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• Getting deadlocks in MySQL

  - by at

  We're very frustratingly getting deadlocks in MySQL. It isn't because of exceeding a lock timeout as the deadlocks happen instantly when they do happen. Here's the SQL code that is executing on 2 separate threads (with 2 separate connections from the connection pool) that produces a deadlock: UPDATE Sequences SET Counter = LAST_INSERT_ID(Counter + 1) WHERE Sequence IS NULL Sequences table has 2 columns: Sequence and Counter The LAST_INSERT_ID allows us to retrieve this updated counter value as per MySQL's recommendation. That works perfect for us, but we get these deadlocks! Why are we getting them and how can we avoid them?? Thanks so much for any help with this.

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• How do I detect if I'm in a 'full screen' bash shell or GUI terminal window?

  - by Nick T

  I have some code in my .bashrc that sets the terminal window title using the currently running command and it works great in Unity, where the terminal is in a window. However, when I'm logging in with the Ctrl + Alt + F1 terminal (whatever it's called), my prompt gets filled with garbage that is various escape sequences that set the (nonexistent) window title. How can I detect from within a bash script if I'm in one or the other?

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• How to perform Cross Join with Linq

  - by berthin

  Cross join consists to perform a Cartesian product of two sets or sequences. The following example shows a simple Cartesian product of the sets A and B: A (a1, a2) B (b1, b2) => C (a1 b1,            a1 b2,            a2 b1,            a2, b2 ) is the Cartesian product's result. Linq to Sql allows using Cross join operations. Cross join is not equijoin, means that no predicate expression of equality in the Join clause of the query. To define a cross join query, you can use multiple from clauses. Note that there's no explicit operator for the cross join. In the following example, the query must join a sequence of Product with a sequence of Pricing Rules: 1: //Fill the data source 2: var products = new List<Product> 3: { 4: new Product{ProductID="P01",ProductName="Amaryl"}, 5: new Product {ProductID="P02", ProductName="acetaminophen"} 6: }; 7:  8: var pricingRules = new List<PricingRule> 9: { 10: new PricingRule {RuleID="R_1", RuleType="Free goods"}, 11: new PricingRule {RuleID="R_2", RuleType="Discount"}, 12: new PricingRule {RuleID="R_3", RuleType="Discount"} 13: }; 14: 15: //cross join query 16: var crossJoin = from p in products 17: from r in pricingRules 18: select new { ProductID = p.ProductID, RuleID = r.RuleID };   Below the definition of the two entities using in the above example.   1: public class Product 2: { 3: public string ProductID { get; set; } 4: public string ProductName { get; set; } 5: } 1: public class PricingRule 2: { 3: public string RuleID { get; set; } 4: public string RuleType { get; set; } 5: }   Doing this: 1: foreach (var result in crossJoin) 2: { 3: Console.WriteLine("({0} , {1})", result.ProductID, result.RuleID); 4: }   The output should be similar on this:   ( P01   -    R_1 )   ( P01   -    R_2 )   ( P01   -    R_3 )   ( P02   -    R_1 )   ( P02   -    R_2 )   ( P02   -    R_3) Conclusion Cross join operation is useful when performing a Cartesian product of two sequences object. However, it can produce very large result sets that may caused a problem of performance. So use with precautions :)

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• MSDN Article for the GetClusterCharacteristics Stored Procedure

  Here is an article I wrote for MSDN that introduces us to the GetClusterCharacteristics stored procedure in SQL Server Data Mining.  It gives us an insight into how the sequences within clusters are derived when using the Sequence Clustering algorithm. Link to article

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• State Transition Constraints

  Data Validation in a database is a lot more complex than seeing if a string parameter really is an integer. A commercial world is full of complex rules for sequences of procedures, of fixed or variable lifespans, Warranties, commercial offers and bids. All this requires considerable subtlety to prevent bad data getting in, and if it does, locating and fixing the problem. Joe Celko shows how useful a State transition graph can be, and how essential it can become with the time aspect added.

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• Perl moderne - L'essentiel des pratiques actuelles, une critique de djibril

  Ce Guide de survie est l'outil indispensable pour programmer en Perl aujourd'hui. Il présente les dernières évolutions de Perl 5 par ses versions 5.10 et 5.12, fortement empreintes de la version 6 en cours de finalisation. CONCIS ET MANIABLE : Facile à transporter, facile à utiliser - finis les livres encombrants ! PRATIQUE ET FONCTIONNEL : Plus de 350 séquences de code pour répondre aux situations les plus courantes et exploiter efficacement les fonctions et les bibliothèques d'un langage qui s'est radicalement modernisé.

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• Why doesn't my implementation of ElGamal work for long text strings?

