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• Microsoft Certifications &ndash; how to prep? and why?

  - by Kelly Jones

  I often get asked by my colleagues, “how do you prepare for Microsoft exams?” Well, the answer for me is a little complicated, so I thought I’d write up here what I do. The first thing I do is go to Microsoft’s website to find the exam that I need to take.  If you’re looking to get a particular certification, then their site lists the exam or exams that you’ll need to pass.  If you’ve already taken an exam, you can log onto the MCP website and use their certification planner.  This little tool tells you what tests you need, based on the exams you’ve already passed.  It is very helpful with the certifications that are multiple tests and especially ones that have electives. Once you’ve identified the test, you can use Microsoft’s website to see the topics that it covers.  This is a good outline to follow when you study.  I’ll keep this handy to reference back throughout my studying to make sure that I’m covering all the topics I need to know. The next step is probably where I am a little different from others.  IF the exam outline covers material that I’ve already been working with, then I’ll skip a lot of the studying and go directly to the practice tests.  However, if I’m looking at the outline and wondering how in the world do you do that? – then it’s time to hit the books. So, where to find study materials?  Try typing in the exam number into any search engine.  You’ll typically find a ton of resources.  If you’re lucky, you’ll find books that others recommend based on their studying and exam experience.  As a Sogeti employee, I have access to three really good resources: an internal company list of all of the consultants who have passed particular tests (on our Connex website), Books 24x7, and Transcender practice exams. Once my studying is done (either through books or experience), I’ll go through the practice exams.  I find them really helpful in getting my knowledge lined up to the thinking process that the exam writers use.  If I’m relying on my experience, then this really helps me to identify gaps in my knowledge that I’ll need to fill. That’s about it.  If I’m doing ok on the practice exams, then I’ll take the real thing.  I’ve found that the practice exams are usually more difficult than then real thing. Oh – one other thing I do related to Microsoft exams – I try to take any beta exams that Microsoft makes available that fall into my skill set.  Microsoft has started a blog to announce these and the seats usually fill up really quick.  The blog is at http://blogs.technet.com/betaexams/ . You don’t get your results instantly, like a normal exam, instead you have to wait for everyone to finish taking the beta exams and for Microsoft to determine which questions they are using and which they are dropping.  So, be prepared to wait six to eight weeks for your results.

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• How should I handle persistence in a Java MUD? OptimisticLockException handling

  - by Chase

  I'm re-implementing a old BBS MUD game in Java with permission from the original developers. Currently I'm using Java EE 6 with EJB Session facades for the game logic and JPA for the persistence. A big reason I picked session beans is JTA. I'm more experienced with web apps in which if you get an OptimisticLockException you just catch it and tell the user their data is stale and they need to re-apply/re-submit. Responding with "try again" all the time in a multi-user game would make for a horrible experience. Given that I'd expect several people to be targeting a single monster during a fight I think the chance of an OptimisticLockException would be high. My view code, the part presenting a telnet CLI, is the EJB client. Should I be catching the PersistenceExceptions and TransactionRolledbackLocalExceptions and just retrying? How do you decide when to stop? Should I switch to pessimistic locking? Is persisting after every user command overkill? Should I be loading the entire world in RAM and dumping the state every couple of minutes? Do I make my session facade a EJB 3.1 singleton which would function as a choke point and therefore eliminating the need to do any type of JPA locking? EJB 3.1 singletons function as a multiple reader/single writer design (you annotate the methods as readers and writers). Basically, what is the best design and java persistence API for highly concurrent data changes in an application where it is not acceptable to present resubmit/retry prompts to the user?

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• Prevent illegal behavior to the registered user

  - by Al Kush

  I am building a website in which this website will be focused on the publishing of novels. Every writers who publish their novels with us will get a royalty from us. And this royalty comes from the user or the reader who read the novel online in our website. When a user search for a novel and want to read that, they will click a link to the page which its content is that novel. The html page for each novels will have a session function that first will force them to login or register to make a payment such as with a credit-card or paypal before accessing that html page. My problem now is if the user has succesfully login and access the html page, I am afraid if the user will copy the content of the novel. Some disccussion out here How to Disable Copy Paste (Browser) have a solution to create it in Flash so that it can't be coppied-paste. But the I think, if the user who access it is a web developer like us they will try to find the path of the file from the link in the page source, and then they can steal it. For now I think it is enough I am explaining this. I hope anyone fully accept this problem (question) with a good idea to solve it.

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• Lightweight spinlocks built from GCC atomic operations?

  - by Thomas

  I'd like to minimize synchronization and write lock-free code when possible in a project of mine. When absolutely necessary I'd love to substitute light-weight spinlocks built from atomic operations for pthread and win32 mutex locks. My understanding is that these are system calls underneath and could cause a context switch (which may be unnecessary for very quick critical sections where simply spinning a few times would be preferable). The atomic operations I'm referring to are well documented here: http://gcc.gnu.org/onlinedocs/gcc-4.4.1/gcc/Atomic-Builtins.html Here is an example to illustrate what I'm talking about. Imagine a RB-tree with multiple readers and writers possible. RBTree::exists() is read-only and thread safe, RBTree::insert() would require exclusive access by a single writer (and no readers) to be safe. Some code: class IntSetTest { private: unsigned short lock; RBTree<int>* myset; public: // ... void add_number(int n) { // Aquire once locked==false (atomic) while (__sync_bool_compare_and_swap(&lock, 0, 0xffff) == false); // Perform a thread-unsafe operation on the set myset->insert(n); // Unlock (atomic) __sync_bool_compare_and_swap(&lock, 0xffff, 0); } bool check_number(int n) { // Increment once the lock is below 0xffff u16 savedlock = lock; while (savedlock == 0xffff || __sync_bool_compare_and_swap(&lock, savedlock, savedlock+1) == false) savedlock = lock; // Perform read-only operation bool exists = tree->exists(n); // Decrement savedlock = lock; while (__sync_bool_compare_and_swap(&lock, savedlock, savedlock-1) == false) savedlock = lock; return exists; } }; (lets assume it need not be exception-safe) Is this code indeed thread-safe? Are there any pros/cons to this idea? Any advice? Is the use of spinlocks like this a bad idea if the threads are not truly concurrent? Thanks in advance. ;)

