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• Emulating a transaction-safe SEQUENCE in MySQL

  - by Michael Pliskin

  We're using MySQL with InnoDB storage engine and transactions a lot, and we've run into a problem: we need a nice way to emulate Oracle's SEQUENCEs in MySQL. The requirements are: - concurrency support - transaction safety - max performance (meaning minimizing locks and deadlocks) We don't care if some of the values won't be used, i.e. gaps in sequence are ok. There is an easy way to archieve that by creating a separate InnoDB table with a counter, however this means it will take part in transaction and will introduce locks and waiting. I am thinking to try a MyISAM table with manual locks, any other ideas or best practices?

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• Operator() as a subscript (C++)

  - by Ivan Gromov

  I use operator() as a subscript operator this way: double CVector::operator() (int i) const { if (i >= 0 && i < this->size) return this->data[i]; else return 0; } double& CVector::operator() (int i) { return (this->data[i]); } It works when I get values, but I get an error when I try to write assign a value using a(i) = 1; UPD: Error text: Unhandled exception at 0x651cf54a (msvcr100d.dll) in CG.exe: 0xC0000005: Access violation reading location 0xccccccc0.

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• Accessing an RSS feed in Flex, works when run from Flash Builder 4, but not when the project is onli

  - by ben

  Hey guys, In my Flex 4 app, I access an RSS feed (I'm using http://news.ycombinator.com/rss as a dummy). It works okay when I run it from Flash Builder 4, but if I export the project and upload it, I get the following error when it tries to load the RSS feed: Error #2044: Unhandled securityError:. text=Error #2048: Security sandbox violation: my_website_url cannot load data from http://news.ycombinator.com/rss. What could be causing this error? Shouldn't RSS be able to be accessed from anywhere? Thanks for reading.

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• Write a network simulator for fun

  - by Jono

  I want to write my own network simulator, for fun and for personal challenge. I hope to learn both new programming techniques, and a little bit more about networking. Previous object-oriented attempts ended very quickly, but I've recently downloaded and played with Microsoft's Axum (a new version was released today) and their Concurrency and Co-ordination Runtime. As I come from a very OO dominant background, I had never heard of Actor-oriented programming before; now it seems I've had my head in the sand until Scala and F# brought the paradigm to me. My questions are: a) is actor-oriented programming a better choice than object-oriented programming for this task, and if so b) where is a good place to start learning actor-oriented design?

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• What do you read?

  - by sixtyfootersdude

  I have almost finished reading all the articles on Joel on software. I am a new developer and hoping to get something interesting to read. Here is what is currently on my list: Java Concurrency in Practice by Brian Goetz sed & awk by Dougherty & Robbins (O'Reilly) The Pragmatic Programmer by Andrew Hunt and David Thomas Head First Design Patterns Can anyone suggest anything else? Would especially like something similar to Joel. Something that is a bit edgy but informative. Pragmatic programmer has some key concepts but is a bit dry.

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• Does this popup view violate HIGS?

  - by brettr

  Will using a popup view to present a comment submission form violate the HIGS? I may have one popup with selections that goes to the final popup. Two popups back to back. This is more similar to a modal type of view than an alert or action sheet as described by the HIGS: http://developer.apple.com/iphone/library/documentation/UserExperience/Conceptual/MobileHIG/ModalViews/ModalViews.html#//apple_ref/doc/uid/TP40006556-CH11-SW1 under the section 'Using Modal Views'. Basically the type of view I'm shooting for is a combination of an alert with a custom view. It's sort of a mini view since it will be centered in the middle of the screen but not take up all of the viewing area. I'm fairly sure that is a violation however, but I'm looking for a few opinions on it. I believe what needs to happen is use a modal view, which will cover the entire view.

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• Why hasn't functional programming taken over yet?

