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  • Why is postgresql update query so slow sometimes, even with index

    - by Matija
    i have a simple update query (foo column type is BOOLEAN (default false)): update tablename set foo = true where id = 234; which "id" is set to (primary) key, and if i run "explain analyze" i got: Index Cond: (id = 234) Total runtime: 0.358 ms but still, i have plenty of unexplained queries at slow log (pgfouine), which took more than 200s (?!): Times executed: 99, Av. duration (s): 70 can anyone please explain, whats the reason for that? (1.5 mio rows in table, postgresql 8.4)

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  • testing a shellcode...

    - by kmitnick
    hey folks, I have this piece of code to test a shellcode but I don't understand it so can anyone explain it to me??? forget about the assembly shellcode, what i want to understand is the C code char shellcode[] = "..."; int main(int argc, char **argv) { int (*func)(); func = (int (*)()) shellcode; (int)(*func)(); } I mean everything, what is the empty () ,please explain it as if you are explaining it to a beginner thnx all

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  • Compare associations between domain objects in Grails

    - by user303979
    I am not sure if I am going about this the best way, but I will try to explain what I am trying to do. I have the following domain classes class User { static hasMany = [goals: Goal] } So each User has a list of Goal objects. I want to be able to take an instance of User and return 5 Users with the highest number of matching Goal objects (with the instance) in their goals list. Can someone kindly explain how I might go about doing this?

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  • How do I check SQLite3 syntax?

    - by Benjamin Oakes
    Is there a way to check the syntax of a SQLite3 script without running it? Basically, I'm looking for the SQLite3 equivalent of ruby -c script.rb, perl -c script.pl, php --syntax-check script.php, etc. I've thought of using explain, but most of the scripts I'd like to check are kept around for reference purposes (and don't necessarily have an associated database). Using explain would also make it hard to use with something like Syntastic. (That is, I'm only wanting to check syntax, not semantics.)

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  • How does a javascript closure work ?

    - by e-satis
    Like the old Albert said : "If you can't explain it to a six-year old, you really don't understand it yourself.”. Well I tried to explain JS closures to a 27 years old friend and completely failed. Can anybody consider than I am 6 and strangely interested in that subject ? EDIT : I have seen the scheme example given in SO, and it did not help.

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  • Strange use of the index in Mysql

    - by user309067
    explain SELECT feed_objects.* FROM feed_objects WHERE (feed_objects.feed_id IN (165,160,159,158,157,153,152,151,150,149,148,147,129,128,127,126,125,124,122,121,120,119,118,117,116,115,114,113,111,110)) ; +----+-------------+--------------+------+---------------+------+---------+------+------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+--------------+------+---------------+------+---------+------+------+-------------+ | 1 | SIMPLE | feed_objects | ALL | by_feed_id | NULL | NULL | NULL | 188 | Using where | +----+-------------+--------------+------+---------------+------+---------+------+------+-------------+ Not used index 'by_feed_id' But when I point less than the values in the "WHERE" - everything is working right explain SELECT feed_objects.* FROM feed_objects WHERE (feed_objects.feed_id IN (165,160,159,158,157,153,152,151,150,149,148,147,129,128,127,125,124)) ; +----+-------------+--------------+-------+---------------+------------+---------+------+------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+--------------+-------+---------------+------------+---------+------+------+-------------+ | 1 | SIMPLE | feed_objects | range | by_feed_id | by_feed_id | 9 | NULL | 18 | Using where | +----+-------------+--------------+-------+---------------+------------+---------+------+------+-------------+ Used index 'by_feed_id' What is the problem?

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  • Simplifying const Overloading?

    - by templatetypedef
    Hello all- I've been teaching a C++ programming class for many years now and one of the trickiest things to explain to students is const overloading. I commonly use the example of a vector-like class and its operator[] function: template <typename T> class Vector { public: T& operator[] (size_t index); const T& operator[] (size_t index) const; }; I have little to no trouble explaining why it is that two versions of the operator[] function are needed, but in trying to explain how to unify the two implementations together I often find myself wasting a lot of time with language arcana. The problem is that the only good, reliable way that I know how to implement one of these functions in terms of the other is with the const_cast/static_cast trick: template <typename T> const T& Vector<T>::operator[] (size_t index) const { /* ... your implementation here ... */ } template <typename T> T& Vector<T>::operator[] (size_t index) { return const_cast<T&>(static_cast<const Vector&>(*this)[index]); } The problem with this setup is that it's extremely tricky to explain and not at all intuitively obvious. When you explain it as "cast to const, then call the const version, then strip off constness" it's a little easier to understand, but the actual syntax is frightening,. Explaining what const_cast is, why it's appropriate here, and why it's almost universally inappropriate elsewhere usually takes me five to ten minutes of lecture time, and making sense of this whole expression often requires more effort than the difference between const T* and T* const. I feel that students need to know about const-overloading and how to do it without needlessly duplicating the code in the two functions, but this trick seems a bit excessive in an introductory C++ programming course. My question is this - is there a simpler way to implement const-overloaded functions in terms of one another? Or is there a simpler way of explaining this existing trick to students? Thanks so much!