  - by angstrom91

  I'm playing with the El Gamal cryptosystem, and my goal is to be able to encipher and decipher long sequences of text. I have come up with a method that works for short sequences, but does not work for long sequences, and I cannot figure out why. El Gamal requires the plaintext to be an integer. I have turned my string into a byte[] using the .getBytes() method for Strings, and then created a BigInteger out of the byte[]. After encryption/decryption, I turn the BigInteger into a byte[] using the .toByteArray() method for BigIntegers, and then create a new String object from the byte[]. This works perfectly when i call ElGamalEncipher with strings up to 129 characters. With 130 or more characters, the output produced from ElGamalDecipher is garbled. Can someone suggest how to solve this issue? Is this an issue with my method of turning the string into a BigInteger? If so, is there a better way to turn my string of text into a BigInteger and back? Below is my encipher/decipher code with a program to demonstrate the problem. import java.math.BigInteger; public class Main { static BigInteger P = new BigInteger("15893293927989454301918026303382412" + "2586402937727056707057089173871237566896685250125642378268385842" + "6917261652781627945428519810052550093673226849059197769795219973" + "9423619267147615314847625134014485225178547696778149706043781174" + "2873134844164791938367765407368476144402513720666965545242487520" + "288928241768306844169"); static BigInteger G = new BigInteger("33234037774370419907086775226926852" + "1714093595439329931523707339920987838600777935381196897157489391" + "8360683761941170467795379762509619438720072694104701372808513985" + "2267495266642743136795903226571831274837537691982486936010899433" + "1742996138863988537349011363534657200181054004755211807985189183" + "22832092343085067869"); static BigInteger R = new BigInteger("72294619754760174015019300613282868" + "7219874058383991405961870844510501809885568825032608592198728334" + "7842806755320938980653857292210955880919036195738252708294945320" + "3969657021169134916999794791553544054426668823852291733234236693" + "4178738081619274342922698767296233937873073756955509269717272907" + "8566607940937442517"); static BigInteger A = new BigInteger("32189274574111378750865973746687106" + "3695160924347574569923113893643975328118502246784387874381928804" + "6865920942258286938666201264395694101012858796521485171319748255" + "4630425677084511454641229993833255506759834486100188932905136959" + "7287419551379203001848457730376230681693887924162381650252270090" + "28296990388507680954"); public static void main(String[] args) { FewChars(); System.out.println(); ManyChars(); } public static void FewChars() { //ElGamalEncipher(String plaintext, BigInteger p, BigInteger g, BigInteger r) BigInteger[] cipherText = ElGamal.ElGamalEncipher("This is a string " + "of 129 characters which works just fine . This is a string " + "of 129 characters which works just fine . This is a s", P, G, R); System.out.println("This is a string of 129 characters which works " + "just fine . This is a string of 129 characters which works " + "just fine . This is a s"); //ElGamalDecipher(BigInteger c, BigInteger d, BigInteger a, BigInteger p) System.out.println("The decrypted text is: " + ElGamal.ElGamalDecipher(cipherText[0], cipherText[1], A, P)); } public static void ManyChars() { //ElGamalEncipher(String plaintext, BigInteger p, BigInteger g, BigInteger r) BigInteger[] cipherText = ElGamal.ElGamalEncipher("This is a string " + "of 130 characters which doesn’t work! This is a string of " + "130 characters which doesn’t work! This is a string of ", P, G, R); System.out.println("This is a string of 130 characters which doesn’t " + "work! This is a string of 130 characters which doesn’t work!" + " This is a string of "); //ElGamalDecipher(BigInteger c, BigInteger d, BigInteger a, BigInteger p) System.out.println("The decrypted text is: " + ElGamal.ElGamalDecipher(cipherText[0], cipherText[1], A, P)); } } import java.math.BigInteger; import java.security.SecureRandom; public class ElGamal { public static BigInteger[] ElGamalEncipher(String plaintext, BigInteger p, BigInteger g, BigInteger r) { // returns a BigInteger[] cipherText // cipherText[0] is c // cipherText[1] is d SecureRandom sr = new SecureRandom(); BigInteger[] cipherText = new BigInteger[2]; BigInteger pText = new BigInteger(plaintext.getBytes()); // 1: select a random integer k such that 1 <= k <= p-2 BigInteger k = new BigInteger(p.bitLength() - 2, sr); // 2: Compute c = g^k(mod p) BigInteger c = g.modPow(k, p); // 3: Compute d= P*r^k = P(g^a)^k(mod p) BigInteger d = pText.multiply(r.modPow(k, p)).mod(p); // C =(c,d) is the ciphertext cipherText[0] = c; cipherText[1] = d; return cipherText; } public static String ElGamalDecipher(BigInteger c, BigInteger d, BigInteger a, BigInteger p) { //returns the plaintext enciphered as (c,d) // 1: use the private key a to compute the least non-negative residue // of an inverse of (c^a)' (mod p) BigInteger z = c.modPow(a, p).modInverse(p); BigInteger P = z.multiply(d).mod(p); byte[] plainTextArray = P.toByteArray(); return new String(plainTextArray); } }

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• C#/.NET Little Wonders: Use Cast() and TypeOf() to Change Sequence Type