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• Using git pull to track a remote branch without merging

  - by J Barlow

  I am using git to track content which is changed by some people and shared "read-only" with others. The "readers" may from time to time need to make a change, but mostly they will not. I want to allow for the git "writers" to rebase pushed branches** if need be, and ensure that the "readers" never accidentally get a merge. That's normally easy enough. git pull origin +master There's one case that seems to cause problems. If a reader makes a local change, the command above will merge. I want pull to be fully automatic if the reader has not made local changes, while if they have made local changes, it should stop and ask for input. I want to track any upstream changes while being careful about merging downstream changes. In a way, I don't really want to pull. I want to track the master branch exactly. ** (I know this is not a best practice, but it seems necessary in our case: we have one main branch that contains most of the work and some topic branches for specific customers with minor changes that need to be isolated. It seems easiest to frequently rebase to keep the topics up to date.)

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• Do programmers need a union?

  - by James A. Rosen

  In light of the acrid responses to the intellectual property clause discussed in my previous question, I have to ask: why don't we have a programmers' union? There are many issues we face as employees, and we have very little ability to organize and negotiate. Could we band together with the writers', directors', or musicians' guilds, or are our needs unique? Has anyone ever tried to start one? If so, why did it fail? (Or, alternatively, why have I never heard of it, despite its success?) later: Keith has my idea basically right. I would also imagine the union being involved in many other topics, including: legal liability for others' use/misuse of our work, especially unintended uses evaluating the quality of computer science and software engineering higher education programs -- unlike many other engineering disciplines, we are not required to be certified on receiving our Bachelor's degrees evangelism and outreach -- especially to elementary school students certification -- not doing it, but working with the companies like ISC(2) and others to make certifications meaningful and useful continuing education -- similar to previous conferences -- maintain a go-to list of organizers and other resources our members can use I would see it less so as a traditional trade union, with little emphasis on: pay -- we tend to command fairly good salaries outsourcing and free trade -- most of use tend to be pretty free-market oriented working conditions -- we're the only industry with Aeron chairs being considered anything like "standard"

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• Properties vs. Fields: Need help grasping the uses of Properties over Fields.

  - by pghtech

  First off, I have read through a list of postings on this topic and I don't feel I have grasped properties because of what I had come to understand about encapsulation and field modifiers (private, public..ect). One of the main aspects of C# that I have come to learn is the importance of data protection within your code by the use of encapsulation. I 'thought' I understood that to be because of the ability of the use of the modifiers (private, public, internal, protected). However, after learning about properties I am sort of torn in understanding not only properties uses, but the overall importance/ability of data protection (what I understood as encapsulation) within C#. To be more specific, everything I have read when I got to properties in C# is that you should try to use them in place of fields when you can because of: 1) they allow you to change the data type when you can't when directly accessing the field directly. 2) they add a level of protection to data access However, from what I 'thought' I had come to know about the use of field modifiers did #2, it seemed to me that properties just generated additional code unless you had some reason to change the type (#1) - because you are (more or less) creating hidden methods to access fields as opposed to directly. Then there is the whole modifiers being able to be added to Properties which further complicates my understanding for the need of properties to access data. I have read a number of chapters from different writers on "properties" and none have really explained a good understanding of properties vs. fields vs. encapsulation (and good programming methods). Can someone explain: 1) why I would want to use properties instead of fields (especially when it appears I am just adding additional code 2) any tips on recognizing the use of properties and not seeing them as simply methods (with the exception of the get;set being apparent) when tracing other peoples code? 3) Any general rules of thumb when it comes to good programming methods in relation to when to use what? Thanks and sorry for the long post - I didn't want to just ask a question that has been asked 100x without explaining why I am asking it again.

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• What is a good programming language/environment for Linux database applications?

  - by Dkellygb

  I could use some advice on my move from the Windows world to Linux. For my business, I have used VB6 and Microsoft Access with both Access databases and SQL server in the past. The easy to use forms, report writers and programming language were perfect for CRUD apps and analysis for our small hotel/restaurant business. After using Linux at home for some time I would like to convert our small business. Our server is already a Linux box using Samba. I am happy with the OpenOffice.org applications instead of Microsoft Office. The only thing which is holding me back is a desktop database application where I can develop the forms and reports we require. Base does not seem to be up to the job yet from my experience. I would like something like VB.Net with visual studio (express) but I would like to avoid Mono – I just don’t see the point of it. (You can correct me if I’m wrong.) But a good collection of forms, controls and a good report writer would be ideal. I have looked at web based stuff like Ruby on Rails, but I think a webserver for our 5 pc network is overkill. I don’t mind running a proper database on our Ubuntu 9.10 server. I may have exposed a few prejudices above but my mind is open. Any thoughts?

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• pthread condition variables on Linux, odd behaviour.

  - by janesconference

  Hi. I'm synchronizing reader and writer processes on Linux. I have 0 or more process (the readers) that need to sleep until they are woken up, read a resource, go back to sleep and so on. Please note I don't know how many reader processes are up at any moment. I have one process (the writer) that writes on a resource, wakes up the readers and does its business until another resource is ready (in detail, I developed a no starve reader-writers solution, but that's not important). To implement the sleep / wake up mechanism I use a Posix condition value, pthread_cond_t. The clients call a pthread_cond_wait() on the variable to sleep, while the server does a pthread_cond_broadcast() to wake them all up. As the manual says, I surround these two calls with a lock/unlock of the associated pthread mutex. The condition variable and the mutex are initialized in the server and shared between processes through a shared memory area (because I'm not working with threads, but with separate processes) an I'm sure my kernel / syscall support it (because I checked _POSIX_THREAD_PROCESS_SHARED). What happens is that the first client process sleeps and wakes up perfectly. When I start the second process, it blocks on its pthread_cond_wait() and never wakes up, even if I'm sure (by the logs) that pthread_cond_broadcast() is called. If I kill the first process, and launch another one, it works perfectly. In other words, the condition variable pthread_cond_broadcast() seems to wake up only one process a time. If more than one process wait on the very same shared condition variable, only the first one manages to wake up correctly, while the others just seem to ignore the broadcast. Why this behaviour? If I send a pthread_cond_broadcast(), every waiting process should wake up, not just one (and, however, not always the same one).