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  • How to free static member variable in C++?

    - by user299831
    Can anybody explain how to free memory of a static member Variable? In my understanding it can only be freed if all the instances of the class are destroyed. I am a little bit helpless at this point... Some Code to explain it: class ball { private: static SDL_Surface *ball_image; }; //FIXME: how to free static Variable? SDL_Surface* ball::ball_image = SDL_LoadBMP("ball.bmp");

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  • binary operator "<"

    - by md004
    Consider this expression as a "selection" control structure on integer "x": 0 < x < 10, with the intention that the structure returns TRUE if "x" is in the range 1..9. Explain why a compiler should not accept this expression. (In particular, what are the issues regarding the binary operator "<"? Explain how a prefix operator could be introduced so the expression can be successfully processed.

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  • Session Regeneration

    - by slier
    Hi guys I got some confusion with session handling in php Ok i know how to regenerate new session id in php by using session_regenerate_id(); The problem is i dont know why i should regenerate new session id I been goggling for some time and up to no avail No one explain why i need to generate new session id Can someone explain why i need to regenerate new session id? Thx in advance

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  • Dependency Properties

    - by developer
    Hi All, Can anybody explain me what a dependency property is in WPF and what is its use. I know there are a lot of tutorials on google for it, but they teach how to create a dependency property. I am confused as to where I would use it. I mean will I use it in XAML? If anybody could explain me in simple terms, that would be great.

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  • Java threads for the beginner

    - by Boba
    I've been trying to explain Java threading to a colleague who has never been exposed to multi-threaded applications, but apparently I'm not a very good teacher. Can anyone recommend a good online or offline resource that can explain threading in a simple, step-by-step manner? I know it's a complex topic, but surely there exists an article, book, or other explanation that can result in an "Aha! I get it, finally!" moment.

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  • what exactly is delegate in C#

    - by Learning.net
    Hi All, can somebody explain the use of delegate..I know that it is used to invoke methods at run time...but exactly what does it mean..can somebody explain it with some simple example, which will help a newcomer to understand delegate better

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  • SQLAuthority News – Amazon Gift Card Raffle for Beta Tester Feedback for NuoDB

    - by pinaldave
    As regular readers know I’ve been spending some time working with the NuoDB beta software. They contacted me last week and asked if I would give you a chance to try their new web-based console for their scalable, SQL-compliant database. They have just put out their final beta release, Beta 9.  It contains a preview of a new web-based “NuoConsole” that will replace and extend the functionality of their current desktop version.  I haven’t spent any time with the new console yet but a really quick look tells me it should make it easier to do deeper monitoring than the older one. It also looks like they have added query-level reporting through the console. I will try to play with it soon. NuoDB is doing a last, big push to get some more feedback from developers before they release their 1.0 product sometime in the next several weeks. Since the console is new, they are especially interested in some quick feedback on it before general availability. For SQLAuthority readers only, NuoDB will raffle off three $50 Amazon gift cards in exchange for your feedback on the NuoConsole preview. Here’s how to Enter Download NuoDBeta 9 here You must build a domain before you can start the console. Launch the Web Console. Windows Code: start java -jar jarnuodbwebconsole.jar Mac, Linux, Solaris, Unix Code: java -jar jar/nuodbwebconsole.jar Access the Web Console: Code: http://localhost:8080 When you have tried it out, go to a short (8 question) survey to enter the raffle Click here for the survey You must complete the survey before midnight EDT on October 17, 2012. Here’s what else they are saying about this last beta before general availability: Beta 9 now supports the Zend PHP framework so that PHP developers can directly integrate web applications with NuoDB. Multi-threaded HDFS support – NuoDB Storage Managers can now be configured to persist data to the high performance Hadoop distributed file system (HDFS). Beta 9 optimizes for multi-thread I/O streams at maximum performance. This enhancement allows users to make Hadoop their core storage with no extra effort which is a pretty cool idea. Improved Performance –On a single transaction node, Beta 9 offers performance comparable with MySQL and MariaDB. As additional nodes are added, NuoDB performance improves significantly at near linear scale. Query & Explain Plan Logging – Beta 9 introduces SQL explain plans for your queries. Qualify queries with the word “EXPLAIN” and NuoDB will respond with the details of the execution plan allowing performance optimization to SQL. Through the NuoConsole, you can now kill hung or long running queries. Java App Server Support – Beta 9 now supports leading Web JEE app servers including JBoss, Tomcat, and ColdFusion. They’ve also reported: Improved PHP/PDO drivers Support for Drupal Faster Ruby on Rails driver The Hibernate Dialect supports version 4.1 And good news for my readers: numerous SQL enhancements They will share the results of the web console feedback with me.  I’ll let you know how it goes. Also the winner of their last contest was Jaime Martínez Lafargue!  Do leave a comment here once you complete the survey.  Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: SQL Authority Tagged: NuoDB

