13500 Labor economics;George.J;Economics;715784761;McGraw-Hill;2010;HD4901B67;Available;circulation;3;7585 Human physiology:from cells to systems;Sherwood.L;Physiology;707558936;Cengage Learning;2010;QP345S32;Out;circulation;3;11135 bobs;thomas;IT;701000000;UC;1006;QA7548;Available;Circulation;7;5050 but when I run it, it outputs this: OperatingSystems;;;0;;;;;;0;0 Internals;;;0;;;;;;0;0 and;;;0;;;;;;0;0 Design;;;0;;;;;;0;0 principles;William.S;IT;741012759;Upper;41012759;Upper;;0;;;;;;0;0 Saddle;;;0;;;;;;0;0 River;2009;QA7676063;Available;circulation;3;11200;lable;circulation;3;11200;;0;;;;;;0;0 Communication;;;0;;;;;;0;0 Thanks in advance, you're a life saver

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  • Hibernate N+1 from select across multiple tables

    - by Marty Pitt
    Given the following hibernate query: String sql = "select distinct changeset " + "from Changeset changeset " + "join fetch changeset.changeEntries as changeEntry " + "join fetch changeEntry.repositoryEntity as repositoryEntity " + "join fetch repositoryEntity.project as project " + "join fetch changeset.author as changesetAuthor " + "where project.id = :projectID "; Why is this resulting in an N+1 problem? I expect this to generate the following single SQL statement (or something similar) select * from Changeset inner join changeEntry on changeset.id = changeEntry.changeset_id inner join repositoryEntity on changeEntry.repositoryentity_id = repositoryentity.id inner join project on repositoryentity.project_id = project.id where project.id = ? Instead, I see many many select statements firing. The data model here looks like this: I would like the full object graph returned from the Select statement in a single trip to the database, which is why I'm explicitly using "fetch" in the hibernate query. The Hibernate log statements are as follows: Hibernate: select distinct changeset0_.id as id2_0_, changeentr1_.id as id1_1_, repository2_.id as id9_2_, project3_.id as id6_3_, user4_.id as id7_4_, changeset0_.author_id as author5_2_0_, changeset0_.createDate as createDate2_0_, changeset0_.message as message2_0_, changeset0_.revision as revision2_0_, changeentr1_.changeType as changeType1_1_, changeentr1_.changeset_id as changeset4_1_1_, changeentr1_.diff as diff1_1_, changeentr1_.repositoryEntity_id as reposito5_1_1_, changeentr1_.repositoryEntityVersion_id as reposito6_1_1_, changeentr1_.sourceChangeEntry_id as sourceCh7_1_1_, changeentr1_.changeset_id as changeset4_0__, changeentr1_.id as id0__, repository2_.project_id as connecti6_9_2_, repository2_.name as name9_2_, repository2_.parent_id as parent7_9_2_, repository2_.path as path9_2_, repository2_.state as state9_2_, repository2_.type as type9_2_, project3_.projectName as connecti2_6_3_, project3_.driverName as driverName6_3_, project3_.isAnonymous as isAnonym4_6_3_, project3_.lastUpdatedRevision as lastUpda5_6_3_, project3_.password as password6_3_, project3_.url as url6_3_, project3_.username as username6_3_, user4_.username as username7_4_, user4_.email as email7_4_, user4_.name as name7_4_, user4_.password as password7_4_, user4_.principles as principles7_4_, user4_.userType as userType7_4_ from Changeset changeset0_ inner join ChangeEntry changeentr1_ on changeset0_.id=changeentr1_.changeset_id inner join RepositoryEntity repository2_ on changeentr1_.repositoryEntity_id=repository2_.id inner join project project3_ on repository2_.project_id=project3_.id inner join users user4_ on changeset0_.author_id=user4_.id where project3_.id=? order by changeset0_.revision desc Hibernate: select repository0_.id as id10_9_, repository0_.changeEntry_id as changeEn2_10_9_, repository0_.repositoryEntity_id as reposito3_10_9_, changeentr1_.id as id1_0_, changeentr1_.changeType as changeType1_0_, changeentr1_.changeset_id as changeset4_1_0_, changeentr1_.diff as diff1_0_, changeentr1_.repositoryEntity_id as reposito5_1_0_, changeentr1_.repositoryEntityVersion_id as reposito6_1_0_, changeentr1_.sourceChangeEntry_id as sourceCh7_1_0_, changeset2_.id as id2_1_, changeset2_.author_id as author5_2_1_, changeset2_.createDate as createDate2_1_, changeset2_.message as message2_1_, changeset2_.revision as revision2_1_, user3_.id as id7_2_, user3_.username as username7_2_, user3_.email as email7_2_, user3_.name as name7_2_, user3_.password as password7_2_, user3_.principles as principles7_2_, user3_.userType as userType7_2_, repository4_.id as id9_3_, repository4_.project_id as connecti6_9_3_, repository4_.name as name9_3_, repository4_.parent_id as parent7_9_3_, repository4_.path as path9_3_, repository4_.state as state9_3_, repository4_.type as type9_3_, project5_.id as id6_4_, project5_.projectName as connecti2_6_4_, project5_.driverName as driverName6_4_, project5_.isAnonymous as isAnonym4_6_4_, project5_.lastUpdatedRevision as lastUpda5_6_4_, project5_.password as password6_4_, project5_.url as url6_4_, project5_.username as username6_4_, repository6_.id as id9_5_, repository6_.project_id as connecti6_9_5_, repository6_.name as name9_5_, repository6_.parent_id as parent7_9_5_, repository6_.path as path9_5_, repository6_.state as state9_5_, repository6_.type as type9_5_, repository7_.id as id10_6_, repository7_.changeEntry_id as changeEn2_10_6_, repository7_.repositoryEntity_id as reposito3_10_6_, repository8_.id as id9_7_, repository8_.project_id as connecti6_9_7_, repository8_.name as name9_7_, repository8_.parent_id as parent7_9_7_, repository8_.path as path9_7_, repository8_.state as state9_7_, repository8_.type as type9_7_, changeentr9_.id as id1_8_, changeentr9_.changeType as changeType1_8_, changeentr9_.changeset_id as changeset4_1_8_, changeentr9_.diff as diff1_8_, changeentr9_.repositoryEntity_id as reposito5_1_8_, changeentr9_.repositoryEntityVersion_id as reposito6_1_8_, changeentr9_.sourceChangeEntry_id as sourceCh7_1_8_ from RepositoryEntityVersion repository0_ left outer join ChangeEntry changeentr1_ on repository0_.changeEntry_id=changeentr1_.id left outer join Changeset changeset2_ on changeentr1_.changeset_id=changeset2_.id left outer join users user3_ on changeset2_.author_id=user3_.id left outer join RepositoryEntity repository4_ on changeentr1_.repositoryEntity_id=repository4_.id left outer join project project5_ on repository4_.project_id=project5_.id left outer join RepositoryEntity repository6_ on repository4_.parent_id=repository6_.id left outer join RepositoryEntityVersion repository7_ on changeentr1_.repositoryEntityVersion_id=repository7_.id left outer join RepositoryEntity repository8_ on repository7_.repositoryEntity_id=repository8_.id left outer join ChangeEntry changeentr9_ on changeentr1_.sourceChangeEntry_id=changeentr9_.id where repository0_.id=? The 2nd one is repeated many times - for a result set of 17 objects, the 2nd statement executed 521 times. I suspect this is as a result of the parent/child relationship in the RepositoryEntity object. For the purposes of this select, I actually only require the parent object fetched. Any suggestions?

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  • Are web service handler chains possible under IIS / ASP.NET

    - by Mike
    I'm working with a client who wants me to implement a particular design in an IIS/ASP.NET environment. This design was already implemented in Java, but I am not sure it is possible using Microsoft technologies. In a Tomcat/Java environment one can create so call Handler Chains. In essence a handler runs on the server on which the web service is running and it intercepts the SOAP message coming to the web service. The handler can perform a number of tasks before passing control to the web service. Some of these tasks may refer to authentication and authorization. Moreover, one can create handler chains, such that the handlers can run in a particular sequence before passing control to the web service. This is a very elegant solution, as certain aspects of authentication and authorization can be automatically performed, without the developer of the client application and of the web service having to invest anything in it. The code for the client application and the web service is not affected. You may find a number of articles on internet on this subject by searching on Google for "web service handler chain". I performed searches for web service handlers in IIS or ASP.NET. I get some hits, but apparently handlers in IIS have another meaning than that described above. My question therefor is: Can handler chains (as available in Java and Tomcat) be created in IIS? If so, how (any article, book, forum...)? Either a negative or a positive answer will be greatly appreciated. Mike

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  • New keyboard for linux: Adesso Tru-Form or MS Natural Keyboard 4000?

    - by Andrea
    Hi folks! I'm going to buy a new ergonomic keyboard for my laptop. In the following, keep in mind I live in Italy. I considered the following models: Adesso PCK-308UB - Adesso Tru-Form™ Pro - Contoured Ergonomic Keyboard with TouchPad-PS2 Pro: has a built-in touchpad in the same position of my laptop somewhat cheaper than the alternative below Cons: the surface doesn't seem to be bowl-shaped. keys seem to lay on a straight slightly-inclined surface. It seems an idea used extensively in other ergonomic keyboards according to a few comments on the net, new Adesso keyboards seem to lack robustness, they're likely to loose small parts after a few weeks or months. Other users, instead, seem to never had any problem in years and swear by their quality and comfortability. Those who had problems, however, lamented a lack of responsiveness from the manufacturer. I'm not sure whether the keyboard, at least the standard keys, and the touchpad will both be recognized correctly under linux distros (I mostly use FC btw) last time I checked, Adesso didn't have local resellers in my country Microsoft Natural Ergonomic Keyboard Pro: recognized as one of the most comfortable keyboards reliable customer service operating in my country AFAIK there are several documented ways to get extra buttons work with linux Cons: it doesn't have a builtin touchpad and has a numeric keypad wasting space to reach mouse But there could be other keyboards I haven't considered yet, so here follows my ideal keyboard wishlist, ordered by priority linux compatible basic ergonomic design, which entails split tilted keyboard and pads advanced ergonomic design, like true-ergonomic's or kinesis , where special keys (like enter, caps-lock...) are placed symmetrically in the middle to be used by thumbs a builtin touchpad/trackball placed under the keyboard. I just love this on my notebook. I think it's pretty effective, since it allows my hand to rest naturally everytime I use it. Any opinion on this? high-quality switches, like cherry's (unsure about this one) additional programmable keys placed near usual ones, to simplify typing shortcuts TIA Andrea

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  • How do photoshop slices and layer comps interact?