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• lambda traits inconsistency across C++0x compilers

  - by Sumant

  I observed some inconsistency between two compilers (g++ 4.5, VS2010 RC) in the way they match lambdas with partial specializations of class templates. I was trying to implement something like boost::function_types for lambdas to extract type traits. Check this for more details. In g++ 4.5, the type of the operator() of a lambda appears to be like that of a free standing function (R (*)(...)) whereas in VS2010 RC, it appears to be like that of a member function (R (C::*)(...)). So the question is are compiler writers free to interpret any way they want? If not, which compiler is correct? See the details below. template <typename T> struct function_traits : function_traits<decltype(&T::operator())> { // This generic template is instantiated on both the compilers as expected. }; template <typename R, typename C> struct function_traits<R (C::*)() const> { // inherits from this one on VS2010 RC typedef R result_type; }; template <typename R> struct function_traits<R (*)()> { // // inherits from this one g++ 4.5 typedef R result_type; }; int main(void) { auto lambda = []{}; function_traits<decltype(lambda)>::result_type *r; // void * } This program compiles on both g++ 4.5 and VS2010 but the function_traits that are instantiated are different as noted in the code.

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• What about race condition in multithreaded reading?

  - by themoob

  Hi, According to an article on IBM.com, "a race condition is a situation in which two or more threads or processes are reading or writing some shared data, and the final result depends on the timing of how the threads are scheduled. Race conditions can lead to unpredictable results and subtle program bugs." . Although the article concerns Java, I have in general been taught the same definition. As far as I know, simple operation of reading from RAM is composed of setting the states of specific input lines (address, read etc.) and reading the states of output lines. This is an operation that obviously cannot be executed simultaneously by two devices and has to be serialized. Now let's suppose we have a situation when a couple of threads access an object in memory. In theory, this access should be serialized in order to prevent race conditions. But e.g. the readers/writers algorithm assumes that an arbitrary number of readers can use the shared memory at the same time. So, the question is: does one have to implement an exclusive lock for read when using multithreading (in WinAPI e.g.)? If not, why? Where is this control implemented - OS, hardware? Best regards, Kuba

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• Retrieving models from form with ModelMultipleChoiceField

  - by colinjameswebb

  I am having difficulties with forms, specifically ModelMultipleChoiceField. I've pieced together this code from various examples, but it sadly doesn't work. I would like to be able to: Search for some Works on work_search.html Display the results of the search, with checkboxes next to each result Select the Works I want, via the checkboxes After pressing Add, display which works were selected. I believe everything is okay except the last part. The page simply displays "works" :( Here is the code - sorry about the length. Models.py class Work(models.Model): title = models.CharField(max_length=200) artist = models.CharField(max_length=200) writers = models.CharField(max_length=200) def __unicode__(self): return self.title + ' - ' + self.artist forms.py class WorkSelectForm(forms.Form): def __init__(self, queryset, *args, **kwargs): super(WorkSelectForm, self).__init__(*args, **kwargs) self.fields['works'] = forms.ModelMultipleChoiceField(queryset=queryset, widget=forms.CheckboxSelectMultiple()) views.py def work_search(request): query = request.GET.get('q', '') if query: qset = ( Q(title__icontains=query) | Q(artist__icontains=query) | Q(writers__icontains=query) ) results = Work.objects.filter(qset).distinct() form = WorkSelectForm(results) return render_to_response("work_search.html", {"form": form, "query": query }) else: results = [] return render_to_response("work_search.html", {"query": query }) def add_works(request): #if request.method == POST: form = WorkSelectForm(request.POST) #if form.isvalid(): items = form.fields['works'].queryset return render_to_response("add_works.html", {"items":items}) work_search.html {% extends "base.html" %} {% block content %} <h1>Search</h1> <form action="." method="GET"> <label for="q">Search: </label> <input type="text" name="q" value="{{ query|escape }}"> <input type="submit" value="Search"> </form> {% if query %} <h2>Results for "{{ query|escape }}":</h2> <form action="add_works" method="post"> <ul> {% if form %} {{ form.as_ul }} {% endif %} </ul> <input type="submit" value="Add"> </form> {% endif %} {% endblock %} add_works.html {% extends "base.html" %} {% block content %} {% if items %} {% for item in items %} {{ item }} {% endfor %} {% else %} <p>Nothing selected</p> {% endif %} {% endblock %}

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• Communication between lexer and parser

  - by FredOverflow

  Every time I write a simple lexer and parser, I stumble upon the same question: how should the lexer and the parser communicate? I see four different approaches: The lexer eagerly converts the entire input string into a vector of tokens. Once this is done, the vector is fed to the parser which converts it into a tree. This is by far the simplest solution to implement, but since all tokens are stored in memory, it wastes a lot of space. Each time the lexer finds a token, it invokes a function on the parser, passing the current token. In my experience, this only works if the parser can naturally be implemented as a state machine like LALR parsers. By contrast, I don't think it would work at all for recursive descent parsers. Each time the parser needs a token, it asks the lexer for the next one. This is very easy to implement in C# due to the yield keyword, but quite hard in C++ which doesn't have it. The lexer and parser communicate through an asynchronous queue. This is commonly known under the title "producer/consumer", and it should simplify the communication between the lexer and the parser a lot. Does it also outperform the other solutions on multicores? Or is lexing too trivial? Is my analysis sound? Are there other approaches I haven't thought of? What is used in real-world compilers? It would be really cool if compiler writers like Eric Lippert could shed some light on this issue.