  - by James Michael Hare

  Once again, in this series of posts I look at the parts of the .NET Framework that may seem trivial, but can help improve your code by making it easier to write and maintain. The index of all my past little wonders posts can be found here. We’ve seen how the Select() extension method lets you project a sequence from one type to a new type which is handy for getting just parts of items, or building new items.  But what happens when the items in the sequence are already the type you want, but the sequence itself is typed to an interface or super-type instead of the sub-type you need? For example, you may have a sequence of Rectangle stored in an IEnumerable<Shape> and want to consider it an IEnumerable<Rectangle> sequence instead.  Today we’ll look at two handy extension methods, Cast<TResult>() and OfType<TResult>() which help you with this task. Cast<TResult>() – Attempt to cast all items to type TResult So, the first thing we can do would be to attempt to create a sequence of TResult from every item in the source sequence.  Typically we’d do this if we had an IEnumerable<T> where we knew that every item was actually a TResult where TResult inherits/implements T. For example, assume the typical Shape example classes: 1: // abstract base class 2: public abstract class Shape { } 3:  4: // a basic rectangle 5: public class Rectangle : Shape 6: { 7: public int Widtgh { get; set; } 8: public int Height { get; set; } 9: } And let’s assume we have a sequence of Shape where every Shape is a Rectangle… 1: var shapes = new List<Shape> 2: { 3: new Rectangle { Width = 3, Height = 5 }, 4: new Rectangle { Width = 10, Height = 13 }, 5: // ... 6: }; To get the sequence of Shape as a sequence of Rectangle, of course, we could use a Select() clause, such as: 1: // select each Shape, cast it to Rectangle 2: var rectangles = shapes 3: .Select(s => (Rectangle)s) 4: .ToList(); But that’s a bit verbose, and fortunately there is already a facility built in and ready to use in the form of the Cast<TResult>() extension method: 1: // cast each item to Rectangle and store in a List<Rectangle> 2: var rectangles = shapes 3: .Cast<Rectangle>() 4: .ToList(); However, we should note that if anything in the list cannot be cast to a Rectangle, you will get an InvalidCastException thrown at runtime.  Thus, if our Shape sequence had a Circle in it, the call to Cast<Rectangle>() would have failed.  As such, you should only do this when you are reasonably sure of what the sequence actually contains (or are willing to handle an exception if you’re wrong). Another handy use of Cast<TResult>() is using it to convert an IEnumerable to an IEnumerable<T>.  If you look at the signature, you’ll see that the Cast<TResult>() extension method actually extends the older, object-based IEnumerable interface instead of the newer, generic IEnumerable<T>.  This is your gateway method for being able to use LINQ on older, non-generic sequences.  For example, consider the following: 1: // the older, non-generic collections are sequence of object 2: var shapes = new ArrayList 3: { 4: new Rectangle { Width = 3, Height = 13 }, 5: new Rectangle { Width = 10, Height = 20 }, 6: // ... 7: }; Since this is an older, object based collection, we cannot use the LINQ extension methods on it directly.  For example, if I wanted to query the Shape sequence for only those Rectangles whose Width is > 5, I can’t do this: 1: // compiler error, Where() operates on IEnumerable<T>, not IEnumerable 2: var bigRectangles = shapes.Where(r => r.Width > 5); However, I can use Cast<Rectangle>() to treat my ArrayList as an IEnumerable<Rectangle> and then do the query! 1: // ah, that’s better! 2: var bigRectangles = shapes.Cast<Rectangle>().Where(r => r.Width > 5); Or, if you prefer, in LINQ query expression syntax: 1: var bigRectangles = from s in shapes.Cast<Rectangle>() 2: where s.Width > 5 3: select s; One quick warning: Cast<TResult>() only attempts to cast, it won’t perform a cast conversion.  That is, consider this: 1: var intList = new List<int> { 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89 }; 2:  3: // casting ints to longs, this should work, right? 4: var asLong = intList.Cast<long>().ToList(); Will the code above work?  No, you’ll get a InvalidCastException. Remember that Cast<TResult>() is an extension of IEnumerable, thus it is a sequence of object, which means that it will box every int as an object as it enumerates over it, and there is no cast conversion from object to long, and thus the cast fails.  In other words, a cast from int to long will succeed because there is a conversion from int to long.  But a cast from int to object to long will not, because you can only unbox an item by casting it to its exact type. For more information on why cast-converting boxed values doesn’t work, see this post on The Dangers of Casting Boxed Values (here). OfType<TResult>() – Filter sequence to only items of type TResult So, we’ve seen how we can use Cast<TResult>() to change the type of our sequence, when we expect all the items of the sequence to be of a specific type.  But what do we do when a sequence contains many different types, and we are only concerned with a subset of a given type? For example, what if a sequence of Shape contains Rectangle and Circle instances, and we just want to select all of the Rectangle instances?  Well, let’s say we had this sequence of Shape: 1: var shapes = new List<Shape> 2: { 3: new Rectangle { Width = 3, Height = 5 }, 4: new Rectangle { Width = 10, Height = 13 }, 5: new Circle { Radius = 10 }, 6: new Square { Side = 13 }, 7: // ... 8: }; Well, we could get the rectangles using Select(), like: 1: var onlyRectangles = shapes.Where(s => s is Rectangle).ToList(); But fortunately, an easier way has already been written for us in the form of the OfType<T>() extension method: 1: // returns only a sequence of the shapes that are Rectangles 2: var onlyRectangles = shapes.OfType<Rectangle>().ToList(); Now we have a sequence of only the Rectangles in the original sequence, we can also use this to chain other queries that depend on Rectangles, such as: 1: // select only Rectangles, then filter to only those more than 2: // 5 units wide... 3: var onlyBigRectangles = shapes.OfType<Rectangle>() 4: .Where(r => r.Width > 5) 5: .ToList(); The OfType<Rectangle>() will filter the sequence to only the items that are of type Rectangle (or a subclass of it), and that results in an IEnumerable<Rectangle>, we can then apply the other LINQ extension methods to query that list further. Just as Cast<TResult>() is an extension method on IEnumerable (and not IEnumerable<T>), the same is true for OfType<T>().  This means that you can use OfType<TResult>() on object-based collections as well. For example, given an ArrayList containing Shapes, as below: 1: // object-based collections are a sequence of object 2: var shapes = new ArrayList 3: { 4: new Rectangle { Width = 3, Height = 5 }, 5: new Rectangle { Width = 10, Height = 13 }, 6: new Circle { Radius = 10 }, 7: new Square { Side = 13 }, 8: // ... 9: }; We can use OfType<Rectangle> to filter the sequence to only Rectangle items (and subclasses), and then chain other LINQ expressions, since we will then be of type IEnumerable<Rectangle>: 1: // OfType() converts the sequence of object to a new sequence 2: // containing only Rectangle or sub-types of Rectangle. 3: var onlyBigRectangles = shapes.OfType<Rectangle>() 4: .Where(r => r.Width > 5) 5: .ToList(); Summary So now we’ve seen two different ways to get a sequence of a superclass or interface down to a more specific sequence of a subclass or implementation.  The Cast<TResult>() method casts every item in the source sequence to type TResult, and the OfType<TResult>() method selects only those items in the source sequence that are of type TResult. You can use these to downcast sequences, or adapt older types and sequences that only implement IEnumerable (such as DataTable, ArrayList, etc.). Technorati Tags: C#,CSharp,.NET,LINQ,Little Wonders,TypeOf,Cast,IEnumerable<T>

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• StreamInsight 2.1, meet LINQ