    - by Steve314
    I'm interested in using Photoshop (I have CS2) for some user interface design. I was hoping to be able to use slices and layer comps to mark out particular elements, and use Javascript scripting to export multiple graphics files and text descriptions (positions and sizes of slices mainly) that will be used by my program. My problem is that I've never used Photoshop for web design, or otherwise used slices, and I'm not confident that I understand how they interact with layer comps. This is what I believe (and hope) is correct... Manual slices aren't affected by layer comps in any way - they aren't saved as part of a layer comp. The same manual slices will be active irrespective of which layer comp is selected. Layer-based slices aren't directly affected by layer comps, but they are indirectly affected in that the layer comp saves details of layer position and style. Thus selecting a layer comp may move a layer and change its style, affecting the location and size of its layer-based slice, or may effectively disable the slice by hiding the layer. Automatic slices aren't directly affected by layer comps, but are indirectly affected due to changes to the layer-based slices. So, layer based slices (which are my main interest) may move, may change size (to accomodate a style such as a drop shadow), and may be effectively disabled by the layer being hidden. Other details (and all details of manual slices) will remain constant irrespective of which layer comp is active. Is that correct?

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  • Disable Windows 7 taskbar grouping. Not combining.

    - by Byran
    I've look near and far but I cannot find a way (setting or hack) to prevent Windows 7 from grouping taskbar buttons together that are "related". I'm not talking about the option to combine or collapse related buttons into one item. I can find that setting at: Taskbar and Start Menu Properties Taskbar Taskbar buttons: This is what I an not looking for: How to Enable or Disable Windows 7 Taskbar Button Grouping I'm talking about how Windows 7 seams to think that it's doing me a favor by grouping all my Google Chrome buttons together and grouping all my Explorer buttons together etc. My workflow in Windows XP was to use the program Taskbar Shuffle to allow me to reorganize my taskbar buttons into related task "groups" I was working on. For example: [Start Button] | [iTunes] [Outlook Express] [Chrome Gmail] [layered design folder] [Photoshop CS4] [exported images folder] [website root folder] [Dreamweaver CS4] [Chrome www.MyAwesomeWebsiteImBuilding.com] [Chrome Recent web search] [some unrelated folder] Windows 7 doesn't seem to let me do this. It wants to do: [Start Button] | [layered design folder][exported images folder][website root folder][some unrelated folder] | [Chrome www.MyAwesomeWebsiteImBuilding.com]Chrome [Gmail][Chrome Recent web search] | [iTunes] | [Outlook Express] | [Photoshop CS4] | [Dreamweaver CS4] Does anyone know of a tool or hack to prevent Windows 7 from grouping taskbar buttons?

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  • Why does 64-bit Windows need a separate "Program Files (x86)" folder?

    - by Stephen Jennings
    I know that on a 64-bit version of Windows the "Program Files" folder is for 64-bit programs and the "Program Files (x86)" folder is for 32-bit programs, but why is this even necessary? By "necessary", I don't mean "why could Microsoft not have made any other design decisions?" because of course they could have. Rather, I mean, "why, given the current design of 64-bit Windows, must 32-bit programs have a separate top-level folder from 64-bit programs?" There are plenty of questions on Super User and elsewhere that assert "one is for 32-bit programs, one is for 64-bit programs", but none that I can find give the reason. From my experience, it doesn't seem to matter whether a 32-bit program is installed in the correct place or not. Does Windows somehow present itself differently to a program running out of "Program Files (x86)"? Is there a description that shows exactly what's different for a program installed in "Program Files (x86)" instead of "Program Files"? I think it's unlikely that Microsoft would introduce a new folder without a legitimate technical reason.

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  • ClickOnce manifest problem