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  • Testing a patch to the Rails mysql adapter

    - by Sleepycat
    I wrote a little monkeypatch to the Rails MySQLAdapter and want to package it up to use it in my other projects. I am trying to write some tests for it but I am still new to testing and I am not sure how to test this. Can someone help get me started? Here is the code I want to test: unless RAILS_ENV == 'production' module ActiveRecord module ConnectionAdapters class MysqlAdapter < AbstractAdapter def select_with_explain(sql, name = nil) explanation = execute_with_disable_logging('EXPLAIN ' + sql) e = explanation.all_hashes.first exp = e.collect{|k,v| " | #{k}: #{v} "}.join log(exp, 'Explain') select_without_explain(sql, name) end def execute_with_disable_logging(sql, name = nil) #:nodoc: #Run a query without logging @connection.query(sql) rescue ActiveRecord::StatementInvalid => exception if exception.message.split(":").first =~ /Packets out of order/ raise ActiveRecord::StatementInvalid, "'Packets out of order' error was received from the database. Please update your mysql bindings (gem install mysql) and read http://dev.mysql.com/doc/mysql/en/password-hashing.html for more information. If you're on Windows, use the Instant Rails installer to get the updated mysql bindings." else raise end end alias_method_chain :select, :explain end end end end Thanks.

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  • Why is MySQL with InnoDB doing a table scan when key exists and choosing to examine 70 times more ro

    - by andysk
    Hello, I'm troubleshooting a query performance problem. Here's an expected query plan from explain: mysql> explain select * from table1 where tdcol between '2010-04-13:00:00' and '2010-04-14 03:16'; +----+-------------+--------------------+-------+---------------+--------------+---------+------+---------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+--------------------+-------+---------------+--------------+---------+------+---------+-------------+ | 1 | SIMPLE | table1 | range | tdcol | tdcol | 8 | NULL | 5437848 | Using where | +----+-------------+--------------------+-------+---------------+--------------+---------+------+---------+-------------+ 1 row in set (0.00 sec) That makes sense, since the index named tdcol (KEY tdcol (tdcol)) is used, and about 5M rows should be selected from this query. However, if I query for just one more minute of data, we get this query plan: mysql> explain select * from table1 where tdcol between '2010-04-13 00:00' and '2010-04-14 03:17'; +----+-------------+--------------------+------+---------------+------+---------+------+-----------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+--------------------+------+---------------+------+---------+------+-----------+-------------+ | 1 | SIMPLE | table1 | ALL | tdcol | NULL | NULL | NULL | 381601300 | Using where | +----+-------------+--------------------+------+---------------+------+---------+------+-----------+-------------+ 1 row in set (0.00 sec) The optimizer believes that the scan will be better, but it's over 70x more rows to examine, so I have a hard time believing that the table scan is better. Also, the 'USE KEY tdcol' syntax does not change the query plan. Thanks in advance for any help, and I'm more than happy to provide more info/answer questions.