  - by Roman Schindlauer

  Someone recently called LINQ “magic” in my hearing. I leapt to LINQ’s defense immediately. Turns out some people don’t realize “magic” is can be a pejorative term. I thought LINQ needed demystification. Here’s your best demystification resource: http://blogs.msdn.com/b/mattwar/archive/2008/11/18/linq-links.aspx. I won’t repeat much of what Matt Warren says in his excellent series, but will talk about some core ideas and how they affect the 2.1 release of StreamInsight. Let’s tell the story of a LINQ query. Compile time It begins with some code: IQueryable<Product> products = ...; var query = from p in products             where p.Name == "Widget"             select p.ProductID; foreach (int id in query) {     ... When the code is compiled, the C# compiler (among other things) de-sugars the query expression (see C# spec section 7.16): ... var query = products.Where(p => p.Name == "Widget").Select(p => p.ProductID); ... Overload resolution subsequently binds the Queryable.Where<Product> and Queryable.Select<Product, int> extension methods (see C# spec sections 7.5 and 7.6.5). After overload resolution, the compiler knows something interesting about the anonymous functions (lambda syntax) in the de-sugared code: they must be converted to expression trees, i.e.,“an object structure that represents the structure of the anonymous function itself” (see C# spec section 6.5). The conversion is equivalent to the following rewrite: ... var prm1 = Expression.Parameter(typeof(Product), "p"); var prm2 = Expression.Parameter(typeof(Product), "p"); var query = Queryable.Select<Product, int>(     Queryable.Where<Product>(         products,         Expression.Lambda<Func<Product, bool>>(Expression.Property(prm1, "Name"), prm1)),         Expression.Lambda<Func<Product, int>>(Expression.Property(prm2, "ProductID"), prm2)); ... If the “products” expression had type IEnumerable<Product>, the compiler would have chosen the Enumerable.Where and Enumerable.Select extension methods instead, in which case the anonymous functions would have been converted to delegates. At this point, we’ve reduced the LINQ query to familiar code that will compile in C# 2.0. (Note that I’m using C# snippets to illustrate transformations that occur in the compiler, not to suggest a viable compiler design!) Runtime When the above program is executed, the Queryable.Where method is invoked. It takes two arguments. The first is an IQueryable<> instance that exposes an Expression property and a Provider property. The second is an expression tree. The Queryable.Where method implementation looks something like this: public static IQueryable<T> Where<T>(this IQueryable<T> source, Expression<Func<T, bool>> predicate) {     return source.Provider.CreateQuery<T>(     Expression.Call(this method, source.Expression, Expression.Quote(predicate))); } Notice that the method is really just composing a new expression tree that calls itself with arguments derived from the source and predicate arguments. Also notice that the query object returned from the method is associated with the same provider as the source query. By invoking operator methods, we’re constructing an expression tree that describes a query. Interestingly, the compiler and operator methods are colluding to construct a query expression tree. The important takeaway is that expression trees are built in one of two ways: (1) by the compiler when it sees an anonymous function that needs to be converted to an expression tree, and; (2) by a query operator method that constructs a new queryable object with an expression tree rooted in a call to the operator method (self-referential). Next we hit the foreach block. At this point, the power of LINQ queries becomes apparent. The provider is able to determine how the query expression tree is evaluated! The code that began our story was intentionally vague about the definition of the “products” collection. Maybe it is a queryable in-memory collection of products: var products = new[]     { new Product { Name = "Widget", ProductID = 1 } }.AsQueryable(); The in-memory LINQ provider works by rewriting Queryable method calls to Enumerable method calls in the query expression tree. It then compiles the expression tree and evaluates it. It should be mentioned that the provider does not blindly rewrite all Queryable calls. It only rewrites a call when its arguments have been rewritten in a way that introduces a type mismatch, e.g. the first argument to Queryable.Where<Product> being rewritten as an expression of type IEnumerable<Product> from IQueryable<Product>. The type mismatch is triggered initially by a “leaf” expression like the one associated with the AsQueryable query: when the provider recognizes one of its own leaf expressions, it replaces the expression with the original IEnumerable<> constant expression. I like to think of this rewrite process as “type irritation” because the rewritten leaf expression is like a foreign body that triggers an immune response (further rewrites) in the tree. The technique ensures that only those portions of the expression tree constructed by a particular provider are rewritten by that provider: no type irritation, no rewrite. Let’s consider the behavior of an alternative LINQ provider. If “products” is a collection created by a LINQ to SQL provider: var products = new NorthwindDataContext().Products; the provider rewrites the expression tree as a SQL query that is then evaluated by your favorite RDBMS. The predicate may ultimately be evaluated using an index! In this example, the expression associated with the Products property is the “leaf” expression. StreamInsight 2.1 For the in-memory LINQ to Objects provider, a leaf is an in-memory collection. For LINQ to SQL, a leaf is a table or view. When defining a “process” in StreamInsight 2.1, what is a leaf? To StreamInsight a leaf is logic: an adapter, a sequence, or even a query targeting an entirely different LINQ provider! How do we represent the logic? Remember that a standing query may outlive the client that provisioned it. A reference to a sequence object in the client application is therefore not terribly useful. But if we instead represent the code constructing the sequence as an expression, we can host the sequence in the server: using (var server = Server.Connect(...)) {     var app = server.Applications["my application"];     var source = app.DefineObservable(() => Observable.Range(0, 10, Scheduler.NewThread));     var query = from i in source where i % 2 == 0 select i; } Example 1: defining a source and composing a query Let’s look in more detail at what’s happening in example 1. We first connect to the remote server and retrieve an existing app. Next, we define a simple Reactive sequence using the Observable.Range method. Notice that the call to the Range method is in the body of an anonymous function. This is important because it means the source sequence definition is in the form of an expression, rather than simply an opaque reference to an IObservable<int> object. The variation in Example 2 fails. Although it looks similar, the sequence is now a reference to an in-memory observable collection: var local = Observable.Range(0, 10, Scheduler.NewThread); var source = app.DefineObservable(() => local); // can’t serialize ‘local’! Example 2: error referencing unserializable local object The Define* methods support definitions of operator tree leaves that target the StreamInsight server. These methods all have the same basic structure. The definition argument is a lambda expression taking between 0 and 16 arguments and returning a source or sink. The method returns a proxy for the source or sink that can then be used for the usual style of LINQ query composition. The “define” methods exploit the compile-time C# feature that converts anonymous functions into translatable expression trees! Query composition exploits the runtime pattern that allows expression trees to be constructed by operators taking queryable and expression (Expression<>) arguments. The practical upshot: once you’ve Defined a source, you can compose LINQ queries in the familiar way using query expressions and operator combinators. Notably, queries can be composed using pull-sequences (LINQ to Objects IQueryable<> inputs), push sequences (Reactive IQbservable<> inputs), and temporal sequences (StreamInsight IQStreamable<> inputs). You can even construct processes that span these three domains using “bridge” method overloads (ToEnumerable, ToObservable and To*Streamable). Finally, the targeted rewrite via type irritation pattern is used to ensure that StreamInsight computations can leverage other LINQ providers as well. Consider the following example (this example depends on Interactive Extensions): var source = app.DefineEnumerable((int id) =>     EnumerableEx.Using(() =>         new NorthwindDataContext(), context =>             from p in context.Products             where p.ProductID == id             select p.ProductName)); Within the definition, StreamInsight has no reason to suspect that it ‘owns’ the Queryable.Where and Queryable.Select calls, and it can therefore defer to LINQ to SQL! Let’s use this source in the context of a StreamInsight process: var sink = app.DefineObserver(() => Observer.Create<string>(Console.WriteLine)); var query = from name in source(1).ToObservable()             where name == "Widget"             select name; using (query.Bind(sink).Run("process")) {     ... } When we run the binding, the source portion which filters on product ID and projects the product name is evaluated by SQL Server. Outside of the definition, responsibility for evaluation shifts to the StreamInsight server where we create a bridge to the Reactive Framework (using ToObservable) and evaluate an additional predicate. It’s incredibly easy to define computations that span multiple domains using these new features in StreamInsight 2.1! Regards, The StreamInsight Team