    - by TWith2Sugars
    We are currently deploying a WPF 4 app via click once and there is a scenario when the installation fails. If the user does not have .Net 4.0 Full install and attempts to install our app the framework installs fine but the app fails to install. If we re-run the installation again the app installs fine. Here is a copy of the log: PLATFORM VERSION INFO Windows : 6.1.7600.0 (Win32NT) Common Language Runtime : 2.0.50727.4927 System.Deployment.dll : 2.0.50727.4927 (NetFXspW7.050727-4900) mscorwks.dll : 2.0.50727.4927 (NetFXspW7.050727-4900) dfdll.dll : 2.0.50727.4927 (NetFXspW7.050727-4900) dfshim.dll : 4.0.31106.0 (Main.031106-0000) SOURCES Deployment url : [URL REMOVED] Server : Apache/2.0.54 Application url : [URL REMOVED] Server : Apache/2.0.54 IDENTITIES Deployment Identity : Graphicly.App.application, Version=0.3.2.0, Culture=neutral, PublicKeyToken=c982228345371fbc, processorArchitecture=msil Application Identity : Graphicly.App.exe, Version=0.3.2.0, Culture=neutral, PublicKeyToken=c982228345371fbc, processorArchitecture=msil, type=win32 APPLICATION SUMMARY * Installable application. ERROR SUMMARY Below is a summary of the errors, details of these errors are listed later in the log. * Dependency Graphicly.WCFClient.dll cannot be processed for patching. Following failure messages were detected: + Exception occurred loading manifest from file Graphicly.WCFClient.dll: the manifest may not be valid or the file could not be opened. + Cannot load internal manifest from component file. * Dependency Microsoft.Surface.Presentation.Design.dll cannot be processed for patching. Following failure messages were detected: + Exception occurred loading manifest from file Microsoft.Surface.Presentation.Design.dll: the manifest may not be valid or the file could not be opened. + Cannot load internal manifest from component file. * Dependency GalaSoft.MvvmLight.WPF4.dll cannot be processed for patching. Following failure messages were detected: + Exception occurred loading manifest from file GalaSoft.MvvmLight.WPF4.dll: the manifest may not be valid or the file could not be opened. + Cannot load internal manifest from component file. * Dependency Graphicly.Infrastructure.dll cannot be processed for patching. Following failure messages were detected: + Exception occurred loading manifest from file Graphicly.Infrastructure.dll: the manifest may not be valid or the file could not be opened. + Cannot load internal manifest from component file. * Dependency Graphicly.AutoUpdater.dll cannot be processed for patching. Following failure messages were detected: + Exception occurred loading manifest from file Graphicly.AutoUpdater.dll: the manifest may not be valid or the file could not be opened. + Cannot load internal manifest from component file. * Dependency System.Windows.Interactivity.dll cannot be processed for patching. Following failure messages were detected: + Exception occurred loading manifest from file System.Windows.Interactivity.dll: the manifest may not be valid or the file could not be opened. + Cannot load internal manifest from component file. * Dependency Microsoft.Surface.Presentation.dll cannot be processed for patching. Following failure messages were detected: + Exception occurred loading manifest from file Microsoft.Surface.Presentation.dll: the manifest may not be valid or the file could not be opened. + Cannot load internal manifest from component file. * Dependency Graphicly.Fonts.dll cannot be processed for patching. Following failure messages were detected: + Exception occurred loading manifest from file Graphicly.Fonts.dll: the manifest may not be valid or the file could not be opened. + Cannot load internal manifest from component file. * Dependency Graphicly.Reader.dll cannot be processed for patching. Following failure messages were detected: + Exception occurred loading manifest from file Graphicly.Reader.dll: the manifest may not be valid or the file could not be opened. + Cannot load internal manifest from component file. * Dependency Microsoft.Surface.Presentation.Generic.dll cannot be processed for patching. Following failure messages were detected: + Exception occurred loading manifest from file Microsoft.Surface.Presentation.Generic.dll: the manifest may not be valid or the file could not be opened. + Cannot load internal manifest from component file. * Dependency Graphicly.Controls.dll cannot be processed for patching. Following failure messages were detected: + Exception occurred loading manifest from file Graphicly.Controls.dll: the manifest may not be valid or the file could not be opened. + Cannot load internal manifest from component file. * Dependency Graphicly.SocialNetwork.dll cannot be processed for patching. Following failure messages were detected: + Exception occurred loading manifest from file Graphicly.SocialNetwork.dll: the manifest may not be valid or the file could not be opened. + Cannot load internal manifest from component file. * Dependency Graphicly.Archive.dll cannot be processed for patching. Following failure messages were detected: + Exception occurred loading manifest from file Graphicly.Archive.dll: the manifest may not be valid or the file could not be opened. + Cannot load internal manifest from component file. * Dependency Graphicly.App.exe cannot be processed for patching. Following failure messages were detected: + Exception occurred loading manifest from file Graphicly.App.exe: the manifest may not be valid or the file could not be opened. + Cannot load internal manifest from component file. * Dependency GalaSoft.MvvmLight.Extras.WPF4.dll cannot be processed for patching. Following failure messages were detected: + Exception occurred loading manifest from file GalaSoft.MvvmLight.Extras.WPF4.dll: the manifest may not be valid or the file could not be opened. + Cannot load internal manifest from component file. * Activation of [URL REMOVED] resulted in exception. Following failure messages were detected: + Exception occurred loading manifest from file GalaSoft.MvvmLight.Extras.WPF4.dll: the manifest may not be valid or the file could not be opened. + Cannot load internal manifest from component file. COMPONENT STORE TRANSACTION FAILURE SUMMARY No transaction error was detected. WARNINGS * The file named Microsoft.Windows.Design.Extensibility.dll does not have a hash specified in the manifest. Hash validation will be ignored. * The file named Ionic.Zip.Reduced.dll does not have a hash specified in the manifest. Hash validation will be ignored. * The file named Newtonsoft.Json.dll does not have a hash specified in the manifest. Hash validation will be ignored. * The file named Microsoft.WindowsAzure.StorageClient.dll does not have a hash specified in the manifest. Hash validation will be ignored. * The file named Dimebrain.TweetSharp.dll does not have a hash specified in the manifest. Hash validation will be ignored. * The file named Microsoft.Windows.Design.Interaction.dll does not have a hash specified in the manifest. Hash validation will be ignored. * The file named HtmlAgilityPack.dll does not have a hash specified in the manifest. Hash validation will be ignored. * The file named Facebook.dll does not have a hash specified in the manifest. Hash validation will be ignored. OPERATION PROGRESS STATUS * [20/05/2010 09:17:33] : Activation of [URL REMOVED] has started. * [20/05/2010 09:17:38] : Processing of deployment manifest has successfully completed. * [20/05/2010 09:17:38] : Installation of the application has started. * [20/05/2010 09:17:39] : Processing of application manifest has successfully completed. * [20/05/2010 09:17:40] : Request of trust and detection of platform is complete. ERROR DETAILS Following errors were detected during this operation. * [20/05/2010 09:17:40] System.Deployment.Application.InvalidDeploymentException (ManifestLoad) - Exception occurred loading manifest from file Graphicly.WCFClient.dll: the manifest may not be valid or the file could not be opened. - Source: System.Deployment - Stack trace: at System.Deployment.Application.Manifest.AssemblyManifest.ManifestLoadExceptionHelper(Exception exception, String filePath) at System.Deployment.Application.Manifest.AssemblyManifest.LoadFromInternalManifestFile(String filePath) at System.Deployment.Application.FileDownloader.AddFilesInHashtable(Hashtable hashtable, AssemblyManifest applicationManifest, String applicationFolder) --- Inner Exception --- System.Deployment.Application.DeploymentException (InvalidManifest) - Cannot load internal manifest from component file. - Source: - Stack trace: * [20/05/2010 09:17:40] System.Deployment.Application.InvalidDeploymentException (ManifestLoad) - Exception occurred loading manifest from file Microsoft.Surface.Presentation.Design.dll: the manifest may not be valid or the file could not be opened. - Source: System.Deployment - Stack trace: at System.Deployment.Application.Manifest.AssemblyManifest.ManifestLoadExceptionHelper(Exception exception, String filePath) at System.Deployment.Application.Manifest.AssemblyManifest.LoadFromInternalManifestFile(String filePath) at System.Deployment.Application.FileDownloader.AddFilesInHashtable(Hashtable hashtable, AssemblyManifest applicationManifest, String applicationFolder) --- Inner Exception --- System.Deployment.Application.DeploymentException (InvalidManifest) - Cannot load internal manifest from component file. - Source: - Stack trace: * [20/05/2010 09:17:40] System.Deployment.Application.InvalidDeploymentException (ManifestLoad) - Exception occurred loading manifest from file GalaSoft.MvvmLight.WPF4.dll: the manifest may not be valid or the file could not be opened. - Source: System.Deployment - Stack trace: at System.Deployment.Application.Manifest.AssemblyManifest.ManifestLoadExceptionHelper(Exception exception, String filePath) at System.Deployment.Application.Manifest.AssemblyManifest.LoadFromInternalManifestFile(String filePath) at System.Deployment.Application.FileDownloader.AddFilesInHashtable(Hashtable hashtable, AssemblyManifest applicationManifest, String applicationFolder) --- Inner Exception --- System.Deployment.Application.DeploymentException (InvalidManifest) - Cannot load internal manifest from component file. - Source: - Stack trace: * [20/05/2010 09:17:40] System.Deployment.Application.InvalidDeploymentException (ManifestLoad) - Exception occurred loading manifest from file Graphicly.Infrastructure.dll: the manifest may not be valid or the file could not be opened. - Source: System.Deployment - Stack trace: at System.Deployment.Application.Manifest.AssemblyManifest.ManifestLoadExceptionHelper(Exception exception, String filePath) at System.Deployment.Application.Manifest.AssemblyManifest.LoadFromInternalManifestFile(String filePath) at System.Deployment.Application.FileDownloader.AddFilesInHashtable(Hashtable hashtable, AssemblyManifest applicationManifest, String applicationFolder) --- Inner Exception --- System.Deployment.Application.DeploymentException (InvalidManifest) - Cannot load internal manifest from component file. - Source: - Stack trace: * [20/05/2010 09:17:40] System.Deployment.Application.InvalidDeploymentException (ManifestLoad) - Exception occurred loading manifest from file