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• Using Lucene to index private data, should I have a separate index for each user or a single index

  - by Nathan Bayles

  I am developing an Azure based website and I want to provide search capabilities using Lucene. (structured json objects would be indexed and stored in Lucene and other content such as Word documents, etc. would be indexed in lucene but stored in blob storage) I want the search to be secure, such that one user would never see a document belonging to another user. I want to allow ad-hoc searches as typed by the user. Lastly, I want to query programmatically to return predefined sets of data, such as "all notes for user X". I think I understand how to add properties to each document to achieve these 3 objectives. (I am listing them here so if anyone is kind enough to answer, they will have better idea of what I am trying to do) My questions revolve around performance and security. Can I improve document security by having a separate index for each user, or is including the user's ID as a parameter in each search sufficient? Can I improve indexing speed and total throughput of the system by having a separate index for each user? My thinking is that having separate indexes would allow me to scale the system by having multiple index writers (perhaps even on different server instances) working at the same time, each on their own index. Any insight would be greatly appreciated. Regards, Nate

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• kernel get stack when signalled

  - by yoavstr

  hi there i write readers and writers where the kernel have to syncronize between them and block writer who already read a massage when i am in the queue waiting I get signal so I do the fallowing while (i_Allready_Read(myf) == ALLREADY_READ || isExistWriter == false ) //while (!(i_Allready_Read(aliveProc,current->pid))) { int i, is_sig = 0; printk(KERN_INFO "\n\n*****entered set in read ******\n\n" ); if (i_Allready_Read(myf) == ALLREADY_READ ) wait_event_interruptible (readWaitQ1, !i_Allready_Read(myf)); else wait_event_interruptible (readWaitQ1, isExistWriter); //printk(KERN_INFO "Read Wakeup %d\n",current->pid); for (i = 0; i < _NSIG_WORDS && !is_sig; i++) { is_sig = current->pending.signal.sig[i] & ~current->blocked.sig[i]; } if (is_sig) { handledClose(myf); module_put (THIS_MODULE); return -EINTR; } } return 0;//success } inline void handledClose(struct file *myf)//v { /* *if we close the writer other writer *would be able to enter to permissiones */ if (myf == writerpid ) { isExistWriter = DOESNT_EXIST; //printk(KERN_INFO "procfs_close : this is pid that just closed %d \n", writerpid); } /* *else its a reader so our numofreaders *need to decremented */ else { removeFromArr(myf); numOfReaders--; } } and my close does nothing ... what did i do wrong?

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• Is there a way to create subdatabases as a kind of subfolders in sql server?

  - by user193655

  I am creating an application where there is main DB and where other data is stored in secondary databases. The secondary databases follow a "plugin" approach. I use SQL Server. A simple installation of the application will just have the mainDB, while as an option one can activate more "plug-ins" and for every plug-in there will be a new database. Now why I made this choice is because I have to work with an exisiting legacy system and this is the smartest thing I could figure to implement the plugin system. MainDB and Plugins DB have exactly the same schema (basically Plugins DB have some "special content", some important data that one can use as a kind of template - think to a letter template for example - in the application). Plugin DBs are so used in readonly mode, they are "repository of content". The "smart" thing is that the main application can also be used by "plugin writers", they just write a DB inserting content, and by making a backup of the database they creaetd a potential plugin (this is why all DBs has the same schema). Those plugins DB are downloaded from internet as there is a content upgrade available, every time the full PlugIn DB is destroyed and a new one with the same name is creaetd. This is for simplicity and even because the size of this DBs is generally small. Now this works, anyway I would prefer to organize the DBs in a kind of Tree structure, so that I can force the PlugIn DBs to be "sub-DBs" of the main application DB. As a workaround I am thinking of using naming rules, like: ApplicationDB (for the main application DB) ApplicationDB_PlugIn_N (for the N-th plugin DB) When I search for plugin 1 I try to connect to ApplicationDB_PlugIn_1, if I don't find the DB i raise an error. This situation can happen for example if som DBA renamed ApplicationDB_Plugin_1. So since those Plugin DBs are really dependant on ApplicationDB only I was trying to "do the subfolder trick". Can anyone suggest a way to do this? Can you comment on this self-made plugin approach I decribed above?

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• Processor, OS : 32bit, 64 bit

  - by Sandbox

  I am new to programming and come from a non-CS background (no formal degree). I mostly program winforms using C#. I am confused about 32 bit and 64 bit.... I mean, have heard about 32 bit OS, 32 bit processor and based on which a program can have maximum memory. How it affects the speed of a program. There are lot more questions which keep coming to mind. I tried to go through some Computer Organization and Architecture books. But, either I am too dumb to understand what is written in there or the writers assume that the reader has some CS background. Can someone explain me these things in a plain simple English or point me to something which does that. EDIT: I have read things like In 32-bit mode, they can access up to 4GB memory; in 64-bit mode, they can access much much more....I want to know WHY to all such things. BOUNTY: Answers below are really good....esp one by Martin. But, I am looking at a thorough explanation, but in plain simple English.

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• How can I be a Guru? Is it possible? [closed]

  - by Kev

  Before 1999, I heard about computer. But, I don't know what it look like. TV? Maybe! Before 2001, I only saw it in book. It looks like a TV. Before 2005, I touched it in reality. It still looks like a TV + Black Box. In 2005, I entered university. I had a cource about Mathematica.I loved programming since then. In 2006, I owned a computer. I was coding C every day. if...else..., for..., while..., switch... entered my life. Since 2007, I have learned Data Structures, Algorithms...Then, C#, Java, Python, HTML/CSS/JavaScript, F#... A lot of languages. I'm still learning new lang. Unfortunately, I only know syntax! I'm always a novice(??)! I know some guru start programming at age of 8 or 12. I admire these gurus who are compiler writers, language designers, architecture designers, Linux hackers... Is it possible to become a guru like me. If possible, how? what should I do now? Any advice? Thank you very much.