  - by pankrax

  I've read some texts about declarative/functional programming (languages), tried out Haskell as well as written one myself. From what I've seen, functional programming has several advantages over the classical imperative style: Stateless programs; No side effects Concurrency; Plays extremely nice with the rising multi-core technology Programs are usually shorter and in some cases easier to read Productivity goes up (example: Erlang) Imperative programming is a very old paradigm (as far as I know) and possibly not suitable for the 21st century Why are companies using or programs written in functional languages still so "rare"? Why, when looking at the advantages of functional programming, are we still using imperative programming languages? Maybe it was too early for it in 1990, but today?

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• does it make sense to send password information during email communication from websites

  - by Samuel

  Most of the online sites on registration do send a link to activate the site and on any further correspondence with the end user they provide information about the site and also provide the login credentials with password in clear text (as given below) Username - [email protected] Password - mysecretpassword What would you do in such a case? From a usability perspective does it make sense to send the password information in clear text or should you just avoid sending this information. I was under the impression that most of the passwords are MD5 hashed before storing in the database and hence the service provider will not have any access to clear text passwords, is this a security violation?

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• Constructor return value

  - by Ivan Gromov

  Could you tell me what is wrong with my class constructor? Code: CVector::CVector (int size_) { if (size_ > 0) { this->size = size_; this->data = new double[size]; for (int i = 0; i < size; i++) { (*this)(i) = i; } } cout << "constructor end" << endl; return; } Usage example: tvector = CVector(6); I get an access violation after "constructor end" output.

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• mysql ON DUPLICATE KEY UPDATE

  - by julio

  Hi-- I'm stuck on a mySQL query using ON DUPLICATE KEY UPDATE. I'm getting the error: mySQL Error: 1062 - Duplicate entry 'hr2461809-3' for key 'fname' The table looks like this: id int(10) NOT NULL default '0', picid int(10) unsigned NOT NULL default '0', fname varchar(255) NOT NULL default '', type varchar(5) NOT NULL default '.jpg', path varchar(255) NOT NULL default '', PRIMARY KEY (id), UNIQUE KEY fname (fname), KEY picid (propid) ) ENGINE=MyISAM DEFAULT CHARSET=utf8; And the query that's breaking is this: INSERT INTO images SET picid=732, fname='hr2461809-3', path='pictures/' ON DUPLICATE KEY UPDATE picid=732, fname='hr2461809-3', path='pictures/' I'm using a very similar query elsewhere in the app with no issues. I'm not sure why this one breaks. I expected that when the UNIQUE KEY on fname gets violated, that it would simply update the row where the violation occurred? Thanks for any help

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• Is it really wrong to version documents using CouchDB's behaviour?

  - by Tomas Sedovic

  This is one of those "I know I shouldn't do this but it's oh so convenient." questions. Sorry about that. I plan to use CouchDB for storing a bunch of documents and keeping their entire revision history. CouchDB does the versioning automatically, but it is strongly discouraged for programmer's use: "You cannot rely on document revisions for any other purpose than concurrency control." From what I've found on the CouchDB wiki, the versions can get deleted either during compaction or during replication. As far as I can tell, Compaction must always be triggered manually and Replication occurs only when there's more than one database server. The question is: if I won't run compaction and will use only single database instance for my documents, can I just use CouchDB's document versioning and expect it to work? What other problems I might run into? E.g. does not running compaction hurt the performance or consume significantly more disk space (than if I did handle the versioning manually)?

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• MaximumErrorCount has now effect

  - by Rob Bowman

  Hi I'm quite new to SSIS - using 2008 version. I have a job that uses a few data flow tasks. On the third one I'm getting a primary key violation on the last row that it needs to insert, but only sometimes! I'd like to ignore this problem for now and let the job continue. I have set the MaximumErrorCount property to 10 for the DataFlowTaks, the SequenceContainer and for the Package but still taks fails and this causes the package to stop. Could anyone please advise how I can get the package to ignore the error? Thanks Rob.