Graphicly.AutoUpdater.dll: the manifest may not be valid or the file could not be opened. - Source: System.Deployment - Stack trace: at System.Deployment.Application.Manifest.AssemblyManifest.ManifestLoadExceptionHelper(Exception exception, String filePath) at System.Deployment.Application.Manifest.AssemblyManifest.LoadFromInternalManifestFile(String filePath) at System.Deployment.Application.FileDownloader.AddFilesInHashtable(Hashtable hashtable, AssemblyManifest applicationManifest, String applicationFolder) --- Inner Exception --- System.Deployment.Application.DeploymentException (InvalidManifest) - Cannot load internal manifest from component file. - Source: - Stack trace: * [20/05/2010 09:17:40] System.Deployment.Application.InvalidDeploymentException (ManifestLoad) - Exception occurred loading manifest from file System.Windows.Interactivity.dll: the manifest may not be valid or the file could not be opened. - Source: System.Deployment - Stack trace: at System.Deployment.Application.Manifest.AssemblyManifest.ManifestLoadExceptionHelper(Exception exception, String filePath) at System.Deployment.Application.Manifest.AssemblyManifest.LoadFromInternalManifestFile(String filePath) at System.Deployment.Application.FileDownloader.AddFilesInHashtable(Hashtable hashtable, AssemblyManifest applicationManifest, String applicationFolder) --- Inner Exception --- System.Deployment.Application.DeploymentException (InvalidManifest) - Cannot load internal manifest from component file. - Source: - Stack trace: * [20/05/2010 09:17:40] System.Deployment.Application.InvalidDeploymentException (ManifestLoad) - Exception occurred loading manifest from file Microsoft.Surface.Presentation.dll: the manifest may not be valid or the file could not be opened. - Source: System.Deployment - Stack trace: at System.Deployment.Application.Manifest.AssemblyManifest.ManifestLoadExceptionHelper(Exception exception, String filePath) at System.Deployment.Application.Manifest.AssemblyManifest.LoadFromInternalManifestFile(String filePath) at System.Deployment.Application.FileDownloader.AddFilesInHashtable(Hashtable hashtable, AssemblyManifest applicationManifest, String applicationFolder) --- Inner Exception --- System.Deployment.Application.DeploymentException (InvalidManifest) - Cannot load internal manifest from component file. - Source: - Stack trace: * [20/05/2010 09:17:40] System.Deployment.Application.InvalidDeploymentException (ManifestLoad) - Exception occurred loading manifest from file Graphicly.Fonts.dll: the manifest may not be valid or the file could not be opened. - Source: System.Deployment - Stack trace: at System.Deployment.Application.Manifest.AssemblyManifest.ManifestLoadExceptionHelper(Exception exception, String filePath) at System.Deployment.Application.Manifest.AssemblyManifest.LoadFromInternalManifestFile(String filePath) at System.Deployment.Application.FileDownloader.AddFilesInHashtable(Hashtable hashtable, AssemblyManifest applicationManifest, String applicationFolder) --- Inner Exception --- System.Deployment.Application.DeploymentException (InvalidManifest) - Cannot load internal manifest from component file. - Source: - Stack trace: * [20/05/2010 09:17:40] System.Deployment.Application.InvalidDeploymentException (ManifestLoad) - Exception occurred loading manifest from file Graphicly.Reader.dll: the manifest may not be valid or the file could not be opened. - Source: System.Deployment - Stack trace: at System.Deployment.Application.Manifest.AssemblyManifest.ManifestLoadExceptionHelper(Exception exception, String filePath) at System.Deployment.Application.Manifest.AssemblyManifest.LoadFromInternalManifestFile(String filePath) at System.Deployment.Application.FileDownloader.AddFilesInHashtable(Hashtable hashtable, AssemblyManifest applicationManifest, String applicationFolder) --- Inner Exception --- System.Deployment.Application.DeploymentException (InvalidManifest) - Cannot load internal manifest from component file. - Source: - Stack trace: * [20/05/2010 09:17:40] System.Deployment.Application.InvalidDeploymentException (ManifestLoad) - Exception occurred loading manifest from file Microsoft.Surface.Presentation.Generic.dll: the manifest may not be valid or the file could not be opened. - Source: System.Deployment - Stack trace: at System.Deployment.Application.Manifest.AssemblyManifest.ManifestLoadExceptionHelper(Exception exception, String filePath) at System.Deployment.Application.Manifest.AssemblyManifest.LoadFromInternalManifestFile(String filePath) at System.Deployment.Application.FileDownloader.AddFilesInHashtable(Hashtable hashtable, AssemblyManifest applicationManifest, String applicationFolder) --- Inner Exception --- System.Deployment.Application.DeploymentException (InvalidManifest) - Cannot load internal manifest from component file. - Source: - Stack trace: * [20/05/2010 09:17:41] System.Deployment.Application.InvalidDeploymentException (ManifestLoad) - Exception occurred loading manifest from file Graphicly.Controls.dll: the manifest may not be valid or the file could not be opened. - Source: System.Deployment - Stack trace: at System.Deployment.Application.Manifest.AssemblyManifest.ManifestLoadExceptionHelper(Exception exception, String filePath) at System.Deployment.Application.Manifest.AssemblyManifest.LoadFromInternalManifestFile(String filePath) at System.Deployment.Application.FileDownloader.AddFilesInHashtable(Hashtable hashtable, AssemblyManifest applicationManifest, String applicationFolder) --- Inner Exception --- System.Deployment.Application.DeploymentException (InvalidManifest) - Cannot load internal manifest from component file. - Source: - Stack trace: * [20/05/2010 09:17:41] System.Deployment.Application.InvalidDeploymentException (ManifestLoad) - Exception occurred loading manifest from file Graphicly.SocialNetwork.dll: the manifest may not be valid or the file could not be opened. - Source: System.Deployment - Stack trace: at System.Deployment.Application.Manifest.AssemblyManifest.ManifestLoadExceptionHelper(Exception exception, String filePath) at System.Deployment.Application.Manifest.AssemblyManifest.LoadFromInternalManifestFile(String filePath) at System.Deployment.Application.FileDownloader.AddFilesInHashtable(Hashtable hashtable, AssemblyManifest applicationManifest, String applicationFolder) --- Inner Exception --- System.Deployment.Application.DeploymentException (InvalidManifest) - Cannot load internal manifest from component file. - Source: - Stack trace: * [20/05/2010 09:17:41] System.Deployment.Application.InvalidDeploymentException (ManifestLoad) - Exception occurred loading manifest from file Graphicly.Archive.dll: the manifest may not be valid or the file could not be opened. - Source: System.Deployment - Stack trace: at System.Deployment.Application.Manifest.AssemblyManifest.ManifestLoadExceptionHelper(Exception exception, String filePath) at System.Deployment.Application.Manifest.AssemblyManifest.LoadFromInternalManifestFile(String filePath) at System.Deployment.Application.FileDownloader.AddFilesInHashtable(Hashtable hashtable, AssemblyManifest applicationManifest, String applicationFolder) --- Inner Exception --- System.Deployment.Application.DeploymentException (InvalidManifest) - Cannot load internal manifest from component file. - Source: - Stack trace: * [20/05/2010 09:17:41] System.Deployment.Application.InvalidDeploymentException (ManifestLoad) - Exception occurred loading manifest from file Graphicly.App.exe: the manifest may not be valid or the file could not be opened. - Source: System.Deployment - Stack trace: at System.Deployment.Application.Manifest.AssemblyManifest.ManifestLoadExceptionHelper(Exception exception, String filePath) at System.Deployment.Application.Manifest.AssemblyManifest.LoadFromInternalManifestFile(String filePath) at System.Deployment.Application.FileDownloader.AddFilesInHashtable(Hashtable hashtable, AssemblyManifest applicationManifest, String applicationFolder) --- Inner Exception --- System.Deployment.Application.DeploymentException (InvalidManifest) - Cannot load internal manifest from component file. - Source: - Stack trace: * [20/05/2010 09:17:41] System.Deployment.Application.InvalidDeploymentException (ManifestLoad) - Exception occurred loading manifest from file GalaSoft.MvvmLight.Extras.WPF4.dll: the manifest may not be valid or the file could not be opened. - Source: System.Deployment - Stack trace: at System.Deployment.Application.Manifest.AssemblyManifest.ManifestLoadExceptionHelper(Exception exception, String filePath) at System.Deployment.Application.Manifest.AssemblyManifest.LoadFromInternalManifestFile(String filePath) at System.Deployment.Application.FileDownloader.AddFilesInHashtable(Hashtable hashtable, AssemblyManifest applicationManifest, String applicationFolder) --- Inner Exception --- System.Deployment.Application.DeploymentException (InvalidManifest) - Cannot load internal manifest from component file. - Source: - Stack trace: * [20/05/2010 09:17:41] System.Deployment.Application.InvalidDeploymentException (ManifestLoad) - Exception occurred loading manifest from file GalaSoft.MvvmLight.Extras.WPF4.dll: the manifest may not be valid or the file could not be opened. - Source: System.Deployment - Stack trace: at System.Deployment.Application.Manifest.AssemblyManifest.ManifestLoadExceptionHelper(Exception exception, String filePath) at System.Deployment.Application.Manifest.AssemblyManifest.LoadFromInternalManifestFile(String filePath) at System.Deployment.Application.DownloadManager.ProcessDownloadedFile(Object sender, DownloadEventArgs e) at System.Deployment.Application.FileDownloader.DownloadModifiedEventHandler.Invoke(Object sender, DownloadEventArgs e) at System.Deployment.Application.FileDownloader.PatchSingleFile(DownloadQueueItem item, Hashtable dependencyTable) at System.Deployment.Application.FileDownloader.PatchFiles(SubscriptionState subState) at System.Deployment.Application.FileDownloader.Download(SubscriptionState subState) at System.Deployment.Application.DownloadManager.DownloadDependencies(SubscriptionState subState, AssemblyManifest deployManifest, AssemblyManifest appManifest, Uri sourceUriBase, String targetDirectory, String group, IDownloadNotification notification, DownloadOptions options) at System.Deployment.Application.ApplicationActivator.DownloadApplication(SubscriptionState subState, ActivationDescription actDesc, Int64 transactionId, TempDirectory& downloadTemp) at System.Deployment.Application.ApplicationActivator.InstallApplication(SubscriptionState& subState, ActivationDescription actDesc) at System.Deployment.Application.ApplicationActivator.PerformDeploymentActivation(Uri activationUri, Boolean isShortcut, String textualSubId, String deploymentProviderUrlFromExtension, BrowserSettings browserSettings, String& errorPageUrl) at System.Deployment.Application.ApplicationActivator.ActivateDeploymentWorker(Object state) --- Inner Exception --- System.Deployment.Application.DeploymentException (InvalidManifest) - Cannot load internal manifest from component file. - Source: - Stack trace: COMPONENT STORE TRANSACTION DETAILS No transaction information is available. I'm baffled. Any ideas what this could be? Cheers Tony