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• server 2008 r2 - wbadmin systemstatebackup - system writer not found in the backup

  - by TWood

  I am trying to manually run a systemstatebackup command on my server 2008 r2 box and I am getting an error code '2155347997' when I view the backup event log details. The command line tells me that I have log files written to the c:\windows\logs\windowsserverbackup\ path but I have no files of the .log type there. My command window tells me "System Writer is not found in the backup". However when I run vssadmin list writers I find System Writer in the list and it shows normal status with no last errors stored. I am running this from an elevated command prompt as well as from a logged on administrator account. My backup target path has permission for network service to have full control and it has plenty of free space. Looking in eventlog I have two VSS error 8194 that happen immediately before the Backup error 517 which has the errorcode 2155347997 listed. All three of these errors are a result of trying to run the command for the systemstatebackup. It's my belief that some VSS related permission is failing and exiting the backup process before it ever gets started. Because of this the initial code that creates the log files must not be running and this is why I have no files. When running the systemstatebackup command from the command prompt and watching the windowsserverbackup directory I do see that I have a Wbadmin.0.etl file which gets created but it is deleted when the backup errors out and stops. I have looked online and there are numerous opinions as to the cause of this error. These are the things I have corrected to try and fix this issue before posting here: Machine runs a HP 1410i smart array controller but at one time also used a LSI scsi card. Used networkadminkb.com's kb# a467 to find one LSI_SCSI entry in HKLMSysCurrentControlSetServices which start was set to 0x0 and I modified to 0x3. No changes. In HKLMSystemCurrentControlSetServicesVSSDiag I gave network service full control where it previously only had "Special Permission". No changes. I followed KB2009272 to manually try to fix system writer. These are all of the things I have tried. What else should I look at to resolve this issue? It may be important to note that I run Mozy Pro on this server and that was known in the past to use VSS for copying operations and it occasionally threw an error. However since an update last year those error event log entries have stopped.

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• A Rose by Any Other Name..

  - by Geoff N. Hiten

  It is always a good start when you can steal a title line from one of the best writers in the English language.  Let’s hope I can make the rest of this post live up to the opening.  One recurring problem with SQL server is moving databases to new servers.  Client applications use a variety of ways to resolve SQL Server names, some of which are not changed easily <cough SharePoint /cough>.  If you happen to be using default instances on both the source and target SQL Server, then the solution is pretty simple.  You create (or bug the network admin until she creates) two DNS “A” records. One points the old name to the new IP address.  The other creates a new alias for the old server, since the original system name is now redirected.  Note this will redirect ALL traffic from the old server to the new server, including RDP and file share connection attempts.    Figure 1 – Microsoft DNS MMC Snap-In   Figure 2 – DNS New Host Dialog Box Both records are necessary so you can still access the old server via an alternate name. Server Role IP Address Name Alias Source 10.97.230.60 SQL01 SQL01_Old Target 10.97.230.80 SQL02 SQL01 Table 1 – Alias List If you or somebody set up connections via IP address, you deserve to have to go to each app and fix it by hand.  That is the only way to fix that particular foul-up. If have to deal with Named Instances either as a source or a target, then it gets more complicated.  The standard fix is to use the SQL Server Configuration Manager (or one of its earlier incarnations) to create a SQL client alias to redirect the connection.  This can be a pain installing and configuring the app on multiple client servers.  The good news is that SQL Server Configuration Manager AND all of its earlier versions simply write a few registry keys.  Extracting the keys into a .reg file makes centralized automated deployment a snap. If the client is a 32-bit system, you have to extract the native key.  If it is a 64-bit, you have to extract the native key and the WoW (32 bit on 64 bit host) key. First, pick a development system to create the actual registry key.  If you do this repeatedly, you can simply edit an existing registry file.  Create the entry using the SQL Configuration Manager.  You must use a 64-bit system to create the WoW key.  The following example redirects from a named instance “SQL01\SQLUtiluty” to a default instance on “SQL02”.   Figure 3 – SQL Server Configuration Manager - Native Figure 3 shows the native key listing. Figure 4 – SQL Server Configuration Manager – WoW If you think you don’t need the WoW key because your app is 64 it, think again.  SQL Server Management Server is a 32-bit app, as are most SQL test utilities.  Always create both keys for 64-bit target systems. Now that the keys exist, we can extract them into a .reg file. Fire up REGEDIT and browse to the following location:  HKLM\Software\Microsoft\MSSQLServer\Client\ConnectTo.  You can also search the registry for the string value of one of the server names (old or new). Right click on the “ConnectTo” label and choose “Export”.  Save with an appropriate name and location.  The resulting file should look something like this: Figure 5 – SQL01_Alias.reg Repeat the process with the location: HKLM\Software\Wow6432Node\Microsoft\MSSQLServer\Client\ConnectTo Note that if you have multiple alias entries, ALL of the entries will be exported.  In that case, you can edit the file and remove the extra aliases. You can edit the files together into a single file.  Just leave a blank line between new keys like this: Figure 6 – SQL01_Alias_All.reg Of course if you have an automatic way to deploy, it makes sense to have an automatic way to Un-deploy.  To delete a registry key, simply edit the .reg file and replace the target with a “-“ sign like so. Figure 7 – SQL01_Alias_UNDO.reg Now we have the ability to move any database to any server without having to install or change any applications on any client server.  The whole process should be transparent to the applications, which makes planning and coordinating database moves a far simpler task.

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• How do you use blog content?