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• Threading Problems in ActionScript 2.0?

  - by yar

  Is it possible to have concurrency problems (thread competition) in an onEnterFrame method in ActionScript 2.0? I have written this cheesy code as a guard: if (!busy) { // I suspect some threading problems: is that even possible in flash busy = true; movePanels(); busy = false; } but this is no assurance against thread competition. If so, how can I do a basic semaphore/lock? Note: I suspect threading problems in my app, but if they're impossible, I'll check my code differently.

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• How should flushing be handled in a doctrine EntityManager instance shared across different services in symfony2?

  - by Jbm

  I have defined several services in symfony 2 which persist changes to the database. These services have the doctrine instance as one of their dependencies: a.given.service: class: Acme\TestBundle\Service\AGivenService arguments: [@doctrine] If I have two different services and both of them persist objects through the EntityManager, which is obtained like this from the doctrine instance: $em = $doctrine->getEntityManager(); Would all services always share the same EntityManager? If so, how should I handle flushing if I wanted to handle all the changes in a single transaction? I have checked this: http://docs.doctrine-project.org/projects/doctrine-orm/en/2.0.x/reference/transactions-and-concurrency.html and it explains how to handle different transactions in a request, but I want to achieve the opposite, which is having different changes in different services handled as a single transaction. Is there a better approach to handle multiple changes in different services? For now my best bet is having a front-end service in charge of calling the other services and doing the flushing afterwards. Backend services would persist objects but would not do any flushing.

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• Tips for measuring the parallelism speed-up in multi-core development.

  - by fnCzar

  I have read many of the good questions and answers around multi-core programming how-tos etc. I am familiar with concurrency, IPC, MPI etc but what I need is advice on how to measure speed-up which will help in making a business case of spending the time to write such code. Please don't answer with "well run it with single-core code then multi-core code and figure out the difference". This is neither a scientific nor a reliable way to measure performance improvement. If you know of tools that will do some of the heavy lifting please mention them. Answers pertaining to methodology will be more fitting but listing tools is ok as well.

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• Is Microsoft CCR gaining any traction?

  - by spender

  Microsoft's Concurrency and Coordination Runtime quite literally saved a project that was running into major issues with deadlocking. Since then I find that I use it more and more frequently for almost anything that requires asynchronous coding producing results that run lighter and faster than before. I can honestly state that it has transformed the way I think about multithread/multicore dev. Despite my personal love for CCR, there appears to be very little buzz surrounding it on the web and was wondering if anyone can offer any reason for this. Are there better alternatives, or is it a lack of promotion from MS, or are people simply happy with the existing tools?

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• When is porting data from MySQL to CouchDB NOT advisable? Seeking cautionary tales

  - by dan

  I've dabbled in CouchDB and I have pretty good MySQL experience. I've also created one production application that uses both. I like MySQL but I've run into scaling/concurrency issues with MySQL that CouchDB advertises itself as a general solution for. The problem is that I have MySQL based applications that are pretty huge, and I don't really know whether it would be a good idea or not to try to port them over to a CouchDB datastore. I don't want to put in a lot of time and effort only to find out that my application is really not a good fit for CouchDB. Is there any sort of informed consensus on when porting a MySQL based app to CouchDB is NOT advisable? Any cautionary tales? I think CouchDB is really cool and want to use it more. I'd also like to know ahead of time what specific types of data querying scenarios CouchDB is really not good for, or if CouchDB can really replace MySQL for all the applications I create going forward.

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• SQL Server Composite Primary Keys

  - by Colin

  I am attempting to replace all records for a give day in a certain table. The table has a composite primary key comprised of 7 fields. One such field is date. I have deleted all records which have a date value of 2/8/2010. When I try to then insert records into the table for 2/8/2010, I get a primary key violation. The records I am attempting to insert are only for 2/8/2010. Since date is a component of the PK, shouldn't there be no way to violate the constraint as long as the date I'm inserting is not already in the table? Thanks in advance.