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• Lazy Evaluation &ndash; Why being lazy in F# blows my mind!

  - by MarkPearl

  First of all – shout out to Peter Adams – from the feedback I have gotten from him on the last few posts of F# that I have done – my mind has just been expanded. I did a blog post a few days ago about infinite sequences – I didn’t really understand what was going on with it, and I still don’t really get it – but I am getting closer. In Peter’s last comment he made mention of Lazy Evaluation. I am ashamed to say that up till then I had never heard about lazy evaluation – how can evaluation be lazy? I mean, I know about lazy loading and that makes sense… but surely something is either evaluated or not! Well… a bit of reading today and I have been enlightened to a point – if you do know of any good articles explaining lazy evaluation please send them to me. So what is lazy evaluation and why is it useful? Lazy evaluation is a process whereby the system only computes the values needed and “ignores” the computations not needed. I’m going out on a limb here, but with this explanation in hand, imagine the following C# code… public int CalculatedVal() { int Val1 = 0; int Val2 = 0; for (int Count = 0; Count < 1000000; Count++) { Val1++; } return Val2; }   Normally, even though Val1 is never needed, the system would loop 1000000 times and add 1 to the current value of Val1. Imagine if the system realized this and so just skipped this segment of code and instead did the following…. public int CalculatedVal() { int Val1 = 0; return Val2; }   A massive saving in computation and wasted effort. Now I am pretty sure it isn’t as simple as this but I think this is the basic idea. For a more detailed explanation of lazy evaluation in c#, Pedram Rezei has a wonderful post on lazy evaluation and makes some C# comparisons. I am not going to take any thunder from him by repeating everything he said since I think he did such a good job of explaining it himself. What I am interested in though is how in F# do you tell something to have lazy evalution, and how do you know if something will be eager or lazy by looking at it. I found this post was useful. From reading around F# by default uses eager evaluation unless explicitly told to use lazy evaluation. One exception to this is sequences, which are lazy by default. Now reading about lazy evaluation has helped me understand more about F# coding… From my understanding of F# because of its declarative nature, most of the actual code you are declaring properties and rules – very little code is actually saying do this right now - but when it comes to a “do this” code section, it then evaluates and optimizes code and applies the rules. So props to lazy evaluation and its optimizations…

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• x86 opcode alignment references and guidelines

  - by mrjoltcola

  I'm generating some opcodes dynamically in a JIT compiler and I'm looking for guidelines for opcode alignment. 1) I've read comments that briefly "recommend" alignment by adding nops after calls 2) I've also read about using nop for optimizing sequences for parallelism. 3) I've read that alignment of ops is good for "cache" performance Usually these comments don't give any supporting references. Its one thing to read a blog or a comment that says, "its a good idea to do such and such", but its another to actually write a compiler that implements specific op sequences and realize most material online, especially blogs, are not useful for practical application. So I'm a believer in finding things out myself (disassembly, etc. to see what real world apps do). This is one case where I need some outside info. I notice compilers will usually start an odd byte instruction immediately after whatever previous instruction sequence there was. So the compiler is not taking any special care in most cases. I see "nop" here or there, but usually it seems nop is used sparingly, if at all. How critical is opcode alignment? Can you provide references for cases that I can actually use for implementation? Thanks.