  - by fatherjack

  Do you write a blog, have you ever thought about it? I think people fall into one of a few categories when it comes to blogs, especially blogs with technical content. Writing articles furiously - daily, twice daily and reading dozens of others. Writing the odd piece of content and read plenty of others' output. Started a blog once and its fizzled out but reading lots. Thought about starting a blog someday but never got around to it, hopping into the occasional blog when a link or a Tweet takes them there. Never thought about writing one but often catching content from them when Google (or other preferred search engine) finds content related to their search. Now I am not saying that either of these is right or wrong, nor am I saying that anyone should feel any compulsion to be in any particular category. What I would say is that you as a blog reader have the power to move blog writers from one category to another. How, you might ask? How do I have any power over a blog writer? It is very simple - feedback. If you give feedback then the blog writer knows that they are reaching an audience, if there is no response then they we are simply writing down our thoughts for what could amount to nothing more than a feeble amount of exercise and a few more key stokes towards the onset of RSI. Most blogs have a mechanism to alert the writer when there are comments, and personally speaking, if an email is received saying there has been a response to a blog article then there is a rush of enthusiasm, a moment of excitement that someone is actually reading and considering the text that was submitted and made available for the whole world to read. I am relatively new to this blog game and could be in some extended honeymoon period as I have also recently been incorporated into the Simple Talk 'stable'. I can understand that once you get to the "Dizzy Heights of Ozar" (www.brentozar.com) then getting comments and feedback might not be such a pleasure and may even be rather more of a chore but that, I guess, is the price of fame. For us mere mortals starting out blogging, getting feedback (or even at the moment for me, simply the hope of getting feedback) is what keeps it going. The hope that you will pick a topic that hasn't been done recently by Brad McGehee, Grant Fritchey,  Paul Randall, Thomas LaRock or any one of the dozen of rock star bloggers listed here or others from SQLServerPedia and so on, and then do it well enough to be found, reviewed, or <shudder> (re)tweeted to bring more visitors is what we are striving for, along with the fact that the content we might produce is something that will be of benefit to others. There is only so much point to typing content that no-one is reading and putting it on a blog. You may as well just write it in a diary. A technical blog is not like, say, a blog covering photography techniques where the way to frame and take a picture stands true whether it was written last week, last year or last century - technical content goes sour, quite quickly. There isn't much call for articles about yesterdays technology unless its something that still applies to current versions too, so some content written no more than 2 years ago isn't worth having now. The combination of a piece of content that you know is going to not last long and the fact that no-one reads it is a strong force against writing anything else. Getting feedback counters that despair and gives a value to writing something new. I would say that any feedback is good but there are obviously comments that are just so negative or otherwise badly phrased that they would hasten the demise of a blog but, in general most feedback will encourage a writer. It may not be a comment that supports or agrees with the main theme of a post but if it generates discussion or opens up a previously unexplored viewpoint it is contributing to the blog and is therefore encouraging to the writer. Even if you only say "thank you" before you leave a blog, having taken a section of script to use for yourself or having been given a few links to some content that has widened your knowledge it will be so welcome to the blog owner. Isn't it also the decent thing to do, acknowledging that you have benefited from another's efforts?

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• What Counts For a DBA: Simplicity

  - by Louis Davidson

  Too many computer processes do an apparently simple task in a bizarrely complex way. They remind me of this strip by one of my favorite artists: Rube Goldberg. In order to keep the boss from knowing one was late, a process is devised whereby the cuckoo clock kisses a live cuckoo bird, who then pulls a string, which triggers a hat flinging, which in turn lands on a rod that removes a typewriter cover…and so on. We rely on creating automated processes to keep on top of tasks. DBAs have a lot of tasks to perform: backups, performance tuning, data movement, system monitoring, and of course, avoiding being noticed.  Every day, there are many steps to perform to maintain the database infrastructure, including: checking physical structures, re-indexing tables where needed, backing up the databases, checking those backups, running the ETL, and preparing the daily reports and yes, all of these processes have to complete before you can call it a day, and probably before many others have started that same day. Some of these tasks are just naturally complicated on their own. Other tasks become complicated because the database architecture is excessively rigid, and we often discover during “production testing” that certain processes need to be changed because the written requirements barely resembled the actual customer requirements.   Then, with no time to change that rigid structure, we are forced to heap layer upon layer of code onto the problematic processes. Instead of a slight table change and a new index, we end up with 4 new ETL processes, 20 temp tables, 30 extra queries, and 1000 lines of SQL code.  Report writers then need to build reports and make magical numbers appear from those toxic data structures that are overly complex and probably filled with inconsistent data. What starts out as a collection of fairly simple tasks turns into a Goldbergian nightmare of daily processes that are likely to cause your dinner to be interrupted by the smartphone doing the vibration dance that signifies trouble at the mill. So what to do? Well, if it is at all possible, simplify the problem by either going into the code and refactoring the complex code to simple, or taking all of the processes and simplifying them into small, independent, easily-tested steps.  The former approach usually requires an agreement on changing underlying structures that requires countless mind-numbing meetings; while the latter can generally be done to any complex process without the same frustration or anger, though it will still leave you with lots of steps to complete, the ability to test each step independently will definitely increase the quality of the overall process (and with each step reporting status back, finding an actual problem within the process will be definitely less unpleasant.) We all know the principle behind simplifying a sequence of processes because we learned it in math classes in our early years of attending school, starting with elementary school. In my 4 years (ok, 9 years) of undergraduate work, I remember pretty much one thing from my many math classes that I apply daily to my career as a data architect, data programmer, and as an occasional indentured DBA: “show your work”. This process of showing your work was my first lesson in simplification. Each step in the process was in fact, far simpler than the entire process.  When you were working an equation that took both sides of 4 sheets of paper, showing your work was important because the teacher could see every step, judge it, and mark it accordingly.  So often I would make an error in the first few lines of a problem which meant that the rest of the work was actually moving me closer to a very wrong answer, no matter how correct the math was in the subsequent steps. Yet, when I got my grade back, I would sometimes be pleasantly surprised. I passed, yet missed every problem on the test. But why? While I got the fact that 1+1=2 wrong in every problem, the teacher could see that I was using the right process. In a computer process, the process is very similar. We take complex processes, show our work by storing intermediate values, and test each step independently. When a process has 100 steps, each step becomes a simple step that is tested and verified, such that there will be 100 places where data is stored, validated, and can be checked off as complete. If you get step 1 of 100 wrong, you can fix it and be confident (that if you did your job of testing the other steps better than the one you had to repair,) that the rest of the process works. If you have 100 steps, and store the state of the process exactly once, the resulting testable chunk of code will be far more complex and finding the error will require checking all 100 steps as one, and usually it would be easier to find a specific needle in a stack of similarly shaped needles.  The goal is to strive for simplicity either in the solution, or at least by simplifying every process down to as many, independent, testable, simple tasks as possible.  For the tasks that really can’t be done completely independently, minimally take those tasks and break them down into simpler steps that can be tested independently.  Like working out division problems longhand, have each step of the larger problem verified and tested.