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• Can we view objets in the JVM memory?

  - by Sebastien Lorber

  Hey, At work we found that on some instances (particulary the slow ones) we have a different behaviour, acquired at the reboot. We guess a cache is not initialized correctly, or maybe a concurrency problem... Anyway it's not reproductible in any other env than production. We actually don't have loggers to activate... it's an old component... Thus i'd like to know if there are tools that can help us to see the different objets present in the JVM memory in order to check the content of the cache... Thank you!

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• Arguments against Create or Update

  - by Nix

  Recently someone stated that they thought all Creates should be CreateOrUpdates. Instinctively i thought bad, but now I am trying to find out if I have any grounds. Situation interface IService{ void Create(Object a); void Update(Object a); } or interface IService{ void CreateOrUpdate(Object a); } My first thought is if you implemented everything CreateOrUpdate then you have no control if someone accidentally sends you wrong data, or concurrency issues where someone changes a "primary" field right before you call update.... But if you remove those cases, are there any other cons?

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• ORACLE -1401 error

  - by Sachin Chourasiya

  I have a stored procedure in Oracle 9i which inserts records in a table. The table has a primary key built to ensure duplicte rows doesnot exists. I am trying to insert a record by calling this stored procedure and it works first time properly. I am again trying to insert a duplicate record and expecting unique constraint violation error. But I am getting ORA-01401 inserted value too large for column I knew its meaning but my query is , if the value inserted is really large then how it got successful in the first attempt.

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• Will my app get rejected because of this ???

  - by A for Alpha

  hi guys... i am developing a ebook reader app for iPad and i am facing a issue related to the design aspects of the bookshelf. I am posting a sample photo of my bookshelf here. I want the book shelf to have a horizontal navigation similar to that of the iBooks. Will this come under violation of Apple's HIG?? Will they consider this design to be a imitation of their iBooks design and reject it?? I'm worried...

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• When is BIG, big enough for a database?

  - by David ???

  I'm developing a Java application that has performance at its core. I have a list of some 40,000 "final" objects, i.e., I have an initialization input data of 40,000 vectors. This data is unchanged throughout the program's run. I am always preforming lookups against a single ID property to retrieve the proper vectors. Currently I am using a HashMap over a sub-sample of a 1,000 vectors, but I'm not sure it will scale to production. When is BIG, actually big enough for a use of DB? One more thing, an SQLite DB is a viable option as no concurrency is involved, so I guess the "threshold" for db use, is perhaps lower.

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• How to check if a pointer is null in C++ Visual 2010

  - by mariomario

  I am having problems here if I want to check if eerste points to nothing i get Blockquote Unhandled exception at 0x003921c6 in Bank.exe: 0xC0000005: Access violation reading location 0xccccccd0. and i am kinda wondering why he justs skips the if statement or doens't stop when the object eerste points to nothing Bank::Bank() { LijstElement *eerste = NULL; LijstElement *laatste = NULL; } Rekening * Bank::getRekening(int rekNr) { if(NULL != eerste) { LijstElement *nummer = eerste; while(nummer->volgende!= NULL) { Rekening *een = nummer->getRekening(); if(een->getRekNr()==rekNr) { return een; } else { nummer = nummer->volgende; } } } return NULL; }

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• How to create unique user key

  - by Grayson Mitchell

  Scenario: I have a fairly generic table (Data), that has an identity column. The data in this table is grouped (lets say by city). The users need an identifier in order for printing on paper forms, etc. The users can only access their cites data, so if they use the identity column for this purpose they will see odd numbers (e.g. a 'New York' user might see 1,37,2028... as the listed keys. Idealy they would see 1,2,3... (or something similar) The problem of course is concurrency, this being a web application you can't just have something like: UserId = Select Count(*)+1 from Data Where City='New York' Has anyone come up with any cunning ways around this problem?

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