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  • ASP.NET MVC Patterns

    - by Sam Striano
    Hello, I am fairly new to MVC, but after playing with it (MVC 3/Razor), I am hooked. I have a few questions: 1) What is the best, or most widely used pattern to develop MVC apps in? Repository, DDD, UOW? 2) I am using the Entity Framework 4, so could some please explain to me or point me to a good source that will explain the Repository Pattern w/EF4? Doesn't EF4 take place as the business layer and the data access layer? Does the Repository Pattern even provide a benefit? 3) Also, one last question, could someone explain the whole relationship between the Controller, the Model and the View? I get the basics, but maybe a little more in depth of the correct way to use it. View Models - Say I have a view that displays customer info, and one that edits it, should I have a view model and an edit model, or can the be passed around? 4) Examples?? Thanks for the help up front, $("Sam") ** EDIT ** Am I on the right track here: Public Class HomeController Inherits System.Web.Mvc.Controller Function Index(ByVal id As Integer) As ActionResult Return View(New HomeModel) End Function <HttpPost()> _ Function Index(ByVal Model As HomeModel) As ActionResult Return View(Model) End Function End Class Public Class HomeModel Private _Repository As IRepository(Of Customer) Public Property Customer As Customer Public Sub New() End Sub Public Sub New(ByVal ID As Integer) _Repository = New CustomerRepository Customer = _Repository.GetByID(ID) End Sub End Class Public Interface IRepository(Of T) Function GetByID(ByVal ID As Integer) As T Sub Add(ByVal Entity As T) Sub Delete(ByVal Entity As T) End Interface Public Class CustomerRepository Implements IRepository(Of Customer) Public Sub Add(ByVal Entity As Customer) Implements IRepository(Of Customer).Add End Sub Public Sub Delete(ByVal Entity As Customer) Implements IRepository(Of Customer).Delete End Sub Public Function GetByID(ByVal ID As Integer) As Customer Implements IRepository(Of Customer).GetByID Return New Customer With {.ID = ID, .FirstName = "Sam", .LastName = "Striano"} End Function End Class Public Class Customer Public Property ID As Integer Public Property FirstName As String Public Property LastName As String End Class

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  • Natural problems to solve using closures

    - by m.u.sheikh
    I have read quite a few articles on closures, and, embarassingly enough, I still don't understand this concept! Articles explain how to create a closure with a few examples, but I don't see any point in paying much attention to them, as they largely look contrived examples. I am not saying all of them are contrived, just that the ones I found looked contrived, and I dint see how even after understanding them, I will be able to use them. So in order to understand closures, I am looking at a few real problems, that can be solved very naturally using closures. For instance, a natural way to explain recursion to a person could be to explain the computation of n!. It is very natural to understand a problem like computing the factorial of a number using recursion. Similarly, it is almost a no-brainer to find an element in an unsorted array by reading each element, and comparing with the number in question. Also, at a different level, doing Object-oriented programming also makes sense. So I am trying to find a number of problems that could be solved with or without closures, but using closures makes thinking about them and solving them easier. Also, there are two types to closures, where each call to a closure can create a copy of the environment variables, or reference the same variables. So what sort of problems can be solved more naturally in which of the closure implementations?

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  • Strange DataTable behaviour

    - by DocSnuggles
    There´s a strange behaviour in my code which I can´t explain... I have worked arround it but I´d like to know the reason of this behaviour. My Code: If dataset.Tables.Count > 0 Then Dim rows() As DataRow = dataset.Tables(0).Select("FileID = " + fileid.ToString) For Each row As DataRow In rows... the one and only table in dataset is: 18 1 1 testpara42 19 1 2 Para2 23 2 1 Para1 24 2 2 Para42 Where the colums are: ParamID - FileID - ParaPos - Paravalue. I want do filter it so that the only rows I get are the ones with the correct fileid... the result when the selection string is "FileID = 1" is an array with 2 rows... everything is fine... but the filter string "FileID = 2" will return 0 Rows... A filter like "FileID < 1" returns 2 Rows correctly. I really cant´t explain this od behaviour, maybe one of the community does. The Table does have more entries but the Filter string just works with the "FileID = 1" selection. Excuse my bad english. Please explain my mistake to me.

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  • How to create a readonly root linux: Can be mounted as writeable for persistent changes?

    - by Mr Anderson
    I'd like a read only file system that runs almost entirely in RAM but the compact flash or hardrive can be mounted and made writeable to make persistent changes. How do I do this on Linux? I've looked at several tutorials but none really explain how to create such a system with the option of being able to mount the storage device and make persistent changes. I looked at this so far: http://chschneider.eu/linux/thin_client/ I also looked on the old gentoo wiki but the article was very specific to Gentoo. I'll be using a debian based Linux but it would be nice I've someone could explain to me how to do this in pretty generic instructions ,that would work on any Linux distro. Thanks.

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