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• Becoming A Great Developer

  - by Lee Brandt

  Image via Wikipedia I’ve been doing the whole programming thing for awhile and reading and watching some of the best in the business. I have come to notice that the really great developers do a few things that (I think) makes them great. Now don’t get me wrong, I am not saying that I am one of these few. I still struggle with doing some of the things that makes one great at development. Coincidently, many of these things also make you a better person period. Believe That Guidance Is Better Than Answers This is one I have no problem with. I prefer guidance any time I am learning from another developer. Answers may get you going, but guidance will leave you stranded. At some point, you will come across a problem that can only be solved by thinking for yourself and this is where that guidance will really come in handy. You can use that guidance and extrapolate whatever technology to salve that problem (if it’s the right tool for solving that problem). The problem is, lots of developers simply want someone to tell them, “Do this, then this, then set that, and write this.” Favor thinking and learn the guidance of doing X and don’t ask someone to show you how to do X, if that makes sense. Read, Read and Read If you don’t like reading, you’re probably NOT going to make it into the Great Developer group. Great developers read books, they read magazines and they read code. Open source playgrounds like SourceForge, CodePlex and GitHub, have made it extremely easy to download code from developers you admire and see how they do stuff. Chances are, if you read their blog too, they’ll even explain WHY they did what they did (see “Guidance” above). MSDN and Code Magazine have not only code samples, but explanations of how to use certain technologies and sometimes even when NOT to use that same technology. Books are also out on just about every topic. I still favor the less technology centric books. For instance, I generally don’t buy books like, “Getting Started with Jiminy Jappets”. I look for titles like, “How To Write More Effective Code” (again, see guidance). The Addison-Wesley Signature Series is a great example of these types of books. They teach technology-agnostic concepts. Head First Design Patterns is another great guidance book. It teaches the "Gang Of Four" Design Patterns in a very easy-to-understand, picture-heavy way (I LIKE pictures). Hang Your Balls Out There Even though the advice came from a 3rd-shift Kinko’s attendant, doesn’t mean it’s not sound advice. Write some code and put it out for others to read, criticize and castigate you for. Understand that there are some real jerks out there who are absolute geniuses. Don’t be afraid to get some great advice wrapped in some really nasty language. Try to take what’s good about it and leave what’s not. I have a tough time with this myself. I don’t really have any code out there that is available for review (other than my demo code). It takes some guts to do, but in the end, there is no substitute for getting a community of developers to critique your code and give you ways to improve. Get Involved Speaking of community, the local and online user groups and discussion forums are a great place to hear about technologies and techniques you might never come across otherwise. Mostly because you might not know to look. But, once you sit down with a bunch of other developers and start discussing what you’re interested in, you may open up a whole new perspective on it. Don’t just go to the UG meetings and watch the presentations either, get out there and talk, socialize. I realize geeks weren’t meant to necessarily be social creatures, but if you’re amongst other geeks, it’s much easier. I’ve learned more in the last 3-4 years that I have been involved in the community that I did in my previous 8 years of coding without it. Socializing works, even if socialism doesn’t. Continuous Improvement Lean proponents might call this “Kaizen”, but I call it progress. We all know, especially in the technology realm, if you’re not moving ahead, you’re falling behind. It may seem like drinking from a fire hose, but step back and pick out the technologies that speak to you. The ones that may you’re little heart go pitter-patter. Concentrate on those. If you’re still overloaded, pick the best of the best. Just know that if you’re not looking at the code you wrote last week or at least last year with some embarrassment, you’re probably stagnating. That’s about all I can say about that, cause I am all out of clichés to throw at it. :0) Write Code Great painters paint, great writers write, and great developers write code. The most sure-fire way to improve your coding ability is to continue writing code. Don’t just write code that your work throws on you, pick that technology you love or are curious to know more about and walk through some blog demo examples. Take the language you use everyday and try to get it to do something crazy. Who knows, you might create the next Google search algorithm! All in all, being a great developer is about finding yourself in all this code. If it is just a job to you, you will probably never be one of the “Great Developers”, but you’re probably okay with that. If, on the other hand, you do aspire to greatness, get out there and GET it. No one’s going hand it to you.

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• Changing the sequencing strategy for File/Ftp Adapter

  - by [email protected]