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  • Authoritative sources about Database vs. Flatfile decision

    - by FastAl
    <tldr>looking for a reference to a book or other undeniably authoritative source that gives reasons when you should choose a database vs. when you should choose other storage methods. I have provided an un-authoritative list of reasons about 2/3 of the way down this post.</tldr> I have a situation at my company where a database is being used where it would be better to use another solution (in this case, an auto-generated piece of source code that contains a static lookup table, searched by binary sort). Normally, a database would be an OK solution even though the problem does not require a database, e.g, none of the elements of ACID are needed, as it is read-only data, updated about every 3-5 years (also requiring other sourcecode changes), and fits in memory, and can be keyed into via binary search (a tad faster than db, but speed is not an issue). The problem is that this code runs on our enterprise server, but is shared with several PC platforms (some disconnected, some use a central DB, etc.), and parts of it are managed by multiple programming units, parts by the DBAs, parts even by mathematicians in another department, etc. These hit their own platform’s version of their databases (containing their own copy of the static data). What happens is that every implementation, every little change, something different goes wrong. There are many other issues as well. I can’t even use a flatfile, because one mode of running on our enterprise server does not have permission to read files (only databases, and of course, its own literal storage, e.g., in-source table). Of course, other parts of the system use databases in proper, less obscure manners; there is no problem with those parts. So why don’t we just change it? I don’t have administrative ability to force a change. But I’m affected because sometimes I have to help fix the problems, but mostly because it causes outages and tons of extra IT time by other programmers and d*mmit that makes me mad! The reason neither management, nor the designers of the system, can see the problem is that they propose a solution that won’t work: increase communication; implement more safeguards and standards; etc. But every time, in a different part of the already-pared-down but still multi-step processes, a few different diligent, hard-working, top performing IT personnel make a unique subtle error that causes it to fail, sometimes after the last round of testing! And in general these are not single-person failures, but understandable miscommunications. And communication at our company is actually better than most. People just don't think that's the case because they haven't dug into the matter. However, I have it on very good word from somebody with extensive formal study of sociology and psychology that the relatively small amount of less-than-proper database usage in this gigantic cross-platform multi-source, multi-language project is bureaucratically un-maintainable. Impossible. No chance. At least with Human Beings in the loop, and it can’t be automated. In addition, the management and developers who could change this, though intelligent and capable, don’t understand the rigidity of this ‘how humans are’ issue, and are not convincible on the matter. The reason putting the static data in sourcecode will solve the problem is, although the solution is less sexy than a database, it would function with no technical drawbacks; and since the sharing of sourcecode already works very well, you basically erase any database-related effort from this section of the project, along with all the drawbacks of it that are causing problems. OK, that’s the background, for the curious. I won’t be able to convince management that this is an unfixable sociological problem, and that the real solution is coding around these limits of human nature, just as you would code around a bug in a 3rd party component that you can’t change. So what I have to do is exploit the unsuitableness of the database solution, and not do it using logic, but rather authority. I am aware of many reasons, and posts on this site giving reasons for one over the other; I’m not looking for lists of reasons like these (although you can add a comment if I've miss a doozy): WHY USE A DATABASE? instead of flatfile/other DB vs. file: if you need... Random Read / Transparent search optimization Advanced / varied / customizable Searching and sorting capabilities Transaction/rollback Locks, semaphores Concurrency control / Shared users Security 1-many/m-m is easier Easy modification Scalability Load Balancing Random updates / inserts / deletes Advanced query Administrative control of design, etc. SQL / learning curve Debugging / Logging Centralized / Live Backup capabilities Cached queries / dvlp & cache execution plans Interleaved update/read Referential integrity, avoid redundant/missing/corrupt/out-of-sync data Reporting (from on olap or oltp db) / turnkey generation tools [Disadvantages:] Important to get right the first time - professional design - but only b/c it's meant to last s/w & h/w cost Usu. over a network, speed issue (best vs. best design vs. local=even then a separate process req's marshalling/netwk layers/inter-p comm) indicies and query processing can stand in the way of simple processing (vs. flatfile) WHY USE FLATFILE: If you only need... Sequential Row processing only Limited usage append only (no reading, no master key/update) Only Update the record you're reading (fixed length recs only) Too big to fit into memory If Local disk / read-ahead network connection Portability / small system Email / cut & Paste / store as document by novice - simple format Low design learning curve but high cost later WHY USE IN-MEMORY/TABLE (tables, arrays, etc.): if you need... Processing a single db/ff record that was imported Known size of data Static data if hardcoding the table Narrow, unchanging use (e.g., one program or proc) -includes a class that will be shared, but encapsulates its data manipulation Extreme speed needed / high transaction frequency Random access - but search is dependent on implementation Following are some other posts about the topic: http://stackoverflow.com/questions/1499239/database-vs-flat-text-file-what-are-some-technical-reasons-for-choosing-one-over http://stackoverflow.com/questions/332825/are-flat-file-databases-any-good http://stackoverflow.com/questions/2356851/database-vs-flat-files http://stackoverflow.com/questions/514455/databases-vs-plain-text/514530 What I’d like to know is if anybody could recommend a hard, authoritative source containing these reasons. I’m looking for a paper book I can buy, or a reputable website with whitepapers about the issue (e.g., Microsoft, IBM), not counting the user-generated content on those sites. This will have a greater change to elicit a change that I’m looking for: less wasted programmer time, and more reliable programs. Thanks very much for your help. You win a prize for reading such a large post!

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  • How do I prove I should put a table of values in source code instead of a database table?