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• Perl strings internals

  - by n0rd

  How does perl strings represented internally? What encoding is used? How do I handle different encodings properly? I've been using perl for quite a long time, but it didn't include a lot of string handling in different encodings, and when I encountered a minor problem that had something to do with encodings I usually resorted to some shamanic actions. Until this moment I thought about perl strings as sequences of bytes, which did fit pretty well for my tasks. Now I need to do some processing of UTF-8 encoded file and here starts trouble. First, I read file into string like this: open(my $in, '<', $ARGV[0]) or die "cannot open file $ARGV[0] for reading"; binmode($in, ':utf8'); my $contents; { local $/; $contents = <$in>; } close($in); then simply print it: print $contents; And I get two things: a warning Wide character in print at <scriptname> line <n> and a garbage in console. So I can conclude that perl strings have a concept of "character" that can be "wide" or not, but when printed these "wide" characters are represented in console as multiple bytes, not as single "character". (I wonder now why did all my previous experience with binary files worked quite how I expected it to work without any "character" issues). Why then I see garbage in console? If perl stores strings as character in some known encoding, I don't think there is a big problem to find out console encoding and print text properly. (I use Windows, BTW). If perl stores strings as multibyte sequences (e.g. using same UTF-8 encoding), why is it done this way? From my C experience handling multibyte strings is PAIN.

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• REST application, Transactions, Cache drop

  - by Julian Davchev

  Hi, I am building REST API in php with memcache layer on top for caching all resources. After some reading experience it turns out it's best when documents are as simple as posible...mainly due to dropping cache sequences. So if there is 'building','room' entities for the 'room' document I would only place the id of the 'building' and not the whole data of it. Then on api client side I would merge data as needed. Problem becomes when I need to update/insert (most cases more than one table). I update one resource but on second update system fails or whatever and there becomes database inconsistancies. I see several solutions: 1. Implement rest transactions which I find wrong and complex as idea is to be stateless and easy. 2. On update/insert actions I pass more complex data (not single entities) so I can force transactions on API level. But this will make it weird that your GET document structure is same as PUT document structure. And again somehow make drop sequences complex. Any pointers are more than welcome. Cheers,

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• Would it be possible to have a UTF-8-like encoding limited to 3 bytes per character?

  - by dan04

  UTF-8 requires 4 bytes to represent characters outside the BMP. That's not bad; it's no worse than UTF-16 or UTF-32. But it's not optimal (in terms of storage space). There are 13 bytes (C0-C1 and F5-FF) that are never used. And multi-byte sequences that are not used such as the ones corresponding to "overlong" encodings. If these had been available to encode characters, then more of them could have been represented by 2-byte or 3-byte sequences (of course, at the expense of making the implementation more complex). Would it be possible to represent all 1,114,112 Unicode code points by a UTF-8-like encoding with at most 3 bytes per character? If not, what is the maximum number of characters such an encoding could represent? By "UTF-8-like", I mean, at minimum: The bytes 0x00-0x7F are reserved for ASCII characters. Byte-oriented find / index functions work correctly. You can't find a false positive by starting in the middle of a character like you can in Shift-JIS.

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• Set "Start With" value for Oracle sequence dynamically

  - by Allan

  I'm trying to create a release script that can be deployed on multiple databases, but where the data can be merged back together at a later date. The obvious way to handle this is to set the sequence numbers for production data sufficiently high in subsequent deployments to prevent collisions. The problem is in coming up with a release script that will accept the environment number and set the "Start With" value of the sequences appropriately. Ideally, I'd like to use something like this: ACCEPT EnvironNum PROMPT 'Enter the Environment Number: ' --[more scripting] CREATE SEQUENCE seq1 START WITH &EnvironNum*100000; --[more scripting] This doesn't work because you can't evaluate a numeric expression in DDL. Another option is to create the sequences using dynamic SQL via PL/SQL. ACCEPT EnvironNum PROMPT 'Enter the Environment Number: ' --[more scripting] EXEC execute immediate 'CREATE SEQUENCE seq1 START WITH ' || &EnvironNum*100000; --[more scripting] However, I'd prefer to avoid this solution as I generally try to avoid issuing DDL in PL/SQL. Finally, the third option I've come up with is simply to accept the Start With value as a substitution variable, instead of the environment number. Does anyone have a better thought on how to go about this?

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• capture text, including tags from string, and then reorder tags with text

  - by Brian

  I have the following text: abcdef<CONVERSION>abcabcabcabc<2007-01-12><name1><2007-01-12>abcabcabcabc<name2><2007-01-11>abcabcabcabc<name3><2007-02-12>abcabcabcabc<name4>abcabcabcabc<2007-03-12><name5><date>abcabcabcabc<name6> I need to use regular expressions in order to clean the above text: The basic extraction rule is: <2007-01-12>abcabcabcabc<name2> I have no problem extracting this pattern. My issue is that within th text I have malformed sequences: If the text doesn't start with a date, and end with a name my extraction fails. For example, the text above may have several mal formed sequences, such as: abcabcabcabc<2007-01-12><name1> Should be: <2007-01-12>abcabcabcabc<name1> Is it possible to have a regular expression that would clean the above, prior to extracting my consistent pattern. In short, i need to find all mal formed patterns, and then take the date tag and put it in front of it, as provided in the example above. Thanks.

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• 2 basic but interesting questions about .NET

  - by b-gen-jack-o-neill

  Hi, when I first saw C#, I thought this must be some joke. I was starting with programming in C. But in C# you could just drag and drop objects, and just write event code to them. It was so simple. Now, I still like C the most, becouse I am very attracted to the basic low level operations, and C is just next level of assembler, with few basic routines, so I like it very much. Even more becouse I write little apps for microcontrollers. But yeasterday I wrote very simple control program for my microcontroller based LED cube in asm, and I needed some way to simply create animation sequences to the Cube. So, I remembered C#. I have practically NO C# skills, but still I created simple program to make animation sequences in about hour with GUI, just with help of google and help of the embeded function descriptions in C#. So, to get to the point, is there some other reason then top speed, to use any other language than C#? I mean, it is so effective. I know that Java is a bit of similiar, but I expect C# to be more Windows effective since its directly from Microsoft. The second question is, what is the advantage of compiling into CIL, and than run by CLR, than directly compile it into machine code? I know that portability is one, but since C# is mainly for Windows, wouldn´t it be more powerfull to just compile it directly? Thanks.