  The File/Ftp Adapter allows the user to configure the outbound write to use a sequence number. For example, if I choose address-data_%SEQ%.txt as the FileNamingConvention, then all my files would be generated as address-data_1.txt, address-data_2.txt,...and so on. But, where does this sequence number come from? The answer lies in the "control directory" for the particular adapter project(or scenario). In general, for every project that use the File or Ftp Adapter, a unique directory is created for book keeping purposes. And since this control directory is required to be unique, the adapter uses a digest to make sure that no two control directories are the same. For example, for my FlatStructure sample, the control information for my project would go under FMW_HOME/user_projects/domains/soainfra/fileftp/controlFiles/[DIGEST]/outbound where the value of DIGEST would differ from one project to another. If you look under this directory, you will see a file control_ob.properties and this is where the sequence number is maintained. Please note that the sequence number is maintained in binary form and you hence you might need a hex editor to view its content. You will also see another zero byte file, SEQ_nnn, but, ignore that for now. We'll get to it some other time. For now, please remember that this extra file is maintained as a backup. One of the challenges faced by the adapter runtime is to guard all writes to the control files so no two threads inadverently try to update them at the same time. And, it does so with the help of a "Mutex". For now, please remember that the mutex comes in different flavors: In-memory DB-based Coherence-based User-defined Again, we will talk about these mutexes some other time. Please note that there might be scenarios, particularly under heavy load, where the mutex might become a bottleneck. The adapter, however,  allows you to change the configuration so that the adapter sequence value comes from a database sequence or a stored procedure and in such situation, the mutex is acually by-passed and thereby resulting in better throughputs. In later releases, the behavior of the adapter would be defaulted to use a db-sequence.  The simplest way to achieve this is by switching your JNDI for the outbound JCA file to use "eis/HAFileAdapter" as shown   But, what does this do? Internally, the adapter runtime creates a sequence on the oracle database. For example, if you do a "select * from user_sequences" in your soa-infra schema, you will see a new sequence being created with name as SEQ_<GUID>__ where the GUID will differ from one project to another. However, if you want to use your own sequence, then it would require you to add a new property to your JCA file called SequenceName as shown below. Please note that you will need to create this sequence on your soainfra schema beforehand.     But, what if we use DB2 or MSSQL Server as the dehydration support? DB2 supports sequences natively but MSSQL Server does not. So, the adapter runtime uses a natively generated sequence for DB2, but, for MSSQL server, the adapter relies on a stored procedure that ships with the product. If you wish to achieve the same result for SOA Suite running DB2 as the dehydration store, simply change your connection factory JNDI name in the JCA file to eis/HAFileAdapterDB2 and for MSSQL, please use eis/HAFileAdapterMSSQL. And, if you wish to use a stored procedure other than the one that ships with the product, you will need to rely on binding properties to override the adapter behavior. Particularly, you will need to instruct the adapter that you wish to use a stored procedure as shown:       Please note that if you're using the File/Ftp Adapter in Append mode, then the adapter runtime degrades the mutex to use pessimistic locks as we don't want writers from different nodes to append to the same file at the same time.                    

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• Thread.Interrupt Is Evil

  - by Alois Kraus

  Recently I have found an interesting issue with Thread.Interrupt during application shutdown. Some application was crashing once a week and we had not really a clue what was the issue. Since it happened not very often it was left as is until we have got some memory dumps during the crash. A memory dump usually means WindDbg which I really like to use (I know I am one of the very few fans of it).  After a quick analysis I did find that the main thread already had exited and the thread with the crash was stuck in a Monitor.Wait. Strange Indeed. Running the application a few thousand times under the debugger would potentially not have shown me what the reason was so I decided to what I call constructive debugging. I did create a simple Console application project and try to simulate the exact circumstances when the crash did happen from the information I have via memory dump and source code reading. The thread that was  crashing was actually MS code from an old version of the Microsoft Caching Application Block. From reading the code I could conclude that the main thread did call the Dispose method on the CacheManger class which did call Thread.Interrupt on the cache scavenger thread which was just waiting for work to do. My first version of the repro looked like this   static void Main(string[] args) { Thread t = new Thread(ThreadFunc) { IsBackground = true, Name = "Test Thread" }; t.Start(); Console.WriteLine("Interrupt Thread"); t.Interrupt(); } static void ThreadFunc() { while (true) { object value = Dequeue(); // block until unblocked or awaken via ThreadInterruptedException } } static object WaitObject = new object(); static object Dequeue() { object lret = "got value"; try { lock (WaitObject) { } } catch (ThreadInterruptedException) { Console.WriteLine("Got ThreadInterruptException"); lret = null; } return lret; } I do start a background thread and call Thread.Interrupt on it and then directly let the application terminate. The thread in the meantime does plenty of Monitor.Enter/Leave calls to simulate work on it. This first version did not crash. So I need to dig deeper. From the memory dump I did know that the finalizer thread was doing just some critical finalizers which were closing file handles. Ok lets add some long running finalizers to the sample. class FinalizableObject : CriticalFinalizerObject { ~FinalizableObject() { Console.WriteLine("Hi we are waiting to finalize now and block the finalizer thread for 5s."); Thread.Sleep(5000); } } class Program { static void Main(string[] args) { FinalizableObject fin = new FinalizableObject(); Thread t = new Thread(ThreadFunc) { IsBackground = true, Name = "Test Thread" }; t.Start(); Console.WriteLine("Interrupt Thread"); t.Interrupt(); GC.KeepAlive(fin); // prevent finalizing it too early // After leaving main the other thread is woken up via Thread.Abort // while we are finalizing. This causes a stackoverflow in the CLR ThreadAbortException handling at this time. } With this changed Main method and a blocking critical finalizer I did get my crash just like the real application. The funny thing is that this is actually a CLR bug. When the main method is left the CLR does suspend all threads except the finalizer thread and declares all objects as garbage. After the normal finalizers were called the critical finalizers are executed to e.g. free OS handles (usually). Remember that I did call Thread.Interrupt as one of the last methods in the Main method. The Interrupt method is actually asynchronous and does wake a thread up and throws a ThreadInterruptedException only once unlike Thread.Abort which does rethrow the exception when an exception handling clause is left. It seems that the CLR does not expect that a frozen thread does wake up again while the critical finalizers are executed. While trying to raise a ThreadInterrupedException the CLR goes down with an stack overflow. Ups not so nice. Why has this nobody noticed for years is my next question. As it turned out this error does only happen on the CLR for .NET 4.0 (x86 and x64). It does not show up in earlier or later versions of the CLR. I have reported this issue on connect here but so far it was not confirmed as a CLR bug. But I would be surprised if my console application was to blame for a stack overflow in my test thread in a Monitor.Wait call. What is the moral of this story? Thread.Abort is evil but Thread.Interrupt is too. It is so evil that even the CLR of .NET 4.0 contains a race condition during the CLR shutdown. When the CLR gurus can get it wrong the chances are high that you get it wrong too when you use this constructs. If you do not believe me see what Patrick Smacchia does blog about Thread.Abort and List.Sort. Not only the CLR creators can get it wrong. The BCL writers do sometimes have a hard time with correct exception handling as well. If you do tell me that you use Thread.Abort frequently and never had problems with it I do suspect that you do not have looked deep enough into your application to find such sporadic errors.

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