    - by FastAl
    <tldr>looking for a reference to a book or other undeniably authoritative source that gives reasons when you should choose a database vs. when you should choose other storage methods. I have provided an un-authoritative list of reasons about 2/3 of the way down this post.</tldr> I have a situation at my company where a database is being used where it would be better to use another solution (in this case, an auto-generated piece of source code that contains a static lookup table, searched by binary sort). Normally, a database would be an OK solution even though the problem does not require a database, e.g, none of the elements of ACID are needed, as it is read-only data, updated about every 3-5 years (also requiring other sourcecode changes), and fits in memory, and can be keyed into via binary search (a tad faster than db, but speed is not an issue). The problem is that this code runs on our enterprise server, but is shared with several PC platforms (some disconnected, some use a central DB, etc.), and parts of it are managed by multiple programming units, parts by the DBAs, parts even by mathematicians in another department, etc. These hit their own platform’s version of their databases (containing their own copy of the static data). What happens is that every implementation, every little change, something different goes wrong. There are many other issues as well. I can’t even use a flatfile, because one mode of running on our enterprise server does not have permission to read files (only databases, and of course, its own literal storage, e.g., in-source table). Of course, other parts of the system use databases in proper, less obscure manners; there is no problem with those parts. So why don’t we just change it? I don’t have administrative ability to force a change. But I’m affected because sometimes I have to help fix the problems, but mostly because it causes outages and tons of extra IT time by other programmers and d*mmit that makes me mad! The reason neither management, nor the designers of the system, can see the problem is that they propose a solution that won’t work: increase communication; implement more safeguards and standards; etc. But every time, in a different part of the already-pared-down but still multi-step processes, a few different diligent, hard-working, top performing IT personnel make a unique subtle error that causes it to fail, sometimes after the last round of testing! And in general these are not single-person failures, but understandable miscommunications. And communication at our company is actually better than most. People just don't think that's the case because they haven't dug into the matter. However, I have it on very good word from somebody with extensive formal study of sociology and psychology that the relatively small amount of less-than-proper database usage in this gigantic cross-platform multi-source, multi-language project is bureaucratically un-maintainable. Impossible. No chance. At least with Human Beings in the loop, and it can’t be automated. In addition, the management and developers who could change this, though intelligent and capable, don’t understand the rigidity of this ‘how humans are’ issue, and are not convincible on the matter. The reason putting the static data in sourcecode will solve the problem is, although the solution is less sexy than a database, it would function with no technical drawbacks; and since the sharing of sourcecode already works very well, you basically erase any database-related effort from this section of the project, along with all the drawbacks of it that are causing problems. OK, that’s the background, for the curious. I won’t be able to convince management that this is an unfixable sociological problem, and that the real solution is coding around these limits of human nature, just as you would code around a bug in a 3rd party component that you can’t change. So what I have to do is exploit the unsuitableness of the database solution, and not do it using logic, but rather authority. I am aware of many reasons, and posts on this site giving reasons for one over the other; I’m not looking for lists of reasons like these (although you can add a comment if I've miss a doozy): WHY USE A DATABASE? instead of flatfile/other DB vs. file: if you need... Random Read / Transparent search optimization Advanced / varied / customizable Searching and sorting capabilities Transaction/rollback Locks, semaphores Concurrency control / Shared users Security 1-many/m-m is easier Easy modification Scalability Load Balancing Random updates / inserts / deletes Advanced query Administrative control of design, etc. SQL / learning curve Debugging / Logging Centralized / Live Backup capabilities Cached queries / dvlp & cache execution plans Interleaved update/read Referential integrity, avoid redundant/missing/corrupt/out-of-sync data Reporting (from on olap or oltp db) / turnkey generation tools [Disadvantages:] Important to get right the first time - professional design - but only b/c it's meant to last s/w & h/w cost Usu. over a network, speed issue (best vs. best design vs. local=even then a separate process req's marshalling/netwk layers/inter-p comm) indicies and query processing can stand in the way of simple processing (vs. flatfile) WHY USE FLATFILE: If you only need... Sequential Row processing only Limited usage append only (no reading, no master key/update) Only Update the record you're reading (fixed length recs only) Too big to fit into memory If Local disk / read-ahead network connection Portability / small system Email / cut & Paste / store as document by novice - simple format Low design learning curve but high cost later WHY USE IN-MEMORY/TABLE (tables, arrays, etc.): if you need... Processing a single db/ff record that was imported Known size of data Static data if hardcoding the table Narrow, unchanging use (e.g., one program or proc) -includes a class that will be shared, but encapsulates its data manipulation Extreme speed needed / high transaction frequency Random access - but search is dependent on implementation Following are some other posts about the topic: http://stackoverflow.com/questions/1499239/database-vs-flat-text-file-what-are-some-technical-reasons-for-choosing-one-over http://stackoverflow.com/questions/332825/are-flat-file-databases-any-good http://stackoverflow.com/questions/2356851/database-vs-flat-files http://stackoverflow.com/questions/514455/databases-vs-plain-text/514530 What I’d like to know is if anybody could recommend a hard, authoritative source containing these reasons. I’m looking for a paper book I can buy, or a reputable website with whitepapers about the issue (e.g., Microsoft, IBM), not counting the user-generated content on those sites. This will have a greater change to elicit a change that I’m looking for: less wasted programmer time, and more reliable programs. Thanks very much for your help. You win a prize for reading such a large post!

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  • Null-free "maps": Is a callback solution slower than tryGet()?

    - by David Moles
    In comments to "How to implement List, Set, and Map in null free design?", Steven Sudit and I got into a discussion about using a callback, with handlers for "found" and "not found" situations, vs. a tryGet() method, taking an out parameter and returning a boolean indicating whether the out parameter had been populated. Steven maintained that the callback approach was more complex and almost certain to be slower; I maintained that the complexity was no greater and the performance at worst the same. But code speaks louder than words, so I thought I'd implement both and see what I got. The original question was fairly theoretical with regard to language ("And for argument sake, let's say this language don't even have null") -- I've used Java here because that's what I've got handy. Java doesn't have out parameters, but it doesn't have first-class functions either, so style-wise, it should suck equally for both approaches. (Digression: As far as complexity goes: I like the callback design because it inherently forces the user of the API to handle both cases, whereas the tryGet() design requires callers to perform their own boilerplate conditional check, which they could forget or get wrong. But having now implemented both, I can see why the tryGet() design looks simpler, at least in the short term.) First, the callback example: class CallbackMap<K, V> { private final Map<K, V> backingMap; public CallbackMap(Map<K, V> backingMap) { this.backingMap = backingMap; } void lookup(K key, Callback<K, V> handler) { V val = backingMap.get(key); if (val == null) { handler.handleMissing(key); } else { handler.handleFound(key, val); } } } interface Callback<K, V> { void handleFound(K key, V value); void handleMissing(K key); } class CallbackExample { private final Map<String, String> map; private final List<String> found; private final List<String> missing; private Callback<String, String> handler; public CallbackExample(Map<String, String> map) { this.map = map; found = new ArrayList<String>(map.size()); missing = new ArrayList<String>(map.size()); handler = new Callback<String, String>() { public void handleFound(String key, String value) { found.add(key + ": " + value); } public void handleMissing(String key) { missing.add(key); } }; } void test() { CallbackMap<String, String> cbMap = new CallbackMap<String, String>(map); for (int i = 0, count = map.size(); i < count; i++) { String key = "key" + i; cbMap.lookup(key, handler); } System.out.println(found.size() + " found"); System.out.println(missing.size() + " missing"); } } Now, the tryGet() example -- as best I understand the pattern (and I might well be wrong): class TryGetMap<K, V> { private final Map<K, V> backingMap; public TryGetMap(Map<K, V> backingMap) { this.backingMap = backingMap; } boolean tryGet(K key, OutParameter<V> valueParam) { V val = backingMap.get(key); if (val == null) { return false; } valueParam.value = val; return true; } } class OutParameter<V> { V value; } class TryGetExample { private final Map<String, String> map; private final List<String> found; private final List<String> missing; public TryGetExample(Map<String, String> map) { this.map = map; found = new ArrayList<String>(map.size()); missing = new ArrayList<String>(map.size()); } void test() { TryGetMap<String, String> tgMap = new TryGetMap<String, String>(map); for (int i = 0, count = map.size(); i < count; i++) { String key = "key" + i; OutParameter<String> out = new OutParameter<String>(); if (tgMap.tryGet(key, out)) { found.add(key + ": " + out.value); } else { missing.add(key); } } System.out.println(found.size() + " found"); System.out.println(missing.size() + " missing"); } } And finally, the performance test code: public static void main(String[] args) { int size = 200000; Map<String, String> map = new HashMap<String, String>(); for (int i = 0; i < size; i++) { String val = (i % 5 == 0) ? null : "value" + i; map.put("key" + i, val); } long totalCallback = 0; long totalTryGet = 0; int iterations = 20; for (int i = 0; i < iterations; i++) { { TryGetExample tryGet = new TryGetExample(map); long tryGetStart = System.currentTimeMillis(); tryGet.test(); totalTryGet += (System.currentTimeMillis() - tryGetStart); } System.gc(); { CallbackExample callback = new CallbackExample(map); long callbackStart = System.currentTimeMillis(); callback.test(); totalCallback += (System.currentTimeMillis() - callbackStart); } System.gc(); } System.out.println("Avg. callback: " + (totalCallback / iterations)); System.out.println("Avg. tryGet(): " + (totalTryGet / iterations)); } On my first attempt, I got 50% worse performance for callback than for tryGet(), which really surprised me. But, on a hunch, I added some garbage collection, and the performance penalty vanished. This fits with my instinct, which is that we're basically talking about taking the same number of method calls, conditional checks, etc. and rearranging them. But then, I wrote the code, so I might well have written a suboptimal or subconsicously penalized tryGet() implementation. Thoughts?