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• Postgresql has broken apt-get on Ubuntu

  - by Raphie Palefsky-Smith

  On ubuntu 12.04, whenever I try to install a package using apt-get I'm greeted by: The following packages have unmet dependencies: postgresql-9.1 : Depends: postgresql-client-9.1 but it is not going to be instal led E: Unmet dependencies. Try 'apt-get -f install' with no packages (or specify a so lution). apt-get install postgresql-client-9.1 generates: The following packages have unmet dependencies: postgresql-client-9.1 : Breaks: postgresql-9.1 (< 9.1.6-0ubuntu12.04.1) but 9.1.3-2 is to be installed apt-get -f install and apt-get remove postgresql-9.1 both give: Removing postgresql-9.1 ... * Stopping PostgreSQL 9.1 database server * Error: /var/lib/postgresql/9.1/main is not accessible or does not exist ...fail! invoke-rc.d: initscript postgresql, action "stop" failed. dpkg: error processing postgresql-9.1 (--remove): subprocess installed pre-removal script returned error exit status 1 Errors were encountered while processing: postgresql-9.1 E: Sub-process /usr/bin/dpkg returned an error code (1) So, apt-get is crippled, and I can't find a way out. Is there any way to resolve this without a re-install? EDIT: apt-cache show postgresql-9.1 returns: Package: postgresql-9.1 Priority: optional Section: database Installed-Size: 11164 Maintainer: Ubuntu Developers <[email protected]> Original-Maintainer: Martin Pitt <[email protected]> Architecture: amd64 Version: 9.1.6-0ubuntu12.04.1 Replaces: postgresql-contrib-9.1 (<< 9.1~beta1-3~), postgresql-plpython-9.1 (<< 9.1.6-0ubuntu12.04.1) Depends: libc6 (>= 2.15), libcomerr2 (>= 1.01), libgssapi-krb5-2 (>= 1.8+dfsg), libkrb5-3 (>= 1.6.dfsg.2), libldap-2.4-2 (>= 2.4.7), libpam0g (>= 0.99.7.1), libpq5 (>= 9.1~), libssl1.0.0 (>= 1.0.0), libxml2 (>= 2.7.4), postgresql-client-9.1, postgresql-common (>= 115~), tzdata, ssl-cert, locales Suggests: oidentd | ident-server, locales-all Conflicts: postgresql (<< 7.5) Breaks: postgresql-plpython-9.1 (<< 9.1.6-0ubuntu12.04.1) Filename: pool/main/p/postgresql-9.1/postgresql-9.1_9.1.6-0ubuntu12.04.1_amd64.deb Size: 4298270 MD5sum: 9ee2ab5f25f949121f736ad80d735d57 SHA1: 5eac1cca8d00c4aec4fb55c46fc2a013bc401642 SHA256: 4e6c24c251a01f1b6a340c96d24fdbb92b5e2f8a2f4a8b6b08a0df0fe4cf62ab Description-en: object-relational SQL database, version 9.1 server PostgreSQL is a fully featured object-relational database management system. It supports a large part of the SQL standard and is designed to be extensible by users in many aspects. Some of the features are: ACID transactions, foreign keys, views, sequences, subqueries, triggers, user-defined types and functions, outer joins, multiversion concurrency control. Graphical user interfaces and bindings for many programming languages are available as well. . This package provides the database server for PostgreSQL 9.1. Servers for other major release versions can be installed simultaneously and are coordinated by the postgresql-common package. A package providing ident-server is needed if you want to authenticate remote connections with identd. Homepage: http://www.postgresql.org/ Description-md5: c487fe4e86f0eac09ed9847282436059 Bugs: https://bugs.launchpad.net/ubuntu/+filebug Origin: Ubuntu Supported: 5y Task: postgresql-server Package: postgresql-9.1 Priority: optional Section: database Installed-Size: 11164 Maintainer: Ubuntu Developers <[email protected]> Original-Maintainer: Martin Pitt <[email protected]> Architecture: amd64 Version: 9.1.5-0ubuntu12.04 Replaces: postgresql-contrib-9.1 (<< 9.1~beta1-3~), postgresql-plpython-9.1 (<< 9.1.5-0ubuntu12.04) Depends: libc6 (>= 2.15), libcomerr2 (>= 1.01), libgssapi-krb5-2 (>= 1.8+dfsg), libkrb5-3 (>= 1.6.dfsg.2), libldap-2.4-2 (>= 2.4.7), libpam0g (>= 0.99.7.1), libpq5 (>= 9.1~), libssl1.0.0 (>= 1.0.0), libxml2 (>= 2.7.4), postgresql-client-9.1, postgresql-common (>= 115~), tzdata, ssl-cert, locales Suggests: oidentd | ident-server, locales-all Conflicts: postgresql (<< 7.5) Breaks: postgresql-plpython-9.1 (<< 9.1.5-0ubuntu12.04) Filename: pool/main/p/postgresql-9.1/postgresql-9.1_9.1.5-0ubuntu12.04_amd64.deb Size: 4298028 MD5sum: 3797b030ca8558a67b58e62cc0a22646 SHA1: ad340a9693341621b82b7f91725fda781781c0fb SHA256: 99aa892971976b85bcf6fb2e1bb8bf3e3fb860190679a225e7ceeb8f33f0e84b Description-en: object-relational SQL database, version 9.1 server PostgreSQL is a fully featured object-relational database management system. It supports a large part of the SQL standard and is designed to be extensible by users in many aspects. Some of the features are: ACID transactions, foreign keys, views, sequences, subqueries, triggers, user-defined types and functions, outer joins, multiversion concurrency control. Graphical user interfaces and bindings for many programming languages are available as well. . This package provides the database server for PostgreSQL 9.1. Servers for other major release versions can be installed simultaneously and are coordinated by the postgresql-common package. A package providing ident-server is needed if you want to authenticate remote connections with identd. Homepage: http://www.postgresql.org/ Description-md5: c487fe4e86f0eac09ed9847282436059 Bugs: https://bugs.launchpad.net/ubuntu/+filebug Origin: Ubuntu Supported: 5y Task: postgresql-server Package: postgresql-9.1 Priority: optional Section: database Installed-Size: 11220 Maintainer: Martin Pitt <[email protected]> Original-Maintainer: Martin Pitt <[email protected]> Architecture: amd64 Version: 9.1.3-2 Replaces: postgresql-contrib-9.1 (<< 9.1~beta1-3~), postgresql-plpython-9.1 (<< 9.1.3-2) Depends: libc6 (>= 2.15), libcomerr2 (>= 1.01), libgssapi-krb5-2 (>= 1.8+dfsg), libkrb5-3 (>= 1.6.dfsg.2), libldap-2.4-2 (>= 2.4.7), libpam0g (>= 0.99.7.1), libpq5 (>= 9.1~), libssl1.0.0 (>= 1.0.0), libxml2 (>= 2.7.4), postgresql-client-9.1, postgresql-common (>= 115~), tzdata, ssl-cert, locales Suggests: oidentd | ident-server, locales-all Conflicts: postgresql (<< 7.5) Breaks: postgresql-plpython-9.1 (<< 9.1.3-2) Filename: pool/main/p/postgresql-9.1/postgresql-9.1_9.1.3-2_amd64.deb Size: 4284744 MD5sum: bad9aac349051fe86fd1c1f628797122 SHA1: a3f5d6583cc6e2372a077d7c2fc7adfcfa0d504d SHA256: e885c32950f09db7498c90e12c4d1df0525038d6feb2f83e2e50f563fdde404a Description-en: object-relational SQL database, version 9.1 server PostgreSQL is a fully featured object-relational database management system. It supports a large part of the SQL standard and is designed to be extensible by users in many aspects. Some of the features are: ACID transactions, foreign keys, views, sequences, subqueries, triggers, user-defined types and functions, outer joins, multiversion concurrency control. Graphical user interfaces and bindings for many programming languages are available as well. . This package provides the database server for PostgreSQL 9.1. Servers for other major release versions can be installed simultaneously and are coordinated by the postgresql-common package. A package providing ident-server is needed if you want to authenticate remote connections with identd. Homepage: http://www.postgresql.org/ Description-md5: c487fe4e86f0eac09ed9847282436059 Bugs: https://bugs.launchpad.net/ubuntu/+filebug Origin: Ubuntu Supported: 5y Task: postgresql-server