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  • Red Gate Coder interviews: Alex Davies

    - by Michael Williamson
    Alex Davies has been a software engineer at Red Gate since graduating from university, and is currently busy working on .NET Demon. We talked about tackling parallel programming with his actors framework, a scientific approach to debugging, and how JavaScript is going to affect the programming languages we use in years to come. So, if we start at the start, how did you get started in programming? When I was seven or eight, I was given a BBC Micro for Christmas. I had asked for a Game Boy, but my dad thought it would be better to give me a proper computer. For a year or so, I only played games on it, but then I found the user guide for writing programs in it. I gradually started doing more stuff on it and found it fun. I liked creating. As I went into senior school I continued to write stuff on there, trying to write games that weren’t very good. I got a real computer when I was fourteen and found ways to write BASIC on it. Visual Basic to start with, and then something more interesting than that. How did you learn to program? Was there someone helping you out? Absolutely not! I learnt out of a book, or by experimenting. I remember the first time I found a loop, I was like “Oh my God! I don’t have to write out the same line over and over and over again any more. It’s amazing!” When did you think this might be something that you actually wanted to do as a career? For a long time, I thought it wasn’t something that you would do as a career, because it was too much fun to be a career. I thought I’d do chemistry at university and some kind of career based on chemical engineering. And then I went to a careers fair at school when I was seventeen or eighteen, and it just didn’t interest me whatsoever. I thought “I could be a programmer, and there’s loads of money there, and I’m good at it, and it’s fun”, but also that I shouldn’t spoil my hobby. Now I don’t really program in my spare time any more, which is a bit of a shame, but I program all the rest of the time, so I can live with it. Do you think you learnt much about programming at university? Yes, definitely! I went into university knowing how to make computers do anything I wanted them to do. However, I didn’t have the language to talk about algorithms, so the algorithms course in my first year was massively important. Learning other language paradigms like functional programming was really good for breadth of understanding. Functional programming influences normal programming through design rather than actually using it all the time. I draw inspiration from it to write imperative programs which I think is actually becoming really fashionable now, but I’ve been doing it for ages. I did it first! There were also some courses on really odd programming languages, a bit of Prolog, a little bit of C. Having a little bit of each of those is something that I would have never done on my own, so it was important. And then there are knowledge-based courses which are about not programming itself but things that have been programmed like TCP. Those are really important for examples for how to approach things. Did you do any internships while you were at university? Yeah, I spent both of my summers at the same company. I thought I could code well before I went there. Looking back at the crap that I produced, it was only surpassed in its crappiness by all of the other code already in that company. I’m so much better at writing nice code now than I used to be back then. Was there just not a culture of looking after your code? There was, they just didn’t hire people for their abilities in that area. They hired people for raw IQ. The first indicator of it going wrong was that they didn’t have any computer scientists, which is a bit odd in a programming company. But even beyond that they didn’t have people who learnt architecture from anyone else. Most of them had started straight out of university, so never really had experience or mentors to learn from. There wasn’t the experience to draw from to teach each other. In the second half of my second internship, I was being given tasks like looking at new technologies and teaching people stuff. Interns shouldn’t be teaching people how to do their jobs! All interns are going to have little nuggets of things that you don’t know about, but they shouldn’t consistently be the ones who know the most. It’s not a good environment to learn. I was going to ask how you found working with people who were more experienced than you… When I reached Red Gate, I found some people who were more experienced programmers than me, and that was difficult. I’ve been coding since I was tiny. At university there were people who were cleverer than me, but there weren’t very many who were more experienced programmers than me. During my internship, I didn’t find anyone who I classed as being a noticeably more experienced programmer than me. So, it was a shock to the system to have valid criticisms rather than just formatting criticisms. However, Red Gate’s not so big on the actual code review, at least it wasn’t when I started. We did an entire product release and then somebody looked over all of the UI of that product which I’d written and say what they didn’t like. By that point, it was way too late and I’d disagree with them. Do you think the lack of code reviews was a bad thing? I think if there’s going to be any oversight of new people, then it should be continuous rather than chunky. For me I don’t mind too much, I could go out and get oversight if I wanted it, and in those situations I felt comfortable without it. If I was managing the new person, then maybe I’d be keener on oversight and then the right way to do it is continuously and in very, very small chunks. Have you had any significant projects you’ve worked on outside of a job? When I was a teenager I wrote all sorts of stuff. I used to write games, I derived how to do isomorphic projections myself once. I didn’t know what the word was so I couldn’t Google for it, so I worked it out myself. It was horrifically complicated. But it sort of tailed off when I started at university, and is now basically zero. If I do side-projects now, they tend to be work-related side projects like my actors framework, NAct, which I started in a down tools week. Could you explain a little more about NAct? It is a little C# framework for writing parallel code more easily. Parallel programming is difficult when you need to write to shared data. Sometimes parallel programming is easy because you don’t need to write to shared data. When you do need to access shared data, you could just have your threads pile in and do their work, but then you would screw up the data because the threads would trample on each other’s toes. You could lock, but locks are really dangerous if you’re using more than one of them. You get interactions like deadlocks, and that’s just nasty. Actors instead allows you to say this piece of data belongs to this thread of execution, and nobody else can read it. If you want to read it, then ask that thread of execution for a piece of it by sending a message, and it will send the data back by a message. And that avoids deadlocks as long as you follow some obvious rules about not making your actors sit around waiting for other actors to do something. There are lots of ways to write actors, NAct allows you to do it as if it was method calls on other objects, which means you get all the strong type-safety that C# programmers like. Do you think that this is suitable for the majority of parallel programming, or do you think it’s only suitable for specific cases? It’s suitable for most difficult parallel programming. If you’ve just got a hundred web requests which are all independent of each other, then I wouldn’t bother because it’s easier to just spin them up in separate threads and they can proceed independently of each other. But where you’ve got difficult parallel programming, where you’ve got multiple threads accessing multiple bits of data in multiple ways at different times, then actors is at least as good as all other ways, and is, I reckon, easier to think about. When you’re using actors, you presumably still have to write your code in a different way from you would otherwise using single-threaded code. You can’t use actors with any methods that have return types, because you’re not allowed to call into another actor and wait for it. If you want to get a piece of data out of another actor, then you’ve got to use tasks so that you can use “async” and “await” to await asynchronously for it. But other than that, you can still stick things in classes so it’s not too different really. Rather than having thousands of objects with mutable state, you can use component-orientated design, where there are only a few mutable classes which each have a small number of instances. Then there can be thousands of immutable objects. If you tend to do that anyway, then actors isn’t much of a jump. If I’ve already built my system without any parallelism, how hard is it to add actors to exploit all eight cores on my desktop? Usually pretty easy. If you can identify even one boundary where things look like messages and you have components where some objects live on one side and these other objects live on the other side, then you can have a granddaddy object on one side be an actor and it will parallelise as it goes across that boundary. Not too difficult. If we do get 1000-core desktop PCs, do you think actors will scale up? It’s hard. There are always in the order of twenty to fifty actors in my whole program because I tend to write each component as actors, and I tend to have one instance of each component. So this won’t scale to a thousand cores. What you can do is write data structures out of actors. I use dictionaries all over the place, and if you need a dictionary that is going to be accessed concurrently, then you could build one of those out of actors in no time. You can use queuing to marshal requests between different slices of the dictionary which are living on different threads. So it’s like a distributed hash table but all of the chunks of it are on the same machine. That means that each of these thousand processors has cached one small piece of the dictionary. I reckon it wouldn’t be too big a leap to start doing proper parallelism. Do you think it helps if actors get baked into the language, similarly to Erlang? Erlang is excellent in that it has thread-local garbage collection. C# doesn’t, so there’s a limit to how well C# actors can possibly scale because there’s a single garbage collected heap shared between all of them. When you do a global garbage collection, you’ve got to stop all of the actors, which is seriously expensive, whereas in Erlang garbage collections happen per-actor, so they’re insanely cheap. However, Erlang deviated from all the sensible language design that people have used recently and has just come up with crazy stuff. You can definitely retrofit thread-local garbage collection to .NET, and then it’s quite well-suited to support actors, even if it’s not baked into the language. Speaking of language design, do you have a favourite programming language? I’ll choose a language which I’ve never written before. I like the idea of Scala. It sounds like C#, only with some of the niggles gone. I enjoy writing static types. It means you don’t have to writing tests so much. When you say it doesn’t have some of the niggles? C# doesn’t allow the use of a property as a method group. It doesn’t have Scala case classes, or sum types, where you can do a switch statement and the compiler checks that you’ve checked all the cases, which is really useful in functional-style programming. Pattern-matching, in other words. That’s actually the major niggle. C# is pretty good, and I’m quite happy with C#. And what about going even further with the type system to remove the need for tests to something like Haskell? Or is that a step too far? I’m quite a pragmatist, I don’t think I could deal with trying to write big systems in languages with too few other users, especially when learning how to structure things. I just don’t know anyone who can teach me, and the Internet won’t teach me. That’s the main reason I wouldn’t use it. If I turned up at a company that writes big systems in Haskell, I would have no objection to that, but I wouldn’t instigate it. What about things in C#? For instance, there’s contracts in C#, so you can try to statically verify a bit more about your code. Do you think that’s useful, or just not worthwhile? I’ve not really tried it. My hunch is that it needs to be built into the language and be quite mathematical for it to work in real life, and that doesn’t seem to have ended up true for C# contracts. I don’t think anyone who’s tried them thinks they’re any good. I might be wrong. On a slightly different note, how do you like to debug code? I think I’m quite an odd debugger. I use guesswork extremely rarely, especially if something seems quite difficult to debug. I’ve been bitten spending hours and hours on guesswork and not being scientific about debugging in the past, so now I’m scientific to a fault. What I want is to see the bug happening in the debugger, to step through the bug happening. To watch the program going from a valid state to an invalid state. When there’s a bug and I can’t work out why it’s happening, I try to find some piece of evidence which places the bug in one section of the code. From that experiment, I binary chop on the possible causes of the bug. I suppose that means binary chopping on places in the code, or binary chopping on a stage through a processing cycle. Basically, I’m very stupid about how I debug. I won’t make any guesses, I won’t use any intuition, I will only identify the experiment that’s going to binary chop most effectively and repeat rather than trying to guess anything. I suppose it’s quite top-down. Is most of the time then spent in the debugger? Absolutely, if at all possible I will never debug using print statements or logs. I don’t really hold much stock in outputting logs. If there’s any bug which can be reproduced locally, I’d rather do it in the debugger than outputting logs. And with SmartAssembly error reporting, there’s not a lot that can’t be either observed in an error report and just fixed, or reproduced locally. And in those other situations, maybe I’ll use logs. But I hate using logs. You stare at the log, trying to guess what’s going on, and that’s exactly what I don’t like doing. You have to just look at it and see does this look right or wrong. We’ve covered how you get to grip with bugs. How do you get to grips with an entire codebase? I watch it in the debugger. I find little bugs and then try to fix them, and mostly do it by watching them in the debugger and gradually getting an understanding of how the code works using my process of binary chopping. I have to do a lot of reading and watching code to choose where my slicing-in-half experiment is going to be. The last time I did it was SmartAssembly. The old code was a complete mess, but at least it did things top to bottom. There wasn’t too much of some of the big abstractions where flow of control goes all over the place, into a base class and back again. Code’s really hard to understand when that happens. So I like to choose a little bug and try to fix it, and choose a bigger bug and try to fix it. Definitely learn by doing. I want to always have an aim so that I get a little achievement after every few hours of debugging. Once I’ve learnt the codebase I might be able to fix all the bugs in an hour, but I’d rather be using them as an aim while I’m learning the codebase. If I was a maintainer of a codebase, what should I do to make it as easy as possible for you to understand? Keep distinct concepts in different places. And name your stuff so that it’s obvious which concepts live there. You shouldn’t have some variable that gets set miles up the top of somewhere, and then is read miles down to choose some later behaviour. I’m talking from a very much SmartAssembly point of view because the old SmartAssembly codebase had tons and tons of these things, where it would read some property of the code and then deal with it later. Just thousands of variables in scope. Loads of things to think about. If you can keep concepts separate, then it aids me in my process of fixing bugs one at a time, because each bug is going to more or less be understandable in the one place where it is. And what about tests? Do you think they help at all? I’ve never had the opportunity to learn a codebase which has had tests, I don’t know what it’s like! What about when you’re actually developing? How useful do you find tests in finding bugs or regressions? Finding regressions, absolutely. Running bits of code that would be quite hard to run otherwise, definitely. It doesn’t happen very often that a test finds a bug in the first place. I don’t really buy nebulous promises like tests being a good way to think about the spec of the code. My thinking goes something like “This code works at the moment, great, ship it! Ah, there’s a way that this code doesn’t work. Okay, write a test, demonstrate that it doesn’t work, fix it, use the test to demonstrate that it’s now fixed, and keep the test for future regressions.” The most valuable tests are for bugs that have actually happened at some point, because bugs that have actually happened at some point, despite the fact that you think you’ve fixed them, are way more likely to appear again than new bugs are. Does that mean that when you write your code the first time, there are no tests? Often. The chance of there being a bug in a new feature is relatively unaffected by whether I’ve written a test for that new feature because I’m not good enough at writing tests to think of bugs that I would have written into the code. So not writing regression tests for all of your code hasn’t affected you too badly? There are different kinds of features. Some of them just always work, and are just not flaky, they just continue working whatever you throw at them. Maybe because the type-checker is particularly effective around them. Writing tests for those features which just tend to always work is a waste of time. And because it’s a waste of time I’ll tend to wait until a feature has demonstrated its flakiness by having bugs in it before I start trying to test it. You can get a feel for whether it’s going to be flaky code as you’re writing it. I try to write it to make it not flaky, but there are some things that are just inherently flaky. And very occasionally, I’ll think “this is going to be flaky” as I’m writing, and then maybe do a test, but not most of the time. How do you think your programming style has changed over time? I’ve got clearer about what the right way of doing things is. I used to flip-flop a lot between different ideas. Five years ago I came up with some really good ideas and some really terrible ideas. All of them seemed great when I thought of them, but they were quite diverse ideas, whereas now I have a smaller set of reliable ideas that are actually good for structuring code. So my code is probably more similar to itself than it used to be back in the day, when I was trying stuff out. I’ve got more disciplined about encapsulation, I think. There are operational things like I use actors more now than I used to, and that forces me to use immutability more than I used to. The first code that I wrote in Red Gate was the memory profiler UI, and that was an actor, I just didn’t know the name of it at the time. I don’t really use object-orientation. By object-orientation, I mean having n objects of the same type which are mutable. I want a constant number of objects that are mutable, and they should be different types. I stick stuff in dictionaries and then have one thing that owns the dictionary and puts stuff in and out of it. That’s definitely a pattern that I’ve seen recently. I think maybe I’m doing functional programming. Possibly. It’s plausible. If you had to summarise the essence of programming in a pithy sentence, how would you do it? Programming is the form of art that, without losing any of the beauty of architecture or fine art, allows you to produce things that people love and you make money from. So you think it’s an art rather than a science? It’s a little bit of engineering, a smidgeon of maths, but it’s not science. Like architecture, programming is on that boundary between art and engineering. If you want to do it really nicely, it’s mostly art. You can get away with doing architecture and programming entirely by having a good engineering mind, but you’re not going to produce anything nice. You’re not going to have joy doing it if you’re an engineering mind. Architects who are just engineering minds are not going to enjoy their job. I suppose engineering is the foundation on which you build the art. Exactly. How do you think programming is going to change over the next ten years? There will be an unfortunate shift towards dynamically-typed languages, because of JavaScript. JavaScript has an unfair advantage. JavaScript’s unfair advantage will cause more people to be exposed to dynamically-typed languages, which means other dynamically-typed languages crop up and the best features go into dynamically-typed languages. Then people conflate the good features with the fact that it’s dynamically-typed, and more investment goes into dynamically-typed languages. They end up better, so people use them. What about the idea of compiling other languages, possibly statically-typed, to JavaScript? It’s a reasonable idea. I would like to do it, but I don’t think enough people in the world are going to do it to make it pick up. The hordes of beginners are the lifeblood of a language community. They are what makes there be good tools and what makes there be vibrant community websites. And any particular thing which is the same as JavaScript only with extra stuff added to it, although it might be technically great, is not going to have the hordes of beginners. JavaScript is always to be quickest and easiest way for a beginner to start programming in the browser. And dynamically-typed languages are great for beginners. Compilers are pretty scary and beginners don’t write big code. And having your errors come up in the same place, whether they’re statically checkable errors or not, is quite nice for a beginner. If someone asked me to teach them some programming, I’d teach them JavaScript. If dynamically-typed languages are great for beginners, when do you think the benefits of static typing start to kick in? The value of having a statically typed program is in the tools that rely on the static types to produce a smooth IDE experience rather than actually telling me my compile errors. And only once you’re experienced enough a programmer that having a really smooth IDE experience makes a blind bit of difference, does static typing make a blind bit of difference. So it’s not really about size of codebase. If I go and write up a tiny program, I’m still going to get value out of writing it in C# using ReSharper because I’m experienced with C# and ReSharper enough to be able to write code five times faster if I have that help. Any other visions of the future? Nobody’s going to use actors. Because everyone’s going to be running on single-core VMs connected over network-ready protocols like JSON over HTTP. So, parallelism within one operating system is going to die. But until then, you should use actors. More Red Gater Coder interviews