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• After Effects Question

  - by Josh

  Question here, not sure if it's the correct stack exchange site, sorry if it isn't. I have an After Effects project for school, and I've created a movie using JPEG sequences (10 @ ~100-200mb/each ). I have the output setting on the composition set to 640x480. I resized each JPEG layer via the fit to comp tool, but when I export the movie as a Quicktime movie, it is 1.1 gig for ~35 seconds of movie at 30fps. What am I doing so horribly wrong here?

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• Virtual terminal with at least 16bit color?

  - by trusktr

  It's 2013 and there should be terminals with more than 256 colors by now (you'd think). Are there any terminals with more than 8bit colors (usually from 8 bit we jump to 16bit) to use with linux? Ideally, I'd like to have a linux terminal with 32bit colors for the foreground and background of each character. So, the functionality would be the same, with escape sequences, but just more of them (or something like that?).

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• Linux 'compose' key sequence extensions

  - by o_O Tync

  Compose key is a great way way to write all these ©–®—… stuff. It's really MUCH more handy than the windows "alt+0169" method. Is there a way to define additional sequences? E.g. I'd like to have "Compose+--" result in "?"

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• less -Sr colourful.log How to view colourful log in less?

  - by Vi

  Both less -r (preserve terminal control sequences) and less -S (chop long lines) work well alone. But using them together breaks things. It chops too late and it wrecks the next line. Reducing COLUMNS environment variable is no op: (man less) But if you have a windowing system which supports TIOCGWINSZ or WIOCGETD, the window system's idea of the screen size takes precedence over the LINES and COLUMNS environment variables. How to view colourful logs with less? Resoved before asked: less -SR

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• How can I check in bash if a shell is running in interactive mode?

  - by Checkers

  How can I tell (in ~/.bashrc) if I'm running in interactive mode, or, say, executing a command over ssh. I want to avoid printing of ANSI escape sequences in .bashrc if it's the latter.

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• Apache kills my Mac. It didn't up until now. What happened?

  - by Konzepz

  Running Web Sharing on Mac (localhost Apache + MySQL settings) kills my Mac. It opens 30-40 httpd sequences, takes up to 90% percent CPU power, and keeps the fan running constantly. sudo apachectl stop keeps the CPU safe, but then again -- I need the Apache running :) What can I do the solve this? Thanks!

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• Windows 64bit Sandboxing software alternatives

  - by Pacifika

  As you might know sandboxing software doesn't work in 64bit Windows due to patchguard. What are the alternatives for a person looking to test untrusted / temporary software? Edit: @Nick I'd prefer an alternative to VMs as I'm not happy with the extended startup time, the extra login sequences and the memory overhead that accompanies booting a VM solution to test something out ocassionally as a home user. Also it's another system that needs to be kept secure and up to date.

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