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  • Inside the Concurrent Collections: ConcurrentDictionary

    - by Simon Cooper
    Using locks to implement a thread-safe collection is rather like using a sledgehammer - unsubtle, easy to understand, and tends to make any other tool redundant. Unlike the previous two collections I looked at, ConcurrentStack and ConcurrentQueue, ConcurrentDictionary uses locks quite heavily. However, it is careful to wield locks only where necessary to ensure that concurrency is maximised. This will, by necessity, be a higher-level look than my other posts in this series, as there is quite a lot of code and logic in ConcurrentDictionary. Therefore, I do recommend that you have ConcurrentDictionary open in a decompiler to have a look at all the details that I skip over. The problem with locks There's several things to bear in mind when using locks, as encapsulated by the lock keyword in C# and the System.Threading.Monitor class in .NET (if you're unsure as to what lock does in C#, I briefly covered it in my first post in the series): Locks block threads The most obvious problem is that threads waiting on a lock can't do any work at all. No preparatory work, no 'optimistic' work like in ConcurrentQueue and ConcurrentStack, nothing. It sits there, waiting to be unblocked. This is bad if you're trying to maximise concurrency. Locks are slow Whereas most of the methods on the Interlocked class can be compiled down to a single CPU instruction, ensuring atomicity at the hardware level, taking out a lock requires some heavy lifting by the CLR and the operating system. There's quite a bit of work required to take out a lock, block other threads, and wake them up again. If locks are used heavily, this impacts performance. Deadlocks When using locks there's always the possibility of a deadlock - two threads, each holding a lock, each trying to aquire the other's lock. Fortunately, this can be avoided with careful programming and structured lock-taking, as we'll see. So, it's important to minimise where locks are used to maximise the concurrency and performance of the collection. Implementation As you might expect, ConcurrentDictionary is similar in basic implementation to the non-concurrent Dictionary, which I studied in a previous post. I'll be using some concepts introduced there, so I recommend you have a quick read of it. So, if you were implementing a thread-safe dictionary, what would you do? The naive implementation is to simply have a single lock around all methods accessing the dictionary. This would work, but doesn't allow much concurrency. Fortunately, the bucketing used by Dictionary allows a simple but effective improvement to this - one lock per bucket. This allows different threads modifying different buckets to do so in parallel. Any thread making changes to the contents of a bucket takes the lock for that bucket, ensuring those changes are thread-safe. The method that maps each bucket to a lock is the GetBucketAndLockNo method: private void GetBucketAndLockNo( int hashcode, out int bucketNo, out int lockNo, int bucketCount) { // the bucket number is the hashcode (without the initial sign bit) // modulo the number of buckets bucketNo = (hashcode & 0x7fffffff) % bucketCount; // and the lock number is the bucket number modulo the number of locks lockNo = bucketNo % m_locks.Length; } However, this does require some changes to how the buckets are implemented. The 'implicit' linked list within a single backing array used by the non-concurrent Dictionary adds a dependency between separate buckets, as every bucket uses the same backing array. Instead, ConcurrentDictionary uses a strict linked list on each bucket: This ensures that each bucket is entirely separate from all other buckets; adding or removing an item from a bucket is independent to any changes to other buckets. Modifying the dictionary All the operations on the dictionary follow the same basic pattern: void AlterBucket(TKey key, ...) { int bucketNo, lockNo; 1: GetBucketAndLockNo( key.GetHashCode(), out bucketNo, out lockNo, m_buckets.Length); 2: lock (m_locks[lockNo]) { 3: Node headNode = m_buckets[bucketNo]; 4: Mutate the node linked list as appropriate } } For example, when adding another entry to the dictionary, you would iterate through the linked list to check whether the key exists already, and add the new entry as the head node. When removing items, you would find the entry to remove (if it exists), and remove the node from the linked list. Adding, updating, and removing items all follow this pattern. Performance issues There is a problem we have to address at this point. If the number of buckets in the dictionary is fixed in the constructor, then the performance will degrade from O(1) to O(n) when a large number of items are added to the dictionary. As more and more items get added to the linked lists in each bucket, the lookup operations will spend most of their time traversing a linear linked list. To fix this, the buckets array has to be resized once the number of items in each bucket has gone over a certain limit. (In ConcurrentDictionary this limit is when the size of the largest bucket is greater than the number of buckets for each lock. This check is done at the end of the TryAddInternal method.) Resizing the bucket array and re-hashing everything affects every bucket in the collection. Therefore, this operation needs to take out every lock in the collection. Taking out mutiple locks at once inevitably summons the spectre of the deadlock; two threads each hold a lock, and each trying to acquire the other lock. How can we eliminate this? Simple - ensure that threads never try to 'swap' locks in this fashion. When taking out multiple locks, always take them out in the same order, and always take out all the locks you need before starting to release them. In ConcurrentDictionary, this is controlled by the AcquireLocks, AcquireAllLocks and ReleaseLocks methods. Locks are always taken out and released in the order they are in the m_locks array, and locks are all released right at the end of the method in a finally block. At this point, it's worth pointing out that the locks array is never re-assigned, even when the buckets array is increased in size. The number of locks is fixed in the constructor by the concurrencyLevel parameter. This simplifies programming the locks; you don't have to check if the locks array has changed or been re-assigned before taking out a lock object. And you can be sure that when a thread takes out a lock, another thread isn't going to re-assign the lock array. This would create a new series of lock objects, thus allowing another thread to ignore the existing locks (and any threads controlling them), breaking thread-safety. Consequences of growing the array Just because we're using locks doesn't mean that race conditions aren't a problem. We can see this by looking at the GrowTable method. The operation of this method can be boiled down to: private void GrowTable(Node[] buckets) { try { 1: Acquire first lock in the locks array // this causes any other thread trying to take out // all the locks to block because the first lock in the array // is always the one taken out first // check if another thread has already resized the buckets array // while we were waiting to acquire the first lock 2: if (buckets != m_buckets) return; 3: Calculate the new size of the backing array 4: Node[] array = new array[size]; 5: Acquire all the remaining locks 6: Re-hash the contents of the existing buckets into array 7: m_buckets = array; } finally { 8: Release all locks } } As you can see, there's already a check for a race condition at step 2, for the case when the GrowTable method is called twice in quick succession on two separate threads. One will successfully resize the buckets array (blocking the second in the meantime), when the second thread is unblocked it'll see that the array has already been resized & exit without doing anything. There is another case we need to consider; looking back at the AlterBucket method above, consider the following situation: Thread 1 calls AlterBucket; step 1 is executed to get the bucket and lock numbers. Thread 2 calls GrowTable and executes steps 1-5; thread 1 is blocked when it tries to take out the lock in step 2. Thread 2 re-hashes everything, re-assigns the buckets array, and releases all the locks (steps 6-8). Thread 1 is unblocked and continues executing, but the calculated bucket and lock numbers are no longer valid. Between calculating the correct bucket and lock number and taking out the lock, another thread has changed where everything is. Not exactly thread-safe. Well, a similar problem was solved in ConcurrentStack and ConcurrentQueue by storing a local copy of the state, doing the necessary calculations, then checking if that state is still valid. We can use a similar idea here: void AlterBucket(TKey key, ...) { while (true) { Node[] buckets = m_buckets; int bucketNo, lockNo; GetBucketAndLockNo( key.GetHashCode(), out bucketNo, out lockNo, buckets.Length); lock (m_locks[lockNo]) { // if the state has changed, go back to the start if (buckets != m_buckets) continue; Node headNode = m_buckets[bucketNo]; Mutate the node linked list as appropriate } break; } } TryGetValue and GetEnumerator And so, finally, we get onto TryGetValue and GetEnumerator. I've left these to the end because, well, they don't actually use any locks. How can this be? Whenever you change a bucket, you need to take out the corresponding lock, yes? Indeed you do. However, it is important to note that TryGetValue and GetEnumerator don't actually change anything. Just as immutable objects are, by definition, thread-safe, read-only operations don't need to take out a lock because they don't change anything. All lockless methods can happily iterate through the buckets and linked lists without worrying about locking anything. However, this does put restrictions on how the other methods operate. Because there could be another thread in the middle of reading the dictionary at any time (even if a lock is taken out), the dictionary has to be in a valid state at all times. Every change to state has to be made visible to other threads in a single atomic operation (all relevant variables are marked volatile to help with this). This restriction ensures that whatever the reading threads are doing, they never read the dictionary in an invalid state (eg items that should be in the collection temporarily removed from the linked list, or reading a node that has had it's key & value removed before the node itself has been removed from the linked list). Fortunately, all the operations needed to change the dictionary can be done in that way. Bucket resizes are made visible when the new array is assigned back to the m_buckets variable. Any additions or modifications to a node are done by creating a new node, then splicing it into the existing list using a single variable assignment. Node removals are simply done by re-assigning the node's m_next pointer. Because the dictionary can be changed by another thread during execution of the lockless methods, the GetEnumerator method is liable to return dirty reads - changes made to the dictionary after GetEnumerator was called, but before the enumeration got to that point in the dictionary. It's worth listing at this point which methods are lockless, and which take out all the locks in the dictionary to ensure they get a consistent view of the dictionary: Lockless: TryGetValue GetEnumerator The indexer getter ContainsKey Takes out every lock (lockfull?): Count IsEmpty Keys Values CopyTo ToArray Concurrent principles That covers the overall implementation of ConcurrentDictionary. I haven't even begun to scratch the surface of this sophisticated collection. That I leave to you. However, we've looked at enough to be able to extract some useful principles for concurrent programming: Partitioning When using locks, the work is partitioned into independant chunks, each with its own lock. Each partition can then be modified concurrently to other partitions. Ordered lock-taking When a method does need to control the entire collection, locks are taken and released in a fixed order to prevent deadlocks. Lockless reads Read operations that don't care about dirty reads don't take out any lock; the rest of the collection is implemented so that any reading thread always has a consistent view of the collection. That leads us to the final collection in this little series - ConcurrentBag. Lacking a non-concurrent analogy, it is quite different to any other collection in the class libraries. Prepare your thinking hats!

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  • Facing Null Pointer Exception while using BIRT

    - by srikanth
    Hi, I am using BIRT APIs in a java program.My code is : package com.tecnotree.mdx.product.utils; import java.util.HashMap; import java.util.logging.Level; import org.eclipse.birt.core.exception.BirtException; import org.eclipse.birt.core.framework.Platform; import org.eclipse.birt.report.engine.api.EngineConfig; import org.eclipse.birt.report.engine.api.EngineConstants; import org.eclipse.birt.report.engine.api.HTMLRenderOption; import org.eclipse.birt.report.engine.api.IReportEngine; import org.eclipse.birt.report.engine.api.IReportEngineFactory; import org.eclipse.birt.report.engine.api.IReportRunnable; import org.eclipse.birt.report.engine.api.IRunAndRenderTask; import org.eclipse.birt.report.engine.api.ReportEngine; public class ExampleReport { public static void main(String[] args) { // Variables used to control BIRT Engine instance ReportEngine eng = null; IReportRunnable design = null; IRunAndRenderTask task = null; HTMLRenderOption renderContext = null; HashMap contextMap = null; HTMLRenderOption options = null; final EngineConfig conf = new EngineConfig(); conf .setEngineHome("C:\\birt-runtime-2_5_2\\birt-runtime-2_5_2\\ReportEngine"); System.out.println("conf " + conf.getBIRTHome()); conf.setLogConfig(null, Level.FINE); try { Platform.startup(conf); } catch (BirtException e1) { // TODO Auto-generated catch block e1.printStackTrace(); } IReportEngineFactory factory = (IReportEngineFactory) Platform .createFactoryObject(IReportEngineFactory.EXTENSION_REPORT_ENGINE_FACTORY); System.out.println("Factory : " + factory.toString()); System.out.println(conf.toString()); IReportEngine engine = factory.createReportEngine(conf); System.out.println("Engine : " + engine); try { design = eng .openReportDesign("C:\\birt-runtime-2_5_2\\birt-runtime-2_5_2\\ReportEngine\\samples\\hello_world.rptdesign"); } catch (Exception e) { System.err .println("An error occured during the opening of the report file!"); e.printStackTrace(); System.exit(-1); } task = eng.createRunAndRenderTask(design); renderContext = new HTMLRenderOption(); renderContext.setImageDirectory("image"); contextMap = new HashMap(); contextMap.put(EngineConstants.APPCONTEXT_HTML_RENDER_CONTEXT, renderContext); task.setAppContext(contextMap); options = new HTMLRenderOption(); options.setOutputFileName("c:/temp/output.html"); options.setOutputFormat("html"); task.setRenderOption(options); try { task.run(); } catch (Exception e) { System.err.println("An error occured while running the report!"); e.printStackTrace(); System.exit(-1); } System.out.println("All went well. Closing program!"); eng.destroy(); } } But i am facing NullPointerException while creating the report. STACKTRACE : Exception in thread "main" java.lang.NullPointerException at org.eclipse.birt.report.engine.api.impl.ReportEngine$EngineExtensionManager.<init>(ReportEngine.java:784) at org.eclipse.birt.report.engine.api.impl.ReportEngine.<init>(ReportEngine.java:109) at org.eclipse.birt.report.engine.api.impl.ReportEngineFactory$1.run(ReportEngineFactory.java:18) at org.eclipse.birt.report.engine.api.impl.ReportEngineFactory$1.run(ReportEngineFactory.java:1) at java.security.AccessController.doPrivileged(Native Method) at org.eclipse.birt.report.engine.api.impl.ReportEngineFactory.createReportEngine(ReportEngineFactory.java:14) at com.tecnotree.mdx.product.utils.ExampleReport.main(ExampleReport.java:47) Please help me regarding this... my project deadline has been reached... Appreciate your Reply Thanks in Advance

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